Hierarchical cortical networks of “voice patches” for processing voices in human brain

Humans have an extraordinary ability to recognize and differentiate voices. It is yet unclear whether voices are uniquely processed in the human brain. To explore the underlying neural mechanisms of voice processing, we recorded electrocorticographic signals from intracranial electrodes in epilepsy patients while they listened to six different categories of voice and nonvoice sounds. Subregions in the temporal lobe exhibited preferences for distinct voice stimuli, which were defined as “voice patches.” Latency analyses suggested a dual hierarchical organization of the voice patches. We also found that voice patches were functionally connected under both task-engaged and resting states. Furthermore, the left motor areas were coactivated and correlated with the temporal voice patches during the sound-listening task. Taken together, this work reveals hierarchical cortical networks in the human brain for processing human voices.

Reduced Effective Connectivity in the Motor Cortex in Parkinson’s Disease

Fast rhythms excess is a hallmark of Parkinson’s Disease (PD). To implement innovative, non-pharmacological, neurostimulation interventions to restore cortical-cortical interactions, we need to understand the neurophysiological mechanisms underlying these phenomena. Here, we investigated effective connectivity on source-level resting-state electroencephalography (EEG) signals in 15 PD participants and 10 healthy controls. First, we fitted multivariate auto-regressive models to the EEG source waveforms. Second, we estimated causal connections using Granger Causality, which provide information on connections’ strength and directionality. Lastly, we sought significant differences connectivity patterns between the two populations characterizing the network graph features—i.e., global efficiency and node strength. Causal brain networks in PD show overall poorer and weaker connections compared to controls quantified as a reduction of global efficiency. Motor areas appear almost isolated, with a strongly impoverished information flow particularly from parietal and occipital cortices. This striking isolation of motor areas may reflect an impaired sensory-motor integration in PD. The identification of defective nodes/edges in PD network may be a biomarker of disease and a potential target for future interventional trials.

Influence of the visuo-proprioceptive illusion of movement and motor imagery of the wrist on EEG cortical excitability among healthy participants

Introduction Motor Imagery (MI) is a powerful tool to stimulate sensorimotor brain areas and is currently used in motor rehabilitation after a stroke. The aim of our study was to evaluate whether an illusion of movement induced by visuo-proprioceptive immersion (VPI) including tendon vibration (TV) and Virtual moving hand (VR) combined with MI tasks could be more efficient than VPI alone or MI alone on cortical excitability assessed using Electroencephalography (EEG). Methods We recorded EEG signals in 20 healthy participants in 3 different conditions: MI tasks involving their non-dominant wrist (MI condition); VPI condition; and VPI with MI tasks (combined condition). Each condition lasted 3 minutes, and was repeated 3 times in randomized order. Our main judgment criterion was the Event-Related De-synchronization (ERD) threshold in sensori-motor areas in each condition in the brain motor area. Results The combined condition induced a greater change in the ERD percentage than the MI condition alone, but no significant difference was found between the combined and the VPI condition (p = 0.07) and between the VPI and MI condition (p = 0.20). Conclusion This study demonstrated the interest of using a visuo-proprioceptive immersion with MI rather than MI alone in order to increase excitability in motor areas of the brain. Further studies could test this hypothesis among patients with stroke to provide new perspectives for motor rehabilitation in this population.

Atypical Integration of Sensory-to-Transmodal Functional Systems Mediates Symptom Severity in Autism

A notable characteristic of autism spectrum disorder (ASD) is co-occurring deficits in low-level sensory processing and high-order social interaction. While there is evidence indicating detrimental cascading effects of sensory anomalies on the high-order cognitive functions in ASD, the exact pathological mechanism underlying their atypical functional interaction across the cortical hierarchy has not been systematically investigated. To address this gap, here we assessed the functional organisation of sensory and motor areas in ASD, and their relationship with subcortical and high-order trandmodal systems. In a resting-state fMRI data of 107 ASD and 113 neurotypical individuals, we applied advanced connectopic mapping to probe functional organization of primary sensory/motor areas, together with targeted seed-based intrinsic functional connectivity (iFC) analyses. In ASD, the connectopic mapping revealed topological anomalies (i.e., excessively more segregated iFC) in the motor and visual areas, the former of which patterns showed association with the symptom severity of restricted and repetitive behaviors. Moreover, the seed-based analysis found diverging patterns of ASD-related connectopathies: decreased iFCs within the sensory/motor areas but increased iFCs between sensory and subcortical structures. While decreased iFCs were also found within the higher-order functional systems, the overall proportion of this anomaly tends to increase along the level of cortical hierarchy, suggesting more dysconnectivity in the higher-order functional networks. Finally, we demonstrated that the association between low-level sensory/motor iFCs and clinical symptoms in ASD was mediated by the high-order transmodal systems, suggesting pathogenic functional interactions along the cortical hierarchy. Findings were largely replicated in the independent dataset. These results highlight that atypical integration of sensory-to-high-order systems contributes to the complex ASD symptomatology.

Surface anatomy and white matter connectivity of the premotor and motor areas

ΣΚΟΠΟΣ: Σκοπός της παρούσας διατριβής είναι η μελέτη της αρχιτεκτονικής, της μορφολογίας και της συσχετιστικής ανατομίας των δεματίων λευκής ουσίας που εμπλέκονται στη συνδεσιμότητα του κινητικού και προκινητικού φλοιού καθώς και της επικουρικής και προ-εκπικουρικής περιοχής. ΜΕΘΟΔΟΣ: Τριάντα (30) ημισφαίρια υγειών ενηλίκων μονιμοποιημένα σε φορμόλη μελετήθηκαν με χρήση της μεθόδου παρασκευής της λευκής ουσίας κατά Klingler. Οι εν λόγω βήμα προς βήμα παρασκευές ολοκληρώθηκαν με κατεύθυνση από έξω προς τα έσω και από έσω προς τα έξω. ΑΠΟΤΕΛΕΣΜΑΤΑ: Αναζητήθηκε η υποφλοιώδης αρχιτεκτονική, η χωρική συσχέτιση και η συνδεσιμότητα τεσσάρων κυρίως μείζονων δεματίων: Α) Το ραχιαίο τμήμα του άνω επιμήκους δεματίου (SLF-I) ανευρέθηκε σταθερά στην έσω επιφάνεια του ημισφαιρίου να συνδέει το προσφηνοειδές λόβιο, την επικουρική και προ-επικουρική κινητική περιοχή. Β) Το Μετωπιαίο Επίμηκες Δεμάτιο(FLS) παρατηρήθηκε σταθερά ως μια πρόσθια συνέχεια του 2ου και 3ου τμήματος του άνω επιμήκους δεματίου(SLF II& SLF III). Το εν λόγω δεμάτιο συνδέει τον προκινητικό με τον προμετωπιαίο φλοιό. Γ) Το Μέτωπο-Κερκοφόρο Δεμάτιο (FCT) ένα ριπιδοειδές σύστημα ινών λευκής ουσίας, καταγράφηκε να συμμετέχει στη συνδεσιμότητα του προμετωπιαίου και προκινητικού φλοιού με την κεφαλή και το σώμα του κερκοφόρου πυρήνα. Δ) Το Φλοιο-καλυπτρικό δεμάτιο (CTT) ανευρέθηκε σταθερά να συνδέει τη μεσεγκεφαλική καλύπτρα με τον κινητικό/προκινητικό φλοιό και τον φλοιό της οπίσθιας κεντρικής έλικας. Κατά τις παρασκευές των εν λόγω δεματίων δεν παρατηρήθηκαν ημισφαιρικές ασυμμετρίες. Τέλος πρότυπα υποτμηματοποίησης προτάθηκαν για όλα τα δεμάτια. ΣΥΜΠΕΡΑΣΜΑΤΑ: Η συνδεσιμότητα και η λειτουργική εξειδίκευση των κινητικών και προκινητικών περιοχών του ανθρώπινου εγκεφάλου παραμένει σε μεγάλο βαθμό ασαφής καθώς ο μεγαλύτερος όγκος πληροφοριών προέρχεται από μελέτες σε πειραματόζωα και δεσμιδογραφικές μελέτες. Χρησιμοποιώντας την τεχνική Παρασκευής της λευκής ουσίας κατά Klingler ως βασική μέθοδο διερεύνησης, η παρούσα μελέτη παρέχει δεδομένα και στοιχεία για την λεπτή ανατομία των σχετιζόμενων με τις παραπάνω περιοχές δεματίων.

The Roles of the Cortical Motor Areas in Sequential Movements

The ability to learn and perform a sequence of movements is a key component of voluntary motor behavior. During the learning of sequential movements, individuals go through distinct stages of performance improvement. For instance, sequential movements are initially learned relatively fast and later learned more slowly. Over multiple sessions of repetitive practice, performance of the sequential movements can be further improved to the expert level and maintained as a motor skill. How the brain binds elementary movements together into a meaningful action has been a topic of much interest. Studies in human and non-human primates have shown that a brain-wide distributed network is active during the learning and performance of skilled sequential movements. The current challenge is to identify a unique contribution of each area to the complex process of learning and maintenance of skilled sequential movements. Here, I bring together the recent progress in the field to discuss the distinct roles of cortical motor areas in this process.

Afferent connections of cytoarchitectural area 6M and surrounding cortex in the marmoset: putative homologues of the supplementary and pre-supplementary motor areas

Cortical projections to the caudomedial frontal cortex were studied using retrograde tracers in marmosets. We tested the hypothesis that cytoarchitectural area 6M includes homologues of the supplementary and pre-supplementary motor areas (SMA and preSMA) of other primates. We found that, irrespective of the injection sites' location within 6M, over half of the labeled neurons were located in motor and premotor areas. Other connections originated in prefrontal area 8b, ventral anterior and posterior cingulate areas, somatosensory areas (3a and 1-2), and areas on the rostral aspect of the dorsal posterior parietal cortex. Although the origin of afferents was similar, injections in rostral 6M received higher percentages of prefrontal afferents, and fewer somatosensory afferents, compared to caudal injections, compatible with differentiation into SMA and preSMA. Injections rostral to 6M (area 8b) revealed a very different set of connections, with increased emphasis in prefrontal and posterior cingulate afferents, and fewer parietal afferents. The connections of 6M were also quantitatively different from those of M1, dorsal premotor areas, and cingulate motor area 24d. These results show that the cortical motor control circuit is conserved in simian primates, indicating that marmosets can be valuable models for studying movement planning and control.