Altered parvalbumin-positive neuron distribution in basal ganglia of individuals with Tourette syndrome

Genetic disruption of Met signaling impairs GABAergic striatal development and cognition

The largest structure of the basal ganglia, the striatum, modulates motor activity and cognitive function and is composed of GABAergic projection neurons and interneurons. To better understand the mechanisms underlying the development of the striatal neurons and their assembly into functional circuits, we used a mouse with a targeted conditional Met mutation in post-mitotic cells of the ventral telencephalon. Characterization of the ontogeny of the striatal neuronal populations demonstrated that disruption of Met signaling specifically altered the GABAergic interneurons. Medium spiny neurons (MSNs) and cholinergic interneurons were largely unaffected. Mice lacking Met signaling have increased numbers of striatal GABAergic interneurons in the lateral sensorimotor areas with distinct behavioral deficits. Motor function and memory formation and consolidation appeared intact, but procedural learning on the cued task of the Morris water maze was delayed. MET is a susceptibility gene in Tourette syndrome and autism, which are human disorders with impaired procedural learning. This study reveals how a striatal targeted disruption in Met signaling after generation of striatal neurons produces behavioral phenotypes shared by Tourette syndrome and autism, linking the human genetics with the mechanism underlying the disorders.

The genetics of child psychiatric disorders: focus on autism and Tourette syndrome

Investigations into the genetics of child psychiatric disorders have finally begun to shed light on molecular and cellular mechanisms of psychopathology. The first strains of success in this notoriously difficult area of inquiry are the result of an increasingly sophisticated appreciation of the allelic architecture of common neuropsychiatric and neurodevelopmental disorders, the consolidation of large patient cohorts now beginning to reach sufficient size to power reliable studies, the emergence of genomic tools enabling comprehensive investigations of rare as well as common genetic variation, and advances in developmental neuroscience that are fueling the rapid translation of genetic findings.

Distinct structural changes underpin clinical phenotypes in patients with Gilles de la Tourette syndrome

Gilles de la Tourette syndrome is a childhood-onset neurodevelopmental disorder characterized by tics that are often associated with psychiatric co-morbidities. The clinical heterogeneity of Gilles de la Tourette syndrome has been attributed to the disturbance of functionally distinct cortico-striato-thalamo-cortical circuits, but this remains to be demonstrated. The aim of this study was to determine the structural correlates of the diversity of symptoms observed in Gilles de la Tourette syndrome. We examined 60 adult patients and 30 age- and gender-matched control subjects using cortical thickness measurement and 3 T high-resolution T(1)-weighted images. Patients were divided into three clinical subgroups: (i) simple tics; (ii) simple and complex tics and (iii) tics with associated obsessive-compulsive disorders. Patients with Gilles de la Tourette syndrome had reduced cortical thickness in motor, premotor, prefrontal and lateral orbito-frontal cortical areas. The severity of tics was assessed using the Yale Global Tic Severity Scale and correlated negatively with cortical thinning in these regions, as well as in parietal and temporal cortices. The pattern of cortical thinning differed among the clinical subgroups of patients. In patients with simple tics, cortical thinning was mostly found in primary motor regions. In patients with simple and complex tics, thinning extended into larger premotor, prefrontal and parietal regions. In patients with associated obsessive-compulsive disorders, there was a trend for reduced cortical thickness in the anterior cingulate cortex and hippocampal morphology was altered. In this clinical subgroup, scores on the Yale-Brown Obsessive-Compulsive Scale correlated negatively with cortical thickness in the anterior cingulate cortex and positively in medial premotor regions. These data support the hypothesis that different symptom dimensions in Gilles de la Tourette syndrome are associated with dysfunction of distinct cortical areas and have clear implications for the current neuroanatomical model of this syndrome.

Elevated expression of MCP-1, IL-2 and PTPR-N in basal ganglia of Tourette syndrome cases

BACKGROUND

Post-infectious autoimmunity has been implicated in pathogenesis of Tourette's syndrome (TS) but no evidence of inflammation in central nervous system has been reported yet. We evaluated the expression of genes encoding selected inflammatory factors in post-mortem specimen of adult TS patients: interferon-γ (a cytokine released from CD8 and Thelper 1 CD4 subset of T lymphocytes), interleukin-2 (IL-2, a growth factor derived from T lymphocytes), interleukin-1 β (a cytokine involved in initiation of inflammation), monocyte chemotactic factor -1 (MCP-1, a marker of chronic inflammation) and CD45 (pan-leukocytic marker). For validation purposes, we determined expression of three genes that were previously reported to be elevated in post-mortem specimen of other TS cases: protein tyrosine phosphatase receptor-N (PTPR-N), PTPR-U and recoverin.

METHODS

Total RNA was isolated from formalin fixed brain tissue sections of basal ganglia area from four patients with TS and four control subjects, and real-time reverse transcription-polymerase chain reaction analysis was employed to quantitatively evaluate gene expression of the selected genes.

RESULTS

Significantly increased expression of MCP-1, IL-2 and PTPR-N was observed in TS cases (6.5-fold, 2.3-fold and 16.1-fold increase, respectively, p<0.05).

CONCLUSIONS

Elevated expression of MCP-1 and IL-2 supports the possibility of chronic inflammatory processes in the basal ganglia. Replication of elevated expression of PTPR-N in TS specimen suggests that pathway(s) involving this molecule may be important in TS pathogenesis.

Enlargement of thalamic nuclei in Tourette syndrome

CONTEXT

The basal ganglia and thalamus together connect in parallel closed-loop circuits with the cortex. Previous imaging studies have shown modifications of the basal ganglia and cortical targets in individuals with Tourette syndrome (TS), but less is known regarding the role of the thalamus in TS pathogenesis.

OBJECTIVE

To study the morphological features of the thalamus in children and adults with TS.

DESIGN

A cross-sectional, case-control study using anatomical magnetic resonance imaging.

SETTING

University research center.

PARTICIPANTS

The 283 participants included 149 with TS and 134 normal control individuals aged 6 to 63 years.

MAIN OUTCOME MEASURES

Conventional volumes and measures of surface morphology of the thalamus.

RESULTS

Analyses of conventional volumes and surface morphology were consistent in demonstrating an enlargement in TS-affected thalami. Overall volumes were 5% larger in the group composed of children and adults with TS. Statistical maps of surface contour demonstrated enlargement over the lateral thalamus. Post hoc testing indicated that differences in IQ, comorbid illnesses, and medication use did not account for these findings.

CONCLUSIONS

Morphological abnormalities in the thalamus, together with the disturbances reported in the sensorimotor cortex, striatum, and globus pallidus, support the hypothesis of a circuitwide disorder within motor pathways in TS. The connectivity and function of the numerous and diverse thalamic nuclei within cortical-subcortical circuits constitute an anatomical crossroad wherein enlargement of motor nuclei may represent activity-dependent hypertrophy within this component of cortical-subcortical motor circuits, or an adaptive response within a larger putative compensatory system that could thereby directly modulate activity in motor circuits to attenuate the severity of tics.

Tbr2-positive intermediate (basal) neuronal progenitors safeguard cerebral cortex expansion by controlling amplification of pallial glutamatergic neurons and attraction of subpallial GABAergic interneurons

Little is known about how, during its formidable expansion in development and evolution, the cerebral cortex is able to maintain the correct balance between excitatory and inhibitory neurons. In fact, while the former are born within the cortical primordium, the latter originate outward in the ventral pallium. Therefore, it remains to be addressed how these two neuronal populations might coordinate their relative amounts in order to build a functional cortical network. Here, we show that Tbr2-positive cortical intermediate (basal) neuronal progenitors (INPs) dictate the migratory route and control the amount of subpallial GABAergic interneurons in the subventricular zone (SVZ) through a non-cell-autonomous mechanism. In fact, Tbr2 interneuron attractive activity is moderated by Cxcl12 chemokine signaling, whose forced expression in the Tbr2 mutants can rescue, to some extent, SVZ cell migration. We thus propose that INPs are able to control simultaneously the increase of glutamatergic and GABAergic neuronal pools, thereby creating a simple way to intrinsically balance their relative accumulation.

Selective activation of striatal fast-spiking interneurons during choice execution

Basal ganglia circuits are essential for the organization and execution of voluntary actions. Within the striatum, fast-spiking interneurons (FSIs) are thought to tightly regulate the activity of medium-spiny projection neurons (MSNs) through feed-forward inhibition, yet few studies have investigated the functional contributions of FSIs in behaving animals. We recorded presumed MSNs and FSIs together with motor cortex and globus pallidus (GP) neurons, in rats performing a simple choice task. MSN activity was widely distributed across the task sequence, especially near reward receipt. By contrast, FSIs showed a coordinated pulse of increased activity as chosen actions were initiated, in conjunction with a sharp decrease in GP activity. Both MSNs and FSIs were direction selective, but neighboring MSNs and FSIs showed opposite selectivity. Our findings suggest that individual FSIs participate in local striatal information processing, but more global disinhibition of FSIs by GP is important for initiating chosen actions while suppressing unwanted alternatives.

An update on Tourette syndrome

Recent advances in our understanding of the phenomenology, etiology, pathophysiology, and treatment of Tourette syndrome are discussed. Tourette syndrome appears to involve dysfunction of limbic and somatosensory "traffic" through the basal ganglia, within corticostriatal-thalamocortical circuits. Dynamic alterations in the balance of these inputs may dictate the manifestations (sensory, motor, affective, and behavioral) of the disorder at any given time. Individualized assessment and treatment are the keys to optimal treatment of this condition.

Neurobiological substrates of Tourette's disorder

OBJECTIVE

This article reviews the available scientific literature concerning the neurobiological substrates of Tourette's disorder (TD).

METHODS

The electronic databases of PubMed, ScienceDirect, and PsycINFO were searched for relevant studies using relevant search terms.

RESULTS

Neuropathological as well as structural and functional neuroimaging studies of TD implicate not only the sensorimotor corticostriatal circuit, but also the limbic and associative circuits as well. Preliminary evidence also points to abnormalities in the frontoparietal network that is thought to maintain adaptive online control. Evidence supporting abnormalities in dopaminergic and noradrenergic neurotransmission remains strong, although the precise mechanisms remain the subject of speculation.

CONCLUSION

Structural and functional abnormalities in multiple parallel corticostriatal circuits may underlie the behavioral manifestations of TD and related neuropsychiatric disorders over the course of development. Further longitudinal research is needed to elucidate these neurobiological substrates.

Levetiracetam as an alternative therapy for Tourette syndrome

Tourette syndrome is a common childhood-onset neuropsychiatric disorder characterized by chronic tics and frequent comorbid conditions such as attention deficit disorder. Most currently used tic-suppressing drugs are frequently associated with serious adverse events. Thus, alternative therapeutic agents with more favorable side-effect profiles are being evaluated. New hypotheses and recent studies involving GABAergic system in the pathophysiology of Tourette syndrome suppose a reason for the evaluation of GABAergic drugs. Levetiracetam is a drug with an atypical GABAergic mechanism of action that might be expected to improve tics. Although trials performed to evaluate the efficacy of levetiracetam in the treatment of Tourette syndrome have provided conflicting results, it may be useful in some patients. The established safe profile of levetiracetam makes this drug an alternative for treatment if intolerance to currently used drugs appears, but additional evaluation with larger and longer duration controlled studies are necessary to assess the real efficacy in patients with Tourette syndrome.

Developmental co-regulation of the beta and gamma GABAA receptor subunits with distinct alpha subunits in the human dorsolateral prefrontal cortex

The GABA(A) receptor (GABA(A)R) is a pentameric chloride ion channel that mediates neuronal inhibition and is commonly comprised of 2alpha, 2beta and 1gamma subunits. These subunits have distinct characteristics that critically impact receptor function. In this study, we sought to determine if developmental expression of the beta and gamma subunit mRNAs in the prefrontal cortex would show complementary or opposing patterns of change as compared to the alpha subunits. Certain GABA(A)R subunit genes are arranged in tandem on the chromosome, and we hypothesized that genomic proximity would lead to co-regulation during development. The mRNA expression of the 3beta and 3gamma subunits was measured in the human dorsolateral prefrontal cortex of 68 individuals aged neonate to adult, using microarray with qPCR validation. Changes between age groups were identified through ANOVA, linear regression and post hoc Fisher LSD tests while a principal component analysis was used to establish co-regulation of GABA(A)R genes. beta1, gamma1 and gamma3 subunits decreased in expression with age whereas gamma2 increased. beta2 showed dynamic regulation with early increases plateauing across childhood and adolescence before decreasing in adulthood while beta3 levels remained relatively constant. Using published alpha subunit data we identified two principal components labeled 'Decreasing' (alpha2, alpha5, beta1, gamma1 and gamma3) and 'Dynamic' (alpha1, alpha4, beta2 and gamma2) responsible for 84% of the variation in GABA(A)R subunit development. This grouping is generally consistent with the chromosomal localization of subunits, lending credence to regional transcriptional control mechanisms. In addition, understanding developmental changes in GABA(A)R subunits could foster better pediatric pharmaceutical treatments.

Gamma oscillation deficits and the onset and early progression of schizophrenia

A fascinating convergence of evidence in recent years has implicated the disturbances of neural synchrony in the gamma frequency band (30-100 Hz) as a major pathophysiologic feature of schizophrenia. Evidence suggests that reduced glutamatergic neurotransmission via the N-methyl-D-aspartate (NMDA) receptors that are localized to inhibitory interneurons, perhaps especially the fast-spiking cells that contain the calcium-binding protein parvalbumin (PV), may contribute to gamma band synchrony deficits. These deficits may underlie the brain's failure to integrate information and hence the manifestations of many symptoms and deficits of schizophrenia. Furthermore, because gamma oscillations are thought to provide the temporal structure that is necessary for synaptic plasticity, gamma oscillation deficits may disturb the developmental synaptic reorganization process that is occurring during the period of late adolescence and early adulthood. This disturbance may contribute to the onset of schizophrenia and the functional deterioration that is characteristic of the early stage of the illness. Finally, reduced NMDA neurotransmission on inhibitory interneurons, including the PV-containing cells, may inflict excitotoxic or oxidative injury to downstream pyramidal neurons, leading to further loss of synapses and dendritic branchings. Hence, a key element in the conceptualization of rational early-intervention and prevention strategies for schizophrenia may involve correcting the abnormal NMDA neurotransmission on inhibitory interneurons-possibly that on the PV-containing neurons, in particular-thereby normalizing gamma oscillation deficits and attenuating downstream neuronal pathology.

Behavior therapy for children with Tourette disorder: a randomized controlled trial

CONTEXT

Tourette disorder is a chronic and typically impairing childhood-onset neurologic condition. Antipsychotic medications, the first-line treatments for moderate to severe tics, are often associated with adverse effects. Behavioral interventions, although promising, have not been evaluated in large-scale controlled trials.

OBJECTIVE

To determine the efficacy of a comprehensive behavioral intervention for reducing tic severity in children and adolescents.

DESIGN, SETTING, AND PARTICIPANTS

Randomized, observer-blind, controlled trial of 126 children recruited from December 2004 through May 2007 and aged 9 through 17 years, with impairing Tourette or chronic tic disorder as a primary diagnosis, randomly assigned to 8 sessions during 10 weeks of behavior therapy (n = 61) or a control treatment consisting of supportive therapy and education (n = 65). Responders received 3 monthly booster treatment sessions and were reassessed at 3 and 6 months following treatment.

INTERVENTION

Comprehensive behavioral intervention.

MAIN OUTCOME MEASURES

Yale Global Tic Severity Scale (range 0-50, score >15 indicating clinically significant tics) and Clinical Global Impressions-Improvement Scale (range 1 [very much improved] to 8 [very much worse]).

RESULTS

Behavioral intervention led to a significantly greater decrease on the Yale Global Tic Severity Scale (24.7 [95% confidence interval {CI}, 23.1-26.3] to 17.1 [95% CI, 15.1-19.1]) from baseline to end point compared with the control treatment (24.6 [95% CI, 23.2-26.0] to 21.1 [95% CI, 19.2-23.0]) (P < .001; difference between groups, 4.1; 95% CI, 2.0-6.2) (effect size = 0.68). Significantly more children receiving behavioral intervention compared with those in the control group were rated as being very much improved or much improved on the Clinical Global Impressions-Improvement scale (52.5% vs 18.5%, respectively; P < .001; number needed to treat = 3). Attrition was low (12/126, or 9.5%); tic worsening was reported by 4% of children (5/126). Treatment gains were durable, with 87% of available responders to behavior therapy exhibiting continued benefit 6 months following treatment.

CONCLUSION

A comprehensive behavioral intervention, compared with supportive therapy and education, resulted in greater improvement in symptom severity among children with Tourette and chronic tic disorder.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00218777.

Quantitative classification of somatostatin-positive neocortical interneurons identifies three interneuron subtypes

Deciphering the circuitry of the neocortex requires knowledge of its components, making a systematic classification of neocortical neurons necessary. GABAergic interneurons contribute most of the morphological, electrophysiological and molecular diversity of the cortex, yet interneuron subtypes are still not well defined. To quantitatively identify classes of interneurons, 59 GFP-positive interneurons from a somatostatin-positive mouse line were characterized by whole-cell recordings and anatomical reconstructions. For each neuron, we measured a series of physiological and morphological variables and analyzed these data using unsupervised classification methods. PCA and cluster analysis of morphological variables revealed three groups of cells: one comprised of Martinotti cells, and two other groups of interneurons with short asymmetric axons targeting layers 2/3 and bending medially. PCA and cluster analysis of electrophysiological variables also revealed the existence of these three groups of neurons, particularly with respect to action potential time course. These different morphological and electrophysiological characteristics could make each of these three interneuron subtypes particularly suited for a different function within the cortical circuit.

Opposite effects of stimulant and antipsychotic drugs on striatal fast-spiking interneurons

Psychomotor stimulants and typical antipsychotic drugs have powerful but opposite effects on mood and behavior, largely through alterations in striatal dopamine signaling. Exactly how these drug actions lead to behavioral change is not well understood, as previous electrophysiological studies have found highly heterogeneous changes in striatal neuron firing. In this study, we examined whether part of this heterogeneity reflects the mixture of distinct cell types present in the striatum, by distinguishing between medium spiny projection neurons (MSNs) and presumed fast-spiking interneurons (FSIs), in freely moving rats. The response of MSNs to both the stimulant amphetamine (0.5 or 2.5 mg/kg) and the antipsychotic eticlopride (0.2 or 1.0 mg/kg) remained highly heterogeneous, with each drug causing both increases and decreases in the firing rate of many MSNs. By contrast, FSIs showed a far more uniform, dose-dependent response to both drugs. All FSIs had decreased firing rate after high eticlopride. After high amphetamine most FSIs increased firing rate, and none decreased. In addition, the activity of the FSI population was positively correlated with locomotor activity, whereas the MSN population showed no consistent response. Our results show a direct relationship between the psychomotor effects of dopaminergic drugs and the firing rate of a specific striatal cell population. Striatal FSIs may have an important role in the behavioral effects of these drugs, and thus may be a valuable target in the development of novel therapies.

Topiramate in treatment of tourette syndrome

OBJECTIVES

To describe the efficacy and safety of topiramate in the treatment of Tourette syndrome (TS).

METHODS

Charts of subjects whose conditions were diagnosed as tic disorders seen at our clinic from 2003 to 2007 were retrospectively reviewed. Patients who met diagnostic criteria for TS and were started on topiramate at our clinic with at least 1 follow-up visit after beginning topiramate were included. The efficacy of topiramate on a subjective scale, the global impression of response (0 = no response/worse, 1 = mild improvement, 2 = moderate improvement, 3 = marked improvement), and adverse effects were recorded for analysis.

RESULTS

Of 453 subjects, 367 met diagnostic criteria for TS and 41 (11.1%; 34 males) were treated with topiramate for tics for 9.43 +/- 7.03 months (range, 1-27 months). Mean age at onset of tics was 6.93 +/- 2.78 years (range, 2-14 years) and at start of topiramate treatment was 14.83 +/- 5.63 years (range, 9-27 years). The average efficacy on tics was 2.15 +/- 1.11, and 75.6% (n = 31) of subjects had moderate to marked improvement and adverse effects included cognitive/language problems (24.4%, n = 10) and aggression or mood swings (9.8%, n = 4).

CONCLUSIONS

This retrospective chart review suggests that topiramate can be used for tics in TS with at least moderate efficacy and typical adverse effects. Randomized controlled trials are needed.

Local dynamics of gap-junction-coupled interneuron networks

Interneurons coupled by both electrical gap-junctions (GJs) and chemical GABAergic synapses are major components of forebrain networks. However, their contributions to the generation of specific activity patterns, and their overall contributions to network function, remain poorly understood. Here we demonstrate, using computational methods, that the topological properties of interneuron networks can elicit a wide range of activity dynamics, and either prevent or permit local pattern formation. We systematically varied the topology of GJ and inhibitory chemical synapses within simulated networks, by changing connection types from local to random, and changing the total number of connections. As previously observed we found that randomly coupled GJs lead to globally synchronous activity. In contrast, we found that local GJ connectivity may govern the formation of highly spatially heterogeneous activity states. These states are inherently temporally unstable when the input is uniformly random, but can rapidly stabilize when the network detects correlations or asymmetries in the inputs. We show a correspondence between this feature of network activity and experimental observations of transient stabilization of striatal fast-spiking interneurons (FSIs), in electrophysiological recordings from rats performing a simple decision-making task. We suggest that local GJ coupling enables an active search-and-select function of striatal FSIs, which contributes to the overall role of cortical-basal ganglia circuits in decision-making.

Decreased number of parvalbumin and cholinergic interneurons in the striatum of individuals with Tourette syndrome

Corticobasal ganglia neuronal ensembles bring automatic motor skills into voluntary control and integrate them into ongoing motor behavior. A 5% decrease in caudate (Cd) nucleus volume is the most consistent structural finding in the brain of patients with Tourette syndrome (TS), but the cellular abnormalities that underlie this decrease in volume are unclear. In this study the density of different types of interneurons and medium spiny neurons (MSNs) in the striatum was assessed in the postmortem brains of 5 TS subjects as compared with normal controls (NC) by unbiased stereological analyses. TS patients demonstrated a 50%-60% decrease of both parvalbumin (PV)+ and choline acetyltransferase (ChAT)+ cholinergic interneurons in the Cd and the putamen (Pt). Cholinergic interneurons were decreased in TS patients in the associative and sensorimotor regions but not in the limbic regions of the striatum, such that the normal gradient in density of cholinergic cells (highest in associative regions, intermediate in sensorimotor and lowest in limbic regions) was abolished. No significant difference was present in the densities of medium-sized calretinin (CR)+ interneurons, MSNs, and total neurons. The selective deficit of PV+ and cholinergic striatal interneurons in TS subjects may result in an impaired cortico/thalamic control of striatal neuron firing in TS.

Distinct roles of GABAergic interneurons in the regulation of striatal output pathways

Striatal GABAergic microcircuits are critical for motor function, yet their properties remain enigmatic due to difficulties in targeting striatal interneurons for electrophysiological analysis. Here, we use Lhx6-GFP transgenic mice to identify GABAergic interneurons and investigate their regulation of striatal direct- and indirect-pathway medium spiny neurons (MSNs). We find that the two major interneuron populations, persistent low-threshold spiking (PLTS) and fast spiking (FS) interneurons, differ substantially in their excitatory inputs and inhibitory outputs. Excitatory synaptic currents recorded from PLTS interneurons are characterized by a small, nonrectifying AMPA receptor-mediated component and a NMDA receptor-mediated component. In contrast, glutamatergic synaptic currents in FS interneurons have a large, strongly rectifying AMPA receptor-mediated component, but no detectable NMDA receptor-mediated responses. Consistent with their axonal morphology, the output of individual PLTS interneurons is relatively weak and sparse, whereas FS interneurons are robustly connected to MSNs and other FS interneurons and appear to mediate the bulk of feedforward inhibition. Synaptic depression of FS outputs is relatively insensitive to firing frequency, and dynamic-clamp experiments reveal that these short-term dynamics enable feedforward inhibition to remain efficacious across a broad frequency range. Surprisingly, we find that FS interneurons preferentially target direct-pathway MSNs over indirect-pathway MSNs, suggesting a potential mechanism for rapid pathway-specific regulation of striatal output pathways.

Multimodality neuroimaging in Tourette syndrome: alpha-[11C] methyl-L-tryptophan positron emission tomography and diffusion tensor imaging studies

Previous studies in Tourette syndrome have reported lateralized abnormalities of neurotransmitters and microstructure of the cortico-striato-thalamo-cortical circuit. The authors analyzed the relationship between serotonin synthesis and microstructural changes in the subcortical structures (caudate nucleus, lentiform nucleus, and thalamus) related to this circuit, using alpha-[(11)C]methyl-L-tryptophan positron emission tomography (PET) and diffusion tensor imaging, respectively, in 16 children with Tourette syndrome. Correlations between diffusion tensor imaging and alpha-[(11)C]methyl-L-tryptophan PET asymmetry values were found in the caudate nucleus. The findings suggested higher serotonin synthesis on the side of more abnormal diffusion, characterized by lower fractional anisotropy and parallel diffusivity but higher perpendicular diffusivity. Altogether, these imaging abnormalities suggest asymmetric immature microstructure in the caudate nucleus associated with abnormally increased serotonin synthesis in Tourette syndrome. The observed diffusion tensor imaging changes are likely related to abnormal connectivity in the cortico-striato-thalamo-cortical circuit, which may result in cortical disinhibition and increased serotonin synthesis; this could provide a new therapeutic target.

An FMRI study of frontostriatal circuits during the inhibition of eye blinking in persons with Tourette syndrome

OBJECTIVE

The authors sought to study activity in neural circuits that subserve the inhibition of a semi-involuntary motor behavior, eye blinking, in children and adults with Tourette syndrome and in healthy comparison subjects.

METHOD

Functional magnetic resonance imaging was used to scan 120 participants (51 with Tourette syndrome and 69 comparison subjects) as they either blinked normally or successfully inhibited eye blinking. The authors compared the blood-oxygen-level dependent signal during these two conditions across the Tourette and comparison groups.

RESULTS

Relative to comparison subjects, patients with Tourette syndrome activated more strongly the frontal cortex and striatum during eye blink inhibition. Activation increased more with age in the dorsolateral and inferolateral prefrontal cortex and caudate nucleus in the Tourette group relative to comparison subjects. In addition, the Tourette group more strongly activated the middle frontal gyrus, dorsal anterior cingulate, and temporal cortices. The severity of tic symptoms in the Tourette group correlated inversely with activation in the putamen and inferolateral prefrontal cortex.

CONCLUSIONS

Frontostriatal activity is increased in persons with Tourette syndrome during the inhibition of eye blinks. Activation of frontostriatal circuits in this population may help to maintain regulatory control over semi-involuntary behaviors, whether these are tics or eye blinks.

Electrophysiology in Gilles de la Tourette syndrome

Abnormalities in basal ganglia–thalamocortical circuits presumably play an important role in the pathophysiology underlying the chronic motor and vocal tics that define Gilles de la Tourette syndrome (GTS). Electrophysiological techniques, above all, the use of transcranial magnetic stimulation – a noninvasive and painless tool to examine the excitability of several different circuits in the human motor cortex – has advanced our understanding of the pathophysiology. Motor thresholds are similar in GTS and healthy subjects; in the resting state, recruitment of motor-evoked potentials above threshold is more gradual in patients with GTS compared with controls. By contrast, recruitment of motor-evoked potentials during preactivation is similar in both groups, as is the duration of the cortical silent period. This suggests that the distribution of excitability in the corticospinal system in patients at rest is different to that in healthy individuals. Importantly, correlation analysis has demonstrated that reduced levels of excitability at rest relate, in pure GTS patients, to video ratings of complex tics as well as hand and finger tics, with less excitability predicting fewer tics. The correlations disappear for measures made during voluntary activation. This suggests that this is an adaptive response to abnormal basal ganglia motor cortex inputs in an effort to reduce unwanted movements, a notion supported by electroencephalogram-coherence studies that demonstrated increased cortico–cortical coupling. Compared with the healthy control group, short intracortical inhibition thresholds are similar in patients with GTS. However, above threshold short intracortical inhibition recruitment and sensory afferent inhibition, a paradigm to examine sensory motor integration, is reduced in patients with GTS. This is consistent with the suggestion that reduced excitability of cortical inhibition is one factor that contributes to the difficulty that patients have in suppressing involuntary tics. In addition, the reduced sensory afferent inhibition indicates that impaired intracortical inhibition may not be limited to the motor cortex, but also involves circuits linking sensory input and motor output.

Decreased GABAA receptors and benzodiazepine binding sites in the anterior cingulate cortex in autism

The anterior cingulate cortex (ACC; BA 24) via its extensive limbic and high order association cortical connectivity to prefrontal cortex is a key part of an important circuitry participating in executive function, affect, and socio-emotional behavior. Multiple lines of evidence, including genetic and imaging studies, suggest that the ACC and gamma-amino-butyric acid (GABA) system may be affected in autism. The benzodiazepine binding site on the GABA(A) receptor complex is an important target for pharmacotherapy and has important clinical implications. The present multiple-concentration ligand-binding study utilized (3)H-muscimol and (3)H-flunitrazepam to determine the number (B(max)), binding affinity (K(d)), and distribution of GABA(A) receptors and benzodiazepine binding sites, respectively, in the ACC in adult autistic and control cases. Compared to controls, the autistic group had significant decreases in the mean density of GABA(A) receptors in the supragranular (46.8%) and infragranular (20.2%) layers of the ACC and in the density of benzodiazepine binding sites in the supragranular (28.9%) and infragranular (16.4%) lamina [corrected]. These findings suggest that in the autistic group this downregulation of both benzodiazepine sites and GABA(A) receptors in the ACC may be the result of increased GABA innervation and/or release disturbing the delicate excitation/inhibition balance of principal neurons as well as their output to key limbic cortical targets. Such disturbances likely underlie the core alterations in socio-emotional behaviors in autism.

Clinical course of Tourette syndrome

OBJECTIVE

Tourette syndrome (TS) is a childhood-onset neuropsychiatric disorder characterized by multiple motor and vocal tics lasting at least a year in duration. Children with TS often experience comorbid conditions such as obsessive-compulsive disorder (OCD) and attention-deficit disorder. The goal of this article was to review the long-term clinical course of tics and comorbid conditions in children with TS.

METHOD

We conducted a traditional literature search to locate relevant articles regarding long-term outcome and prognosis in TS and tic disorders.

RESULTS

Tics typically have an onset between the ages of 4 and 6 years and reach their worst-ever severity between the ages of 10 and 12 years. On average, tic severity declines during adolescence. By early adulthood, roughly three-quarters of children with TS will have greatly diminished tic symptoms and over one-third will be tic free. Comorbid conditions, such as OCD and other anxiety and depressive disorders, are more common during the adolescence and early adulthood of individuals with TS than in the general population.

CONCLUSION

Although tics are the sine qua non of TS, they are often not the most enduring or impairing symptoms in children with TS. Measures used to enhance self-esteem, such as encouraging strong friendships and the exploration of interests, are crucial to ensuring positive adulthood outcome in TS.

Transcranial magnetic stimulation in Gilles de la Tourette syndrome

The cause of Gilles de la Tourette syndrome (GTS), a chronic motor and vocal tic disorder of childhood onset, remains unknown. Abnormalities in basal ganglia-thalamo-cortical circuits presumably play an important role in the pathophysiology underlying the involuntary tics. The use of transcranial magnetic stimulation (TMS), a noninvasive and painless tool to examine the excitability of several different circuits in the human motor cortex has advanced our understanding of the pathophysiology. Motor thresholds are similar in GTS and healthy subjects; in the resting state, recruitment of motor evoked potentials (MEPs) above threshold is more gradual in patients than controls. In contrast, recruitment of MEPs during preactivation is similar in both groups, as is the duration of the cortical silent period. This suggests that the distribution of excitability in the corticospinal system in patients at rest is different to that in healthy individuals. Importantly, correlation analysis showed that reduced levels of excitability at rest relate, in pure GTS patients, to video ratings of complex tics, and hand and finger tics, with less excitability predicting fewer tics. The correlations disappear for measures made during voluntary activation. This suggests that this is an adaptive response to abnormal basal ganglia-motor cortex inputs in an effort to reduce unwanted movements, a notion supported by electroencephalography-coherence studies that show increased cortico-cortical coupling. Compared to the healthy control group, short intracortical inhibition (SICI) thresholds are similar. However, above-threshold SICI recruitment and sensory afferent inhibition (SAI), a paradigm to examine sensory motor integration, are reduced in patients. This is consistent with the suggestion that reduced excitability of cortical inhibition is one factor that contributes to the difficulty that patients have in suppressing involuntary tics. In addition the reduced SAI indicates that impaired intracortical inhibition may not be limited to the motor cortex but also involves circuits linking sensory input and motor output. GTS with attention deficit hyperactivity disorder comorbidity is associated with more extensive changes in the excitability of motor cortex circuits than pure GTS or GTS+obsessive-compulsive disorder. The extent to which various different neuronal circuits are affected may be relevant for the phenotype of Tourette spectrum disorders.

Task control signals in pediatric tourette syndrome show evidence of immature and anomalous functional activity

Tourette Syndrome (TS) is a pediatric movement disorder that may affect control signaling in the brain. Previous work has proposed a dual-networks architecture of control processing involving a task-maintenance network and an adaptive control network (Dosenbach et al., 2008). A prior resting-state functional connectivity MRI (rs-fcMRI) analysis in TS has revealed functional immaturity in both putative control networks, with "anomalous" correlations (i.e., correlations outside the typical developmental range) limited to the adaptive control network (Church et al., 2009). The present study used functional MRI (fMRI) to study brain activity related to adaptive control (by studying start-cues signals), and to task-maintenance (by studying signals sustained across a task set). Two hypotheses from the previous rs-fcMRI results were tested. First, adaptive control (i.e., start-cue) activity will be altered in TS, including activity inconsistent with typical development ("anomalous"). Second, group differences found in task-maintenance (i.e., sustained) activity will be consistent with functional immaturity in TS. We examined regions found through a direct comparison of adolescents with and without TS, as well as regions derived from a previous investigation that showed differences between unaffected children and adults. The TS group showed decreased start-cue signal magnitude in regions where start-cue activity is unchanged over typical development, consistent with anomalous adaptive control. The TS group also had higher magnitude sustained signals in frontal cortex regions that overlapped with regions showing differences over typical development, consistent with immature task-maintenance in TS. The results demonstrate task-related fMRI signal differences anticipated by the atypical functional connectivity found previously in adolescents with TS, strengthening the evidence for functional immaturity and anomalous signaling in control networks in adolescents with TS.

Corticostriatal Interactions during Learning, Memory Processing, and Decision Making

This mini-symposium aims to integrate recent insights from anatomy, behavior, and neurophysiology, highlighting the anatomical organization, behavioral significance, and information-processing mechanisms of corticostriatal interactions. In this summary of topics, which is not meant to provide a comprehensive survey, we will first review the anatomy of corticostriatal circuits, comparing different ways by which "loops" of cortical-basal ganglia circuits communicate. Next, we will address the causal importance and systems-neurophysiological mechanisms of corticostriatal interactions for memory, emphasizing the communication between hippocampus and ventral striatum during contextual conditioning. Furthermore, ensemble recording techniques have been applied to compare information processing in the dorsal and ventral striatum to predictions from reinforcement learning theory. We will next discuss how neural activity develops in corticostriatal areas when habits are learned. Finally, we will evaluate the role of GABAergic interneurons in dynamically transforming cortical inputs into striatal output during learning and decision making.

Fast oscillations in cortical-striatal networks switch frequency following rewarding events and stimulant drugs

Oscillations may organize communication between components of large-scale brain networks. Although gamma-band oscillations have been repeatedly observed in cortical-basal ganglia circuits, their functional roles are not yet clear. Here I show that, in behaving rats, distinct frequencies of ventral striatal local field potential oscillations show coherence with different cortical inputs. The approximately 50 Hz gamma oscillations that normally predominate in awake ventral striatum are coherent with piriform cortex, whereas approximately 80-100 Hz high-gamma oscillations are coherent with frontal cortex. Within striatum, entrainment to gamma rhythms is selective to fast-spiking interneurons, with distinct fast-spiking interneuron populations entrained to different gamma frequencies. Administration of the psychomotor stimulant amphetamine or the dopamine agonist apomorphine causes a prolonged decrease in approximately 50 Hz power and increase in approximately 80-100 Hz power. The same frequency switch is observed for shorter epochs spontaneously in awake, undrugged animals and is consistently provoked for < 1 s following reward receipt. Individual striatal neurons can participate in these brief high-gamma bursts with, or without, substantial changes in firing rate. Switching between discrete oscillatory states may allow different modes of information processing during decision-making and reinforcement-based learning, and may also be an important systems-level process by which stimulant drugs affect cognition and behavior.

Symptom dimensions and subtypes of obsessive-compulsive disorder: a developmental perspective

In the absence of definitive etiological markers for obsessive-compulsive disorder (OCD% obsessive-compulsive (OC) symptom dimensions may offer a fruitful point of orientation. These dimensions can be understood as defining potentially overlapping clinical features that may be continuous with "normal" worries first evident in childhood. Although the understanding of the dimensional structure of OC symptoms is still imperfect, a recent large-scale meta-analysis has confirmed the presence of at least four separa ble symptom dimensions in children, as well as adults, with OCD. A dimensional approach does not exclude other methods to parse OCD. Thus far, a pediatric age of onset, the presence of other family members with OCD, and the individual's "tic-related" status appear to be potentially useful categorical distinctions. Although the OC symptom dimensions appear to be valid for all ages, it is unlikely that the underlying genetic vulnerability factors and neurobiological substrates for each of these symptom dimensions are the same across the course of development.

The developmental integration of cortical interneurons into a functional network

The central goal of this manuscript is to survey our present knowledge of how cortical interneuron subtypes are generated. To achieve this, we will first define what is meant by subtype diversity. To this end, we begin by considering the mature properties that differentiate between the different populations of cortical interneurons. This requires us to address the difficulties involved in determining which characteristics allow particular interneurons to be assigned to distinct subclasses. Having grappled with this thorny issue, we will then proceed to review the progressive events in development involved in the generation of interneuron diversity. Starting with their origin and specification within the subpallium, we will follow them up through the first postnatal weeks during their integration into a functional network. Finally, we will conclude by calling the readers attention to the devastating consequences that result from developmental failures in the formation of inhibitory circuits within the cortex.

Striatal [11C]dihydrotetrabenazine and [11C]methylphenidate binding in Tourette syndrome

OBJECTIVE

Tourette syndrome (TS) is a common neurodevelopmental disorder marked by tics and behavioral comorbidities. Clinical pharmacology suggests that dopaminergic signaling abnormalities are part of the pathophysiology of TS. Prior molecular imaging studies of nigrostriatal dopaminergic terminal markers report conflicting results. Our goal was to characterize the distribution of nigrostriatal dopaminergic terminals in subjects with TS.

METHODS

Thirty-three adult subjects with TS were studied with PET using [11C]dihydrotetrabenazine (DTBZ), a ligand for the type 2 vesicular monoamine transporter, and with [11C] methylphenidate (MP), a ligand for the plasmalemmal dopamine transporter. Subjects were characterized with standard rating instruments for tic severity, obsessive-compulsive behaviors, and attentional deficits.

RESULTS

We found no differences between subjects with TS and control subjects in DTBZ and MP binding in any striatal region. There was no correlation between binding measures and clinical variables. Ventral striatal DTBZ and MP binding distributions in subjects with TS were normal.

CONCLUSIONS

We found no evidence of increased striatal dopaminergic innervation in Tourette syndrome (TS). Discrepancy between our present results and those of other studies may be explained by heterogeneity of TS.

Gap junctions between striatal fast-spiking interneurons regulate spiking activity and synchronization as a function of cortical activity

Striatal fast-spiking (FS) interneurons are interconnected by gap junctions into sparsely connected networks. As demonstrated for cortical FS interneurons, these gap junctions in the striatum may cause synchronized spiking, which would increase the influence that FS neurons have on spiking by the striatal medium spiny (MS) neurons. Dysfunction of the basal ganglia is characterized by changes in synchrony or periodicity, thus gap junctions between FS interneurons may modulate synchrony and thereby influence behavior such as reward learning and motor control. To explore the roles of gap junctions on activity and spike synchronization in a striatal FS population, we built a network model of FS interneurons. Each FS connects to 30-40% of its neighbors, as found experimentally, and each FS interneuron in the network is activated by simulated corticostriatal synaptic inputs. Our simulations show that the proportion of synchronous spikes in FS networks with gap junctions increases with increased conductance of the electrical synapse; however, the synchronization effects are moderate for experimentally estimated conductances. Instead, the main tendency is that the presence of gap junctions reduces the total number of spikes generated in response to synaptic inputs in the network. The reduction in spike firing is due to shunting through the gap junctions; which is minimized or absent when the neurons receive coincident inputs. Together these findings suggest that a population of electrically coupled FS interneurons may function collectively as input detectors that are especially sensitive to synchronized synaptic inputs received from the cortex.

Developmentally regulated and evolutionarily conserved expression of SLITRK1 in brain circuits implicated in Tourette syndrome

Tourette syndrome (TS) is an inherited developmental neuropsychiatric disorder characterized by vocal and motor tics. Multiple lines of neurophysiological evidence implicate dysfunction in the corticostriatal-thalamocortical circuits in the etiology of TS. We recently identified rare sequence variants in the Slit and Trk-like family member 1 (SLITRK1) gene associated with TS. SLITRK1, a single-pass transmembrane protein, displays similarities to the SLIT family of secreted ligands, which have roles in axonal repulsion and dendritic patterning, but its function and developmental expression remain largely unknown. Here we provide evidence that SLITRK1 has a developmentally regulated expression pattern in projection neurons of the corticostriatal-thalamocortical circuits. SLITRK1 is further enriched in the somatodendritic compartment and cytoplasmic vesicles of cortical pyramidal neurons in mouse, monkey, and human brain, observations suggestive of an evolutionarily conserved function in mammals. SLITRK1 is transiently expressed in the striosomal/patch compartment of the mammalian striatum and moreover is associated with the direct output pathway; adult striatal expression is confined to cholinergic interneurons. These analyses demonstrate that the expression of SLITRK1 is dynamic and specifically associated with the circuits most commonly implicated in TS and related disorders, suggesting that SLITRK1 contributes to the development of corticostriatal-thalamocortical circuits.

Structural changes in the somatosensory system correlate with tic severity in Gilles de la Tourette syndrome

Gilles de la Tourette syndrome (GTS) is a neuropsychiatric disorder characterized by multiple motor and vocal tics. Previous structural MRI studies have identified regional abnormalities in grey matter, especially in the basal ganglia. These findings are consistent with the assumption of alterations in cortico-striato-thalamo-cortical circuits and dopaminergic neurotransmission playing a major role in the pathophysiology of GTS. Additionally, recent imaging studies suggested an involvement of sensory-motor cortices in the pathophysiology of GTS. However, little is known about the role of white matter changes in GTS. In this study, we aimed to examine whether GTS is associated with abnormalities in white matter microstructure and whether these changes are correlated with tic severity. In a morphometric study based on diffusion tensor MRI of the whole brain, we compared brain tissue diffusion characteristics between 15 unmedicated adults with GTS without psychiatric co-morbidity and 15 healthy age- and sex-matched controls. We performed voxel-based morphometry (VBM) of regional fractional anisotropy (FA) values to identify regional differences in white matter microstructure between the groups. We also tested for a linear relationship between regional FA values and clinical scores of tic severity. Probabilistic fibre tracking was applied to characterize anatomical connectivity of those areas showing differences in regional FA. Compared with healthy controls, GTS patients showed bilateral FA increases in white matter underlying the post- and precentral gyrus, below the left supplementary motor area, and in the right ventro-postero-lateral part of the thalamus. The peak increase in FA was located below the left postcentral gyrus. Probabilistic tractography identified transcallosal and ipsilateral cerebello-thalamo-cortical pathways of the somatosensory system passing through this subcortical region. In patients, regional FA in this region showed an inverse linear relationship with tic severity. These findings demonstrate, for the first time, structural alterations in somatosensory pathways in GTS. Changes of water diffusion characteristics point towards reduced branching in somatosensory pathways in GTS patients. The negative correlation between higher regional FA values and fewer tics suggests that these alterations of white matter microstructure represent adaptive reorganization of somatosensory processing in GTS.

Symptom dimensions and subtypes of obsessive-compulsive disorder: a developmental perspective

In the absence of definitive etiological markers for obsessive-compulsive disorder (OCD% obsessive-compulsive (OC) symptom dimensions may offer a fruitful point of orientation. These dimensions can be understood as defining potentially overlapping clinical features that may be continuous with "normal" worries first evident in childhood. Although the understanding of the dimensional structure of OC symptoms is still imperfect, a recent large-scale meta-analysis has confirmed the presence of at least four separa ble symptom dimensions in children, as well as adults, with OCD. A dimensional approach does not exclude other methods to parse OCD. Thus far, a pediatric age of onset, the presence of other family members with OCD, and the individual's "tic-related" status appear to be potentially useful categorical distinctions. Although the OC symptom dimensions appear to be valid for all ages, it is unlikely that the underlying genetic vulnerability factors and neurobiological substrates for each of these symptom dimensions are the same across the course of development.

Many specialists for suppressing cortical excitation

Cortical computations are critically dependent on GABA-releasing neurons for dynamically balancing excitation with inhibition that is proportional to the overall level of activity. Although it is widely accepted that there are multiple types of interneurons, defining their identities based on qualitative descriptions of morphological, molecular and physiological features has failed to produce a universally accepted ‘parts list’, which is needed to understand the roles that interneurons play in cortical processing. A list of features has been published by the Petilla Interneurons Nomenclature Group, which represents an important step toward an unbiased classification of interneurons. To this end some essential features have recently been studied quantitatively and their association was examined using multidimensional cluster analyses. These studies revealed at least 3 distinct electrophysiological, 6 morphological and 15 molecular phenotypes. This is a conservative estimate of the number of interneuron types, which almost certainly will be revised as more quantitative studies will be performed and similarities will be defined objectively. It is clear that interneurons are organized with physiological attributes representing the most general, molecular characteristics the most detailed and morphological features occupying the middle ground. By themselves, none of these features are sufficient to define classes of interneurons. The challenge will be to determine which features belong together and how cell type-specific feature combinations are genetically specified.

Neurosurgical strategies for Gilles de la Tourette's syndrome

Tourette's syndrome (TS) is a neurological disorder characterized by motor and vocal tics that typically begin in childhood and often are accompanied by psychiatric comorbidities. Symptoms of TS may be socially disabling and cause secondary medical complications. Pharmacological therapies remain the mainstay of symptom management. For the subset of patients in whom TS symptoms are medically recalcitrant and do not dissipate by adulthood, neurosurgery may offer an alternative treatment strategy. Greater understanding of the neuroanatomic and pathophysiologic basis of TS has facilitated the development of surgical procedures that aim to ameliorate TS symptoms by lesions or deep brain stimulation of cerebral structures. Herein, the rationale for the surgical management of TS is discussed and neurosurgical experiences since the 1960s are reviewed. The necessity for neurosurgical strategies to be performed with appropriate ethical considerations is highlighted.

Generation of Cre-transgenic mice using Dlx1/Dlx2 enhancers and their characterization in GABAergic interneurons

DLX1 and DLX2 transcription factors are necessary for forebrain GABAergic neuron differentiation, migration, and survival. We generated transgenic mice that express Cre-recombinase under the control of two ultra-conserved DNA elements near the Dlx1 and 2 locus termed I12b and URE2. We show that Cre-recombinase is active in a "Dlx-pattern" in the embryonic forebrain of transgenic mice. I12b-Cre is more active than URE2-Cre in the medial ganglionic eminences and its derivatives. Fate-mapping of EGFP+ cells in adult Cre;Z/EG animals demonstrated that GABAergic neurons, but not glia, are labeled. Most NPY+, nNOS+, parvalbumin+, and somatostatin+ cells are marked by I12b-Cre in the cortex and hippocampus, while 25-40% of these interneuron subtypes are labeled by URE2-Cre. Labeling of neurons generated between E12.5 to E15.5 indicated differences in birth-dates of EGFP+ cells that populate the olfactory bulb, hippocampus, and cortex. Finally, we provide the first in vivo evidence that both I12b and URE2 are direct targets of DLX2 and require Dlx1 and Dlx2 expression for proper activity.

Uncoordinated firing rate changes of striatal fast-spiking interneurons during behavioral task performance

Basal ganglia circuits make key contributions to decision making. Distributed, synchronous feedforward inhibition of striatal medium spiny neurons by fast-spiking GABAergic interneurons (FSIs) has been argued to be important for the suppression of unwanted actions, and a deficit in FSIs has been found in human patients with Tourette syndrome. However, no studies have yet examined how striatal FSIs change their activity during behavioral tasks. Here I describe 36 presumed striatal FSIs recorded in rats during well practiced performance of a radial maze win-stay task. Although most FSIs showed robust task-related activity, the temporal patterns of firing rate change were highly idiosyncratic. In contrast to other classes of striatal neurons, FSIs showed little or no coordinated population response to major task events such as instruction cues or rewards. Even when multiple FSIs were recorded simultaneously from the same local region of striatum, firing rate changes were dissimilar, and no clear evidence for synchronous firing was found using cross-correlograms (18 FSI pairs examined). These results suggest that FSIs play a more complex role in the information processing achieved by striatal microcircuits than supposed by current theoretical models.

Habits, rituals, and the evaluative brain

Scientists in many different fields have been attracted to the study of habits because of the power habits have over behavior and because they invoke a dichotomy between the conscious, voluntary control over behavior, considered the essence of higher-order deliberative behavioral control, and lower-order behavioral control that is scarcely available to consciousness. A broad spectrum of behavioral routines and rituals can become habitual and stereotyped through learning. Others have a strong innate basis. Repetitive behaviors can also appear as cardinal symptoms in a broad range of neurological and neuropsychiatric illness and in addictive states. This review suggests that many of these behaviors could emerge as a result of experience-dependent plasticity in basal ganglia-based circuits that can influence not only overt behaviors but also cognitive activity. Culturally based rituals may reflect privileged interactions between the basal ganglia and cortically based circuits that influence social, emotional, and action functions of the brain.

Thinning of sensorimotor cortices in children with Tourette syndrome

The basal ganglia portions of cortico-striato-thalamo-cortical (CSTC) circuits have consistently been implicated in the pathogenesis of Tourette syndrome, whereas motor and sensorimotor cortices in these circuits have been relatively overlooked. Using magnetic resonance imaging, we detected cortical thinning in frontal and parietal lobes in groups of Tourette syndrome children relative to controls. This thinning was most prominent in ventral portions of the sensory and motor homunculi that control the facial, orolingual and laryngeal musculature that is commonly involved in tic symptoms. Correlations of cortical thickness in sensorimotor regions with tic symptoms suggest that these brain regions are important in the pathogenesis of Tourette syndrome.

Deficiency in inhibitory cortical interneurons associates with hyperactivity in fibroblast growth factor receptor 1 mutant mice

BACKGROUND

Motor hyperactivity due to hyper-dopaminergic neurotransmission in the basal ganglia is well characterized; much less is known about the role of the neocortex in controlling motor behavior.

METHODS

Locomotor behavior and motor, associative, and spatial learning were examined in mice with conditional null mutations of fibroblast growth factor receptor 1 (Fgfr1) restricted to telencephalic neural precursors (Fgfr1(f/f;hGfapCre)). Locomotor responses to a dopamine agonist (Amphetamine 2 mg/kg and Methylphenidate 10 mg/kg) and antagonists (SCH233390 .025 mg/kg and Haloperidol .2 mg/kg) were assessed. Stereological and morphological characterization of various monoaminergic, excitatory, and inhibitory neuronal subtypes was performed.

RESULTS

Fgfr1(f/f;hGfapCre) mice have spontaneous locomotor hyperactivity characterized by longer bouts of locomotion and fewer resting points that is significantly reduced by the D1 and D2 receptor antagonists. No differences in dopamine transporter, tyrosine hydroxylase, or serotonin immunostaining were observed in Fgfr1(f/f;hGfapCre) mice. There was no change in cortical pyramidal neurons, but parvalbumin+, somatostatin+, and calbindin+ inhibitory interneurons were reduced in number in the cerebral cortex. The decrease in parvalbumin+ interneurons in cortex correlated with the extent of hyperactivity.

CONCLUSIONS

Dysfunction in specific inhibitory cortical circuits might account for deficits in behavioral control, providing insights into the neurobiology of psychiatric disorders.

Deep brain stimulation in Tourette's syndrome

A 48-year-old man with severe, lifelong Tourette's syndrome (TS) characterized by forceful self-injurious motor tics and obsessive-compulsive disorder was treated with bilateral deep brain stimulation (DBS). The decision to treat was based on his progressive neurological impairment (left sided weakness secondary to spinal cord injury) because of his relentless, violent head jerks. Electrodes were implanted at the level of the medial part of the thalamus (centromedian nucleus, the substantia periventricularis, and the nucleus ventro-oralis internus). DBS resulted in a substantial reduction of tics. These data show that bilateral DBS of the thalamus can have a good effect on severe tics in adult patients suffering from intractable TS.