Network-level neuroplasticity in cortico-basal ganglia pathways

Tuina therapy promotes behavioral improvement and brain plasticity in rats with peripheral nerve injury and repair

INTRODUCTION

Tuina is currently one of the popular complementary and alternative methods of rehabilitation therapy. Tuina can improve patients' pain and mobility function. However, the underlying physiological mechanism remains largely unknown, which might limit its further popularization in clinical practice. The aim of this study is to explore the short-term and long-term changes in brain functional activity following Tuina intervention for peripheral nerve injury repair.

METHODS

A total of 16 rats were equally divided into the intervention group and the control group. Rats in the intervention group received Tuina therapy applying on the gastrocnemius muscle of the right side for 4 months following sciatic nerve transection and immediate repair, while the control group received nerve transection and repair only. The block-design functional magnetic resonance imaging scan was applied in both groups at 1 and 4 months after the surgery. During the scan, both the injured and intact hindpaw was electrically stimulated according to a "boxcar" paradigm.

RESULTS

When stimulating the intact hindpaw, the intervention group exhibited significantly lower activation in the somatosensory area, limbic/paralimbic areas, pain-regulation areas, and basal ganglia compared to the control group, with only the prefrontal area showing higher activation. After 4 months of sciatic nerve injury, the control group exhibited decreased motor cortex activity compared to the activity observed at 1 month, and the intervention group demonstrated stronger bilateral motor cortex activity compared to the control group.

CONCLUSION

Tuina therapy on the gastrocnemius muscle of rats with sciatic nerve injury can effectively alleviate pain and maintain the motor function of the affected limb. In addition, Tuina therapy reduced the activation level of pain-related brain regions and inhibited the decreased activity of the motor cortex caused by nerve injury, reflecting the impact of peripheral stimulation on brain plasticity.

Investigating the Migraine Cycle over 21 Consecutive Days Using Proton Magnetic Resonance Spectroscopy and Resting-State fMRI: A Pilot Study

Recent neuroimaging studies have revealed important aspects of the underlying pathophysiological mechanisms of migraine suggesting abnormal brain energy metabolism and altered functional connectivity. Proton magnetic resonance spectroscopy (1H-MRS) studies investigated migraine patients in the interictal or ictal state. This first-of-its-kind study aimed to investigate the whole migraine cycle using 1H-MRS and resting-state functional magnetic resonance imaging (fMRI). A migraine patient underwent 1H-MRS and resting-state fMRI for 21 consecutive days, regardless of whether he was in an interictal or ictal state. Metabolite ratios were assessed and compared to the intrinsic connectivity of subcortical brain areas. Probable migraine phase-dependent changes in N-acetyl aspartate (NAA)/total creatine (tCr) and choline (Cho)/tCr levels are found in the left occipital lobe and left basal ganglia. NAA reflects neuronal integrity and Cho cellular membrane turnover. Such abnormalities may increase the susceptibility to excitatory migraine triggers. Functional connectivity between the right hippocampus and right or left pallidum was strongly correlated to the NAA/Cho ratio in the right thalamus, suggesting neurochemical modulation of these brain areas through thalamic connections. To draw statistically significant conclusions a larger cohort is needed.

Understanding the Significance of the Hypothalamic Nature of the Subthalamic Nucleus

The subthalamic nucleus (STN) is an essential component of the basal ganglia and has long been considered to be a part of the ventral thalamus. However, recent neurodevelopmental data indicated that this nucleus is of hypothalamic origin which is now commonly acknowledged. In this work, we aimed to verify whether the inclusion of the STN in the hypothalamus could influence the way we understand and conduct research on the organization of the whole ventral and posterior diencephalon. Developmental and neurochemical data indicate that the STN is part of a larger glutamatergic posterior hypothalamic region that includes the premammillary and mammillary nuclei. The main anatomic characteristic common to this region involves the convergent cortical and pallidal projections that it receives, which is based on the model of the hyperdirect and indirect pathways to the STN. This whole posterior hypothalamic region is then integrated into distinct functional networks that interact with the ventral mesencephalon to adjust behavior depending on external and internal contexts.

Using Fractional Amplitude of Low-Frequency Fluctuations and Functional Connectivity in Patients With Post-stroke Cognitive Impairment for a Simulated Stimulation Program

Stroke causes alterations in local spontaneous neuronal activity and related networks functional connectivity. We hypothesized that these changes occur in patients with post-stroke cognitive impairment (PSCI). Fractional amplitude of low-frequency fluctuations (fALFF) was calculated in 36 patients with cognitive impairment, including 16 patients with hemorrhagic stroke (hPSCI group), 20 patients with ischemic stroke (iPSCI group). Twenty healthy volunteers closely matched to the patient groups with respect to age and gender were selected as the healthy control group (HC group). Regions with significant alteration were regarded as regions of interest (ROIs) using the one-way analysis of variance, and then the seed-based functional connectivity (FC) with other regions in the brain was analyzed. Pearson correlation analyses were performed to investigate the correlation between functional indexes and cognitive performance in patients with PSCI. Our results showed that fALFF values of bilateral posterior cingulate cortex (PCC)/precuneus and bilateral anterior cingulate cortex in the hPSCI group were lower than those in the HC group. Compared with the HC group, fALFF values were lower in the superior frontal gyrus and basal ganglia in the iPSCI group. Correlation analysis showed that the fALFF value of left PCC was positively correlated with MMSE scores and MoCA scores in hPSCI. Besides, the reduction of seed-based FC values was reported, especially in regions of the default-mode network (DMN) and the salience network (SN). Abnormalities of spontaneous brain activity and functional connectivity are observed in PSCI patients. The decreased fALFF and FC values in DMN of patients with hemorrhagic and SN of patients with ischemic stroke may be the pathological mechanism of cognitive impairment. Besides, we showed how to use fALFF values and functional connectivity maps to specify a target map on the cortical surface for repetitive transcranial magnetic stimulation (rTMS).

Cerebral glucose metabolism in bipolar disorder: A voxel-based meta-analysis of positron emission tomography studies

BACKGROUND

Previous positron emission tomography studies have reported the changes of cerebral glucose metabolism in bipolar disorder. However, the findings across studies remain controversial, containing differing results.

METHODS

A systematic literature search of the PubMed, Embase, Cochrane Library, and Web of Science databases was conducted. We conducted a voxel-wide meta-analysis of cerebral glucose metabolism studies, using the seed-based mapping approach, in patients with bipolar disorder (BD).

RESULTS

We identified 7 studies suitable for inclusion, which included a total of 126 individuals with BD and 160 healthy controls. The most consistent and robust findings were an increase in cerebral glucose metabolism in the right precentral gyrus and a decrease in the left superior temporal gyrus, left middle temporal gyrus, and cerebellum. Additionally, the sex distribution and illness duration had significant moderating effects on cerebral glucose metabolism alterations.

CONCLUSIONS

Cerebral glucose metabolism alterations in these brain regions are likely to reflect the disease-related functional abnormalities such as emotion and cognition. These findings contribute to a better understanding of the neurobiological underpinnings of bipolar disorder.

LIMITATIONS

This study was done at a study level and cannot be addressed at the patient level. Subgroup analysis of BD I and BD II is not possible due to limited literature data.

A basal ganglia-like cortical-amygdalar-hypothalamic network mediates feeding behavior

The insular cortex (INS) is extensively connected to the central nucleus of the amygdala (CEA), and both regions send convergent projections into the caudal lateral hypothalamus (LHA) encompassing the parasubthalamic nucleus (PSTN). However, the organization of the network between these structures has not been clearly delineated in the literature, although there has been an upsurge in functional studies related to these structures, especially with regard to the cognitive and psychopathological control of feeding. We conducted tract-tracing experiments from the INS and observed a pathway to the PSTN region that runs parallel to the canonical hyperdirect pathway from the isocortex to the subthalamic nucleus (STN) adjacent to the PSTN. In addition, an indirect pathway with a relay in the central amygdala was also observed that is similar in its structure to the classic indirect pathway of the basal ganglia that also targets the STN. C-Fos experiments showed that the PSTN complex reacts to neophobia and sickness induced by lipopolysaccharide or cisplatin. Chemogenetic (designer receptors exclusively activated by designer drugs [DREADD]) inhibition of tachykininergic neurons (Tac1) in the PSTN revealed that this nucleus gates a stop "no-eat" signal to refrain from feeding when the animal is subjected to sickness or exposed to a previously unknown source of food. Therefore, our anatomical findings in rats and mice indicate that the INS-PSTN network is organized in a similar manner as the hyperdirect and indirect basal ganglia circuitry. Functionally, the PSTN is involved in gating feeding behavior, which is conceptually homologous to the motor no-go response of the adjacent STN.

L-DOPA-Induced Motor Impairment and Overexpression of Corticostriatal Synaptic Components Are Improved by the mGluR5 Antagonist MPEP in 6-OHDA-Lesioned Rats

Levodopa (L-DOPA) is still the most effective drug for the treatment of Parkinson's disease (PD). However, the long-term therapy often triggers L-DOPA-induced dyskinesia (LID). Metabotropic glutamate receptor type 5 (mGluR5) is abundant in the basal ganglia, and its inhibition is thought to modulate postsynaptic excitatory synaptic transmission and glutamate hyperactivity in PD and LID. In this report, we examined the effects of mGluR5-specific antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP) on LID and synaptic components in the PD model rat. We found the selective mGluR5 antagonist MPEP attenuated abnormal involuntary movements, prolonged the duration of rotational response, reversed the decrease of left forepaw adjusting steps, and reduced overexpression of striatal mGluR5 in the LID rats. Moreover, our results showed much thicker postsynaptic densities, narrower synapse cleft, as well as the increased ratio of perforated synapses induced by L-DOPA treatment, while coadministration of L-DOPA and MPEP reversed these postsynaptic effects. Finally, MPEP reduced overexpression of the two postsynaptic proteins (PSD-95 and SAP102) induced by L-DOPA treatment. Hence, these results provide evidence that aberrant neural plasticity at corticostriatal synapses in the striatum is closely correlated with the occurrence of LID, and targeted inhibition of mGluR5 by MPEP alleviates LID in the PD rat model.

Exploring the moderating effects of dopaminergic polymorphisms and childhood adversity on brain morphology in schizophrenia-spectrum disorders

Genetic and environmental etiologies may contribute to schizophrenia and its associated neurobiological profile. We examined the interaction between dopaminergic polymorphisms, childhood adversity and diagnosis (schizophrenia/schizoaffective disorder) on dopamine-related brain structures. Childhood adversity histories and structural MRI data were obtained from 249 (153 schizophrenia/schizoaffective, 96 controls) participants registered in the Australian Schizophrenia Research Bank. Polymorphisms in DRD2 and COMT were genotyped and a dopaminergic risk allelic load (RAL) was calculated. Regression analysis was used to test the main and interaction effects of RAL, childhood adversity and diagnosis on volumes of dopamine-related brain structures (caudate, putamen, nucleus accumbens, dorsolateral prefrontal cortex and hippocampus). A schizophrenia/schizoaffective diagnosis showed significant main effects on bilateral hippocampus, left dorsolateral prefrontal cortex and bilateral putamen volumes. RAL showed a significant main effect on left putamen volumes. Furthermore, across the whole sample, a significant two-way interaction between dopaminergic RAL and childhood adversity was found for left putamen volumes. No brain structure volumes were predicted by a three-way interaction that included diagnosis. Our finding suggests the left putamen may be particularly sensitive to dopaminergic gene-environment interactions regardless of diagnosis. However, larger studies are needed to assess whether these interactions are more or less pronounced in those with schizophrenia/schizoaffective disorders.

Effects of exercise and enrichment on behaviour in CD-1 mice

A host of scholarly work has characterized the positive effects of exercise and environmental enrichment on behaviour and cognition in animal studies. The purpose of this study was to investigate the uptake and longitudinal impact of exercise and enrichment on the behavioural phenotype of male and female CD-1 mice. CD-1 mice housed in standard (STD) or exercise and enrichment (EE) conditions post-weaning were tested in the 3-chamber sociability test, open field, and elevated plus maze and exercise activity was monitored throughout the enrichment protocol. Male and female EE mice both showed reduced anxiety and activity in the open field and elevated plus maze relative to sex-matched STD mice. EE altered social behaviours in a sex-specific fashion, with only female EE mice showing increased social preference relative to female STD mice and a preference for social novelty only present in male EE mice. This sexual dimorphism was not observed to be a product of exercise uptake, as CD-1 mice of both sexes demonstrated a consistent trend of wheel rotation frequencies. These findings suggest the importance of considering variables such as sex and strain on experimental design variables in future work on environmental enrichment.

Sensory Alterations in Patients with Isolated Idiopathic Dystonia: An Exploratory Quantitative Sensory Testing Analysis

Abnormalities in the somatosensory system are increasingly being recognized in patients with dystonia. The aim of this study was to investigate whether sensory abnormalities are confined to the dystonic body segments or whether there is a wider involvement in patients with idiopathic dystonia. For this purpose, we recruited 20 patients, 8 had generalized, 5 had segmental dystonia with upper extremity involvement, and 7 had cervical dystonia. In total, there were 13 patients with upper extremity involvement. We used Quantitative Sensory Testing (QST) at the back of the hand in all patients and at the shoulder in patients with cervical dystonia. The main finding on the hand QST was impaired cold detection threshold (CDT), dynamic mechanical allodynia (DMA), and thermal sensory limen (TSL). The alterations were present on both hands, but more pronounced on the side more affected with dystonia. Patients with cervical dystonia showed a reduced CDT and hot detection threshold (HDT), enhanced TSL and DMA at the back of the hand, whereas the shoulder QST only revealed increased cold pain threshold and DMA. In summary, QST clearly shows distinct sensory abnormalities in patients with idiopathic dystonia, which may also manifest in body regions without evident dystonia. Further studies with larger groups of dystonia patients are needed to prove the consistency of these findings.

Longitudinal increases of brain metabolite levels in 5-10 year old children

Longitudinal magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI) studies reveal significant changes in brain structure and structural networks that occur together with cognitive and behavioral maturation in childhood. However, the underlying cellular changes accompanying brain maturation are less understood. Examining regional age-related changes in metabolite levels provides insight into the physiology of neurodevelopment. Magnetic resonance spectroscopy (MRS) measures localize brain metabolism. The majority of neuroimaging studies of healthy development are from the developed world. In a longitudinal MRS study of 64 South African children aged 5 to 10 years old (29 female; 29 HIV exposed, uninfected), we examined the age-related trajectories of creatine (Cr+PCr), N-acetyl-aspartate (NAA), the combined NAA+N-acetyl-aspartyl-glutamate (NAAG), choline (GPC+PCh), glutamate (Glu) and the combined Glu+glutamine (Glu+Gln) in voxels within gray and white matter, as well as subcortically in the basal ganglia (BG). In frontal gray matter, we found age-related increases in Cr+PCr, NAA, NAA+NAAG and Glu+Gln levels pointing to synaptic activity likely related to learning. In the BG we observed increased levels of Glu, Glu+Gln and NAA+NAAG with age that point to subcortical synaptic reorganization. In white matter, we found increased levels of Cr+PCr, NAA, NAA+NAAG, Glu and Glu+Gln with age, implicating these metabolites in ongoing myelination. We observed no sex-age or HIV exposure-age interactions, indicating that physiological changes are independent of sex during this time period. The metabolite trajectories presented, therefore, provide a critical benchmark of normal cellular growth for a low socioeconomic pediatric population in the developing world against which pathology and abnormal development may be compared.

Cell Therapy for Parkinson's Disease: Only Young Onset Patients Allowed? Reflections about the Results of Recent Clinical Trials with Cell Therapy and the Progression of Parkinson's Disease

The selection of the best candidates for surgery among Parkinson's disease (PD) patients is a debated topic. This could be particularly important for transplantation studies in which patients with advanced PD and motor complications refractory to conventional pharmacological treatments are usually included. The development of lesions in nondopaminergic structures, which apparently are unaffected by the intervention, could eventually lead to the appearance of disabling, treatment-resistant symptoms. This has been considered as the crucial factor responsible for the outcome of any therapeutic procedure. However, other factors might be involved. It is suggested in this article that the rate of progression of PD and the effects of ageing are more important than the extradopaminergic involvement in the final outcome. Rate of progression of PD is critically related to the power of compensatory mechanisms, which are age related and under the control of still unknown genes. Thus, patients with young onset parkinsonism (YOP), either caused by gene mutations or not, could be the best candidates for surgery because they have a slower disease progression and more competent compensatory mechanisms. On the other hand, this can also explain the appearance of unexpected side effects such as the “runaway” dyskinesias reported following transplantation.

Disrupted functional connectivity between the periaqueductal gray and other brain regions in a rat model of recurrent headache

Functional connectivity (FC) has been used to investigate the pathophysiology of migraine. We aimed to identify atypical FC between the periaqueductal gray (PAG) and other brain areas in rats induced by repeated meningeal nociception. The rat model was established by infusing an inflammatory soup (IS) through supradural catheters in conscious rats. Quiescent and face-grooming behaviors were observed to assess nociceptive behavior. FC analysis seeded on the PAG was performed on rats 21 days after IS infusion. The rats exhibited nociceptive behavior correlates of human behaviors associated with migraine after IS infusion. The PAG showed increased FC with the prefrontal cortex, cingulate gyrus, and motor cortex but decreased FC with the basal ganglia, dorsal lateral thalamus, internal capsule and prelimbic cortex in the rat model. The atypical FC of the PAG with brain regions in the rat model that are involved in nociception, somatosensory processing, emotional processing, and pain modulation are consistent with the clinical data from migraineurs, indicate that resting-state FC changes in migraine patients may be a consequence of headache attacks, and further validate this rat model of chronic migraine.

Specific brain activation patterns associated with two neuromuscular electrical stimulation protocols

The influence of neuromuscular electrical stimulation (NMES) parameters on brain activation has been scarcely investigated. We aimed at comparing two frequently used NMES protocols - designed to vary in the extent of sensory input. Whole-brain functional magnetic resonance imaging was performed in sixteen healthy subjects during wide-pulse high-frequency (WPHF, 100 Hz–1 ms) and conventional (CONV, 25 Hz–0.05 ms) NMES applied over the triceps surae. Each protocol included 20 isometric contractions performed at 10% of maximal force. Voluntary plantar flexions (VOL) were performed as control trial. Mean force was not different among the three protocols, however, total current charge was higher for WPHF than for CONV. All protocols elicited significant activations of the sensorimotor network, cerebellum and thalamus. WPHF resulted in lower deactivation in the secondary somatosensory cortex and precuneus. Bilateral thalami and caudate nuclei were hyperactivated for CONV. The modulation of the NMES parameters resulted in differently activated/deactivated regions related to total current charge of the stimulation but not to mean force. By targeting different cerebral brain regions, the two NMES protocols might allow for individually-designed rehabilitation training in patients who can no longer execute voluntary movements.

Spatially Compact Neural Clusters in the Dorsal Striatum Encode Locomotion Relevant Information

An influential striatal model postulates that neural activities in the striatal direct and indirect pathways promote and inhibit movement, respectively. Normal behavior requires coordinated activity in the direct pathway to facilitate intended locomotion and indirect pathway to inhibit unwanted locomotion. In this striatal model, neuronal population activity is assumed to encode locomotion relevant information. Here, we propose a novel encoding mechanism for the dorsal striatum. We identified spatially compact neural clusters in both the direct and indirect pathways. Detailed characterization revealed similar cluster organization between the direct and indirect pathways, and cluster activities from both pathways were correlated with mouse locomotion velocities. Using machine-learning algorithms, cluster activities could be used to decode locomotion relevant behavioral states and locomotion velocity. We propose that neural clusters in the dorsal striatum encode locomotion relevant information and that coordinated activities of direct and indirect pathway neural clusters are required for normal striatal controlled behavior. VIDEO ABSTRACT.

Cdk5 Modulates Long-Term Synaptic Plasticity and Motor Learning in Dorsolateral Striatum

The striatum controls multiple cognitive aspects including motivation, reward perception, decision-making and motor planning. In particular, the dorsolateral striatum contributes to motor learning. Here we define an approach for investigating synaptic plasticity in mouse dorsolateral cortico-striatal circuitry and interrogate the relative contributions of neurotransmitter receptors and intracellular signaling components. Consistent with previous studies, we show that long-term potentiation (LTP) in cortico-striatal circuitry is facilitated by dopamine, and requires activation of D1-dopamine receptors, as well as NMDA receptors (NMDAR) and their calcium-dependent downstream effectors, including CaMKII. Moreover, we assessed the contribution of the protein kinase Cdk5, a key neuronal signaling molecule, in cortico-striatal LTP. Pharmacological Cdk5 inhibition, brain-wide Cdk5 conditional knockout, or viral-mediated dorsolateral striatal-specific loss of Cdk5 all impaired dopamine-facilitated LTP or D1-dopamine receptor-facilitated LTP. Selective loss of Cdk5 in dorsolateral striatum increased locomotor activity and attenuated motor learning. Taken together, we report an approach for studying synaptic plasticity in mouse dorsolateral striatum and critically implicate D1-dopamine receptor, NMDAR, Cdk5, and CaMKII in cortico-striatal plasticity. Furthermore, we associate striatal plasticity deficits with effects upon behaviors mediated by this circuitry. This approach should prove useful for the study of the molecular basis of plasticity in the dorsolateral striatum.

Decreased functional connectivity density in pain-related brain regions of female migraine patients without aura

Migraine is one of the most prevalent neurological disorders which is suggested to be associated with dysfunctions of the central nervous system. The purpose of the present study was to detect the altered functional connectivity architecture in the large-scale network of the whole brain in migraine without aura (MWoA). Meanwhile, the brain functional hubs which are targeted by MWoA could be identified. A new voxel-based method named functional connectivity density (FCD) mapping was applied to resting-state functional magnetic resonance imaging data of 55 female MWoA patients and 44 age-matched female healthy controls (HC). Comparing to HC, MWoA patients showed abnormal short-range FCD values in bilateral hippocampus, bilateral insula, right amygdale, right anterior cingulate cortex, bilateral putamen, bilateral caudate nucleus and the prefrontal cortex. The results suggested decreased intraregional connectivity of these pain-related brain regions in female MWoA. In addition, short-range FCD values in left prefrontal cortex, putamen and caudate nucleus were significantly negatively correlated with duration of disease in MWoA group, implying the repeated migraine attacks over time may consistently affect the resting-state functional connectivity architecture of these brain hubs. Our findings revealed the dysfunction of brain hubs in female MWoA, and suggested the left prefrontal cortex, putamen and caudate nucleus served as sensitive neuroimaging markers for reflecting the disease duration of female MWoA. This may provide us new insights into the changes in the organization of the large-scale brain network in MWoA.

Regional homogeneity abnormalities in patients with tension-type headache: a resting-state fMRI study

Tension-type headache (TTH) is the most prevalent type of primary headache. Many studies have shown that the pathogenesis of primary headache is associated with fine structural or functional changes. However, these studies were mainly based on migraine. The present study aimed to investigate whether TTH patients show functional disturbances compared with healthy subjects. We used restingstate functional magnetic resonance imaging (fMRI) and regional homogeneity (ReHo) analysis to identify changes in the local synchronization of spontaneous activity in patients with TTH. Ten patients with TTH and 10 age-, gender-, and education-matched healthy controls participated in the study. After demographic and clinical characteristics were acquired, a 3.0-T MRI system was used to obtain resting-state fMRIs. Compared with healthy controls, the TTH group exhibited significantly lower ReHo values in the bilateral caudate nucleus, the precuneus, the putamen, the left middle frontal gyrus, and the superior frontal gyrus. There was no correlation between mean ReHo values in TTH patients and duration of TTH, number of attacks, duration of daily attacks, Visual Analogue Scale score, or Headache Impact Test-6 score. These results suggest that TTH patients exhibit reduced synchronization of neuronal activity in multiple regions involved in the integration and processing of pain signals.

Functional dynamics of primate cortico-striatal networks during volitional movements

The motor cortex and dorsal striatum (caudate nucleus and putamen) are key regions in motor processing but the interface between the cortex and striatum is not well understood. While dorsal striatum integrates information from multiple brain regions to shape motor learning and habit formation, the disruption of cortico-striatal circuits compromises the functionality of these circuits resulting in a multitude of neurologic disorders, including Parkinson's disease. To better understand the modulation of the cortico-striatal circuits we recorded simultaneously single neuron activity from four brain regions, primary motor, and sensory cortices, together with the rostral and caudal segments of the putamen in rhesus monkeys performing a visual motor task. Results show that spatial and temporal-task related firing relationships between these cortico-striatal circuit regions were modified by the independent administration of the two drugs (cocaine and baclofen). Spatial tuning and correlated firing of neurons from motor cortex and putamen were severely disrupted by cocaine and baclofen on correct trials, while the two drugs have dramatically decreased the functional connectivity of the motor cortical-striatal network. These findings provide insight into the modulation of cortical-striatal firing related to movement with implications for therapeutic approaches to Parkinson's disease and related disorders.

Emerging concepts in the physiological basis of dystonia

Work over the past 2 decades has led to substantial changes in our understanding of dystonia pathophysiology. Three general abnormalities appear to underlie the pathophysiological substrate. The first is a loss of inhibition. This makes sense considering that it may be responsible for the excess of movement and for the overflow phenomena seen in dystonia. A second abnormality is sensory dysfunction which is related to the mild sensory complaints in patients with focal dystonias and may be responsible for some of the motor dysfunction. Third, evidence from animal models of dystonia as well as from patients with primary dystonia has revealed significant alterations of synaptic plasticity characterized by a disruption of homeostatic plasticity, with a prevailing facilitation of synaptic potentiation, together with the loss of synaptic inhibitory processes. We speculate that during motor learning this abnormal plasticity may lead to an abnormal sensorimotor integration, leading to consolidation of abnormal motor engrams. If so, then removing this abnormal plasticity might have little immediate effect on dystonic movements because bad motor memories have already been ''learned'' and are difficult to erase. These considerations might explain the delayed clinical effects of deep brain stimulation (DBS) in patients with generalized dystonia. Current lines of research will be discussed from a network perspective. © 2013 Movement Disorder Society.

Compulsivity, impulsivity, and the DSM-5 process

Compulsivity and impulsivity are cross-cutting, dimensional symptom domains that span traditional diagnostic boundaries. We examine compulsivity and impulsivity from several perspectives and present implications for these symptom domains as they relate to classification. We describe compulsivity and impulsivity as general concepts, from the perspectives of the Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5) Research Planning Agenda, and from the DSM-5 workgroups, literature reviews, and field trials. Finally, we detail alternative modes of classification for compulsivity and impulsivity in line with the Research Domain Criteria (RDoC) and International Classification of Diseases (ICD-11).

Spatial distribution of D1R- and D2R-expressing medium-sized spiny neurons differs along the rostro-caudal axis of the mouse dorsal striatum

The striatum projection neurons are striatonigral and striatopallidal medium-sized spiny neurons (MSNs) that preferentially express D1 (D1R) and D2 (D2R) dopamine receptors, respectively. It is generally assumed that these neurons are physically intermingled, without cytoarchitectural organization although this has not been tested. To address this question we used BAC transgenic mice expressing enhanced green fluorescence (EGFP) under the control of Drd1a or Drd2 promoter and spatial point pattern statistics. We demonstrate that D1R- and D2R-expressing MSNs are randomly distributed in most of the dorsal striatum, whereas a specific region in the caudal striatum, adjacent to the GPe, lacks neurons expressing markers for indirect pathway neurons. This area comprises almost exclusively D1R-expressing MSNs. These neurons receive excitatory inputs from the primary auditory cortex and the medial geniculate thalamic nucleus and a rich dopamine innervation. This area contains cholinergic and GABAergic interneurons but apparently no D2R/A2aR modulation because no fluorescence was detected in the neuropil of Drd2-EGFP or Drd2-Cre, and Adora-Cre BAC transgenic mice crossed with reporter mice. This striatal area that expresses calbindin D28k, VGluT1 and 2, is poor in μ opiate receptors and preproenkephalin. Altogether, the differences observed in D1R-MSNs, D2R-MSNs, and interneurons densities, as well as the anatomical segregation of D1R- and D2R/A2aR-expressing MSNs suggest that there are regional differences in the organization of the striatum.

Differential striatal spine pathology in Parkinson's disease and cocaine addiction: a key role of dopamine?

In the striatum, the dendritic tree of the two main populations of projection neurons, called "medium spiny neurons (MSNs)", are covered with spines that receive glutamatergic inputs from the cerebral cortex and thalamus. In Parkinson's disease (PD), striatal MSNs undergo an important loss of dendritic spines, whereas aberrant overgrowth of striatal spines occurs following chronic cocaine exposure. This review examines the possibility that opposite dopamine dysregulation is one of the key factors that underlies these structural changes. In PD, nigrostriatal dopamine degeneration results in a significant loss of dendritic spines in the dorsal striatum, while rodents chronically exposed to cocaine and other psychostimulants, display an increase in the density of "thin and immature" spines in the nucleus accumbens (NAc). In rodent models of PD, there is evidence that D2 dopamine receptor-containing MSNs are preferentially affected, while D1-positive cells are the main targets of increased spine density in models of addiction. However, such specificity remains to be established in primates. Although the link between the extent of striatal spine changes and the behavioral deficits associated with these disorders remains controversial, there is unequivocal evidence that glutamatergic synaptic transmission is significantly altered in both diseased conditions. Recent studies have suggested that opposite calcium-mediated regulation of the transcription factor myocyte enhancer factor 2 (MEF2) function induces these structural defects. In conclusion, there is strong evidence that dopamine is a major, but not the sole, regulator of striatal spine pathology in PD and addiction to psychostimulants. Further studies of the role of glutamate and other genes associated with spine plasticity in mediating these effects are warranted.

Action selection performance of a reconfigurable basal ganglia inspired model with Hebbian-Bayesian Go-NoGo connectivity

Several studies have shown a strong involvement of the basal ganglia (BG) in action selection and dopamine dependent learning. The dopaminergic signal to striatum, the input stage of the BG, has been commonly described as coding a reward prediction error (RPE), i.e., the difference between the predicted and actual reward. The RPE has been hypothesized to be critical in the modulation of the synaptic plasticity in cortico-striatal synapses in the direct and indirect pathway. We developed an abstract computational model of the BG, with a dual pathway structure functionally corresponding to the direct and indirect pathways, and compared its behavior to biological data as well as other reinforcement learning models. The computations in our model are inspired by Bayesian inference, and the synaptic plasticity changes depend on a three factor Hebbian–Bayesian learning rule based on co-activation of pre- and post-synaptic units and on the value of the RPE. The model builds on a modified Actor-Critic architecture and implements the direct (Go) and the indirect (NoGo) pathway, as well as the reward prediction (RP) system, acting in a complementary fashion. We investigated the performance of the model system when different configurations of the Go, NoGo, and RP system were utilized, e.g., using only the Go, NoGo, or RP system, or combinations of those. Learning performance was investigated in several types of learning paradigms, such as learning-relearning, successive learning, stochastic learning, reversal learning and a two-choice task. The RPE and the activity of the model during learning were similar to monkey electrophysiological and behavioral data. Our results, however, show that there is not a unique best way to configure this BG model to handle well all the learning paradigms tested. We thus suggest that an agent might dynamically configure its action selection mode, possibly depending on task characteristics and also on how much time is available.

Combinatorial topography and cell-type specific regulation of the ERK pathway by dopaminergic agonists in the mouse striatum

Therapeutic agents and drugs of abuse regulate the extracellular signal-regulated kinase (ERK) cascade signaling in the medium-sized spiny neurons (MSNs) of the striatum. However, whether this regulation is associated with specific cortical and thalamic inputs has never been studied. We used Drd2-EGFP BAC-transgenic mice to undertake a topographical and cell-type specific analysis of ERK phosphorylation and two of its downstream targets histone H3 and ribosomal protein S6 (rS6) in the dorsal striatum following injection of SKF81297 (D1R-like agonist), quinpirole (D2R-like agonist) or apomorphine (non selective DA receptor agonist). In striatal areas receiving inputs from the cingulate/prelimbic, visual and auditory cortex, SKF81297 treatment increased phosphorylation of ERK, histone H3 and rS6 selectively in EGFP-negative MSNs of Drd2-EGFP mice. In contrast, no regulation was found in striatal region predominantly targeted by the sensorimotor and motor cortex. Apomorphine slightly enhanced ERK and rS6, but not histone H3 phosphorylation. This regulation occurred exclusively in EGFP-negative neurons mostly in striatal sectors receiving connections from the insular, visual and auditory cortex. Quinpirole administration inhibited basal ERK activation but did not change histone H3 and rS6 phosphorylation throughout the rostrocaudal axis of the dorsal striatum. This anatomo-functional study indicates that D1R and D2R agonists produce a unique topography and cell-type specific regulation of the ERK cascade signaling in the mouse striatum, and that those patterns are closely associated with particular cortical and thalamic inputs. This work evidences the need of a precise identification of the striatal areas under study to further understand striatal plasticity.

Bidirectional plasticity in striatonigral synapses: a switch to balance direct and indirect basal ganglia pathways

There is no hypothesis to explain how direct and indirect basal ganglia (BG) pathways interact to reach a balance during the learning of motor procedures. Both pathways converge in the substantia nigra pars reticulata (SNr) carrying the result of striatal processing. Unfortunately, the mechanisms that regulate synaptic plasticity in striatonigral (direct pathway) synapses are not known. Here, we used electrophysiological techniques to describe dopamine D(1)-receptor-mediated facilitation in striatonigral synapses in the context of its interaction with glutamatergic inputs, probably coming from the subthalamic nucleus (STN) (indirect pathway) and describe a striatonigral cannabinoid-dependent long-term synaptic depression (LTD). It is shown that striatonigral afferents exhibit D(1)-receptor-mediated facilitation of synaptic transmission when NMDA receptors are inactive, a phenomenon that changes to cannabinoid-dependent LTD when NMDA receptors are active. This interaction makes SNr neurons become coincidence-detector switching ports: When inactive, NMDA receptors lead to a dopamine-dependent enhancement of direct pathway output, theoretically facilitating movement. When active, NMDA receptors result in LTD of the same synapses, thus decreasing movement. We propose that SNr neurons, working as logical gates, tune the motor system to establish a balance between both BG pathways, enabling the system to choose appropriate synergies for movement learning and postural support.

Migraine attacks the Basal Ganglia

Background

With time, episodes of migraine headache afflict patients with increased frequency, longer duration and more intense pain. While episodic migraine may be defined as 1-14 attacks per month, there are no clear-cut phases defined, and those patients with low frequency may progress to high frequency episodic migraine and the latter may progress into chronic daily headache (> 15 attacks per month). The pathophysiology of this progression is completely unknown. Attempting to unravel this phenomenon, we used high field (human) brain imaging to compare functional responses, functional connectivity and brain morphology in patients whose migraine episodes did not progress (LF) to a matched (gender, age, age of onset and type of medication) group of patients whose migraine episodes progressed (HF).

Results

In comparison to LF patients, responses to pain in HF patients were significantly lower in the caudate, putamen and pallidum. Paradoxically, associated with these lower responses in HF patients, gray matter volume of the right and left caudate nuclei were significantly larger than in the LF patients. Functional connectivity analysis revealed additional differences between the two groups in regard to response to pain.

Conclusions

Supported by current understanding of basal ganglia role in pain processing, the findings suggest a significant role of the basal ganglia in the pathophysiology of the episodic migraine.

Huntington's Disease

Huntington's disease (HD) is the most common inherited neurodegenerative disease and is characterized by uncontrolled excessive motor movements and cognitive and emotional deficits. The mutation responsible for HD leads to an abnormally long polyglutamine (polyQ) expansion in the huntingtin (Htt) protein, which confers one or more toxic functions to mutant Htt leading to neurodegeneration. The polyQ expansion makes Htt prone to aggregate and accumulate, and manipulations that mitigate protein misfolding or facilitate the clearance of misfolded proteins tend to slow disease progression in HD models. This article will focus on HD and the evidence that it is a conformational disease.

CSC counteracts l-DOPA-induced overactivity of the corticostriatal synaptic ultrastructure and function in 6-OHDA-lesioned rats

l-DOPA remains the gold-standard treatment for Parkinson's disease (PD). However, the emergence of l-DOPA-induced dyskinesia (LID) and motor fluctuations represents a major clinical problem in PD. The selective localization of adenosine A(2A) receptors to the basal ganglia and specifically to the indirect output pathway appear to be crucial both in the pathogenesis of PD and in the development of LID. In this study, we investigated the effects of a 3-week treatment with l-DOPA (50mg/kg/day+benserazide 12.5mg/kg/day, twice daily, i.p.) alone or combined with adenosine A(2A) receptor antagonist 8-(3-Chlorostyryl)caffeine (CSC) (5mg/kg/day, twice daily), on the rotational motor response duration, abnormal involuntary movements (AIM) and the associated striatal expression of adenosine A(2A) receptor in rats with a nigrostriatal lesion. CSC treatment ameliorated the shortening of the rotational motor response duration, partly attenuated dyskinesia and reduced striatal expression of adenosine A(2A) receptor induced by l-DOPA. Electron microscopy technique results showed that the postsynapse density depth was much thicker, synapse cleft width was narrower and the ratio of perforated synapses significantly increased in the l-DOPA-treated rats, while systemic coadministration of CSC with l-DOPA attenuated the overactivity of corticostriatal synaptic ultrastructure and function induced by l-DOPA. In conclusion, CSC by means of its dual action as A(2A) receptor antagonist and MAO-B inhibitor ameliorated the changed behavior, expression of adenosine A(2A) receptor and postsynaptic effects, observed in the 6-OHDA-lesioned rats, pointing out to its potential benefit for the treatment of LID.

Cadmium effects on 24h changes in glutamate, aspartate, glutamine, GABA and taurine content of rat striatum

This work evaluates the possible changes in 24 h variations of striatal aspartate, glutamate, glutamine, gamma-aminobutyric acid (GABA) and taurine content after oral cadmium treatment. Male rats were submitted to cadmium exposure at two doses (25 and 50 mg/L of cadmium chloride (CdCl(2))) in the drinking water for 30 days. Control rats received cadmium-free water. After the treatment, rats were killed at six different time intervals throughout a 24 h cycle. Differential effects of cadmium on 24 h amino acid fluctuations were observed. Metal exposure modified the daily pattern of the amino acids concentration found in control animals, except for GABA and taurine with the lowest dose used. Exposure to 25 mg/L of CdCl(2) decreased mean content of aspartate, as well as GABA concentration. These results suggest that cadmium exposure affects 24 h changes of the studied amino acids concentration in the striatum, and those changes may be related to alterations in striatal function.

A key role of the basal ganglia in pain and analgesia--insights gained through human functional imaging

The basal ganglia (BG) are composed of several nuclei involved in neural processing related to the execution of motor, cognitive and emotional activities. Preclinical and clinical data have implicated a role for these structures in pain processing. Recently neuroimaging has added important information on BG activation in conditions of acute pain, chronic pain and as a result of drug effects. Our current understanding of alterations in cortical and sub-cortical regions in pain suggests that the BG are uniquely involved in thalamo-cortico-BG loops to integrate many aspects of pain. These include the integration of motor, emotional, autonomic and cognitive responses to pain.

Effect of L-Dopa on metabotropic glutamate receptor 5 in the brain of parkinsonian monkeys

Behavioral investigations of selective and potent metabotropic glutamate receptor type 5 (mGluR5) antagonists in animal models suggest involvement of mGluR5 in compensatory mechanisms of the basal ganglia circuitry in Parkinson's disease and levodopa (L-Dopa) induced motor complications. This study investigated mGluR5 changes in MPTP lesioned monkeys. The effect of a chronic 1 month treatment with L-Dopa on mGluR5-specific binding and mRNA levels was investigated in MPTP monkeys killed 4 or 24 h after their last L-Dopa administration. [(3)H]ABP688 specific binding in the putamen was elevated in L-Dopa-treated MPTP monkeys killed 24 h but not 4 h after their last L-Dopa dose compared with vehicle-treated MPTP monkeys. Caudate nucleus [(3)H]ABP688-specific binding was elevated in both groups of L-Dopa treated compared with vehicle-treated MPTP monkeys. In contrast, caudate nucleus and putamen mGluR5 mRNA levels were elevated only in L-Dopa-treated MPTP monkeys killed 4 h after their last L-Dopa administration. MPTP monkeys killed 4 h after their last L-Dopa treatment showed higher caudate nucleus and putamen L-Dopa concentrations compared with those killed after 24 h. Hence, mGluR5 in the putamen are sensitive to presence of L-Dopa leading to a rapid decrease of [(3)H]ABP688-specific binding possibly involving a direct mGluR5/dopamine receptors interaction.

Loss of laterality in chronic cocaine users: an fMRI investigation of sensorimotor control

Movement disturbances are often overlooked consequences of chronic cocaine abuse. The purpose of this study was to systematically investigate sensorimotor performance in chronic cocaine users and characterize changes in brain activity among movement-related regions of interest (ROIs) in these users. Functional magnetic resonance imaging data were collected from 14 chronic cocaine users and 15 age- and gender-matched controls. All participants performed a sequential finger-tapping task with their dominant, right hand interleaved with blocks of rest. For each participant, percent signal change from rest was calculated for seven movement-related ROIs in both the left and right hemisphere. Cocaine users had significantly longer reaction times and higher error rates than controls. Whereas the controls used a left-sided network of motor-related brain areas to perform the task, cocaine users activated a less lateralized pattern of brain activity. Users had significantly more activity in the ipsilateral (right) motor and premotor cortical areas, anterior cingulate cortex and the putamen than controls. These data demonstrate that, in addition to the cognitive and affective consequences of chronic cocaine abuse, there are also pronounced alterations in sensorimotor control in these individuals, which are associated with functional alterations throughout movement-related neural networks.

Neurological considerations: autism and Parkinson's disease

Within the spectrum of disorders that manifest obsessive-compulsive (OC) features lies a sub-cluster of neurological conditions. Autism and Parkinson's disease (PD) are examples of two such neurological disorders that seem quite dissimilar on the surface. Yet, both conditions can include repetitive behaviors of a compulsive-impulsive nature. Furthermore, while autism and PD differ in other associated symptom domains that shape the course of each disorder, both disorders share some phenomenology in the core domain of repetitive behaviors and involve basal ganglia and frontal lobe dysfunction, similar to OC disorder (OCD). Accordingly, examination of the similarities and differences between autism and PD may provide insight into the pathophysiology and treatment of OC spectrum disorders. The current review focuses on the phenomenology, comorbidity, course of illness, family history, brain circuitry, and treatment of autism and PD, as they relate to OCD and OC spectrum disturbances.

Development of large-scale functional brain networks in children

Large-scale rewiring of brain circuits in children leads to emergence of hierarchical organization in the mature adult brain.

The ontogeny of large-scale functional organization of the human brain is not well understood. Here we use network analysis of intrinsic functional connectivity to characterize the organization of brain networks in 23 children (ages 7–9 y) and 22 young-adults (ages 19–22 y). Comparison of network properties, including path-length, clustering-coefficient, hierarchy, and regional connectivity, revealed that although children and young-adults' brains have similar “small-world” organization at the global level, they differ significantly in hierarchical organization and interregional connectivity. We found that subcortical areas were more strongly connected with primary sensory, association, and paralimbic areas in children, whereas young-adults showed stronger cortico-cortical connectivity between paralimbic, limbic, and association areas. Further, combined analysis of functional connectivity with wiring distance measures derived from white-matter fiber tracking revealed that the development of large-scale brain networks is characterized by weakening of short-range functional connectivity and strengthening of long-range functional connectivity. Importantly, our findings show that the dynamic process of over-connectivity followed by pruning, which rewires connectivity at the neuronal level, also operates at the systems level, helping to reconfigure and rebalance subcortical and paralimbic connectivity in the developing brain. Our study demonstrates the usefulness of network analysis of brain connectivity to elucidate key principles underlying functional brain maturation, paving the way for novel studies of disrupted brain connectivity in neurodevelopmental disorders such as autism.

The disruption of normal brain organization in humans is believed to underlie a number of behavioral conditions, such as autism spectrum disorders (ASD) and attention-deficit/hyperactivity disorder (ADHD). To gain insight into how normal brain organization develops, we mapped functional brain connectivity in children and young adults, and used a network analysis to characterize and compare the organization of brain networks. Comparison of network properties revealed that while children and young adults' brains have similar organization at the global level, there were several key differences in connectivity. For example, children's brains had less of a hierarchical organization than young-adults. Most importantly, we show that the dynamic process of over-connectivity followed by pruning, which rewires connectivity at the neuronal level, also operates at the systems level, reconfiguring and rebalancing subcortical and paralimbic connectivity in the developing brain. Our findings demonstrate the utility of using network analyses of multimodal brain connectivity to study maturation of brain circuits, and suggest new avenues for future research on neurodevelopmental disorders such as ASD and ADHD.

Impact of serotonin 2C receptor null mutation on physiology and behavior associated with nigrostriatal dopamine pathway function

The impact of serotonergic neurotransmission on brain dopaminergic pathways has substantial relevance to many neuropsychiatric disorders. A particularly prominent role has been ascribed to the inhibitory effects of serotonin 2C receptor (5-HT(2C)R) activation on physiology and behavior mediated by the mesolimbic dopaminergic pathway, particularly in the terminal region of the nucleus accumbens. The influence of this receptor subtype on functions mediated by the nigrostriatal dopaminergic pathway is less clear. Here we report that a null mutation eliminating expression of 5-HT(2C)Rs produces marked alterations in the activity and functional output of this pathway. 5-HT(2C)R mutant mice displayed increased activity of substantia nigra pars compacta (SNc) dopaminergic neurons, elevated baseline extracellular dopamine concentrations in the dorsal striatum (DSt), alterations in grooming behavior, and enhanced sensitivity to the stereotypic behavioral effects of d-amphetamine and GBR 12909. These psychostimulant responses occurred in the absence of phenotypic differences in drug-induced extracellular dopamine concentration, suggesting a phenotypic alteration in behavioral responses to released dopamine. This was further suggested by enhanced behavioral responses of mutant mice to the D(1) receptor agonist SKF 81297. Differences in DSt D(1) or D(2) receptor expression were not found, nor were differences in medium spiny neuron firing patterns or intrinsic membrane properties following dopamine stimulation. We conclude that 5-HT(2C)Rs regulate nigrostriatal dopaminergic activity and function both at SNc dopaminergic neurons and at a locus downstream of the DSt.

A role for dopamine in temporal decision making and reward maximization in parkinsonism

Converging evidence implicates striatal dopamine (DA) in reinforcement learning, such that DA increases enhance "Go learning" to pursue actions with rewarding outcomes, whereas DA decreases enhance "NoGo learning" to avoid non-rewarding actions. Here we test whether these effects apply to the response time domain. We employ a novel paradigm which requires the adjustment of response times to a single response. Reward probability varies as a function of response time, whereas reward magnitude changes in the opposite direction. In the control condition, these factors exactly cancel, such that the expected value across time is constant (CEV). In two other conditions, expected value increases (IEV) or decreases (DEV), such that reward maximization requires either speeding up (Go learning) or slowing down (NoGo learning) relative to the CEV condition. We tested patients with Parkinson's disease (depleted striatal DA levels) on and off dopaminergic medication, compared with age-matched controls. While medicated, patients were better at speeding up in the DEV relative to CEV conditions. Conversely, nonmedicated patients were better at slowing down to maximize reward in the IEV condition. These effects of DA manipulation on cumulative Go/NoGo response time adaptation were captured with our a priori computational model of the basal ganglia, previously applied only to forced-choice tasks. There were also robust trial-to-trial changes in response time, but these single trial adaptations were not affected by disease or medication and are posited to rely on extrastriatal, possibly prefrontal, structures.

Loss of functional specificity in the dorsal striatum of chronic cocaine users

BACKGROUND

Although research into the effects of cocaine has focused on the ventral striatum, recent reports have identified a significant role for the dorsal striatum. Given the importance of the dorsal striatum in motor control, the purpose of the present study was to investigate potential sensorimotor deficits among cocaine users and the functional basis of these deficits within the striatum.

METHODS

Functional magnetic resonance imaging data were collected from 14 right-handed, non-treatment seeking chronic cocaine users and 14 age and gender matched controls during performance of two finger-sequencing paradigms that differentially activate the caudate (internally-guided) and the putamen (externally-guided) interleaved with blocks of rest. The total percent signal change in the dorsal striatum and the contribution of the left and right caudate and putamen were calculated and compared across groups and tasks.

RESULTS

Significant deficits in sensorimotor control were observed in cocaine users for both motor tasks, with the most severe impairments present during internally-guided movements. Cocaine users lacked the typical functional segregation observed in the dorsal striatum of the control subjects. The total percent signal change in the dorsal striatum was not significantly different between the groups, but cocaine users activated significantly less contralateral caudate and putamen for internally-guided versus externally-guided movements, respectively.

CONCLUSION

These data provide clear evidence that chronic cocaine users have significant motor performance deficits that are accompanied by disrupted processing within the dorsal striatum. These data suggest the effects of cocaine extend beyond the confines of the motivational domains of the ventral striatum.

Learning processing in the basal ganglia: a mosaic of broken mirrors

In the present review we propose a model to explain the role of the basal ganglia in sensorimotor and cognitive functions based on a growing body of behavioural, anatomical, physiological, and neurochemical evidence accumulated over the last decades. This model proposes that the body and its surrounding environment are represented in the striatum in a fragmented and repeated way, like a mosaic consisting of the fragmented images of broken mirrors. Each fragment forms a functional unit representing articulated parts of the body with motion properties, objects of the environment which the subject can approach or manipulate, and locations the subject can move to. These units integrate the sensory properties and movements related to them. The repeated and widespread distribution of such units amplifies the combinatorial power of the associations among them. These associations depend on the phasic release of dopamine in the striatum triggered by the saliency of stimuli and will be reinforced by the rewarding consequences of the actions related to them. Dopamine permits synaptic plasticity in the corticostriatal synapses. The striatal units encoding the same stimulus/action send convergent projections to the internal segment of the globus pallidus (GPi) and to the substantia nigra pars reticulata (SNr) that stimulate or hold the action through a thalamus-frontal cortex pathway. According to this model, this is how the basal ganglia select actions based on environmental stimuli and store adaptive associations as nondeclarative memories such as motor skills, habits, and memories formed by Pavlovian and instrumental conditioning.

An MRI study of age-related white and gray matter volume changes in the rhesus monkey

We applied the automated MRI segmentation technique Template Driven Segmentation (TDS) to dual-echo spin echo (DE SE) images of eight young (5-12 years), six middle-aged (16-19 years) and eight old (24-30 years) rhesus monkeys. We analyzed standardized mean volumes for 18 anatomically defined regions of interest (ROI's) and found an overall decrease from young to old age in the total forebrain (5.01%), forebrain parenchyma (5.24%), forebrain white matter (11.53%), forebrain gray matter (2.08%), caudate nucleus (11.79%) and globus pallidus (18.26%). Corresponding behavioral data for five of the young, five of the middle-aged and seven of the old subjects on the Delayed Non-matching to Sample (DNMS) task, the Delayed-recognition Span Task (DRST) and the Cognitive Impairment Index (CII) were also analyzed. We found that none of the cognitive measures were related to ROI volume changes in our sample size of monkeys.

Bursting in substantia nigra pars reticulata neurons in vitro: possible relevance for Parkinson disease

Projection neurons of the substantia nigra reticulata (SNr) convey basal ganglia (BG) processing to thalamocortical and brain stem circuits responsible for movement. Two models try to explain pathological BG performance during Parkinson disease (PD): the rate model, which posits an overexcitation of SNr neurons due to hyperactivity in the indirect pathway and hypoactivity of the direct pathway, and the oscillatory model, which explains PD as the product of pathological pattern generators disclosed by dopamine reduction. These models are, apparently, incompatible. We tested the predictions of the rate model by increasing the excitatory drive and reducing the inhibition on SNr neurons in vitro. This was done pharmacologically with bath application of glutamate agonist N-methyl-d-aspartate and GABA(A) receptor blockers, respectively. Both maneuvers induced bursting behavior in SNr neurons. Therefore synaptic changes forecasted by the rate model induce the electrical behavior predicted by the oscillatory model. In addition, we found evidence that Ca(V)3.2 Ca(2+) channels are a critical step in generating the bursting firing pattern in SNr neurons. Other ion channels involved are: hyperpolarization-activated cation channels, high-voltage-activated Ca(2+) channels, and Ca(2+)-activated K(+) channels. However, although these channels shape the temporal structure of bursting, only Ca(V)3.2 Ca(2+) channels are indispensable for the initiation of the bursting pattern.

Dopamine-dependent long term potentiation in the dorsal striatum is reduced in the R6/2 mouse model of Huntington's disease

The striatum is critically important in motor, cognitive and emotional functions, as highlighted in neurological disorders such as Huntington's disease (HD) where these functions are compromised. The R6/2 mouse model of HD shows progressive motor and cognitive impairments and alterations in striatal dopamine and glutamate release. To determine whether or not dopamine-dependent neuronal plasticity is also altered in the dorsolateral striatum of R6/2 mice, we compared long term potentiation (LTP) and long term depression (LTD) in striatal slices from R6/2 mice with that seen in slices from wild type (WT) mice. In adult WT mice (aged 8-19 weeks), frequency-dependent bidirectional plasticity was observed. High frequency stimulation (four 0.5 s trains at 100 Hz, inter-train interval 10 s) induced LTP (134+/-5% of baseline), while low frequency stimulation (4 Hz for 15 min) induced LTD (80+/-5% of baseline). LTP and LTD were significantly blocked by the N-methyl-D-aspartic acid (NMDA) receptor antagonist D(-)-2-amino-5-phosphonopentanoic acid (D-AP5) (to 93+/-6% and 103+/-8% of baseline respectively), indicating that they are both dependent on NMDA glutamate receptor activation. LTP was significantly blocked by the dopamine D1 receptor antagonist R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride (SCH-23390) (98+/-8% of baseline), indicating that LTP is dependent on activation of dopamine D(1)-type receptors, whereas LTD was not significantly different (90+/-7%). In adult R6/2 mice (aged 8-19 weeks), LTP was significantly reduced (to 110+/-4% of baseline), while LTD was not significantly different from that seen in WT mice (85+/-6%). These data show that R6/2 mice have impaired dopamine-dependent neuronal plasticity in the striatum. As dopamine-dependent plasticity is a proposed model of striatum-based motor and cognitive functions, this impairment could contribute to deficits seen in R6/2 mice.

Single unit and population responses during inhibitory gating of striatal activity in freely moving rats

The striatum is thought to be an essential region for integrating diverse information in the brain. Rapid inhibitory gating (IG) of sensory input is most likely an early factor necessary for appropriate integration to be completed. Gating is currently evaluated in clinical settings and is dramatically altered in a variety of psychiatric illnesses. Basic neuroscience research using animals has revealed specific neural sites involved in IG including the hippocampus, thalamus, brainstem, amygdala and medial prefrontal cortex. The present study investigated local IG in the basal ganglia structure of the striatum using chronic recording microwires. We obtained both single unit activations and local field potentials (LFPs) in awake behaving rats from each wire during the standard two-tone paradigm. Single units responded with different types of activations including a phasic and sustained excitation, an inhibitory response and a combination response that contained both excitatory and inhibitory components. IG was observed in all the response types; however, non-gating was observed in a large proportion of responses as well. Positive wave field potentials at 50-60 ms post-stimulus (P60) showed consistent gating across the wire arrays. No significant correlations were found between single unit and LFP measures of gating during the initial baseline session. Gating was strengthened (Tamp/Camp ratios approaching 0) following acute stress (saline injection) at both the single unit and LFP level due to the reduction in the response to the second tone. Alterations in sensory responding reflected by changes in the neural response to the initial tone were primarily observed following long-term internal state deviation (food deprivation) and during general locomotion. Overall, our results support local IG by single neurons in striatum but also suggest that rapid inhibition is not the dominant activation profile observed in other brain regions.

Temporal dynamics of basal ganglia response and connectivity during verbal working memory

Research on the neural basis of working memory (WM) has generally focused on neocortical regions; comparatively little is known about the role of subcortical structures. There is growing evidence that the basal ganglia are involved in WM, but their contribution to different component processes of WM is poorly understood. We examined the temporal dynamics of basal ganglia response and connectivity during the encoding, maintenance and response phases of a Sternberg WM task. During the encoding and maintenance phases, WM-load-dependent activation was observed in the left anterior caudate, anterior putamen and globus pallidus; activation in the right anterior caudate was observed only during the maintenance phase. During the response phase, the basal ganglia were equally active in both the high-load and low-load WM conditions. Caudate and putamen activations were primarily localized to the (rostral) associative parts of the basal ganglia, consistent with the putative role of these regions in cognitive processing. Effective connectivity analyses revealed increased WM-load-dependent interaction of the left anterior caudate with the left posterior parietal cortex during all three phases of the task; with the visual association cortex, including the fusiform gyrus and inferior temporal gyrus, only during the encoding phase; with the ventrolateral prefrontal cortex during the encoding and maintenance phases; with the pre-supplementary motor area during the maintenance and response phases; and with the dorsolateral prefrontal and anterior cingulate cortices only during the response phase. Taken together with known neuroanatomy of the basal ganglia, these results suggest that the anterior caudate helps to link signals in distinct functional networks during different phases of the WM task. Our study offers new insight into the integrative and adaptive role of the basal ganglia in higher cognitive function.

Visuomotor learning in immersive 3D virtual reality in Parkinson's disease and in aging

Successful adaptation to novel sensorimotor contexts critically depends on efficient sensory processing and integration mechanisms, particularly those required to combine visual and proprioceptive inputs. If the basal ganglia are a critical part of specialized circuits that adapt motor behavior to new sensorimotor contexts, then patients who are suffering from basal ganglia dysfunction, as in Parkinson's disease should show sensorimotor learning impairments. However, this issue has been under-explored. We tested the ability of 8 patients with Parkinson's disease (PD), off medication, ten healthy elderly subjects and ten healthy young adults to reach to a remembered 3D location presented in an immersive virtual environment. A multi-phase learning paradigm was used having four conditions: baseline, initial learning, reversal learning and aftereffect. In initial learning, the computer altered the position of a simulated arm endpoint used for movement feedback by shifting its apparent location diagonally, requiring thereby both horizontal and vertical compensations. This visual distortion forced subjects to learn new coordinations between what they saw in the virtual environment and the actual position of their limbs, which they had to derive from proprioceptive information (or efference copy). In reversal learning, the sign of the distortion was reversed. Both elderly subjects and PD patients showed learning phase-dependent difficulties. First, elderly controls were slower than young subjects when learning both dimensions of the initial biaxial discordance. However, their performance improved during reversal learning and as a result elderly and young controls showed similar adaptation rates during reversal learning. Second, in striking contrast to healthy elderly subjects, PD patients were more profoundly impaired during the reversal phase of learning. PD patients were able to learn the initial biaxial discordance but were on average slower than age-matched controls in adapting to the horizontal component of the biaxial discordance. More importantly, when the biaxial discordance was reversed, PD patients were unable to make appropriate movement corrections. Therefore, they showed significantly degraded learning indices relative to age-matched controls for both dimensions of the biaxial discordance. Together, these results suggest that the ability to adapt to a sudden biaxial visuomotor discordance applied in three-dimensional space declines in normal aging and Parkinson disease. Furthermore, the presence of learning rate differences in the PD patients relative to age-matched controls supports an important contribution of basal ganglia-related circuits in learning novel visuomotor coordinations, particularly those in which subjects must learn to adapt to sensorimotor contingencies that were reversed from those just learned.