Limbic Cortical Areas Research Articles

483 Network Analysis of the Thalamic RNS in Patients With Drug Resistant Epilepsy: Insights to Improve Surgical Targeting

INTRODUCTION: Approximately 30% of epilepsy patients are refractory to pharmacotherapy. Patients with drug-resistant epilepsy (DRE) with seizure foci located bilaterally or in the eloquent cortex may be ineligible for resective surgery. For such cases, responsive neurostimulation (RNS) is a viable treatment strategy. METHODS: Retrospective analysis of 23 patients treated with thalamic RNS of the centromedian (CM) and anterior nuclei of the thalamus (ANT) from 2015-2022. Clinical features and seizure outcomes were recorded. RNS electrodes were used to model the electrical field using the parameters at last follow up. Patient-specific probabilistic tractography was used to define the network of the seizure onset zone (SOZ) and its thalamic involvement. Each patient’s probabilistic map was used to define the area of highest connectivity of the thalamus with the seizure network. Each of these patient-specific thalamic areas demonstrating highest connectivity with the seizure network were correlated with electrode position, stimulation modeling, and seizure outcomes. RESULTS: Seizure network from neocortical areas were highly connected to the CM and from limbic cortical areas to the ANT, MD, and parafascicularis nuclei. Results of the correlation analysis between connectivity, stimulation modelling of the RNS electrode, and seizure outcomes will be presented along with illustrative cases of patient-specific targeting using tractography for RNS placement. CONCLUSIONS: Probabilistic tractography is useful to define the networks associated with improved seizure control in thalamic RNS. The identification of these networks prior to surgery could help to identify specific corticothalamic connections and their anatomical trajectories to optimize the implantation of the leads for better and more predictable seizure control.

A structural connectivity atlas of limbic brainstem nuclei.

Understanding the structural connectivity of key brainstem nuclei with limbic cortical regions is essential to the development of therapeutic neuromodulation for depression, chronic pain, addiction, anxiety and movement disorders. Several brainstem nuclei have been identified as the primary central nervous system (CNS) source of important monoaminergic ascending fibers including the noradrenergic locus coeruleus, serotonergic dorsal raphe nucleus, and dopaminergic ventral tegmental area. However, due to practical challenges to their study, there is limited data regarding their in vivo anatomic connectivity in humans. To evaluate the structural connectivity of the following brainstem nuclei with limbic cortical areas: locus coeruleus, ventral tegmental area, periaqueductal grey, dorsal raphe nucleus, and nucleus tractus solitarius. Additionally, to develop a group average atlas of these limbic brainstem structures to facilitate future analyses. Each nucleus was manually masked from 197 Human Connectome Project (HCP) structural MRI images using FSL software. Probabilistic tractography was performed using FSL's FMRIB Diffusion Toolbox. Connectivity with limbic cortical regions was calculated and compared between brainstem nuclei. Results were aggregated to produce a freely available MNI structural atlas of limbic brainstem structures. A general trend was observed for a high probability of connectivity to the amygdala, hippocampus and DLPFC with relatively lower connectivity to the orbitofrontal cortex, NAc, hippocampus and insula. The locus coeruleus and nucleus tractus solitarius demonstrated significantly greater connectivity to the DLPFC than amygdala while the periaqueductal grey, dorsal raphe nucleus, and ventral tegmental area did not demonstrate a significant difference between these two structures. Monoaminergic and other modulatory nuclei in the brainstem project widely to cortical limbic regions. We describe the structural connectivity across the several key brainstem nuclei theorized to influence emotion, reward, and cognitive functions. An increased understanding of the anatomic basis of the brainstem's role in emotion and other reward-related processing will support targeted neuromodulatary therapies aimed at alleviating the symptoms of neuropsychiatric disorders.

Cortical Serotonergic and Catecholaminergic Denervation in MPTP-Treated Parkinsonian Monkeys.

Decreased cortical serotonergic and catecholaminergic innervation of the frontal cortex has been reported at early stages of Parkinson's disease (PD). However, the limited availability of animal models that exhibit these pathological features has hampered our understanding of the functional significance of these changes during the course of the disease. In the present study, we assessed longitudinal changes in cortical serotonin and catecholamine innervation in motor-symptomatic and asymptomatic monkeys chronically treated with low doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Densitometry and unbiased stereological techniques were used to quantify changes in serotonin and tyrosine hydroxylase (TH) immunoreactivity in frontal cortices of 3 control monkeys and 3 groups of MPTP-treated monkeys (motor-asymptomatic [N = 2], mild parkinsonian [N = 3], and moderate parkinsonian [N = 3]). Our findings revealed a significant decrease (P<0.001) in serotonin innervation of motor (Areas 4 and 6), dorsolateral prefrontal (Areas 9 and 46), and limbic (Areas 24 and 25) cortical areas in motor-asymptomatic MPTP-treated monkeys. Both groups of symptomatic MPTP-treated animals displayed further serotonin denervation in these cortical regions (P<0.0001). A significant loss of serotonin-positive dorsal raphe neurons was found in the moderate parkinsonian group. On the other hand, the intensity of cortical TH immunostaining was not significantly affected in motor asymptomatic MPTP-treated monkeys, but underwent a significant reduction in the moderate symptomatic group (P<0.05). Our results indicate that chronic intoxication with MPTP induces early pathology in the corticopetal serotonergic system, which may contribute to early non-motor symptoms in PD.

Whole-brain mapping of monosynaptic inputs to midbrain cholinergic neurons

The cholinergic midbrain is involved in a wide range of motor and cognitive processes. Cholinergic neurons of the pedunculopontine (PPN) and laterodorsal tegmental nucleus (LDT) send long-ranging axonal projections that target sensorimotor and limbic areas in the thalamus, the dopaminergic midbrain and the striatal complex following a topographical gradient, where they influence a range of functions including attention, reinforcement learning and action-selection. Nevertheless, a comprehensive examination of the afferents to PPN and LDT cholinergic neurons is still lacking, partly due to the neurochemical heterogeneity of this region. Here we characterize the whole-brain input connectome to cholinergic neurons across distinct functional domains (i.e. PPN vs LDT) using conditional transsynaptic retrograde labeling in ChAT::Cre male and female rats. We reveal that input neurons are widely distributed throughout the brain but segregated into specific functional domains. Motor related areas innervate preferentially the PPN, whereas limbic related areas preferentially innervate the LDT. The quantification of input neurons revealed that both PPN and LDT receive similar substantial inputs from the superior colliculus and the output of the basal ganglia (i.e. substantia nigra pars reticulata). Notably, we found that PPN cholinergic neurons receive preferential inputs from basal ganglia structures, whereas LDT cholinergic neurons receive preferential inputs from limbic cortical areas. Our results provide the first characterization of inputs to PPN and LDT cholinergic neurons and highlight critical differences in the connectome among brain cholinergic systems thus supporting their differential roles in behavior.

Deep brain stimulation of the subthalamic nucleus in obsessive–compulsives disorders: long-term follow-up of an open, prospective, observational cohort

BackgroundObsessive–compulsive disorder (OCD) is a major cause of disability in western country and responsible for severe impairment of quality of life. About 10% of patients present with severe OCD symptoms...

Quantitative MRI-Based Analysis Identifies Developmental Limbic Abnormalities in PCDH19 Encephalopathy.

Protocadherin-19 (PCDH19) is a calcium dependent cell-adhesion molecule involved in neuronal circuit formation with prevalent expression in the limbic structures. PCDH19-gene mutations cause a developmental encephalopathy with prominent infantile onset focal seizures, variably associated with intellectual disability and autistic features. Diagnostic neuroimaging is usually unrevealing. We used quantitative MRI to investigate the cortex and white matter in a group of 20 PCDH19-mutated patients. By a statistical comparison between quantitative features in PCDH19 brains and in a group of age and sex matched controls, we found that patients exhibited bilateral reductions of local gyrification index (lGI) in limbic cortical areas, including the parahippocampal and entorhinal cortex and the fusiform and lingual gyri, and altered diffusivity features in the underlying white matter. In patients with an earlier onset of seizures, worse psychiatric manifestations and cognitive impairment, reductions of lGI and diffusivity abnormalities in the limbic areas were more pronounced. Developmental abnormalities involving the limbic structures likely represent a measurable anatomic counterpart of the reduced contribution of the PCDH19 protein to local cortical folding and white matter organization and are functionally reflected in the phenotypic features involving cognitive and communicative skills as well as local epileptogenesis.

Topography Impacts Topology: Anatomically Central Areas Exhibit a "High-Level Connector" Profile in the Human Cortex.

Degree centrality is a widely used measure in complex networks. Within the brain, degree relates to other topological features, with high-degree nodes (i.e., hubs) exhibiting high betweenness centrality, participation coefficient, and within-module z-score. However, increasing evidence from neuroanatomical and predictive processing literature suggests that topological properties of a brain network may also be impacted by topography, that is, anatomical (spatial) distribution. More specifically, cortical limbic areas (agranular and dysgranular cortices), which occupy an anatomically central position, have been proposed to be topologically central and well suited to initiate predictions in the cerebral cortex. We estimated anatomical centrality and showed that it positively correlated with betweenness centrality, participation coefficient, and communicability, analogously to degree. In contrast to degree, however, anatomical centrality negatively correlated with within-module z-score. Our data suggest that degree centrality and anatomical centrality reflect distinct contributions to cortical organization. Whereas degree would be more related to the amount of information integration performed by an area, anatomical centrality would be more related to an area's position in the predictive hierarchy. Highly anatomically central areas may function as "high-level connectors," integrating already highly integrated information across modules. These results are consistent with a high-level, domain-general limbic workspace, integrated by highly anatomically central cortical areas.

The rough sound of salience enhances aversion through neural synchronisation

Being able to produce sounds that capture attention and elicit rapid reactions is the prime goal of communication. One strategy, exploited by alarm signals, consists in emitting fast but perceptible amplitude modulations in the roughness range (30–150 Hz). Here, we investigate the perceptual and neural mechanisms underlying aversion to such temporally salient sounds. By measuring subjective aversion to repetitive acoustic transients, we identify a nonlinear pattern of aversion restricted to the roughness range. Using human intracranial recordings, we show that rough sounds do not merely affect local auditory processes but instead synchronise large-scale, supramodal, salience-related networks in a steady-state, sustained manner. Rough sounds synchronise activity throughout superior temporal regions, subcortical and cortical limbic areas, and the frontal cortex, a network classically involved in aversion processing. This pattern correlates with subjective aversion in all these regions, consistent with the hypothesis that roughness enhances auditory aversion through spreading of neural synchronisation.

Brain-wide Mapping of Mono-synaptic Afferents to Different Cell Types in the Laterodorsal Tegmentum

The laterodorsal tegmentum (LDT) is a brain structure involved in distinct behaviors including arousal, reward, and innate fear. How environmental stimuli and top-down control from high-order sensory and limbic cortical areas converge and coordinate in this region to modulate diverse behavioral outputs remains unclear. Using a modified rabies virus, we applied monosynaptic retrograde tracing to the whole brain to examine the LDT cell type specific upstream nuclei. The LDT received very strong midbrain and hindbrain afferents and moderate cortical and hypothalamic innervation but weak connections to the thalamus. The main projection neurons from cortical areas were restricted to the limbic lobe, including the ventral orbital cortex (VO), prelimbic, and cingulate cortices. Although different cell populations received qualitatively similar inputs, primarily via afferents from the periaqueductal gray area, superior colliculus, and the LDT itself, parvalbumin-positive (PV+) GABAergic cells received preferential projections from local LDT neurons. With regard to the different subtypes of GABAergic cells, a considerable number of nuclei, including those of the ventral tegmental area, central amygdaloid nucleus, and VO, made significantly greater inputs to somatostatin-positive cells than to PV+ cells. Diverse inputs to the LDT on a system-wide level were revealed.

Advanced visual network and cerebellar hyperresponsiveness to trigeminal nociception in migraine with aura

BackgroundDespite the growing body of advanced studies investigating the neuronal correlates of pain processing in patients with migraine without aura (MwoA), only few similar studies have been conducted in patients with migraine with aura (MwA). Therefore, we aimed to explore the functional brain response to trigeminal noxious heat stimulation in patients with MwA.MethodsSeventeen patients with MwA and 15 age- and sex-matched healthy controls (HC) underwent whole-brain blood oxygen level–dependent (BOLD) fMRI during trigeminal noxious heat stimulation. To examine the specificity of any observed differences between patients with MwA and HC, the functional response of neural pathways to trigeminal noxious heat stimulation in patients with MwA was compared with 18 patients with MwoA. Secondary analyses investigated the correlations between BOLD signal changes and clinical parameters of migraine severity.ResultsWe observed a robust cortical and subcortical pattern of BOLD response to trigeminal noxious heat stimulation across all participants. Patients with MwA showed a significantly increased activity in higher cortical areas known to be part of a distributed network involved in advanced visual processing, including lingual gyrus, inferior parietal lobule, inferior frontal gyrus and medial frontal gyrus. Moreover, a significantly greater cerebellar activation was observed in patients with MwA when compared with both patients with MwA and HC. Interestingly, no correlations were found between migraine severity parameters and magnitude of BOLD response in patients with MwA.ConclusionOur findings, characterized by abnormal visual pathway response to trigeminal noxious heat stimulation, support the role of a functional integration between visual and trigeminal pain networks in the pathophysiological mechanisms underlying migraine with aura. Moreover, they expand the concept of “neurolimbic-pain network” as a model of MwoA including both limbic dysfunction and cortical dys-excitability. Indeed, we suggest a model of “neurolimbic-visual-pain network” in MwA patients, characterized by dysfunctional correlations between pain-modulating circuits not only with the cortical limbic areas but with advanced visual areas as well. Furthermore, the abnormal cerebellar response to trigeminal noxious heat stimulation may suggest a dysfunctional cerebellar inhibitory control on thalamic sensory gating, impinging on the advanced visual processing cortical areas in patients with MwA.

The role of phosphodiesterase 4 in excessive daytime sleepiness in Parkinson's disease

IntroductionPreclinical studies suggest a link between cAMP/PKA signalling, phosphodiesterase 4 (PDE4) expression and excessive daytime sleepiness (EDS). Here, we investigated in vivo the association between PDE4 expression and EDS in Parkinson's disease (PD) patients using [11C]rolipram PET and MR imaging. MethodsEighteen participants, 12 PD and 6 healthy controls, underwent one [11C]rolipram PET and a multi-modal MRI scan. Probabilistic tractography was performed on subjects’ diffusion data to functionally parcellate the striatum according with projections to limbic cortical areas. The severity of EDS was assessed using the Epworth Sleepiness Scale (ESS). To assess PDE4 expression in PD patients with EDS, the PD cohort was divided according to the presence (n = 5) or absence (n = 7) of EDS, defined using validated cut-off of score ≥10 on the ESS as score ≥10 on the ESS. ResultsPD patients with EDS showed significantly increased [11C]rolipram volume of distribution (VT) in the caudate (P = 0.029), hypothalamus (P = 0.013), hippocampus (P = 0.036) and limbic striatum (P = 0.030) compared to patients without EDS. Furthermore, higher ESS scores correlated with increased [11C]rolipram VT in the caudate (r = 0.77; P = 0.003), hypothalamus (r = 0.84; P = 0.001), hippocampus (r = 0.81; P = 0.001) and limbic subdivisions of the striatum (r = 0.80; P = 0.003). ConclusionOur findings translate into humans preclinical data indicating that EDS is associated with elevated PDE4 in regions regulating sleep. The severity of EDS in PD was associated with elevated PDE4 expression; thus, suggesting a role of PDE4 in the pathophysiology of EDS in PD.

The Migraine Premonitory Phase

The premonitory phase of migraine is defined as the presence of nonpainful symptomatology occurring hours to days before the onset of headache. Symptoms can include neck stiffness, yawning, thirst, and increased frequency of micturition. Clinical recognition of these symptoms is important to ensure early and effective attack management. Further understanding of the clinical phenotype and neurobiological mediation of these symptoms is important in the advancement of therapeutics research in both acute and preventive treatments of migraine. Since 2014, functional imaging studies have been conducted during the premonitory stage of migraine and have provided novel insights into the early neurobiology and anatomy of the earliest stage of the migraine attack. These studies have shown early involvement of subcortical brain areas including the hypothalamus, substantia nigra, dorsal pons, and various limbic cortical areas, including the anterior cingulate cortex during the premonitory phase. More recent work has revealed altered hypothalamic-brainstem functional connectivity during migraine, which starts before the onset of pain. These exciting findings have provided functional correlation of the symptoms experienced by patients and changes seen on functional brain imaging. This article focuses on the prevalence, phenotype, and proposed neurobiology of premonitory symptomatology in migraineurs as well as the scope of future research.

SP 9. Individualized identification of the motor part of the subthalamic nucleus in Parkinson’s disease

Introduction The subthalamic nucleus (STN), a well known target for deep brain stimulation (DBS) in Parkinson’s disease (PD), is involved in motor, limbic, and cognitive processes ( Temel et al., 2005) . To achieve a successful outcome of DBS surgery the electrode should be placed in its motor part. In current clinical practice, targeting is performed with anatomical 1.5 T or 3T MR images, that display the STN as a homogenous structure. Consistent and patient specific identification of the motor, associative, and limbic zones of the STN with 3T MRI has been demonstrated to be challenging ( Lambert et al., 2012) . Objectives In this study, ultra-high field (7T) MRI was used to map the motor and non-motor areas of the STN in individual patients with PD. Patients and methods The study was approved by the Institutional Review Board at the University of Minnesota and the Local Medical Ethics Committee at Maastricht University Medical Center. Seventeen PD patients (five female, mean age = 62 years), were scanned on a 7T MR scanner (Magnetom 7T Siemens). Three scans were performed: a T1-weighted, a T2-weighted, and a diffusion-weighted scan performed twice with opposite phase encoding directions, along 50 directions with a b-value of 1500 s/mm 2 and 4 b0-volumes (see Table 1 ). Five patients were scanned with slight deviations to this protocol. The motor and non-motor territories of each patient’s STN were identified by tracing their structural connections to the limbic, associative, motor and remaining cortical areas. To this end, the cortex of a reference brain ( Grabner et al., 2006) , was manually divided into these four areas ( Fig. 1 A,B) and registered to each patient’s T1-weighted image. The STNs were manually delineated on each patient’s T2-weighted image and registered to the T1-space as well. Finally probabilistic fiber tracking with each STN as a seed region was performed in T1-space with the FMRIB Software Library (FSL) ( Jenkinson et al., 2012) based on a three-fiber model ( Behrens, 2007) . Results The STNs, with volumes ranging from 75.8 mm 3 to 183.9 mm 3 , were clearly visible on the T2-weighted images( Fig. 1 C) and a clear segregation of the territories was observed ( Fig. 1 D). In all 34 STNs, the superior posterolateral area was connected to the motor cortical area. The volume of the motor area varied from 17.2% to 78.7% of the total STN volume, with an average of 55.3%. In all 34 STNs, the overlapping region in the center was connected to the associative cortical area. Connections to the limbic cortical areas were found in 30 STNs, all from the inferior anteromedial tip of the STN, but with varying sizes. Finally connections to the remaining cortical areas were only found sporadically. Conclusions These results show that ultra-high field MRI can be used to identify the motor and non-motor areas of the STN for each patient individually. The great variability between patients, in volumes of the STN and the motor area also indicate that this mapping should be performed on an individual patient basis. Further studies are currently underway to infer if these maps indeed improve clinical outcome.

Kainic acid-induced albumin leak across the blood-brain barrier facilitates epileptiform hyperexcitability in limbic regions.

Systemic administration of kainic acid (KA) is a widely used procedure utilized to develop a model of temporal lobe epilepsy (TLE). Despite its ability to induce status epilepticus (SE) in vivo, KA applied to in vitro preparations induces only interictal-like activity and/or isolated ictal discharges. The possibility that extravasation of the serum protein albumin from the vascular compartment enhances KA-induced brain excitability is investigated here. Epileptiform activity was induced by arterial perfusion of 6 μm KA in the in vitro isolated guinea pig brain preparation. Simultaneous field potential recordings were carried out bilaterally from limbic (CA1, dentate gyrus [DG], and entorhinal cortex) and extralimbic regions (piriform cortex and neocortex). Blood-brain barrier (BBB) breakdown associated with KA-induced epileptiform activity was assessed by parenchymal leakage of intravascular fluorescein-isothiocyanate albumin. Seizure-induced brain inflammation was evaluated by western blot analysis of interleukin (IL)-1β expression in brain tissue. KA infusion caused synchronized activity at 15-30 Hz in limbic (but not extralimbic) cortical areas, associated with a brief, single seizure-like event. A second bolus of KA, 60 min after the induction of the first ictal event, did not further enhance excitability. Perfusion of serum albumin between the two administrations of KA enhanced epileptiform discharges and allowed a recurrent ictal event during the second KA infusion. Our data show that arterial KA administration selectively alters the synchronization of limbic networks. However, KA is not sufficient to generate recurrent seizures unless serum albumin is co-perfused during KA administration. These findings suggest a role of serum albumin in facilitating acute seizure generation.

Interhemispheric connections between the infralimbic and entorhinal cortices: The endopiriform nucleus has limbic connections that parallel the sensory and motor connections of the claustrum.

We have previously shown that the claustrum is part of an interhemispheric circuit that interconnects somesthetic-motor and visual-motor cortical regions. The role of the claustrum in processing limbic information, however, is poorly understood. Some evidence suggests that the dorsal endopiriform nucleus (DEn), which lies immediately ventral to the claustrum, has connections with limbic cortical areas and should be considered part of a claustrum-DEn complex. To determine whether DEn has similar patterns of cortical connections as the claustrum, we used anterograde and retrograde tracing techniques to elucidate the connectivity of DEn. Following injections of retrograde tracers into DEn, labeled neurons appeared bilaterally in the infralimbic (IL) cortex and ipsilaterally in the entorhinal and piriform cortices. Anterograde tracer injections in DEn revealed labeled terminals in the same cortical regions, but only in the ipsilateral hemisphere. These tracer injections also revealed extensive longitudinal projections throughout the rostrocaudal extent of the nucleus. Dual retrograde tracer injections into IL and lateral entorhinal cortex (LEnt) revealed intermingling of labeled neurons in ipsilateral DEn, including many double-labeled neurons. In other experiments, anterograde and retrograde tracers were separately injected into IL of each hemisphere of the same animal. This revealed an interhemispheric circuit in which IL projects bilaterally to DEn, with the densest terminal labeling appearing in the contralateral hemisphere around retrogradely labeled neurons that project to IL in that hemisphere. By showing that DEn and claustrum have parallel sets of connections, these results suggest that DEn and claustrum perform similar functions in processing limbic and sensorimotor information, respectively. J. Comp. Neurol. 525:1363-1380, 2017. © 2016 Wiley Periodicals, Inc.

Basolateral and central amygdala differentially recruit and maintain dorsolateral striatum-dependent cocaine-seeking habits.

In the development of addiction, drug seeking becomes habitual and controlled by drug-associated cues, and the neural locus of control over behaviour shifts from the ventral to the dorsolateral striatum. The neural mechanisms underlying this functional transition from recreational drug use to drug-seeking habits are unknown. Here we combined functional disconnections and electrophysiological recordings of the amygdalo-striatal networks in rats trained to seek cocaine to demonstrate that functional shifts within the striatum are driven by transitions from the basolateral (BLA) to the central (CeN) amygdala. Thus, while the recruitment of dorsolateral striatum dopamine-dependent control over cocaine seeking is triggered by the BLA, its long-term maintenance depends instead on the CeN. These data demonstrate that limbic cortical areas both tune the function of cognitive territories of the striatum and thereby underpin maladaptive cocaine-seeking habits.

Claustrum: a case for directional, excitatory, intrinsic connectivity in the rat.

Claustrum, a gray matter structure that underlies the neocortex, is reciprocally connected with many neocortical and limbic cortical areas. This connectivity positions claustrum ideally for the integration or coordination of widespread cortical activity. In anatomical studies using multiple planes of section, claustrum has distinct subregions based on latexin immunohistochemistry, and an approximately rostro-caudal alignment of fusiform cells supporting a laminar intrinsic organization. Physiological studies of claustral connectivity in disinhibited brain slices demonstrate (1) intrinsic connectivity sufficient to generate spontaneous synchronized burst discharges, (2) activity spread within the oblique laminae that contained the principal cellular axis, and (3) segregation of activity as evidenced by the absence of spread within coronal planes. Activity spread depended on glutamatergic synaptic transmission, and activity restrictions did not depend on inhibitory circuits. We conclude that the claustrum has an intrinsic excitatory connectivity that is constrained in approximately rostro-caudal laminae, with minimal cross-communication between laminae. Further, claustrum has the intrinsic capability of generating synchronized population activity and facilitating its spread within laminae, a feature that may contribute to seizure generation and spread.

Multilocus Genetic Profile for Glutamatergic Pathway and Frontostriatal Connectivity in Obsessive-compulsive Disorder

Introduction Research integrating neuroimaging and molecular genetics has yielded important insights into how variability in brain chemistry predicts brain function and structure, behaviour and risk for psychopathology. Disrupted neurotransmission of glutamate within corticalstriatal-thalamocortical circuitry has been hypothesized to play a role in the pathogenesis of Obsessive-Compulsive Disorder (OCD). Candidate gene studies have identified associations between variants in glutamate system genes and OCD, particularly for SLC1A1, although these results remain controversial after GWAS and meta-analytical approaches. Objectives To examine the effects of multiple polymorphisms of the glutamatergic pathway on frontostriatal connectivity, measured by resting state functional magnetic resonance imaging (fMRI), in OCD. Methods Individual multilocus genetic profile scores (MGPS) reflecting the additive effects of multiple alleles of the glutamatergic pathway, analysed by the Affymetrix GeneticChip® SNP array, were compiled for 134 OCD patients and 63 healthy controls. Association between these genetic scores and brain functional connectivity patterns between the dorsal and ventral striatal regions and limbic cortical areas including the orbitofrontal cortex and surrounding areas, such as the anterior prefrontal and perigenual anterior cingulate cortex, were investigated. Results In the entire group, glutamatergic MGPS were significantly associated with connectivity patterns involving the ventral striatum and orbitofrontal cortex. Distinct relationships between MGPS and functional connectivity between the ventral striatum, amygdala, ventromedial frontal cortex and insula between OCD and healthy subjects emerged. Conclusions Glutamatergic genetic risk variants are related to normal frontostriatal connectivity; a fact that might explain the role of glutamatergic pathway disruptions in the susceptibility to develop OCD.

Uppermost synchronized generators of spike–wave activity are localized in limbic cortical areas in late-onset absence status epilepticus

PurposeAbsence status (AS) epilepticus with generalized spike–wave pattern is frequently found in severely ill patients in whom several disease states co-exist. The cortical generators of the ictal EEG pattern and EEG functional connectivity (EEGfC) of this condition are unknown. The present study investigated the localization of the uppermost synchronized generators of spike–wave activity in AS. MethodSeven patients with late-onset AS were investigated by EEG spectral analysis, LORETA (Low Resolution Electromagnetic Tomography) source imaging, and LSC (LORETA Source Correlation) analysis, which estimates cortico-cortical EEGfC among 23 ROIs (regions of interest) in each hemisphere. ResultsAll the patients showed generalized ictal EEG activity. Maximum Z-scored spectral power was found in the 1–6Hz and 12–14Hz frequency bands. LORETA showed that the uppermost synchronized generators of 1–6Hz band activity were localized in frontal and temporal cortical areas that are parts of the limbic system. For the 12–14Hz band, abnormally synchronized generators were found in the antero-medial frontal cortex. Unlike the rather stereotyped spectral and LORETA findings, the individual EEGfC patterns were very dissimilar. ConclusionThe findings are discussed in the context of nonconvulsive seizure types and the role of the underlying cortical areas in late-onset AS. The diversity of the EEGfC patterns remains an enigma. Localizing the cortical generators of the EEG patterns contributes to understanding the neurophysiology of the condition.

First evidence of a hyperdirect prefrontal pathway in the primate: precise organization for new insights on subthalamic nucleus functions

The direct connections from the cortex to the subthalamic nucleus (STN), the so-called hyperdirect pathway, is known for the cortical motor areas and plays a top–down executive control on basal ganglia (BG). However, little was known regarding the projections onto the STN from anterior and ventral prefrontal regions involved in more integrated functions such as decision making or reward related processes. The large-scale study by Haynes and Haber aimed to trace the hyperdirect pathway from different territories of the prefrontal cortex and motor areas to determine the levels of convergence and segregation of these projections onto the different subterritories of the STN. Their first objective was to delineate all frontal inputs to the STN in monkeys, extending to primate those already described in rodents (Berendse and Groenewegen, 1991). They impressively targeted many areas constitutive of four prefrontal regions: ventromedial prefrontal cortex (vmPFC), orbitofrontal cortex (OFC), dorsal anterior cingulate cortex (dACC) and dorsal prefrontal cortex (dPFC), and established that all of them project onto the STN. These cortices are differentially involved in cognitive, motivational and emotional processes. Do these distinct information funnel in the STN or remain processed separately by STN subterritories? The second objective was to delineate a limbic STN based on the topography of the projections from areas of the vmPFC, OFC, and dACC, involved in reward-related processes. The authors mapped the limbic part of the STN from the medial tip of the nucleus to the lateral part of the LH. However, since not all areas from the vmPFC and OFC and other limbic cortices have been investigated, the study does not allow to assess the exact extent of this limbic STN. Finally, the authors examined the convergence and/or segregation of cortico-STN fibers from motor, cognitive and limbic cortical areas. The central part of the STN receives overlapping projections from the majority of labeled cortical afferences. However, motor projections to the dorsal lateral extremities seem to be isolated from those forming the limbic territories, located at the medial tip of the nucleus.