Inferior Motor Cortex Research Articles

Transient, developmental functional and structural connectivity abnormalities in the thalamocortical motor network in Rolandic epilepsy

Rolandic epilepsy (RE) is the most common focal, idiopathic, developmental epilepsy, characterized by a transient period of sleep-potentiated seizures and epileptiform discharges in the inferior Rolandic cortex during childhood. The cause of RE remains unknown but converging evidence has identified abnormalities in the Rolandic thalamocortical circuit. To better localize this transient disease, we evaluated Rolandic thalamocortical functional and structural connectivity in the sensory and motor circuits separately during the symptomatic and asymptomatic phases of this disease. We collected high resolution structural, diffusion, and resting state functional MRI data in a prospective cohort of children with active RE (n = 17), resolved RE (n = 21), and controls (n = 33). We then computed the functional and structural connectivity between the inferior Rolandic cortex and the ventrolateral (VL) nucleus of the thalamus (efferent pathway) and the ventroposterolateral (VPL) nucleus of the thalamus (afferent pathway) across development in children with active, resolved RE and controls. We compared connectivity with age in each group using linear mixed-effects models. We found that children with active RE have increasing thalamocortical functional connectivity between the VL thalamus and inferior motor cortex with age (p = 0.022) that is not observed in controls or resolved RE. In contrast, children with resolved RE have increasing thalamocortical structural connectivity between the VL nucleus and the inferior motor cortex with age (p = 0.025) that is not observed in controls or active RE. No relationships were identified between VPL nuclei and the inferior sensory cortex with age in any group. These findings localize the functional and structural thalamocortical circuit disruption in RE to the efferent thalamocortical motor pathway. Further work is required to determine how these circuit abnormalities contribute to the emergence and resolution of symptoms in this developmental disease.

Evolution of the Central Mechanisms of Oral Speech

The communicative system is most developed in social animals and represents a determinative factor in human evolution. Here we address the possible evolutionary ways of the emergence and formation of speech functions. Specifically, we discuss the possibility of the formation of voluntary voice control at the early stages of Homo evolution on the anatomo-physiological basis of the gesture control system. The possible morphofunctional basis for the evolutionary emergence of speech is considered. The structure and connectivity of different regions of the cerebral cortex (temporal, inferior, parietal) are compared in humans and monkeys. Anatomy of the auditory cortex is well known to be relatively alike in different primate species, likewise are the pathways that link the auditory cortex with the associative areas of the anterior temporal cortex and the ventrolateral prefrontal cortex (human homologs of these structures form the ventral speech stream). At the same time, the pathways that link the auditory cortex with the ventral premotor and inferior motor cortex and make up in humans the dorsal speech stream are poorly developed in monkeys. The underdevelopment of this speech stream accounts for communication in monkeys based on gestural speech, because the morphological basis for voluntarily regulated vocalization and articulation has not yet formed during their evolution. The emergence of a sophisticated communication system based on oral speech may have been possible due to a gradual accumulation of evolutionary changes in speech-related and some other brain structures and, most importantly, a complication of connectivity between them. The evolution of speech is discussed in terms of its close association with tool use and labor activity.

ЭВОЛЮЦИЯ ЦЕНТРАЛЬНЫХ МЕХАНИЗМОВ УСТНОЙ РЕЧИ

The communicative system is most developed in social animals and is decisive in human evolution. The article discusses the possible evolutionary ways of the emergence and speech function formation. The possibility of the voice control formation on the anatomical and physiological basis of the gesture control system at the early stages of Homo evolution is discussed. The possible morphofunctional basis for the speech appearance is considered. The structure and connections of cerebral cortex various parts (temporal, inferior, parietal), in humans and monkeys is compared. It is known that the anatomy of the auditory cortex in different primate species is relatively similar, as well as the connections of the auditory cortex with the associative zones of the anterior temporal cortex and the ventrolateral prefrontal cortex (in humans, the homologues of these structures form the ventral speech pathway). At the same time, the connections of the auditory cortex with the ventral premotor and inferior motor cortex, which constitute the human dorsal speech pathway, are poorly developed in monkeys. The underdevelopment of this pathway determines the development of communication in monkeys on the basis of gestural speech, since the morphological basis for voluntary-regulated vocalization and articulation has not formed during their evolution. Complex communication system based on oral speech could be formed on the basis of gradually accumulated evolutionary changes in speech (and not only) brain structures, and most importantly - the connectivity between them. The evolution of speech is discussed in terms of its close relationship with the instrument-labor activity.

Afferent subcortical connections into the motor cortical larynx area in the rhesus monkey

In three rhesus monkeys ( Macaca mulatta), the inferior motor cortex was explored by electrical stimulation for sites yielding vocal fold adduction. The retrograde tracer wheat germ-agglutinin-conjugated horseradish peroxidase was injected into the effective sites. Within the forebrain, retrogradely labeled cells were found in the claustrum, basal nucleus of Meynert, substantia innominata, extended amygdala, lateral and posterior hypothalamic area, field H of Forel, and a number of thalamic nuclei with the strongest labeling in the nuclei ventralis lateralis, ventralis posteromedialis, including its parvocellular part, medialis dorsalis and centrum medianum, and weaker labeling in the nuclei ventralis anterior, ventralis posterolateralis, intermediodorsalis, paracentralis, parafascicularis and pulvinaris anterior. In the midbrain, labeling was found in the deep mesencephalic nucleus, ventral tegmental area, and substantia nigra. In the lower brainstem, labeled cells were found in the pontine reticular formation, median and dorsal raphe nuclei, medial parabrachial nucleus, and locus coeruleus. The findings are discussed in terms of the possible role of these structures in voluntary vocal control.