A spiking self-organizing map combining STDP, oscillations, and continuous learning

The self-organizing map (SOM) is a neural network algorithm to create topographically ordered spatial representations of an input data set using unsupervised learning. The SOM algorithm is inspired by the feature maps found in mammalian cortices but lacks some important functional properties of its biological equivalents. Neurons have no direct access to global information, transmit information through spikes and may be using phasic coding of spike times within synchronized oscillations, receive continuous input from the environment, do not necessarily alter network properties such as learning rate and lateral connectivity throughout training, and learn through relative timing of action potentials across a synaptic connection. In this paper, a network of integrate-and-fire neurons is presented that incorporates solutions to each of these issues through the neuron model and network structure. Results of the simulated experiments assessing map formation using artificial data as well as the Iris and Wisconsin Breast Cancer datasets show that this novel implementation maintains fundamental properties of the conventional SOM, thereby representing a significant step toward further understanding of the self-organizational properties of the brain while providing an additional method for implementing SOMs that can be utilized for future modeling in software or special purpose spiking neuron hardware.

Dopamine preferentially inhibits NMDA receptor-mediated EPSCs by acting on presynaptic D1 receptors in nucleus accumbens during postnatal development

Nucleus accumbens (nAcb), a major site of action of drugs of abuse and dopamine (DA) signalling in MSNs (medium spiny neurons), is critically involved in mediating behavioural responses of drug addiction. Most studies have evaluated the effects of DA on MSN firing properties but thus far, the effects of DA on a cellular circuit involving glutamatergic afferents to the nAcb have remained rather elusive. In this study we attempted to characterize the effects of dopamine (DA) on evoked glutamatergic excitatory postsynaptic currents (EPSCs) in nAcb medium spiny (MS) neurons in 1 to 21 day-old rat pups. The EPSCs evoked by local nAcb stimuli displayed both AMPA/KA and NMDA receptor-mediated components. The addition of DA to the superfusing medium produced a marked decrease of both components of the EPSCs that did not change during the postnatal period studied. Pharmacologically isolated AMPA/KA receptor-mediated response was inhibited on average by 40% whereas the isolated NMDA receptor-mediated EPSC was decreased by 90%. The effect of DA on evoked EPSCs were mimicked by the D₁-like receptor agonist SKF 38393 and antagonized by the D₁-like receptor antagonist SCH 23390 whereas D₂-like receptor agonist or antagonist respectively failed to mimic or to block the action of DA. DA did not change the membrane input conductance of MS neurons or the characteristics of EPSCs produced by the local administration of glutamate in the presence of tetrodotoxin. In contrast, DA altered the paired-pulse ratio of evoked EPSCs. The present results show that the activation D₁-like dopaminergic receptors modulate glutamatergic neurotransmission by preferentially inhibiting NMDA receptor-mediated EPSC through presynaptic mechanisms.

Virtual environments for the transfer of navigation skills in the blind: a comparison of directed instruction vs. video game based learning approaches

For profoundly blind individuals, navigating in an unfamiliar building can represent a significant challenge. We investigated the use of an audio-based, virtual environment called Audio-based Environment Simulator (AbES) that can be explored for the purposes of learning the layout of an unfamiliar, complex indoor environment. Furthermore, we compared two modes of interaction with AbES. In one group, blind participants implicitly learned the layout of a target environment while playing an exploratory, goal-directed video game. By comparison, a second group was explicitly taught the same layout following a standard route and instructions provided by a sighted facilitator. As a control, a third group interacted with AbES while playing an exploratory, goal-directed video game however, the explored environment did not correspond to the target layout. Following interaction with AbES, a series of route navigation tasks were carried out in the virtual and physical building represented in the training environment to assess the transfer of acquired spatial information. We found that participants from both modes of interaction were able to transfer the spatial knowledge gained as indexed by their successful route navigation performance. This transfer was not apparent in the control participants. Most notably, the game-based learning strategy was also associated with enhanced performance when participants were required to find alternate routes and short cuts within the target building suggesting that a ludic-based training approach may provide for a more flexible mental representation of the environment. Furthermore, outcome comparisons between early and late blind individuals suggested that greater prior visual experience did not have a significant effect on overall navigation performance following training. Finally, performance did not appear to be associated with other factors of interest such as age, gender, and verbal memory recall. We conclude that the highly interactive and immersive exploration of the virtual environment greatly engages a blind user to develop skills akin to positive near transfer of learning. Learning through a game play strategy appears to confer certain behavioral advantages with respect to how spatial information is acquired and ultimately manipulated for navigation.

Biologic scaffold for CNS repair

Injury to the CNS typically results in significant morbidity and endogenous repair mechanisms are limited in their ability to restore fully functional CNS tissue. Biologic scaffolds composed of individual purified components have been shown to facilitate functional tissue reconstruction following CNS injury. Extracellular matrix scaffolds derived from mammalian tissues retain a number of bioactive molecules and their ability for CNS repair has recently been recognized. In addition, novel biomaterials for dural mater repairs are of clinical interest as the dura provides barrier function and maintains homeostasis to CNS. The present article describes the application of regenerative medicine principles to the CNS tissues and dural mater repair. While many approaches have been exploring the use of cells and/or therapeutic molecules, the strategies described herein focus upon the use of extracellular matrix scaffolds derived from mammalian tissues that are free of cells and exogenous factors.

Calcium signaling in Parkinson's disease

Calcium (Ca(2+)) is an almost universal second messenger that regulates important activities of all eukaryotic cells. It is of critical importance to neurons, which have developed extensive and intricate pathways to couple the Ca(2+) signal to their biochemical machinery. In particular, Ca(2+) participates in the transmission of the depolarizing signal and contributes to synaptic activity. During aging and in neurodegenerative disease processes, the ability of neurons to maintain an adequate energy level can be compromised, thus impacting on Ca(2+) homeostasis. In Parkinson's disease (PD), many signs of neurodegeneration result from compromised mitochondrial function attributable to specific effects of toxins on the mitochondrial respiratory chain and/or to genetic mutations. Despite these effects being present in almost all cell types, a distinguishing feature of PD is the extreme selectivity of cell loss, which is restricted to the dopaminergic neurons in the ventral portion of the substantia nigra pars compacta. Many hypotheses have been proposed to explain such selectivity, but only recently it has been convincingly shown that the innate autonomous activity of these neurons, which is sustained by their specific Cav1.3 L-type channel pore-forming subunit, is responsible for the generation of basal metabolic stress that, under physiological conditions, is compensated by mitochondrial buffering. However, when mitochondria function becomes even partially compromised (because of aging, exposure to environmental factors or genetic mutations), the metabolic stress overwhelms the protective mechanisms, and the process of neurodegeneration is engaged. The characteristics of Ca(2+) handling in neurons of the substantia nigra pars compacta and the possible involvement of PD-related proteins in the control of Ca(2+) homeostasis will be discussed in this review.

Antioxidant gene therapy against neuronal cell death

Oxidative stress is a common hallmark of neuronal cell death associated with neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, as well as brain stroke/ischemia and traumatic brain injury. Increased accumulation of reactive species of both oxygen (ROS) and nitrogen (RNS) has been implicated in mitochondrial dysfunction, energy impairment, alterations in metal homeostasis and accumulation of aggregated proteins observed in neurodegenerative disorders, which lead to the activation/modulation of cell death mechanisms that include apoptotic, necrotic and autophagic pathways. Thus, the design of novel antioxidant strategies to selectively target oxidative stress and redox imbalance might represent important therapeutic approaches against neurological disorders. This work reviews the evidence demonstrating the ability of genetically encoded antioxidant systems to selectively counteract neuronal cell loss in neurodegenerative diseases and ischemic brain damage. Because gene therapy approaches to treat inherited and acquired disorders offer many unique advantages over conventional therapeutic approaches, we discussed basic research/clinical evidence and the potential of virus-mediated gene delivery techniques for antioxidant gene therapy.

Impaired emotional empathy and related social network deficits in cocaine users

Chronic cocaine users consistently display neurochemical and functional alterations in brain areas involved in social cognition (e.g. medial and orbitofrontal cortex). Although social functioning plays a crucial role in the development and treatment of drug dependence, studies investigating social cognition in cocaine users are lacking. Therefore, we investigated mental perspective taking ('theory of mind') and emotional and cognitive empathy in recreational (RCU) and dependent (DCU) cocaine users. Furthermore, we related these measures to real-life indicators of social functioning. One-hundred cocaine users (69 RCU, 31 DCU) and 68 stimulant-naïve healthy controls were tested with the Multifaceted Empathy Test (MET), Movie for the Assessment of Social Cognition (MASC) and Reading the Mind in the Eyes Test (RMET). The Social Network Questionnaire was conducted to assess social network size. Furthermore, participants provided information on committed criminal offenses. RCU and DCU showed less emotional empathy compared to controls (MET), whereas cognitive empathy was not impaired (MET, RMET). Additionally, DCU made more errors in mental perspective taking (MASC). Notably, cocaine users committed more criminal offenses and displayed a smaller social network and higher cocaine use was correlated with less social contacts. Diminished mental perspective taking was tentatively correlated with more intense cocaine use as well. Finally, younger age of onset of cocaine use was associated with more pronounced empathy impairment. In conclusion, social cognition impairments in cocaine users were related to real-life social functioning and should therefore be considered in therapy and prevention strategies.

Effects of visual attention on chromatic and achromatic detection sensitivities

Visual attention has a significant effect on various visual functions, such as response time, detection and discrimination sensitivity, and color appearance. It has been suggested that visual attention may affect visual functions in the early visual pathways. In this study we examined selective effects of visual attention on sensitivities of the chromatic and achromatic pathways to clarify whether visual attention modifies responses in the early visual system. We used a dual task paradigm in which the observer detected a peripheral test stimulus presented at 4 deg eccentricities while the observer concurrently carried out an attention task in the central visual field. In experiment 1, it was confirmed that peripheral spectral sensitivities were reduced more for short and long wavelengths than for middle wavelengths with the central attention task so that the spectral sensitivity function changed its shape by visual attention. This indicated that visual attention affected the chromatic response more strongly than the achromatic response. In experiment 2 it was obtained that the detection thresholds increased in greater degrees in the red-green and yellow-blue chromatic directions than in the white-black achromatic direction in the dual task condition. In experiment 3 we showed that the peripheral threshold elevations depended on the combination of color-directions of the central and peripheral stimuli. Since the chromatic and achromatic responses were separately processed in the early visual pathways, the present results provided additional evidence that visual attention affects responses in the early visual pathways.

Sensory nerves and transient receptor potential vanilloid 1 channels in CO(2) regulation of cerebrovascular tone

This study investigated the involvement of sensory nerves and, in particular, neuronal transient receptor potential vanilloid (TRPV) 1 channels, in the CO(2)-mediated regulation of cerebrovascular tone. Basilar artery diameter and blood flow velocity in the ventral midbrain were determined in a rat cranial window preparation by digital imaging and laser-Doppler flowmetry, respectively. Superfusion of the basilar artery with capsaicin, a selective TRPV1 receptor agonist, caused a transient relaxation, consistent with acute desensitization of neuronal TRPV1 channels. Constriction to respiratory hypocapnia remained unaffected following capsaicin superfusion. Denervation of sensory nerves by repeated capsaicin injection of neonates also did not reduce the respiratory hypocapnia constriction of the basilar artery as well as the decreased flow velocity in the ventral midbrain in adults. These findings suggest that sensory nerves and, in particular, neuronal TRPV1 channels, do not play a role in respiratory hypocapnia constriction and decreased flow, at least in rat basilar artery and ventral midbrain.

Adult cortical plasticity following injury: Recapitulation of critical period mechanisms?

A primary goal of research on developmental critical periods (CPs) is the recapitulation of a juvenile-like state of malleability in the adult brain that might enable recovery from injury. These ambitions are often framed in terms of the simple reinstatement of enhanced plasticity in the growth-restricted milieu of an injured adult brain. Here, we provide an analysis of the similarities and differences between deprivation-induced and injury-induced cortical plasticity, to provide for a nuanced comparison of these remarkably similar processes. As a first step, we review the factors that drive ocular dominance plasticity in the primary visual cortex of the uninjured brain during the CP and in adults, to highlight processes that might confer adaptive advantage. In addition, we directly compare deprivation-induced cortical plasticity during the CP and plasticity following acute injury or ischemia in mature brain. We find that these two processes display a biphasic response profile following deprivation or injury: an initial decrease in GABAergic inhibition and synapse loss transitions into a period of neurite expansion and synaptic gain. This biphasic response profile emphasizes the transition from a period of cortical healing to one of reconnection and recovery of function. Yet while injury-induced plasticity in adult shares several salient characteristics with deprivation-induced plasticity during the CP, the degree to which the adult injured brain is able to functionally rewire, and the time required to do so, present major limitations for recovery. Attempts to recapitulate a measure of CP plasticity in an adult injury context will need to carefully dissect the circuit alterations and plasticity mechanisms involved while measuring functional behavioral output to assess their ultimate success.

Efficient construction of rAAV-based gene targeting vectors by Golden Gate cloning

The recombinant adeno-associated virus (rAAV) has proven to be an efficient and attractive tool for targeted genome engineering. Here we present a novel method employing the Golden Gate cloning strategy for fast and efficient construction of rAAV-based gene knockout or single-nucleotide knockin vectors. Two vectors, pGolden-Neo and pGolden-Hyg, were generated as common assembling modules to confer antibiotic resistance to the targeting vector. To validate the method, we then generated two rAAV-based targeting vectors: pAAV-pTP53-KO and pAAV-hTau(P301L)-KI. Furthermore, we generated a pGolden-AAV plasmid that allows one-step generation of an rAAV-based targeting vector. Our new methodology for rAAV targeting vector assembly is efficient, accurate, time-saving, and cost-effective.

Relationship between cognitive dysfunction, gait, and motor impairment in children and adolescents with neurofibromatosis type 1

AIM

Motor skill impairment and cognitive dysfunction are commonly reported features of neurofibromatosis type 1 (NF1). We characterized and determined the relationship between motor impairment, gait variables, and cognitive function in children and adolescents with NF1.

METHOD

Motor function, gait, and neurocognitive abilities were assessed in 46 children and adolescents with NF1 (26 males, 20 females; age range 7-17 y; mean age 11 y 1 mo, SD 3 y 2 mo). Tests to establish correlations between neurocognitive, motor, and gait variables were performed.

RESULTS

Compared with normative data, 28/39 of our NF1 cohort demonstrated impaired performance for balance and upper limb coordination and 16/38 for running speed and agility. Gait data revealed a strategy to preserve balance at the expense of velocity, with the unexpected exception of a tendency for reduced base of support. Neurocognitive testing confirmed mean IQ in the low average range (86.0) and deficits in spatial working memory and strategy generation. Significant correlations between a number of neurocognitive measures and motor abilities and gait were identified. The largest associations were between gait width and spatial working memory (r=0.594) and running speed and agility with strategy generation (r=0.549).

INTERPRETATION

We have identified a relationship between balance, running speed and agility, gait, and cognition in children with NF1. Findings suggest a shared abnormal neurodevelopmental process underlying some cognitive and motor abilities in NF1. Results are discussed within the context of evidence highlighting abnormal dopamine-mediated corticostriatal circuitry in NF1.

Rule Activity Related to Spatial and Numerical Magnitudes: Comparison of Prefrontal, Premotor, and Cingulate Motor Cortices

In everyday situations, quantitative rules, such as “greater than/less than,” need to be applied to a multitude of magnitude comparisons, be they sensory, spatial, temporal, or numerical. We have previously shown that rules applied to different magnitudes are encoded in the lateral PFC. To investigate if and how other frontal lobe areas also contribute to the encoding of quantitative rules applied to multiple magnitudes, we trained monkeys to switch between “greater than/less than” rules applied to either line lengths (spatial magnitudes) or dot numerosities (discrete numerical magnitudes). We recorded single-cell activity from the dorsal premotor cortex (dPMC) and cingulate motor cortex (CMA) and compared it with PFC activity. We found the largest proportion of quantitative rule-selective cells in PFC (24% of randomly selected cells), whereas neurons in dPMC and CMA rarely encoded the rule (6% of the cells). In addition, rule selectivity of individual cells was highest in PFC neurons compared with dPMC and CMA neurons. Rule-selective neurons that simultaneously represented the “greater than/less than” rules applied to line lengths and numerosities (“rule generalists”) were exclusively present in PFC. In dPMC and CMA, however, neurons primarily encoded rules applied to only one of the two magnitude types (“rule specialists”). Our data suggest a special involvement of PFC in representing quantitative rules at an abstract level, both in terms of the proportion of neurons engaged and the coding capacities.

Alzheimer's disease, enzyme targets and drug discovery struggles: from natural products to drug prototypes

Alzheimer's disease (AD) is an incapacitating neurodegenerative disease that slowly destroys brain cells. This disease progressively compromises both memory and cognition, culminating in a state of full dependence and dementia. Currently, AD is the main cause of dementia in the elderly and its prevalence in the developed world is increasing rapidly. Classic drugs, such as acetylcholinesterase inhibitors (AChEIs), fail to decline disease progression and display several side effects that reduce patient's adhesion to pharmacotherapy. The past decade has witnessed an increasing focus on the search for novel AChEIs and new putative enzymatic targets for AD, like β- and γ-secretases, sirtuins, caspase proteins and glycogen synthase kinase-3 (GSK-3). In addition, new mechanistic rationales for drug discovery in AD that include autophagy and synaptogenesis have been discovered. Herein, we describe the state-of-the-art of the development of recent enzymatic inhibitors and enhancers with therapeutic potential on the treatment of AD.

When benefitting a patient increases the risk for harm for third persons - the case of treating pedophilic Parkinsonian patients with deep brain stimulation

This paper investigates the question whether it is ethically justified to treat Parkinsonian patients with known or suspected pedophilia with deep brain stimulation - given increasing evidence that this treatment might cause impulse control disorders, disinhibition, and hypersexuality. This specific question is not as exotic as it looks at a first glance. First, the same issue is raised for all other types of sexual orientation or behavior which imply a high risk for harming other persons, e.g. sexual sadism. Second, there are also several (psychotropic) drugs as well as legal and illegal leisure drugs which bear severe risks for other persons. We show that Beauchamp and Childress' biomedical ethics fails to derive a veto against medical interventions which produce risks for third persons by making the patients dangerous to others. Therefore, our case discussion reveals a blind spot of the ethics of principles. Although the first intuition might be to forbid the application of deep brain stimulation to pedophilic patients, we argue against such a simple way out, since in some patients the reduction of dopaminergic drugs allowed by deep brain stimulation of the nucleus subthalamicus improves impulsive control disorders, including hypersexuality. Therefore, we propose a strategy consisting of three steps: (1) risk assessment, (2) shared decision-making, and (3) risk management and safeguards.

A novel in vivo model of tau propagation with rapid and progressive neurofibrillary tangle pathology: the pattern of spread is determined by connectivity, not proximity

Intracellular inclusions composed of hyperphosphorylated filamentous tau are a hallmark of Alzheimer’s disease, progressive supranuclear palsy, Pick’s disease and other sporadic neurodegenerative tauopathies. Recent in vitro and in vivo studies have shown that tau aggregates do not only seed further tau aggregation within neurons, but can also spread to neighbouring cells and functionally connected brain regions. This process is referred to as ‘tau propagation’ and may explain the stereotypic progression of tau pathology in the brains of Alzheimer’s disease patients. Here, we describe a novel in vivo model of tau propagation using human P301S tau transgenic mice infused unilaterally with brain extract containing tau aggregates. Infusion-related neurofibrillary tangle pathology was first observed 2 weeks post-infusion and increased in a stereotypic, time-dependent manner. Contralateral and anterior/posterior spread of tau pathology was also evident in nuclei with strong synaptic connections (efferent and afferent) to the site of infusion, indicating that spread was dependent on synaptic connectivity rather than spatial proximity. This notion was further supported by infusion-related tau pathology in white matter tracts that interconnect these regions. The rapid and robust propagation of tau pathology in this model will be valuable for both basic research and the drug discovery process.

Neural substrates of social status inference: roles of medial prefrontal cortex and superior temporal sulcus

The negotiation of social order is intimately connected to the capacity to infer and track status relationships. Despite the foundational role of status in social cognition, we know little about how the brain constructs status from social interactions that display it. Although emerging cognitive neuroscience reveals that status judgments depend on the intraparietal sulcus, a brain region that supports the comparison of targets along a quantitative continuum, we present evidence that status judgments do not necessarily reduce to ranking targets along a quantitative continuum. The process of judging status also fits a social interdependence analysis. Consistent with third-party perceivers judging status by inferring whose goals are dictating the terms of the interaction and who is subordinating their desires to whom, status judgments were associated with increased recruitment of medial pFC and STS, brain regions implicated in mental state inference.

Anatomical substrates for direct interactions between hippocampus, medial prefrontal cortex, and the thalamic nucleus reuniens

The reuniens nucleus in the midline thalamus projects to the medial prefrontal cortex (mPFC) and the hippocampus, and has been suggested to modulate interactions between these regions, such as spindle-ripple correlations during sleep and theta band coherence during exploratory behavior. Feedback from the hippocampus to the nucleus reuniens has received less attention but has the potential to influence thalamocortical networks as a function of hippocampal activation. We used the retrograde tracer cholera toxin B conjugated to two fluorophores to study thalamic projections to the dorsal and ventral hippocampus and to the prelimbic and infralimbic subregions of mPFC. We also examined the feedback connections from the hippocampus to reuniens. The goal was to evaluate the anatomical basis for direct coordination between reuniens, mPFC, and hippocampus by looking for double-labeled cells in reuniens and hippocampus. In confirmation of previous reports, the nucleus reuniens was the origin of most thalamic afferents to the dorsal hippocampus, whereas both reuniens and the lateral dorsal nucleus projected to ventral hippocampus. Feedback from hippocampus to reuniens originated primarily in the dorsal and ventral subiculum. Thalamic cells with collaterals to mPFC and hippocampus were found in reuniens, across its anteroposterior axis, and represented, on average, about 8 % of the labeled cells in reuniens. Hippocampal cells with collaterals to mPFC and reuniens were less common (~1 % of the labeled subicular cells), and located in the molecular layer of the subiculum. The results indicate that a subset of reuniens cells can directly coordinate activity in mPFC and hippocampus. Cells with collaterals in the hippocampus-reuniens-mPFC network may be important for the systems consolidation of memory traces and for theta synchronization during exploratory behavior.

The cerebellum and addiction: insights gained from neuroimaging research

Although cerebellar alterations have been consistently noted in the addiction literature, the pathophysiology of this link remains unclear. The cerebellum is commonly classified as a motor structure, but human functional neuroimaging along with clinical observations in cerebellar stroke patients and anatomical tract tracing in non-human primates suggests its involvement in cognitive and affective processing. A comprehensive literature search on the role of the cerebellum in addiction was performed. This review article (1) considers the potential role of the cerebellum in addiction; (2) summarizes the cerebellar structural alterations linked to addiction; (3) presents the functional neuroimaging evidence linking the cerebellum with addiction; and (4) proposes a model for addiction that underscores the role of the cerebellum. The data implicate the cerebellum as an intermediary between motor and reward, motivation and cognitive control systems, as all are relevant etiologic factors in addiction. Furthermore, consideration of these findings could contribute to deeper and more sophisticated insights into normal reward and motivational function. The goal of this review is to spread awareness of cerebellar involvement in addictive processes, and to suggest a preliminary model for its potential role.

Neuroelectrical imaging investigation of cortical activity during listening to music in prelingually deaf children with cochlear implants

OBJECTIVE

To date, no objective measure of the pleasantness of music perception by children with cochlear implants has been reported. The EEG alpha asymmetries of pre-frontal cortex activation are known to relate to emotional/affective engagement in a perceived stimulus. More specifically, according to the "withdrawal/approach" model, an unbalanced de-synchronization of the alpha activity in the left prefrontal cortex has been associated with a positive affective state/approach toward a stimulus, and an unbalanced de-synchronization of the same activity in the right prefrontal cortex with a negative affective state/withdrawal from a stimulus. In the present study, High-Resolution EEG with Source Reconstruction was used to compare the music-induced alpha asymmetries of the prefrontal cortex in a group of prelingually deaf implanted children and in a control group of normal-hearing children.

METHODS

Six normal-hearing and six age-matched deaf children using a unilateral cochlear implants underwent High-Resolution EEG recordings as they were listening to a musical cartoon. Musical stimuli were delivered in three versions: Normal, Distort (reverse audio flow) and Mute. The EEG alpha rhythm asymmetry was analyzed: Power Spectral Density was calculated for each Region of Interest, together with a right-left imbalance index. A map of cortical activation was then reconstructed on a realistic cortical model.

RESULTS

Asymmetries of EEG alpha rhythm in the prefrontal cortices were observed in both groups. In the normal-hearing children, the asymmetries were consistent with the withdrawal/approach model, whereas in cochlear implant users they were not. Moreover, in implanted children a different pattern of alpha asymmetries in extrafrontal cortical areas was noticed as compared to normal-hearing subjects.

CONCLUSIONS

The peculiar pattern of alpha asymmetries in implanted children's prefrontal cortex in response to musical stimuli suggests an inability by these subjects to discriminate normal from dissonant music and to appreciate the pleasantness of normal music. High-Resolution EEG may prove to be a promising tool for objectively measuring prefrontal cortex alpha asymmetries in child cochlear implant users.

Sensory cortex lesion triggers compensatory neuronal plasticity

BACKGROUND

Lesions to the human brain often cause dramatic impairments in the life of patients because of the very limited capacity of the mammalian nervous system to regenerate. On the other hand, neuronal tissue has a high capacity to reorganize itself so that loss of function due to brain damage may be compensated through neuroplastic reorganization of undamaged tissue in brain regions adjacent or contralateral to the lesion site. In this study we investigated the effect of serial lesions of the auditory cortices (AC) in both hemispheres of Mongolian gerbils on discrimination performance for fast amplitude modulated tones (AM). Healthy animals were trained to discriminate two fast AM, an ability that has previously been shown to critically depend on cortical processing. Their ability to maintain significant discrimination performance was retested after unilateral AC lesion, and again after lesion of the contralateral AC, with 15 days of continuing training in between the two lesions.

RESULTS

After bilateral cortical ablation of both AC and 45 days of training the animals show no change in pure tone detection threshold as measured with modulation of the acoustic startle reflex which has been shown to rely on subcortical structures. In contrast to simultaneous bilateral ablation of AC that results in complete loss of AM discrimination ability in this paradigm we found compensatory plasticity that seems to be triggered by unilateral cortical ablation with subsequent training and that is able to almost fully compensate for the lost cortical functions.

CONCLUSIONS

Our results demonstrate that AM discrimination ability that normally depends on AC may be transferred to other brain regions when the brain has time to activate compensatory plasticity between the lesions of the two AC hemispheres. For this process to take place obviously one intact AC hemisphere is needed. This finding may open perspectives for new therapeutic strategies that may alleviate the impairments after multiple ischemic strokes.

Mild impairments of motor imagery skills in children with DCD

It has been hypothesized that the underlying mechanism of clumsy motor behaviour in children with Developmental Coordination Disorder (DCD) is caused by a deficit in the internal modelling for motor control. An internal modelling deficit can be shown on a behavioural level by a task that requires motor imagery. Motor imagery skills are suggested to be related to anticipatory action planning, but motor imagery and action planning have not been tested within the same child. In the present study, action planning and motor imagery skills were assessed in 82 children between 7 and 12 years of age. Twenty-one of these children met the criteria for DCD, which was assessed by the McCarron Assessment of Neuromuscular Development and 56 of these children were used in the control group. Motor imagery was tested by a mental rotation task of hands that were shown from a back and palm point of view. The results show that motor imagery is affected in children with DCD but only in conditions with complex task constraints (i.e., rotation of hand stimuli presented in palm view). These results provide partial support for the internal modelling deficit hypothesis. We were not able to elicit motor planning deficits in this group, however, and argue that more complex planning tasks may be needed to identify such deficits.

Cognitive neuroscience of social emotions and implications for psychopathology: examining embarrassment, guilt, envy, and schadenfreude

Social emotions are affective states elicited during social interactions and integral for promoting socially appropriate behaviors and discouraging socially inappropriate ones. Social emotion-processing deficits significantly impair interpersonal relationships, and play distinct roles in the manifestation and maintenance of clinical symptomatology. Elucidating the neural correlates of discrete social emotions can serve as a window to better understanding and treating neuropsychiatric disorders. Moral cognition and social emotion-processing broadly recruit a fronto-temporo-subcortical network, supporting empathy, perspective-taking, self-processing, and reward-processing. The present review specifically examines the neural correlates of embarrassment, guilt, envy, and schadenfreude. Embarrassment and guilt are self-conscious emotions, evoked during negative evaluation following norm violations and supported by a fronto-temporo-posterior network. Embarrassment is evoked by social transgressions and recruits greater anterior temporal regions, representing conceptual social knowledge. Guilt is evoked by moral transgressions and recruits greater prefrontal regions, representing perspective-taking and behavioral change demands. Envy and schadenfreude are fortune-of-other emotions, evoked during social comparison and supported by a prefronto-striatal network. Envy represents displeasure in others' fortunes, and recruits increased dorsal anterior cingulate cortex, representing cognitive dissonance, and decreased reward-related striatal regions. Schadenfreude represents pleasure in others' misfortunes, and recruits reduced empathy-related insular regions and increased reward-related striatal regions. Implications for psychopathology and treatment design are discussed.

Ccm3, a gene associated with cerebral cavernous malformations, is required for neuronal migration

Loss of function of cerebral cavernous malformation 3 (CCM3) results in an autosomal dominant cerebrovascular disorder. Here, we uncover a developmental role for CCM3 in regulating neuronal migration in the neocortex. Using cell type-specific gene inactivation in mice, we show that CCM3 has both cell autonomous and cell non-autonomous functions in neural progenitors and is specifically required in radial glia and newly born pyramidal neurons migrating through the subventricular zone, but not in those migrating through the cortical plate. Loss of CCM3 function leads to RhoA activation, alterations in the actin and microtubule cytoskeleton affecting neuronal morphology, and abnormalities in laminar positioning of primarily late-born neurons, indicating CCM3 involvement in radial glia-dependent locomotion and possible interaction with the Cdk5/RhoA pathway. Thus, we identify a novel cytoplasmic regulator of neuronal migration and demonstrate that its inactivation in radial glia progenitors and nascent neurons produces severe malformations of cortical development.

Reduced binding potential of GABA-A/benzodiazepine receptors in individuals at ultra-high risk for psychosis: an [18F]-fluoroflumazenil positron emission tomography study

BACKGROUND

Altered transmission of gamma-aminobutyric acid (GABA), a major inhibitory neurotransmitter, may contribute to the development of schizophrenia. The purpose of the present study was to investigate the presence of GABA-A/benzodiazepine (BZ) receptor binding abnormalities in individuals at ultra-high risk (UHR) for psychosis in comparison with normal controls using [(18)F]-fluoroflumazenil (FFMZ) positron emission tomography (PET). In particular, we set regions of interest in the striatum (caudate, putamen, and nucleus accumbens) and medial temporal area (hippocampus and parahippocampal gyrus).

METHODS

Eleven BZ-naive people at UHR and 15 normal controls underwent PET scanning using [(18)F]-FFMZ to measure GABA-A/BZ receptor binding potential. The regional group differences between UHR individuals and normal controls were analyzed using Statistical Parametric Mapping 8 software. Participants were evaluated using the structured interview for prodromal syndromes and neurocognitive function tasks.

RESULTS

People at UHR demonstrated significantly reduced binding potential of GABA-A/BZ receptors in the right caudate.

CONCLUSIONS

Altered GABAergic transmission and/or the imbalance of inhibitory and excitatory systems in the striatum may be present at the putative prodromal stage and play a pivotal role in the pathophysiology of psychosis.

Smoking but not cocaine use is associated with lower cerebral metabotropic glutamate receptor 5 density in humans

Long-lasting neuroadaptations in the glutamatergic corticostriatal circuitry have been suggested to be responsible for the persisting nature of drug addiction. In particular, animal models have linked the metabotropic glutamate receptor 5 (mGluR5) to drug-seeking behavior and extinction learning. Accordingly, blocking mGluR5s attenuated self-administration of cocaine and other addictive drugs in rats. How these animal findings extend to humans remains unclear. Therefore, we investigated if human cocaine users (CU) exhibit altered mGluR5 availability compared with drug-naïve control subjects. Seventeen male controls (11 smokers) and 18 male cocaine users (13 smokers) underwent positron emission tomography with (11)C-ABP688 to quantify mGluR5 availability in 12 volumes of interest in addiction-related brain areas. Drug use was assessed by self-report and quantitative hair toxicology. CU and controls did not significantly differ in regional mGluR5 availability. In contrast, smokers (n=24) showed significantly lower mGluR5 density throughout the brain (mean 20%) compared with non-smokers (n=11). In terms of effect sizes, lower mGluR5 availability was most pronounced in the caudate nucleus (d=1.50, 21%), insula (d=1.47, 20%), and putamen (d=1.46, 18%). Duration of smoking abstinence was positively associated with mGluR5 density in all brain regions of interest, indicating that lower mGluR5 availability was particularly pronounced in individuals who had smoked very recently. Specifically tobacco smoking was associated with lower mGluR5 availability in both CU and controls, while cocaine use was not linked to detectable mGluR5 alterations. These findings have important implications regarding the development of novel pharmacotherapies aimed at facilitating smoking cessation.

Influence of social environment on loneliness in older adults: Moderation by polymorphism in the CRHR1

OBJECTIVE

Both adverse social environments and genetic factors contribute to loneliness in old age. Mixed findings between older adults' social relations with their children and their levels of loneliness suggested that a gene × social environment interaction may be operating. We examine whether the effects of infrequent contact with children and low levels of perceived social support from children on loneliness in older adults are moderated by two candidate single nucleotide polymorphisms (i.e., rs1876831 and rs242938) in the corticotrophin releasing hormone receptor 1 (CRHR1) gene.

DESIGN

This was a longitudinal observational study.

SETTING

and

PARTICIPANTS

A population-based sub-sample of 1,374 community-dwelling older adults aged 65 years and older was examined from both the 2003-2004 and 2006-2007 English Longitudinal Study of Aging assessments.

MEASUREMENTS

Our main outcome measure is loneliness, which was assessed by four items extracted from the ULCA loneliness scale.

RESULTS

Compared with older adults carrying the CT/TT genotypes, individuals homozygous for the C allele of rs1876831 reported higher levels of loneliness in the context of infrequent social contact with children and lower levels of perceived social support from children. No gene × social environment interactions were found for loneliness between rs242938 and an adverse social environment related to children.

CONCLUSIONS

This study provides the first evidence in humans that the CRHR1 gene interacts with exposure to a negative social environment to predict loneliness in older adults.

5-HT neurons of the area postrema become c-Fos-activated after increases in plasma sodium levels and transmit interoceptive information to the nucleus accumbens

Serotonergic (5-hydroxytryptamine, 5-HT) neurons of the area postrema (AP) represent one neuronal phenotype implicated in the regulation of salt appetite. Tryptophan hydroxylase (Tryp-OH, synthetic enzyme-producing 5-HT) immunoreactive neurons in the AP of rats become c-Fos-activated following conditions in which plasma sodium levels are elevated; these include intraperitoneal injections of hypertonic saline and sodium repletion. Non-Tryp-OH neurons also became c-Fos-activated. Sodium depletion, which induced an increase in plasma osmolality but caused no significant change in the plasma sodium concentration, had no effect on the c-Fos activity in the AP. Epithelial sodium channels are expressed in the Tryp-OH-immunoreactive AP neurons, possibly functioning in the detection of changes in plasma sodium levels. Since little is known about the neural circuitry of these neurons, we tested whether the AP contributes to a central pathway that innervates the reward center of the brain. Stereotaxic injections of pseudorabies virus were made in the nucleus accumbens (NAc), and after 4 days, this viral tracer produced retrograde transneuronal labeling in the Tryp-OH and non-Tryp-OH AP neurons. Both sets of neurons innervate the NAc via a multisynaptic pathway. Besides sensory information regarding plasma sodium levels, the AP→NAc pathway may also transmit other types of chemosensory information, such as those related to metabolic functions, food intake, and immune system to the subcortical structures of the reward system. Because these subcortical regions ultimately project to the medial prefrontal cortex, different types of chemical signals from visceral systems may influence affective functions.

Distinct regions of prefrontal cortex are associated with the controlled retrieval and selection of social information

Research in social neuroscience has uncovered a social knowledge network that is particularly attuned to making social judgments. However, the processes that are being performed by both regions within this network and those outside of this network that are nevertheless engaged in the service of making a social judgment remain unclear. To help address this, we drew upon research in semantic memory, which suggests that making a semantic judgment engages 2 distinct control processes: A controlled retrieval process, which aids in bringing goal-relevant information to mind from long-term stores, and a selection process, which aids in selecting the information that is goal-relevant from the information retrieved. In a neuroimaging study, we investigated whether controlled retrieval and selection for social information engage distinct portions of both the social knowledge network and regions outside this network. Controlled retrieval for social information engaged an anterior ventrolateral portion of the prefrontal cortex, whereas selection engaged both the dorsomedial prefrontal cortex and temporoparietal junction within the social knowledge network. These results suggest that the social knowledge network may be more involved with the selection of social information than the controlled retrieval of it and incorporates lateral prefrontal regions in accessing memory for making social judgments.

Interference with AMPA receptor endocytosis: effects on behavioural and neurochemical correlates of amphetamine sensitization in male rats

BACKGROUND

Behavioural sensitization has been linked to drug craving in both clinical and preclinical studies of addiction. Increased motor activity is accompanied by enhanced dopamine (DA) release, particularly in the nucleus accumbens (NAcc). The neural bases of sensitization are linked to alterations in synaptic connections that also underlie learning and memory. The present study uses an "interference" peptide, Tat-GluA2(3Y), that blocks long-term depression (LTD) at glutamatergic synapses by disrupting the endocytosis of α- amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors (AMPARs), to explore the role of this form of synaptic plasticity in the induction and maintenance of sensitization.

METHODS

Rats were given 5 injections of d-amphetamine (d-AMPH, 1.0 mg/kg, intraperitoneal) every second day. Tat-GluA2(3Y), was administered by 2 different routes (intravenously and intracerebrally to the ventral tegmental area [VTA] or to the NAcc) before each injection of d-AMPH. After a 14-day drug-free period, expression of behavioural sensitization was evoked by a challenge injection of d-AMPH (0.5 mg/kg, intraperitoneal). Dopamine efflux in the NAcc was measured by high-pressure liquid chromatography with electrochemical detection analyses of brain dialysates on days 1, 9 and 24 of the intravenous peptide experiment.

RESULTS

Systemic administration of Tat-GluA2(3Y) during the induction phase blocked maintenance of behavioural sensitization and attenuated the maintenance of neurochemical sensitization. Intra-VTA infusion of Tat-GluA2(3Y) before each administration of d-AMPH did not affect induction, but inhibited maintenance and subsequent expression of sensitization, whereas intra-NAcc infusion of the peptide did not affect induction or maintenance of sensitization.

LIMITATIONS

The relevance of behavioural sensitization in rodents is related to the development of craving and does not provide direct measures of drug reinforcement.

CONCLUSION

These findings confirm that drug-induced neuroplasticity is labile and may be subject to disruption at a time when long-lasting associations between drug reward and contextual stimuli are formed. Furthermore, the unique ability of Tat-GluA2(3Y) to block maintenance of behavioural sensitization implicates LTD in the consolidation of essential associative memories. Tat-GluA2(3Y) has the unique ability to disrupt functional neuroadaptations triggered by repeated psychostimulant exposure and therefore may protect against the development of craving and drug seeking behaviours.

More than a rhythm of life: breathing as a binder of orofacial sensation

When rodents engage in the exploration of novel stimuli, breathing occurs at an accelerated rate that is synchronous with whisking. We review the recently observed relationships between breathing and the sensations of smell and vibrissa-based touch. We consider the hypothesis that the breathing rhythm serves not only as a motor drive signal, but also as a common clock that binds these two senses into a common percept. This possibility may be extended to include taste through the coordination of licking with breathing. Here we evaluate the status of experimental evidence that pertains to this hypothesis.

Dihydrotestosterone treatment delays the conversion from mild cognitive impairment to Alzheimer's disease in SAMP8 mice

The senescence-accelerated-prone mouse 8 (SAMP8) has been proposed as a suitable, naturally derived animal model for Alzheimer's disease (AD). In the current study, we focus on the problem whether SAMP8 mice show abnormal behavioral and neuropathological signs before they present the characteristic of AD. Our results demonstrated that given the presence of the senescent, behavioral and neuropathological characteristics, the "middle-aged" SAMP8 mice appear to be a suitable and naturally derived animal model for MCI basic research. There is relatively less evidence that androgen may be involved in the pathogenesis of AD. We determined testosterone (T) levels of SAMR1 and SAMP8 mice and found that the marked age-related decrease in serum androgen levels may be one of the risk factors for Alzheimer's dementia. We also evaluated the interventional effect on MCI phase by dihydrotestosterone (DHT) in male SAMP8 mice and found that timely and appropriate androgen intervention can postpone the onset and improve the symptoms of dementia.

Maternal choline supplementation: a nutritional approach for improving offspring health?

The modulatory role of choline on the fetal epigenome and the impact of in utero choline supply on fetal programming and health are of great interest. Studies in animals and/or humans suggest that maternal choline supplementation during pregnancy benefits important physiologic systems such as offspring cognitive function, response to stress, and cerebral inhibition. Because alterations in offspring phenotype frequently coincide with epigenetic modifications and changes in gene expression, maternal choline supplementation may be a nutritional strategy to improve lifelong health of the child. Future studies are warranted to elucidate further the effect of choline on the fetal epigenome and to determine the level of maternal choline intake required for optimal offspring physiologic function.

Sleep enhances inhibitory behavioral control in discrimination learning in rats

Sleep supports the consolidation of memory, and it has been proposed that this enhancing effect of sleep pertains in particular to memories which are encoded under control of prefrontal-hippocampal circuitry into an episodic memory system. Furthermore, repeated reactivation and transformation of such memories during sleep are thought to promote the de-contextualization of these memories. Here, we aimed to establish a behavioral model for the study of such sleep-dependent system consolidation in rats, using a go/nogo conditional discrimination learning task known to essentially depend on prefrontal-hippocampal function. Different groups of rats were trained to criterion on this task and, then, subjected to 80-min retention intervals filled with spontaneous morning sleep, sleep deprivation, or spontaneous evening wakefulness. In a subsequent test phase, the speed of relearning of the discrimination task was examined as indicator of memory, whereby rats were either tested in the same context as during training or in a different context. Sleep promoted relearning of the conditional discrimination task, and this effect was similar for testing memory in the same or different context (p < 0.001). Independent of sleep and wakefulness during the retention interval, animals showed faster relearning when tested in the same context as during learning, compared with testing in a different context (p < 0.001). The benefitting effect of sleep on discrimination learning was primarily due to an enhancing effect on response suppression during the nogo stimulus. We infer from these results that sleep enhances memory for inhibitory behavioral control in a generalized context-independent manner and thereby might eventually also contribute to the abstraction of schema-like representations.

Estrogen protects against the detrimental effects of repeated stress on glutamatergic transmission and cognition

Converging evidence suggests that females and males show different responses to stress; however, little is known about the mechanism underlying the sexually dimorphic effects of stress. In this study, we found that young female rats exposed to 1 week of repeated restraint stress show no negative effects on temporal order recognition memory (TORM), a cognitive process controlled by the prefrontal cortex (PFC), which was contrary to the impairment in TORM observed in stressed males. Concomitantly, normal glutamatergic transmission and glutamate receptor surface expression in PFC pyramidal neurons were found in repeatedly stressed females, in contrast to the significant reduction seen in stressed males. The detrimental effects of repeated stress on TORM and glutamate receptors were unmasked in stressed females when estrogen receptors were inhibited or knocked down in PFC, and were prevented in stressed males with the administration of estradiol. Blocking aromatase, the enzyme for the biosynthesis of estrogen, revealed the stress-induced glutamatergic deficits and memory impairment in females, and the level of aromatase was significantly higher in the PFC of females than in males. These results suggest that estrogen protects against the detrimental effects of repeated stress on glutamatergic transmission and PFC-dependent cognition, which may underlie the stress resilience of females.

The knockout of secretin in cerebellar Purkinje cells impairs mouse motor coordination and motor learning

Secretin (SCT) was first considered to be a gut hormone regulating gastrointestinal functions when discovered. Recently, however, central actions of SCT have drawn intense research interest and are supported by the broad distribution of SCT in specific neuronal populations and by in vivo physiological studies regarding its role in water homeostasis and food intake. The direct action of SCT on a central neuron was first discovered in cerebellar Purkinje cells in which SCT from cerebellar Purkinje cells was found to potentiate GABAergic inhibitory transmission from presynaptic basket cells. Because Purkinje neurons have a major role in motor coordination and learning functions, we hypothesize a behavioral modulatory function for SCT. In this study, we successfully generated a mouse model in which the SCT gene was deleted specifically in Purkinje cells. This mouse line was tested together with SCT knockout and SCT receptor knockout mice in a full battery of behavioral tasks. We found that the knockout of SCT in Purkinje neurons did not affect general motor ability or the anxiety level in open field tests. However, knockout mice did exhibit impairments in neuromuscular strength, motor coordination, and motor learning abilities, as shown by wire hanging, vertical climbing, and rotarod tests. In addition, SCT knockout in Purkinje cells possibly led to the delayed development of motor neurons, as supported by the later occurrence of key neural reflexes. In summary, our data suggest a role in motor coordination and motor learning for SCT expressed in cerebellar Purkinje cells.

The exception does not rule: attention constrains form preparation in word production

Form preparation in word production, the benefit of exploiting a useful common sound (such as the first phoneme) of iteratively spoken small groups of words, is notoriously fastidious, exhibiting a seemingly categorical, all-or-none character and a corresponding susceptibility to "killers" of preparation. In particular, the presence of a single exception item in a group of otherwise phonologically consistent words has been found to eliminate the benefit of knowing a majority characteristic. This has been interpreted to mean that form preparation amounts to partial production and thus provides a window on fundamental processes of phonological word encoding (e.g., Levelt, Roelofs, & Meyer, 1999). However, preparation of only fully distributed properties appears to be nonoptimal and is difficult to reconcile with the sensitivity of cognitive responses to probabilities in other domains. We show here that the all-or-none characteristic of form preparation is specific to task format. Preparation for sets that included an exception item occurred in ecologically valid production tasks, picture naming (Experiment 1), and word naming (Experiment 2). Preparation failed only in the commonly used, but indirect and resource-intensive, associative cuing task (Experiment 3). We outline an account of form preparation in which anticipation of word-initial phonological fragments uses a limited-capacity, sustained attentional capability that points to rather than enacts possibilities for imminent speech.