Effect of electroacupuncture stimulation of "Sibai"(ST2) and "Quanliao"(SI18) on excitatory neurons of sensorimotor cortex in mice

OBJECTIVES

To observe the activation state and neuronal types of somatosensory cortex and the primary motor cortex induced by electroacupuncture (EA) stimulation of "Sibai" (ST2) and "Quanliao" (SI18) acupoints in mice.

METHODS

Male C57BL/6J mice were randomly divided into blank control and EA groups, with 6 mice in each group. Rats of the EA group received EA stimulation (2 Hz, 0.6 mA) at ST2 and SI18 for 30 minutes. Samples were collected after EA intervention, and immunofluorescence staining was performed to quantify the expression of the c-Fos gene (proportion of c-Fos positive cells) in the somatosensory cortex and primary motor cortex. The co-labelled cells of calcium/calmodulin-dependent protein kinase Ⅱ (CaMKⅡ) and gamma-aminobutyric acid (GABA) in the somatosensory cortex and primary motor cortex were observed and counted by using microscope after immunofluorescence staining. Another 10 mice were used to detect the calcium activity of excitatory neurons in the somatosensory cortex and primary motor cortex by fiber photometry.

RESULTS

In comparison with the blank control group, the number of c-Fos positive cells, and the proportion of c-Fos and CaMKⅡ co-labelled cells in both the somatosensory cortex and primary motor cortex were significantly increased after EA stimulation (P<0.05). No significant changes were found in the proportion of c-Fos and GABA co-labeled cells in both the somatosensory cortex and primary motor cortex after EA. Results of fiber optic calcium imaging technology showed that the spontaneous calcium activity of excitatory neurons in both somatosensory cortex and primary motor cortex were obviously increased during EA compared with that before EA (P<0.01), and strikingly reduced after cessation of EA compared with that during EA (P<0.05).

CONCLUSIONS

Under physiological conditions, EA of ST2 and SI18 can effectively activate excitatory neurons in the somatosensory cortex and primary motor cortex.

Obesity differentially effects the somatosensory cortex and striatum of TgF344-AD rats

Lifestyle choices leading to obesity, hypertension and diabetes in mid-life contribute directly to the risk of late-life Alzheimer's disease (AD). However, in late-life or in late-stage AD conditions, obesity reduces the risk of AD and disease progression. To examine the mechanisms underlying this paradox, TgF344-AD rats were fed a varied high-carbohydrate, high-fat (HCHF) diet to induce obesity from nine months of age representing early stages of AD to twelve months of age in which rats exhibit the full spectrum of AD symptomology. We hypothesized regions primarily composed of gray matter, such as the somatosensory cortex (SSC), would be differentially affected compared to regions primarily composed of white matter, such as the striatum. We found increased myelin and oligodendrocytes in the somatosensory cortex of rats fed the HCHF diet with an absence of neuronal loss. We observed decreased inflammation in the somatosensory cortex despite increased AD pathology. Compared to the somatosensory cortex, the striatum had fewer changes. Overall, our results suggest that the interaction between diet and AD progression affects myelination in a brain region specific manner such that regions with a lower density of white matter are preferentially affected. Our results offer a possible mechanistic explanation for the obesity paradox.

Organization of Somatosensory Cortex in the South American Rodent Paca (Cuniculus paca)

INTRODUCTION

The study of non-laboratory species has been part of a broader effort to establish the basic organization of the mammalian neocortex, as these species may provide unique insights relevant to cortical organization, function, and evolution.

METHODS

In the present study, the organization of three somatosensory cortical areas of the medium-sized (5-11 kg body mass) Amazonian rodent, the paca (Cuniculus paca), was determined using a combination of electrophysiological microelectrode mapping and histochemical techniques (cytochrome oxidase and NADPH diaphorase) in tangential sections.

RESULTS

Electrophysiological mapping revealed a somatotopically organized primary somatosensory cortical area (S1) located in the rostral parietal cortex with a characteristic foot-medial/head-lateral contralateral body surface representation similar to that found in other species. S1 was bordered laterally by two regions housing neurons responsive to tactile stimuli, presumably the secondary somatosensory (S2) and parietal ventral (PV) cortical areas that evinced a mirror-reversal representation (relative to S1) of the contralateral body surface. The limits of the putative primary visual (V1) and primary auditory (A1) cortical areas, as well as the complete representation of the contralateral body surface in S1, were determined indirectly by the histochemical stains. Like the barrel field described in small rodents, we identified a modular arrangement located in the face representation of S1.

CONCLUSIONS

The relative location, somatotopic organization, and pattern of neuropil histochemical reactivity in the three paca somatosensory cortical areas investigated are similar to those described in other mammalian species, providing additional evidence of a common plan of organization for the somatosensory cortex in the rostral parietal cortex of mammals.

Acupoint catgut embedding attenuates fibromyalgia pain through attenuation of TRPV1 signaling pathway in mouse

Objectives

Chronic pain is considered as pain lasting for more than three months and has emerged as a global health problem affecting individuals and society. Chronic extensive pain is the main syndrome upsetting individuals with fibromyalgia (FM), accompanied by anxiety, obesity, sleep disturbances, and depression, Transient receptor potential vanilloid 1 (TRPV1) has been reported to transduce inflammatory and pain signals to the brain.

Materials and Methods

Acupoint catgut embedding (ACE) is a novel acupuncture technique that provides continuous effects and convenience. ACE was performed at the bilateral ST36 acupoint.

Results

We demonstrated similar pain levels among all groups at baseline. After cold stress, chronic mechanical or thermal nociception was induced (D14: mechanical: 1.85 ± 0.13 g; thermal: 4.85 ± 0.26 s) and reversed in ACE-treated mice (D14: mechanical: 3.99 ± 0.16 g; thermal: 7.42 ± 0.45 s) as well as Trpv1-/- group (Day 14, mechanical: 4.25 ± 0.2 g; thermal: 7.91 ± 0.21 s) mice. Inflammatory mediators were augmented in FM individuals and were abridged after ACE management and TRPV1 gene loss. TRPV1 and its linked mediators were increased in the thalamus (THA), somatosensory cortex (SSC), medial prefrontal cortex (mPFC), and anterior cingulate cortex (ACC) in FM mice. The up-regulation of these mediators was diminished in ACE and Trpv1-/- groups.

Conclusion

We suggest that chronic pain can be modulated by ACE or Trpv1-/-. ACE-induced analgesia via TRPV1 signaling pathways may be beneficial targets for FM treatment.

Interactive effects of pain and arousal state on heart rate and cortical activity in the mouse anterior cingulate and somatosensory cortices

Sensory disconnection is a hallmark of sleep, yet the cortex retains some ability to process sensory information. Acute noxious stimulation during sleep increases the heart rate and the likelihood of awakening, indicating that certain mechanisms for pain sensing and processing remain active. However, processing of somatosensory information, including pain, during sleep remains underexplored. To assess somatosensation in natural sleep, we simultaneously recorded heart rate and local field potentials in the anterior cingulate (ACC) and somatosensory (S1) cortices of naïve, adult male mice, while applying noxious and non-noxious stimuli to their hind paws throughout their sleep-wake cycle. Noxious stimuli evoked stronger heart rate increases in both wake and non-rapid eye movement sleep (NREMS), and resulted in larger awakening probability in NREMS, as compared to non-noxious stimulation, suggesting differential processing of noxious and non-noxious information during sleep. Somatosensory information differentially reached S1 and ACC in sleep, eliciting complex transient and sustained responses in the delta, alpha, and gamma frequency bands as well as somatosensory evoked potentials. These dynamics depended on sleep state, the behavioral response to the stimulation and stimulation intensity (non-noxious vs. noxious). Furthermore, we found a correlation of the heart rate with the gamma band in S1 in the absence of a reaction in wake and sleep for noxious stimulation. These findings confirm that somatosensory information, including nociception, is sensed and processed during sleep even in the absence of a behavioral response.

Altered excitation-inhibition balance in the primary sensorimotor cortex to proprioceptive hand stimulation in cerebral palsy

OBJECTIVE

Our objective was to clarify the primary sensorimotor (SM1) cortex excitatory and inhibitory alterations in hemiplegic (HP) and diplegic (DP) cerebral palsy (CP) by quantifying SM1 cortex beta power suppression and rebound with magnetoencephalography (MEG).

METHODS

MEG was recorded from 16 HP and 12 DP adolescents, and their 32 healthy controls during proprioceptive stimulation of the index fingers evoked by a movement actuator. The related beta power changes were computed with Temporal Spectral Evolution (TSE). Peak strengths of beta suppression and rebound were determined from representative channels over the SM1 cortex.

RESULTS

Beta suppression was stronger contralateral to the stimulus and rebound was weaker ipsilateral to the stimulation in DP compared to controls. Beta modulation strengths did not differ significantly between HP and the control group.

CONCLUSIONS

The emphasized beta suppression in DP suggests less efficient proprioceptive processing in the SM1 contralateral to the stimulation. Their weak rebound further indicates reduced intra- and/or interhemispheric cortical inhibition, which is a potential neuronal mechanism for their bilateral motor impairments.

SIGNIFICANCE

The excitation-inhibition balance of the SM1 cortex related to proprioception is impaired in diplegic CP. Therefore, the cortical and behavioral proprioceptive deficits should be better diagnosed and considered to better target individualized effective rehabilitation in CP.

Excitability of somatosensory cortex is increased in ALS: A SEP recovery function study

OBJECTIVE

Neuronal loss in the somatosensory, as well as the motor cortex in amyotrophic lateral sclerosis (ALS), indicative of a structural abnormality has been reported. Previously we have shown that afferent inhibition was impaired in ALS, suggestive of sensory involvement. In this study, we aimed to evaluate excitability changes in the somatosensory cortex of ALS patients.

METHODS

ALS patients underwent a paired pulse somatosensory evoked potential (SEP) paradigm at various interstimulus intervals (ISI). The amplitude ratio obtained by dividing the amplitude of paired pulse SEP stimulation S2 (paired pulse stimulation) to S1 (the single pulse stimulation) was considered the somatosensory cortex excitability parameter. Findings were compared to the results obtained from healthy controls. Resting motor threshold (RMT) was also assessed in the ALS group.

RESULTS

An increased S2/S1 ratio was found in the ALS group in every ISI examined. Additionally, the reduced inhibition correlated negatively with forced vital capacity, Medical Research Council sum score, median nerve compound muscle action potential amplitude, while there was a positive association with Penn upper motor neuron score and sural nerve conduction velocity. No correlation existed with RMT.

CONCLUSIONS

Our findings demonstrated increased somatosensory cortical excitability in ALS, which was associated with clinical parameters such as reduced pulmonary function and motor strength.

SIGNIFICANCE

Somatosensory cortical excitability is impaired in ALS. Whether this is associated with increased motor cortical excitability requires further studies.

Increased excitability and reduced GABAergic levels in somatosensory cortex under chronic spinal cord injury

The complete or partial damage of ascending somatosensory pathways produced by a spinal cord injury triggers changes in the somatosensory cortex consisting in a functional expansion of activity from intact cortical regions towards deafferented ones, a process known as cortical reorganization. However, it is still unclear whether cortical reorganization depends on the severity of the spinal cord damage or if a spinal cord injury always leads to a similar cortical reorganization process in the somatosensory cortex. To answer these open questions in the field, we obtained longitudinal somatosensory evoked responses from bilateral hindlimb and forelimb cortex from animals with chronic full-transection or contusive spinal cord injury at thoracic level (T9-T10) to induce sensory deprivation of hindlimb cortex while preserving intact the forelimb cortex. Electrophysiological recordings from the four locations were obtained before lesion and weekly for up to 4 weeks. Our results show that cortical reorganization depends on the type of spinal cord injury, which tends to be more bilateral in full transection while is more unilateral in the model of contusive spinal cord injury. Moreover, in full transection of spinal cord, the deafferented and intact cortex exhibited similar increments of somatosensory evoked responses in both models of spinal cord injury - a feature observed in about 80% of subjects. The other 20% were unaffected by the injury indicating that cortical reorganization does not undergo in all subjects. In addition, we demonstrated an increased probability of triggered up-states in animals with spinal cord injury. This data indicates increased cortical excitability that could be proposed as a new feature of cortical reorganization. Finally, decreased levels of GABA marker GAD67 across cortical layers were only found in those animals with increased somatosensory evoked responses, but not in the unaffected population. In conclusion, cortical reorganization depends on the types of spinal cord injuries, and suggest that the phenomenon is strongly determined by cortical circuits. Moreover, changes in GABAergic transmission at the deprived cortex may be considered one of the mechanisms underlying the process of cortical reorganization and increased excitability.

Reassessing referral of touch following peripheral deafferentation: The role of contextual bias

Some amputees have been famously reported to perceive facial touch as arising from their phantom hand. These referred sensations have since been replicated across multiple neurological disorders and were classically interpreted as a perceptual correlate of cortical plasticity. Common to all these and related studies is that participants might have been influenced in their self-reports by the experimental design or related contextual biases. Here, we investigated whether referred sensations reports might be confounded by demand characteristics (e.g., compliance, expectation, suggestion). Unilateral upper-limb amputees (N = 18), congenital one-handers (N = 19), and two-handers (N = 22) were repeatedly stimulated with computer-controlled vibrations on 10 body-parts and asked to report the occurrence of any concurrent sensations on their hand(s). To further manipulate expectations, we gave participants the suggestion that some of these vibrations had a higher probability to evoke referred sensations. We also assessed similarity between (phantom) hand and face representation in primary somatosensory cortex (S1), using functional Magnetic Resonance Imaging (fMRI) multivariate representational similarity analysis. We replicated robust reports of referred sensations in amputees towards their phantom hand; however, the frequency and distribution of reported referred sensations were similar across groups. Moreover, referred sensations were evoked by stimulation of multiple body-parts and similarly reported on both the intact and phantom hand in amputees. Face-to-phantom-hand representational similarity was not different in amputees' missing hand region, compared with controls. These findings weaken the interpretation of referred sensations as a perceptual correlate of S1 plasticity and reveal the need to account for contextual biases when evaluating anomalous perceptual phenomena.

Pneumatic tactile stimulus delivery system for studying brain responses evoked by active finger touch with fMRI

BACKGROUND

Primates use their hands to actively touch objects and collect information. To study tactile information processing, it is important for participants to experience tactile stimuli through active touch while monitoring brain activities.

NEW METHOD

Here, we developed a pneumatic tactile stimulus delivery system (pTDS) that delivers various tactile stimuli on a programmed schedule and allows voluntary finger touches during MRI scanning. The pTDS uses a pneumatic actuator to move tactile stimuli and place them in a finger hole. A photosensor detects the time when an index finger touches a tactile stimulus, enabling the analysis of the touch-elicited brain responses.

RESULTS

We examined brain responses while the participants actively touched braille objects presented by the pTDS. BOLD responses during tactile perception were significantly stronger in a finger touch area of the contralateral somatosensory cortex compared with that of visual perception.

CONCLUSION

The pTDS enables MR studies of brain mechanisms for tactile processes through natural finger touch.

Cortical maps of somatosensory perception in human

Tactile and movement-related somatosensory perceptions are crucial for our daily lives and survival. Although the primary somatosensory cortex is thought to be the key structure of somatosensory perception, various cortical downstream areas are also involved in somatosensory perceptual processing. However, little is known about whether cortical networks of these downstream areas can be dissociated depending on each perception, especially in human. We address this issue by combining data from direct cortical stimulation (DCS) for eliciting somatosensation and data from high-gamma band (HG) elicited during tactile stimulation and movement tasks. We found that artificial somatosensory perception is elicited not only from conventional somatosensory-related areas such as the primary and secondary somatosensory cortices but also from a widespread network including superior/inferior parietal lobules and premotor cortex. Interestingly, DCS on the dorsal part of the fronto-parietal area including superior parietal lobule and dorsal premotor cortex often induces movement-related somatosensations, whereas that on the ventral one including inferior parietal lobule and ventral premotor cortex generally elicits tactile sensations. Furthermore, the HG mapping results of the movement and passive tactile stimulation tasks revealed considerable similarity in the spatial distribution between the HG and DCS functional maps. Our findings showed that macroscopic neural processing for tactile and movement-related perceptions could be segregated.

Activity-dependent regulation of the BAX/BCL-2 pathway protects cortical neurons from apoptotic death during early development

During early brain development, homeostatic removal of cortical neurons is crucial and requires multiple control mechanisms. We investigated in the cerebral cortex of mice whether the BAX/BCL-2 pathway, an important regulator of apoptosis, is part of this machinery and how electrical activity might serve as a set point of regulation. Activity is known to be a pro-survival factor; however, how this effect is translated into enhanced survival chances on a neuronal level is not fully understood. In this study, we show that caspase activity is highest at the neonatal stage, while developmental cell death peaks at the end of the first postnatal week. During the first postnatal week, upregulation of BAX is accompanied by downregulation of BCL-2 protein, resulting in a high BAX/BCL-2 ratio when neuronal death rates are high. In cultured neurons, pharmacological blockade of activity leads to an acute upregulation of Bax, while elevated activity results in a lasting increase of BCL-2 expression. Spontaneously active neurons not only exhibit lower Bax levels than inactive neurons but also show almost exclusively BCL-2 expression. Disinhibition of network activity prevents the death of neurons overexpressing activated CASP3. This neuroprotective effect is not the result of reduced caspase activity but is associated with a downregulation of the BAX/BCL-2 ratio. Notably, increasing neuronal activity has a similar, non-additive effect as the blockade of BAX. Conclusively, high electrical activity modulates BAX/BCL-2 expression and leads to higher tolerance to CASP3 activity, increases survival, and presumably promotes non-apoptotic CASP3 functions in developing neurons.

Modulation of somatosensation by transcranial magnetic stimulation over somatosensory cortex: a systematic review

Over the last three decades, transcranial magnetic stimulation (TMS) has gained popularity as a tool to modulate human somatosensation. However, the effects of different stimulation types on the multiple distinct subdomains of somatosensation (e.g., tactile perception, proprioception and pain) have not been systematically compared. This is especially notable in the case of newer theta-burst stimulation protocols now in widespread use. Here, we aimed to systematically and critically review the existing TMS literature and provide a complete picture of current knowledge regarding the role of TMS in modulating human somatosensation across stimulation protocols and somatosensory domains. Following the PRISMA guidelines, fifty-four studies were included in the current review and were compared based on their methodologies and results. Overall, findings from these studies provide evidence that different types of somatosensation can be both disrupted and enhanced by targeted stimulation of specific somatosensory areas. Some mixed results, however, were reported in the literature. We discussed possible reasons for these mixed results, methodological limitations of existing investigations, and potential avenues for future research.

Analogous cognitive strategies for tactile learning in the rodent and human brain

Evolution has molded individual species' sensory capacities and abilities. In rodents, who mostly inhabit dark tunnels and burrows, the whisker-based somatosensory system has developed as the dominant sensory modality, essential for environmental exploration and spatial navigation. In contrast, humans rely more on visual and auditory inputs when collecting information from their surrounding sensory space in everyday life. As a result of such species-specific differences in sensory dominance, cognitive relevance and capacities, the evidence for analogous sensory-cognitive mechanisms across species remains sparse. However, recent research in rodents and humans yielded surprisingly comparable processing rules for detecting tactile stimuli, integrating touch information into percepts, and goal-directed rule learning. Here, we review how the brain, across species, harnesses such processing rules to establish decision-making during tactile learning, following canonical circuits from the thalamus and the primary somatosensory cortex up to the frontal cortex. We discuss concordances between empirical and computational evidence from micro- and mesoscopic circuit studies in rodents to findings from macroscopic imaging in humans. Furthermore, we discuss the relevance and challenges for future cross-species research in addressing mutual context-dependent evaluation processes underpinning perceptual learning.

Higher-order thalamic nuclei facilitate the generalization and maintenance of spike-and-wave discharges of absence seizures

Spike-and-wave discharges (SWDs), generated by the cortico-thalamo-cortical (CTC) network, are pathological, large amplitude oscillations and the hallmark of absence seizures (ASs). SWDs begin in a cortical initiation network in both humans and animal models, including the Genetic Absence Epilepsy Rats from Strasbourg (GAERS), where it is located in the primary somatosensory cortex (S1). The behavioral manifestation of an AS occurs when SWDs spread from the cortical initiation site to the whole brain, however, the mechanisms behind this rapid propagation remain unclear. Here we investigated these processes beyond the principal CTC network, in higher-order (HO) thalamic nuclei (lateral posterior (LP) and posterior (PO) nuclei) since their diffuse connectivity and known facilitation of intracortical communications make these nuclei key candidates to support SWD generation and maintenance. In freely moving GAERS, multi-site LFP in LP, PO and multiple cortical regions revealed a novel feature of SWDs: during SWDs there are short periods (named SWD-breaks) when cortical regions far from S1, such the primary visual cortex (V1), become transiently unsynchronized from the ongoing EEG rhythm. Inactivation of HO nuclei with local muscimol injections or optogenetic perturbation of HO nuclei activity increased the occurrence of SWD-breaks and the former intervention also increased the SWD propagation-time from S1. The neural underpinnings of these findings were explored further by silicon probe recordings from single units of PO which uncovered two previously unknown groups of excitatory neurons based on their burst firing dynamics at SWD onset. Moreover, a switch from tonic to burst firing at SWD onset was shown to be an important feature since it was much less prominent for non-generalized events, i.e. SWDs that remained local to S1. Additionally, one group of neurons showed a reverse of this switch during SWD-breaks, demonstrating the importance of this firing pattern throughout the SWD. In summary, these results support the view that multiple HO thalamic nuclei are utilized at SWD onset and contribute to cortical synchrony throughout the paroxysmal discharge.

Bayesian prediction of psychophysical detection responses from spike activity in the rat sensorimotor cortex

Decoding of sensorimotor information is essential for brain-computer interfaces (BCIs) as well as in normal functioning organisms. In this study, Bayesian models were developed for the prediction of binary decisions of 10 awake freely-moving male/female rats based on neural activity in a vibrotactile yes/no detection task. The vibrotactile stimuli were 40-Hz sinusoidal displacements (amplitude: 200 µm, duration: 0.5 s) applied on the glabrous skin. The task was to depress the right lever for stimulus detection and left lever for stimulus-off condition. Spike activity was recorded from 16-channel microwire arrays implanted in the hindlimb representation of primary somatosensory cortex (S1), overlapping also with the associated representation in the primary motor cortex (M1). Single-/multi-unit average spike rate (R_d) within the stimulus analysis window was used as the predictor of the stimulus state and the behavioral response at each trial based on a Bayesian network model. Due to high neural and psychophysical response variability for each rat and also across subjects, mean R_d was not correlated with hit and false alarm rates. Despite the fluctuations in the neural data, the Bayesian model for each rat generated moderately good accuracy (0.60-0.90) and good class prediction scores (recall, precision, F1) and was also tested with subsets of data (e.g. regular vs. fast spike groups). It was generally observed that the models were better for rats with lower psychophysical performance (lower sensitivity index A'). This suggests that Bayesian inference and similar machine learning techniques may be especially helpful during the training phase of BCIs or for rehabilitation with neuroprostheses.

Somatosensory ECoG-based brain-machine interface with electrical stimulation on medial forebrain bundle

Brain-machine interface (BMI) provides an alternative route for controlling an external device with one's intention. For individuals with motor-related disability, the BMI technologies can be used to replace or restore motor functions. Therefore, BMIs for movement restoration generally decode the neural activity from the motor-related brain regions. In this study, however, we designed a BMI system that uses sensory-related neural signals for BMI combined with electrical stimulation for reward. Four-channel electrocorticographic (ECoG) signals were recorded from the whisker-related somatosensory cortex of rats and converted to extract the BMI signals to control the one-dimensional movement of a dot on the screen. At the same time, we used operant conditioning with electrical stimulation on medial forebrain bundle (MFB), which provides a virtual reward to motivate the rat to move the dot towards the desired center region. The BMI task training was performed for 7 days with ECoG recording and MFB stimulation. Animals successfully learned to move the dot location to the desired position using S1BF neural activity. This study successfully demonstrated that it is feasible to utilize the neural signals from the whisker somatosensory cortex for BMI system. In addition, the MFB electrical stimulation is effective for rats to learn the behavioral task for BMI.

Somatosensory prediction in the premature neonate brain

Sensory prediction (SP) is at the core of early cognitive development. Impaired SP may be a key to understanding the emergence of neurodevelopmental disorders, however there is little data on how and when this skill emerges. We set out to provide evidence of SP in the brain of premature neonates in the fundamental sensory modality: touch. Using Diffuse Correlation Spectroscopy, we measured blood flow changes in the somatosensory cortex of premature neonates presented with a vibrotactile stimulation-omission sequence. When ISI was fixed, participants presented a decrease in blood flow during stimulus omissions, starting when a stimulus should begin: the expectation of a certain stimulus onset induced deactivation of the somatosensory cortex. When ISI was jittered, we observed an increase in blood flow during omissions: the expectation of a likely but not certain stimulus onset induced activation of the somatosensory cortex. Our results reveal SP in the brain as early as four weeks before term, based on the temporal structure of a unimodal somatosensory stimulation, and show that SP produces opposite regulation of activity in the somatosensory cortex depending on how liable is stimulus onset. Future studies will investigate the predictive value of somatosensory prediction on neurodevelopment in this vulnerable population.

Inhibiting Human Aversive Memory by Transcranial Theta-Burst Stimulation to the Primary Sensory Cortex

BACKGROUND

Predicting adverse events from past experience is fundamental for many biological organisms. However, some individuals suffer from maladaptive memories that impair behavioral control and well-being, e.g., after psychological trauma. Inhibiting the formation and maintenance of such memories would have high clinical relevance. Previous preclinical research has focused on systemically administered pharmacological interventions, which cannot be targeted to specific neural circuits in humans. Here, we investigated the potential of noninvasive neural stimulation on the human sensory cortex in inhibiting aversive memory in a laboratory threat conditioning model.

METHODS

We build on an emerging nonhuman literature suggesting that primary sensory cortices may be crucially required for threat memory formation and consolidation. Immediately before conditioning innocuous somatosensory stimuli (conditioned stimuli [CS]) to aversive electric stimulation, healthy human participants received continuous theta-burst transcranial magnetic stimulation (cTBS) to individually localized primary somatosensory cortex in either the CS-contralateral (experimental) or CS-ipsilateral (control) hemisphere. We measured fear-potentiated startle to infer threat memory retention on the next day, as well as skin conductance and pupil size during learning.

RESULTS

After overnight consolidation, threat memory was attenuated in the experimental group compared with the control cTBS group. There was no evidence that this differed between simple and complex CS or that CS identification or initial learning were affected by cTBS.

CONCLUSIONS

Our results suggest that cTBS to the primary sensory cortex inhibits threat memory, likely by an impact on postlearning consolidation. We propose that noninvasive targeted stimulation of the sensory cortex may provide a new avenue for interfering with aversive memories in humans.

Thalamocortical bistable switch as a theoretical model of fibromyalgia pathogenesis inferred from a literature survey

Fibromyalgia (FM) is an unsolved central pain processing disturbance. We aim to provide a unifying model for FM pathogenesis based on a loop network involving thalamocortical regions, i.e., the ventroposterior lateral thalamus (VPL), the somatosensory cortex (SC), and the thalamic reticular nucleus (TRN). The dynamics of the loop have been described by three differential equations having neuron mean firing rates as variables and containing Hill functions to model mutual interactions among the loop elements. A computational analysis conducted with MATLAB has shown a transition from monostability to bistability of the loop behavior for a weakening of GABAergic transmission between TRN and VPL. This involves the appearance of a high-firing-rate steady state, which becomes dominant and is assumed to represent pathogenic pain processing giving rise to chronic pain. Our model is consistent with a bulk of literature evidence, such as neuroimaging and pharmacological data collected on FM patients, and with correlations between FM and immunoendocrine conditions, such as stress, perimenopause, chronic inflammation, obesity, and chronic dizziness. The model suggests that critical targets for FM treatment are to be found among immunoendocrine pathways leading to GABA/glutamate imbalance having an impact on the thalamocortical system.

Fingolimod increases parvalbumin-positive neurons in adult mice

In recent years, it has been shown that central nervous system agents, such as antidepressants and antiepileptic drugs, reopen a critical period in mature animals. Fingolimod, which is used for the treatment of multiple sclerosis, also restores neuroplasticity. In this study, we investigated the effects of parvalbumin (PV)-positive neurons and perineuronal nets (PNN) on fingolimod administration with respect to neuroplasticity. Fingolimod was chronically administered intraperitoneally to mature mice. PV-positive neurons and PNN in the hippocampus, prefrontal cortex, and somatosensory cortex were analyzed. An increase in PV-positive neurons was observed in the hippocampus, prefrontal cortex, and somatosensory cortex of the fingolimod-treated mice. An increase in Wisteria floribunda agglutinin-positive PNN was confirmed in mice treated with fingolimod in the somatosensory cortex only. Fingolimod increased the density of PV-positive neurons in the brains of mature mice. The results indicate that fingolimod may change the critical period in mature animals.

Response of the somatosensory cortex following thermal stimuli to dental implants

In the current study, we investigated the cortical response of the somatosensory cortex following thermal stimuli to dental implants. Five implants were inserted at the site of the left upper canine with immediate implant placement protocols in five cats. Intrinsic signal optical imaging was applied to measure the cortical responses evoked by thermal sensing via dental implants. The cortical response evoked by 60 g of tactile stimulus to implants was also examined. The response strength and activated location were compared between implants and natural teeth. Thermal stimuli via the implant could evoke reliable cortical responses in the tooth-related region. However, the response amplitude evoked by the cold stimuli applied to the implants was significantly lower than that evoked by the cold stimuli applied to the natural teeth, indicating that the implants were less sensitive to thermal change than the natural tooth. The response evoked by tactile stimuli to implants was significantly stronger than that evoked by cold stimuli. Thermal and tactile stimuli activated the same location of the tooth-related somatosensory cortex in both the implants and natural teeth. Therefore, the thermal change in implants could be detected at the cortical response level. Multimodal sensory integration of thermal and tactile functions existed for implants.

Acupuncture points injection mitigates chronic pain through transient receptor potential V1 in mice

OBJECTIVES

Tissue injury in peripheral sites can result in long-term potentiation in nociceptive neurons and surrounding glial cells, potentially resulting in the development of chronic inflammatory pain (CIP). Acupoint injection (AI) is similar to Western phototherapy, which injects solutions at specific sites to mitigate chronic pain. AI has shown greater benefits compared with acupuncture. In this study, we examined the therapeutic effect and explored the underlying mechanisms of AI in mice CIP model.

MATERIALS AND METHODS

We injected thrice complete Freund's adjuvant (CFA) into the mouse's hind paw to induce CIP.

RESULTS

We found that, after two weeks, CFA injection significantly induced mechanical and thermal hyperalgesia which were attenuated by AI treatment. Transient receptor potential V1 (TRPV1) channels and associated molecules were all increased in CIP in mice dorsal root ganglion (DRG), spinal cord (SC), thalamus, and somatosensory cortex (SSC). The aforementioned molecules were mitigated in AI and Trpv1 knockout mice. Furthermore, Iba1-positive cells (microglial marker) were also potentiated and shared a similar tendency with TRPV1.

CONCLUSION

These findings suggest that AI can alleviate chronic pain by reducing TRPV1 overexpression in both neuronal and microglial cells. Our results suggest new potential therapeutic targets for AI in chronic pain.

Transcranial alternating current stimulation modulates cortical processing of somatosensory information in a frequency- and time-specific manner

Neural oscillations can be modulated by non-invasive brain stimulation techniques, including transcranial alternating current stimulation (tACS). However, direct evidence of tACS effects at the cortical level in humans is still limited. In a tACS-electroencephalography co-registration setup, we investigated the ability of tACS to modulate cortical somatosensory information processing as assessed by somatosensory-evoked potentials (SEPs). To better elucidate the neural substrates of possible tACS effects we also recorded peripheral and spinal SEPs components, high-frequency oscillations (HFOs), and long-latency reflexes (LLRs). Finally, we studied whether changes were limited to the stimulation period or persisted thereafter. SEPs, HFOs, and LLRs were recorded during tACS applied at individual mu and beta frequencies and at the theta frequency over the primary somatosensory cortex (S1). Sham-tACS was used as a control condition. In a separate experiment, we assessed the time course of mu-tACS effects by recording SEPs before (T0), during (T1), and 1 min (T2) and 10 min (T3) after stimulation. Mu-tACS increased the amplitude of the N20 component of SEPs compared to both sham and theta-tACS. No differences were found between sham, beta-, and theta-tACS conditions. Also, peripheral and spinal SEPs, P25, HFOs, and LLRs did not change during tACS. Finally, mu-tACS-induced modulation of N20 amplitude specifically occurred during stimulation (T1) and vanished afterwards (i.e., at T2 and T3). Our findings suggest that TACS applied at the individual mu frequency is able to modulate early somatosensory information processing at the S1 level and the effect is limited to the stimulation period.

Vasoactive intestinal peptide (VIP) conducts the neuronal activity during absence seizures: GABA seems to be the main mediator of VIP

Absence epilepsy is classified as a childhood generalized epilepsy syndrome with distinctive electroencephalographic patterns. The Wistar Albino Glaxo originating from Rijswijk (WAG/Rij) strain is a very well validated animal model of absence epilepsy that also shows behavioral deficits. In addition to the gastrointestinal system, VIP is highly expressed throughout numerous brain regions, and it plays crucial roles as a neurotransmitter and as a neuromodulatory, neurotrophic and neuroprotective factor in both the central and peripheral nervous systems. In this study, adult WAG/Rij rats were divided into two groups (n = 10): a group that was administered VIP (25 ng/kg i.p.) every 2 days for 15 days and an age-matched control group that was administered physiological saline. Electrical brain activity and behavior (depressive- like behavior, learning and memory and anxiety) were investigated in both groups. In addition, the extracellular concentrations of GABA and glutamate and the GABA/glutamate ratio were measured by high-performance liquid chromatography in microdialysate samples collected from the somatosensorial cortex of WAG/Rij rats. Our results demonstrated that VIP treatment significantly suppressed the total duration and number of spike wave discharges in WAG/Rij rats. However, VIP had no significant effect on behavior. VIP increased the extracellular concentration of GABA and the GABA/glutamate ratio in the somatosensory cortex. In conclusion, VIP has suppressive effects on absence seizures, possibly by increasing the GABA concentration and inducing the transformation of glutamate to GABA in the somatosensory cortex of WAG/Rij rats.

Tactile sensation of natural teeth and dental implants in the somatosensory cortex

PURPOSE

This study aimed to investigate the cortical response characteristics evoked by natural teeth and implants.

METHODS

Five cats were subjected to intrinsic signal optical imaging to measure the cortical responses evoked by natural teeth and implants. The difference in tactile sensation between the implant and natural tooth was compared in detail at the cortical response level.

RESULTS

Some similarities were observed between the implants and natural teeth. The stimulating-response curves of the implants and natural teeth were generally S-curves, and both implants and natural teeth preferred labial-lingual direction stimulation. The implants and natural teeth differed in terms of their tactile sensitivity: implants were weaker than natural teeth in terms of both static and dynamic sensitivity. However, after saturation, there was no significant difference in tactile strength between implants and natural teeth.

CONCLUSIONS

Both natural teeth and implants are able to distinguish the tactile strength and stimulation direction. Although implants are less sensitive than the natural tooth, the maximal tactile function and directional preference of implants are similar to those of natural teeth.

Longitudinal fMRI measures of cortical reactivation and hand use with and without training after sensory loss in primates

In a series of previous studies, we demonstrated that damage to the dorsal column in the cervical spinal cord deactivates the contralateral somatosensory hand cortex and impairs hand use in a reach-to-grasp task in squirrel monkeys. Nevertheless, considerable cortical reactivation and behavioral recovery occurs over the following weeks to months after lesion. This timeframe may also be a window for targeted therapies to promote cortical reactivation and functional reorganization, aiding in the recovery process. Here we asked if and how task specific training of an impaired hand would improve behavioral recovery and cortical reorganization in predictable ways, and if recovery related cortical changes would be detectable using noninvasive functional magnetic resonance imaging (fMRI). We further asked if invasive neurophysiological mapping reflected fMRI results. A reach-to-grasp task was used to test impairment and recovery of hand use before and after dorsal column lesions (DC-lesion). The activation and organization of the affected primary somatosensory cortex (area 3b) was evaluated with two types of fMRI - either blood oxygenation level dependent (BOLD) or cerebral blood volume (CBV) with a contrast agent of monocrystalline iron oxide nanocolloid (MION) - before and after DC-lesion. At the end of the behavioral and fMRI studies, microelectrode recordings in the somatosensory areas 3a, 3b and 1 were used to characterize neuronal responses and verify the somatotopy of cortical reactivations. Our results indicate that even after nearly complete DC lesions, monkeys had both considerable post-lesion behavioral recovery, as well as cortical reactivation assessed with fMRI followed by extracellular recordings. Generalized linear regression analyses indicate that lesion extent is correlated with the behavioral outcome, as well as with the difference in the percent signal change from pre-lesion peak activation in fMRI. Monkeys showed behavioral recovery and nearly complete cortical reactivation by 9-12 weeks post-lesion (particularly when the DC-lesion was incomplete). Importantly, the specific training group revealed trends for earlier behavioral recovery and had higher magnitude of fMRI responses to digit stimulation by 5-8 weeks post-lesion. Specific kinematic measures of hand movements in the selected retrieval task predicted recovery time and related to lesion characteristics better than overall task performance success. For measures of cortical reactivation, we found that CBV scans provided stronger signals to vibrotactile digit stimulation as compared to BOLD scans, and thereby may be the preferred non-invasive way to study the cortical reactivation process after sensory deprivations from digits. When the reactivation of cortex for each of the digits was considered, the reactivation by digit 2 stimulation as measured with microelectrode maps and fMRI maps was best correlated with overall behavioral recovery.

Computational approach to understand temporal and spatial tactile transmission processes from mechanical stimuli of the index fingertip to the primary somatosensory cortex

Mechanisms of information transmission using tactile sense are one of major concerns in producing simulated experience in virtual or augmented reality as well as in compensating elderly or impaired people with diminished tactile sensory function. However, important mechanism of the difference of peak latency in the primary somatosensory cortex (SI) between electrical and mechanical stimulations of finger skin is not fully understood. We propose a computational approach to fuse a computational model to simulate temporal and spatial transmission processes from mechanical stimuli to the SI and experimental method using a magnetoencephalograph (MEG). In our model, a tactile model that combined a three-dimensional mechanical model of fingertip skin and a neurophysiological model of a slowly adapting type 1 (SA1) mechanoreceptor was integrated with a somatosensory evoked field (SEF) response model. Electrical and mechanical stimulations were applied to the same locations of the right or left index fingertips of three subjects using a MEG. By identifying parameters of the SEF response model using the electrical stimulation test data, predicted first peak latency due to a mechanical stimulus was identical to its average value obtained from the mechanical stimulation test data, while the spatial map predicted at the multiple SA1 receptors qualitatively corresponded to the MEG image map in the timings of peak latency. This suggests that mechanical change in the skin and neurophysiological responses generate the difference of peak latency in SI between electrical and mechanical stimulations. The computational approach has the potential for detailed investigation of mechanisms of tactile information transmission.

Intact tactile anisotropy despite altered hand perception in complex regional pain syndrome: rethinking the role of the primary sensory cortex in tactile and perceptual dysfunction

Complex Regional Pain Syndrome (CRPS) is characterised by pain, autonomic, sensory and motor abnormalities. It is associated with changes in the primary somatosensory cortex (S1 representation), reductions in tactile sensitivity (tested by two-point discrimination), and alterations in perceived hand size or shape (hand perception). The frequent co-occurrence of these three phenomena has led to the assumption that S1 changes underlie tactile sensitivity and perceptual disturbances. However, studies underpinning such a presumed relationship use tactile sensitivity paradigms that involve the processing of both non-spatial and spatial cues. Here, we used a task that evaluates anisotropy (i.e., orientation-dependency; a feature of peripheral and S1 representation) to interrogate spatial processing of tactile input in CRPS and its relation to hand perception. People with upper limb CRPS (n = 14) and controls with (n = 15) or without pain (n = 19) judged tactile distances between stimuli-pairs applied across and along the back of either hand to provide measures of tactile anisotropy. Hand perception was evaluated using a visual scaling task and questionnaires. Data were analysed with generalised estimating equations. Contrary to our hypotheses, tactile anisotropy was bilaterally preserved in CRPS, and the magnitude of anisotropic perception bias was comparable between groups. Hand perception was distorted in CRPS but not related to the magnitude of anisotropy or bias. Our results suggest against impairments in spatial processing of tactile input, and by implication S1 representation, as the cause of distorted hand perception in CRPS. Further work is warranted to elucidate the mechanisms of somatosensory dysfunction and distorted hand perception in CRPS.

Perineuronal net abnormalities in Slc13a4+/- mice are rescued by postnatal administration of N-acetylcysteine

Disruptions to either sulfate supply or sulfation enzymes can affect brain development and have long-lasting effects on brain function, yet our understanding of the molecular mechanisms governing this are incomplete. Perineuronal nets (PNNs) are highly sulfated, specialized extracellular matrix structures that regulate the maturation of synaptic connections and neuronal plasticity. We have previously shown that mice heterozygous for the brain sulfate transporter Slc13a4 have abnormal social interactions, memory, exploratory behaviors, stress and anxiety of postnatal origin, pointing to potential deficits in PNN biology, and implicate SLC13A4 as a critical factor required for regulating normal synaptic connectivity and function. Here, we sought to investigate aberrant PNN formation as a potential mechanism contributing to the functional deficits displayed by Slc13a4^+/- mice. Following social interactions, we reveal reduced neuronal activation in the somatosensory cortex of Slc13a4^+/- mice, and altered inhibitory and excitatory postsynaptic currents. In line with this, we found a reduction in parvalbumin-expressing neurons decorated with PNNs, as well as reduced expression of markers for PNN maturation. Finally, we reveal that postnatal administration of N-acetylcysteine prevented PNN abnormalities from manifesting in Slc13a4^+/- adult animals. Collectively, these data highlight a central role for postnatal SLC13A4 in normal PNN formation, circuit function and subsequent animal behavior.

Somatosensory versus cerebellar contributions to proprioceptive changes associated with motor skill learning: A theta burst stimulation study

BACKGROUND

It is well established that proprioception (position sense) is important for motor control, yet its role in motor learning and associated plasticity is not well understood. We previously demonstrated that motor skill learning is associated with enhanced proprioception and changes in sensorimotor neurophysiology. However, the neural substrates mediating these effects are unclear.

OBJECTIVE

To determine whether suppressing activity in the cerebellum and somatosensory cortex (S1) affects proprioceptive changes associated with motor skill learning.

METHODS

54 healthy young adults practiced a skill involving visually-guided 2D reaching movements through an irregular-shaped track using a robotic manipulandum with their right hand. Proprioception was measured using a passive two-alternative choice task before and after motor practice. Continuous theta burst stimulation (cTBS) was delivered over S1 or the cerebellum (CB) at the end of training for two consecutive days. We compared group differences (S1, CB, Sham) in proprioception and motor skill, quantified by a speed-accuracy function, measured on a third consecutive day (retention).

RESULTS

As shown previously, the Sham group demonstrated enhanced proprioceptive sensitivity after training and at retention. The S1 group had impaired proprioceptive function at retention through online changes during practice, whereas the CB group demonstrated offline decrements in proprioceptive function. All groups demonstrated motor skill learning. However, the magnitude of learning differed between the CB and Sham groups, consistent with a role for the cerebellum in motor learning.

CONCLUSION

Overall, these findings suggest that the cerebellum and S1 are important for distinct aspects of proprioceptive changes during skill learning.

Methylmercury induces hyperalgesia/allodynia through spinal cord dorsal horn neuronal activation and subsequent somatosensory cortical circuit formation in rats

Methylmercury (MeHg) is known to cause serious neurological deficits in humans. In this study, we investigated the occurrence of MeHg-mediated neuropathic pain and identified the underlying pathophysiological mechanism in a rat model of MeHg exposure. Rats were exposed to MeHg (20 ppm in drinking water) for 3 weeks. Neurological damage was observed in the primary afferent neuronal system, including the dorsal root nerve and the dorsal column of the spinal cord. The MeHg-exposed rats showed hyperalgesia/allodynia, compared to controls, as evidenced by a significant decrease in the threshold of mechanical pain evaluated using an algometer with calibrated forceps. Immunohistochemistry revealed the accumulation of activated microglia in the dorsal root nerve, dorsal column, and dorsal horn of the spinal cord. Western blot analyses of the dorsal part of the spinal cord demonstrated an increase in inflammotoxic and inflammatory cytokines and a neuronal activation related protein, phospho-CRE bunding protein (CREB). The results suggest that dorsal horn neuronal activation was mediated by inflammatory factors excreted by accumulated microglia. Furthermore, analyses of the cerebral cortex demonstrated increased expression of phospho-CREB and thrombospondin-1, which is known to be an important factor for excitatory synapse formation, specifically in the somatosensory cortical area. In addition, the expression of pre- and post-synaptic markers was increased in this cortex area. These results suggested that the new cortical circuit was wired specifically in the somatosensory cortex. In conclusion, MeHg-mediated dorsal horn neuronal activation with inflammatory microglia might induce somatosensory cortical rewiring, leading to hyperalgesia/allodynia.

Sensorimotor Perturbation Induces Late and Transient Molecular Synaptic Proteins Activation and Expression Changes

Plasticity of the cerebral cortex following a modification of the sensorimotor experience takes place in several steps that can last from few hours to several months. Among the mechanisms involved in the dynamic modulation of the cerebral cortex in adults, it is commonly proposed that short-term plasticity reflects changes in synaptic connections. Here, we were interested in the time-course of synaptic plasticity taking place in the somatosensory primary cortex all along a 14-day period of sensorimotor perturbation (SMP), as well as during a recovery phase up to 24 h. Activation and expression level of pre- (synapsin 1, synaptophysin, synaptotagmin 1) and postsynaptic (AMPA and NMDA receptors) proteins, postsynaptic density scaffold proteins (PSD-95 and Shank2), and cytoskeletal proteins (neurofilaments-L and M, β3-tubulin, synaptopodin, N-cadherin) were determined in cortical tissue enriched in synaptic proteins. During the SMP period, most changes were observed as soon as D7 in the presynaptic compartment and were followed, at D14, by changes in the postsynaptic compartment. These changes persisted at least until 24 h of recovery. Proteins involved in synapse structure (scaffolding, adhesion, cytoskeletal) were mildly affected and almost exclusively at D14. We concluded that experience-dependent reorganization of somatotopic cortical maps is accompanied by changes in synaptic transmission with a very close time-course.

Mesoscale hierarchical organization of primary somatosensory cortex captured by resting-state-fMRI in humans

The primary somatosensory cortex (S1) plays a key role in the processing and integration of afferent somatosensory inputs along an anterior-to-posterior axis, contributing towards necessary human function. It is believed that anatomical connectivity can be used to probe hierarchical organization, however direct characterization of this principle in-vivo within humans remains elusive. Here, we use resting-state functional connectivity as a complement to anatomical connectivity to investigate topographical principles of human S1. We employ a novel approach to examine mesoscopic variations of functional connectivity, and demonstrate a topographic organisation spanning the region's hierarchical axis that strongly correlates with underlying microstructure while tracing along architectonic Brodmann areas. Our findings characterize anatomical hierarchy of S1 as a 'continuous spectrum' with evidence supporting a functional boundary between areas 3b and 1. The identification of this topography bridges the gap between structure and connectivity, and may be used to help further current understanding of sensorimotor deficits.

Predictive coding models for pain perception

Pain is a complex, multidimensional experience that involves dynamic interactions between sensory-discriminative and affective-emotional processes. Pain experiences have a high degree of variability depending on their context and prior anticipation. Viewing pain perception as a perceptual inference problem, we propose a predictive coding paradigm to characterize evoked and non-evoked pain. We record the local field potentials (LFPs) from the primary somatosensory cortex (S1) and the anterior cingulate cortex (ACC) of freely behaving rats-two regions known to encode the sensory-discriminative and affective-emotional aspects of pain, respectively. We further use predictive coding to investigate the temporal coordination of oscillatory activity between the S1 and ACC. Specifically, we develop a phenomenological predictive coding model to describe the macroscopic dynamics of bottom-up and top-down activity. Supported by recent experimental data, we also develop a biophysical neural mass model to describe the mesoscopic neural dynamics in the S1 and ACC populations, in both naive and chronic pain-treated animals. Our proposed predictive coding models not only replicate important experimental findings, but also provide new prediction about the impact of the model parameters on the physiological or behavioral read-out-thereby yielding mechanistic insight into the uncertainty of expectation, placebo or nocebo effect, and chronic pain.

5-HT/GABA interaction in neurodevelopment and plasticity

The adult brain is the result of a multistages complex neurodevelopmental process involving genetic, molecular and microenvironmental factors as well as diverse patterns of electrical activity. In the postnatal life, immature neuronal circuits undergo an experience-dependent maturation during critical periods of plasticity, but the brain still retains plasticity during adult life. In all these stages, the neurotransmitter GABA plays a pivotal role. In this chapter, we will describe the interaction of 5-HT with GABA in regulating neurodevelopment and plasticity.

Non-informative vision improves spatial tactile discrimination on the shoulder but does not influence detection sensitivity

Vision of the body has been reported to improve tactile acuity even when vision is not informative about the actual tactile stimulation. However, it is currently unclear whether this effect is limited to body parts such as hand, forearm or foot that can be normally viewed, or it also generalizes to body locations, such as the shoulder, that are rarely before our own eyes. In this study, subjects consecutively performed a detection threshold task and a numerosity judgment task of tactile stimuli on the shoulder. Meanwhile, they watched either a real-time video showing their shoulder or simply a fixation cross as control condition. We show that non-informative vision improves tactile numerosity judgment which might involve tactile acuity, but not tactile sensitivity. Furthermore, the improvement in tactile accuracy modulated by vision seems to be due to an enhanced ability in discriminating the number of adjacent active electrodes. These results are consistent with the view that bimodal visuotactile neurons sharp tactile receptive fields in an early somatosensory map, probably via top-down modulation of lateral inhibition.

Fear-related signals are prioritised in visual, somatosensory and spatial systems

The human brain has evolved a multifaceted fear system, allowing threat detection to enable rapid adaptive responses crucial for survival. Although many cortical and subcortical brain areas are believed to be involved in the survival circuits detecting and responding to threat, the amygdala has reportedly a crucial role in the fear system. Here, we review evidence demonstrating that fearful faces, a specific category of salient stimuli indicating the presence of threat in the surrounding, are preferentially processed in the fear system and in the connected sensory cortices, even when they are presented outside of awareness or are irrelevant to the task. In the visual domain, we discuss evidence showing in hemianopic patients that fearful faces, via a subcortical colliculo-pulvinar-amygdala pathway, have a privileged visual processing even in the absence of awareness and facilitate responses towards visual stimuli in the intact visual field. Moreover, evidence showing that somatosensory cortices prioritise fearful-related signals, to the extent that tactile processing is enhanced in the presence of fearful faces, will be also reported. Finally, we will review evidence revealing that fearful faces have a pivotal role in modulating responses in peripersonal space, in line with the defensive functional definition of PPS.

The response of the neuronal activity in the somatosensory cortex after high-intensity intermediate-frequency magnetic field exposure to the spinal cord in rats under anesthesia and waking states

Novel technologies using the intermediate-frequency magnetic field (IF-MF) in living environments are becoming popular with the advance in electricity utilization. However, the biological effects induced by the high-intensity and burst-type IF-MF exposure used in the wireless power transfer technologies for electric vehicles or medical devices, such as the magnetic stimulation techniques, are not well understood. Here, we developed an experimental platform using rats, that combined an 18 kHz, high-intensity (Max. 88 mT), Gaussian-shaped burst IF-MF exposure system with an in vivo extracellular recording system. In this paper, we aimed to report the qualitative differences in stimulus responses in the regions of the somatosensory cortex and peripheral nerve fibers that were induced by the IF-MF exposure to the rat spinal cord. We also report the modulation of the stimulus responses in the somatosensory cortex under anesthesia or waking states. Using this experimental platform, we succeeded in the detection of the motor evoked potentials or the neuronal activity in the somatosensory cortex that was induced by the IF-MF exposure to the spinal cord in rats. Compared to the state of anesthesia, the neuronal activities in the somatosensory cortex was enhanced during the waking state. On the other hand, these neuronal responses could not be confirmed by the IF-MF exposure-related coil sound only. Our experimental results indicated the basic knowledge of the biological responses and excitation mechanisms of the spinal cord stimulation by the IF-MF exposure.

Increased intrinsic excitability and decreased synaptic inhibition in aged somatosensory cortex pyramidal neurons

Sensorimotor performance declines during advanced age, partially due to deficits in somatosensory acuity. Cortical receptive field expansion contributes to somatosensory deficits, suggesting increased excitability or decreased inhibition in primary somatosensory cortex (S1) pyramidal neurons. To ascertain changes in excitability and inhibition, we measured both properties in neurons from vibrissal S1 in brain slices from young and aged mice. Because adapting and non-adapting neurons-the principal pyramidal types in layer 5 (L5)-differ in intrinsic properties and inhibitory inputs, we determined age-dependent changes according to neuron type. We found an age-dependent increase in intrinsic excitability in adapting neurons, caused by a decrease in action potential threshold. Surprisingly, in non-adapting neurons we found both an increase in excitability caused by increased input resistance, and a decrease in synaptic inhibition. Spike frequency adaptation, already small in non-adapting neurons, was further reduced by aging, whereas sag, a manifestation of I_h, was increased. Therefore, aging caused both decreased inhibition and increased intrinsic excitability, but these effects were specific to pyramidal neuron type.

Protective role of mirtazapine in adult female Mecp2+/- mice and patients with Rett syndrome

BACKGROUND

Rett syndrome (RTT), an X-linked neurodevelopmental rare disease mainly caused by MECP2-gene mutations, is a prototypic intellectual disability disorder. Reversibility of RTT-like phenotypes in an adult mouse model lacking the Mecp2-gene has given hope of treating the disease at any age. However, adult RTT patients still urge for new treatments. Given the relationship between RTT and monoamine deficiency, we investigated mirtazapine (MTZ), a noradrenergic and specific-serotonergic antidepressant, as a potential treatment.

METHODS

Adult heterozygous-Mecp2 (HET) female mice (6-months old) were treated for 30 days with 10 mg/kg MTZ and assessed for general health, motor skills, motor learning, and anxiety. Motor cortex, somatosensory cortex, and amygdala were analyzed for parvalbumin expression. Eighty RTT adult female patients harboring a pathogenic MECP2 mutation were randomly assigned to treatment to MTZ for insomnia and mood disorders (mean age = 23.1 ± 7.5 years, range = 16-47 years; mean MTZ-treatment duration = 1.64 ± 1.0 years, range = 0.08-5.0 years). Rett clinical severity scale (RCSS) and motor behavior assessment scale (MBAS) were retrospectively analyzed.

RESULTS

In HET mice, MTZ preserved motor learning from deterioration and normalized parvalbumin levels in the primary motor cortex. Moreover, MTZ rescued the aberrant open-arm preference behavior observed in HET mice in the elevated plus-maze (EPM) and normalized parvalbumin expression in the barrel cortex. Since whisker clipping also abolished the EPM-related phenotype, we propose it is due to sensory hypersensitivity. In patients, MTZ slowed disease progression or induced significant improvements for 10/16 MBAS-items of the M1 social behavior area: 4/7 items of the M2 oro-facial/respiratory area and 8/14 items of the M3 motor/physical signs area.

CONCLUSIONS

This study provides the first evidence that long-term treatment of adult female heterozygous Mecp2^tm1.1Bird mice and adult Rett patients with the antidepressant mirtazapine is well tolerated and that it protects from disease progression and improves motor, sensory, and behavioral symptoms.

Orientation-selective and directional deep brain stimulation in swine assessed by functional MRI at 3T

Functional MRI (fMRI) has become an important tool for probing network-level effects of deep brain stimulation (DBS). Previous DBS-fMRI studies have shown that electrical stimulation of the ventrolateral (VL) thalamus can modulate sensorimotor cortices in a frequency and amplitude dependent manner. Here, we investigated, using a swine animal model, how the direction and orientation of the electric field, induced by VL-thalamus DBS, affects activity in the sensorimotor cortex. Adult swine underwent implantation of a novel 16-electrode (4 rows × 4 columns) directional DBS lead in the VL thalamus. A within-subject design was used to compare fMRI responses for (1) directional stimulation consisting of monopolar stimulation in four radial directions around the DBS lead, and (2) orientation-selective stimulation where an electric field dipole was rotated 0°−360° around a quadrangle of electrodes. Functional responses were quantified in the premotor, primary motor, and somatosensory cortices. High frequency electrical stimulation through leads implanted in the VL thalamus induced directional tuning in cortical response patterns to varying degrees depending on DBS lead position. Orientation-selective stimulation showed maximal functional response when the electric field was oriented approximately parallel to the DBS lead, which is consistent with known axonal orientations of the cortico-thalamocortical pathway. These results demonstrate that directional and orientation-selective stimulation paradigms in the VL thalamus can tune network-level modulation patterns in the sensorimotor cortex, which may have translational utility in improving functional outcomes of DBS therapy.

Direct Activation of Cortical Neurons in the Primary Somatosensory Cortex of the Rat in Vivo Using Focused Ultrasound

We address the recent controversy over whether focused ultrasound (FUS) activates cortical neurons directly or indirectly by initially activating auditory pathways. We obtained two types of evidence that FUS can directly activate cortical neurons. The depth profile of the local field potential (LFP) in the barrel cortex of the rat in vivo indicated a generator was located within the cortical gray matter. The onset and peak latencies of the initial component p1 were 3.2 ± 0.25 ms (mean ± standard error of the mean) and 7.6 ± 0.12 ms, respectively, for the direct cortical response (DCR), 6.8 ± 0.40 and 14.3 ± 0.54 ms for the FUS-evoked LFP (4 MHz, 3.2 MPa, 50 or 300 µs/pulse, 1-20 pulses at 1 kHz) and 6.9 ± 0.51 and 15.8 ± 0.94 ms for the LFP evoked by 1-ms deflection of the C2 whisker projecting to the same area. The peak latency of the FUS p1 was statistically (t-test) longer than the DCR, but shorter than the whisker p1 at p < 0.005.

Machine Learning for Neural Decoding

Despite rapid advances in machine learning tools, the majority of neural decoding approaches still use traditional methods. Modern machine learning tools, which are versatile and easy to use, have the potential to significantly improve decoding performance. This tutorial describes how to effectively apply these algorithms for typical decoding problems. We provide descriptions, best practices, and code for applying common machine learning methods, including neural networks and gradient boosting. We also provide detailed comparisons of the performance of various methods at the task of decoding spiking activity in motor cortex, somatosensory cortex, and hippocampus. Modern methods, particularly neural networks and ensembles, significantly outperform traditional approaches, such as Wiener and Kalman filters. Improving the performance of neural decoding algorithms allows neuroscientists to better understand the information contained in a neural population and can help to advance engineering applications such as brain–machine interfaces. Our code package is available at github.com/kordinglab/neural_decoding.

High fat diet accelerates and exacerbates microgliosis and neuronal damage/death in the somatosensory cortex after transient forebrain ischemia in gerbils

Obesity has been known as an independent risk factor for stroke. Effects of high-fat diet (HFD)-induced obesity on neuronal damage in the somatosensory cortex of animal models of cerebral ischemia have not been studied yet. In this study, HFD-induced obesity was used to study the impact of obesity on neuronal damage/loss and microgliosis in the somatosensory cortex of a gerbil model of 5-min transient forebrain ischemia. We used gerbils fed normal diet (ND) and HFD and chronologically examined microgliosis (microglial cell activation) by ionized calcium-binding adapter molecule 1 (Iba-1) immunohistochemistry. In addition, we examined neuronal damage or death by using neuronal nuclear protein (NeuN, a neuronal marker) immunohistochemistry and Fluoro-Jade B (F-J B, a marker for neuronal degeneration) histofluorescence staining. We found that ischemia-induced microgliosis in ND-fed gerbils was increased from 2 days post-ischemia; however, ischemia-mediated microgliosis in HFD-fed gerbils increased from 1 day post-ischemia and more accelerated with time than that in the ND-fed gerbils. Ischemia-induced neuronal death/loss in the somatosensory cortex in the ND-fed gerbils was apparently found at 5 days post-ischemia. However, in the HFD-fed gerbils, neuronal death/loss was shown from 2 days post-ischemia and progressively exacerbated at 5 days post-ischemia. Our findings indicate that HFD can evoke earlier microgliosis and more detrimental neuronal death/loss in the somatosensory cortex after transient ischemia than ND evokes.

Importance of body representations in social-cognitive development: New insights from infant brain science

There is significant interest in the ways the human body, both one's own and that of others, is represented in the human brain. In this chapter we focus on body representations in infancy and synthesize relevant findings from both infant cognitive neuroscience and behavioral experiments. We review six experiments in infant neuroscience that have used novel EEG and MEG methods to explore infant neural body maps. We then consider results from behavioral studies of social imitation and examine what they contribute to our understanding of infant body representations at a psychological level. Finally, we interweave both neuroscience and behavioral lines of research to ground new theoretical claims about early infant social cognition. We propose, based on the evidence, that young infants can represent the bodily acts of others and their own bodily acts in commensurate terms. Infants initially recognize correspondences between self and other-they perceive that others are "like me" in terms of bodies and bodily actions. This capacity for registering and using self-other equivalence mappings has far-reaching implications for mechanisms of developmental change. Infants can learn about the affordances and powers of their own body by watching adults' actions and their causal consequences. Reciprocally, infants can enrich their understanding of other people's internal states by taking into account the way they themselves feel when they perform similar acts. The faces, bodies, and matching actions of people are imbued with unique meaning because they can be mapped to the infant's own body and behavior.

Pharmacological activation of mGlu5 receptors with the positive allosteric modulator VU0360172, modulates thalamic GABAergic transmission

Previous studies have shown that injection of the mGlu5 receptor positive allosteric modulator (PAM) VU0360172 into either the thalamus or somatosensory cortex markedly reduces the frequency of spike-and-wave discharges (SWDs) in the WAG/Rij model of absence epilepsy. Here we have investigated the effects of VU0360172 on GABA transport in the thalamus and somatosensory cortex, as possible modes of action underlying the suppression of SWDs. Systemic VU0360172 injections increase GABA uptake in thalamic synaptosomes from epileptic WAG/Rij rats. Consistent with this observation, VU0360172 could also enhance thalamic GAT-1 protein expression, depending on the dosing regimen. This increase in GAT-1 expression was also observed in the thalamus from non-epileptic rats (presymptomatic WAG/Rij and Wistar) and appeared to occur selectively in neurons. The tonic GABA_A receptor current present in ventrobasal thalamocortical neurons was significantly reduced by VU0360172 consistent with changes in GAT-1 and GABA uptake. The in vivo effects of VU0360172 (reduction in tonic GABA current and increase in GAT-1 expression) could be reproduced in vitro by treating thalamic slices with VU0360172 for at least 1 h and appeared to be dependent on the activation of PLC. Thus, the effects of VU0360172 do not require an intact thalamocortical circuit. In the somatosensory cortex, VU0360172 reduced GABA uptake but did not cause significant changes in GAT-1 protein levels. These findings reveal a novel mechanism of regulation mediated by mGlu5 receptors, which could underlie the powerful anti-absence effect of mGlu5 receptor enhancers in animal models.

Pentylenetetrazol kindling induces cortical astrocytosis and increased expression of extracellular matrix molecules in mice

Although epilepsy is one of the most common chronic neurological disorders with a prevalence of approximately 1.0 %, the underlying pathophysiology remains to be elucidated. Understanding the molecular and cellular mechanisms involved in the development of epilepsy is important for the development of appropriate therapeutic strategy. In this study, we investigated the effects of status epilepticus on astrocytes, microglia, and extracellular matrix (ECM) molecules in the somatosensory cortex and piriform cortex of mice. Activation of astrocytes was observed in many cortices except the retrosplenial granular cortex after pentylenetetrazol (PTZ)-induced kindling in mice. Activated astrocytes in the cortex were found in layers 1-3 but not in layers 4-6. In the somatosensory and piriform cortices, no change was observed in the number of parvalbumin (PV)-positive neurons and PV-positive neurons covered with perineuronal nets. However, the amount of ECM in the extracellular space increased. The expression of VGLUT1- and GAD67-positive synapses also increased. Thus, in the PTZ-kindling epilepsy mice model, an increase in the number of ECM molecules and activation of astrocytes were observed in the somatosensory cortex and piriform cortex. These results indicate that PTZ-induced seizures affect not only the hippocampus but also other cortical areas. Our study findings may help to develop new therapeutic approaches to prevent seizures or their sequelae.

The GluN3 subunit regulates ion selectivity within native N-methyl-d-aspartate receptors

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The GluN3 subunit is the least understood of all subunits that make up functional NMDARs in the brain.

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We show through ion substitution experiments that NMDARs containing GluN3 are more permeable to Ca²⁺ than those containing just GluN1 and GluN2.

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We attribute these differences to their ability to screen for Ca²⁺ over Na⁺.

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Subunit-dependent cation selectivity represents a hitherto unrealized mechanism for finer control of Ca²⁺ influx enhancing the repertoire of synaptic NMDARs.

Glutamatergic N-methyl-d-aspartate receptors (NMDARs) are heterotetrameric proteins whose subunits are derived from three gene families, GRIN1 (codes for GluN1), GRIN2 (GluN2) and GRIN3 (GluN3). In addition to providing binding sites for glutamate and the co-agonist glycine, these subunits in their di (d-) and tri (t-) heteromeric configurations regulate various aspects of receptor function in the brain. For example, the decay kinetics of NMDAR-mediated synaptic currents depend on the type of GluN2 subunit (GluN2A-GluN2D) in the receptor subunit composition. While much is known about the contributions of GluN1 and GluN2 to d-NMDAR function, we know comparatively little about how GluN3 influences the function of t-NMDARs composed of one or more subunits from each of the three gene families. We report here that in addition to altering kinetics and voltage-dependent properties, the GluN3 subunit endows these receptors with ion selectivity wherein influx of Ca²⁺ is preferred over Na⁺. This became apparent in the process of assessing Ca²⁺ permeability through these receptors and is of significance given that NMDARs are generally believed to be nonselective to cations and increased selectivity can lead to enhanced permeability. This was true of two independent brain regions where t-NMDARs are expressed, the somatosensory cortex, where both receptor subtypes are expressed at separate inputs onto single neurons, and the entorhinal cortex, where they are co-expressed at individual synaptic inputs. Based on this data and the sequence of amino acids lining selectivity filters within these subunits, we propose GluN3 to be a regulatory subunit for ion selectivity in t-NMDARs.

Optical imaging reveals functional domains in primate sensorimotor cortex

Motor cortex (M1) and somatosensory cortex (S1) are central to arm and hand control. Efforts to understand encoding in M1 and S1 have focused on temporal relationships between neural activity and movement features. However, it remains unclear how the neural activity is spatially organized within M1 and S1. Optical imaging methods are well-suited for revealing the spatio-temporal organization of cortical activity, but their application is sparse in monkey sensorimotor cortex. Here, we investigate the effectiveness of intrinsic signal optical imaging (ISOI) for measuring cortical activity that supports arm and hand control in a macaque monkey. ISOI revealed spatial domains that were active in M1 and S1 in response to instructed reaching and grasping. The lateral M1 domains overlapped the hand representation and contained a population of neurons with peak firing during grasping. In contrast, the medial M1 domain overlapped the arm representation and a population of neurons with peak firing during reaching. The S1 domain overlapped the hand representations of areas 1 and 2 and a population of neurons with peak firing upon hand contact with the target. Our single unit recordings indicate that ISOI domains report the locations of spatial clusters of functionally related neurons. ISOI is therefore an effective tool for surveilling the neocortex for “hot zones” of activity that supports movement. Combining the strengths of ISOI with other imaging modalities (e.g., fMRI, 2-photon) and with electrophysiological methods can open new frontiers in understanding the spatio-temporal organization of cortical signals involved in movement control.