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Efferent projections of the motorcortical larynx area in the rhesus monkey (Macaca mulatta)
| Content Provider | Semantic Scholar |
|---|---|
| Author | Simonyan, Kristina |
| Copyright Year | 2003 |
| Abstract | The cortical larynx area is that part of the motor cortex, which controls laryngeal muscles. This area is indispensable for speech and song. Lesions in the cortical larynx area in man, if bilateral, cause severe disturbances in speech production and articulation with a loss of voluntary fine control of vocal patterns. The aim of the study is a better understanding of the central nervous control of phonation. The present study was carried out in the following way. The experimental animals were 3 rhesus monkeys, Macaca mulatta. Under general anesthesia, the motorcortex of the animals was explored for sites yielding vocal fold movements. Identification of the larynx area was made with the help of electrical brain stimulation by aid of a monopolar stimulation electrode. Vocal fold adduction was observed under indirect laryngoscopy. When sites yielding vocal fold adduction were found, they were injected with an anterograde tracer, biotin dextranamine, by the aid of a microsyringe. After a survival period of 7 weeks, the animals were perfused with physiological saline and paraformaldehyde solutions. The brains were removed from the skull, sectioned on the cryotom, and immunohistologically processed. The following projections were found out. Heavy projections were traced into the surrounding ventral and dorsal premotor cortex, primary motor cortex, the homologue of Broca's area, fronto- and parietoopercular cortex (including secondary somatosensory cortex), granular insula, rostralmost primary somatosensory cortex, supplementary motor area, anterior cingulate gyrus, and dorsal postarcuate cortex. Medium projections could be traced to the ventrolateral prefrontal and lateral orbital cortex, primary somatosensory areas 3b and 2, agranular and dysgranular insula, and posteroinferior parietal cortex. Minor projections ended in the lateral and dorsolateral prefrontal cortex, primary somatosensory area 1, and cortex within the intraparietal sulcus and posterior sulcus temporalis superior. The majority of the structures received a bilateral projection, with an ipsilateral predominance. Subcortical projections could be traced within the forebrain to the putamen, caudate nucleus, claustrum, zona incerta, field H of Forel, and a number of thalamic nuclei with the heaviest projections to the nuclei ventralis lateralis, ventralis posteromedialis, including its parvocellular part, medialis dorsalis, centralis medialis, centrum medianum, and reuniens. In the midbrain, labelling was found in the deep mesencephalic nucleus. No labelling was found in the red nucleus and periaqueductal region. In the lower brainstem, fibres terminated in the pontine and medullary reticular formation, locus coeruleus, nucleus subcoeruleus, medial parabrachial nucleus, nucleus of the spinal trigeminal tract, solitary tract nucleus, and facial nucleus. No projections were found to the nuclei ambiguus and retroambiguus. The majority of the subcortical projections were again bilateral with an ipsilateral predominance. The present study makes clear that the cortical larynx area is connected with a very large number of areas in the forebrain and brainstem, which might represent potential candidates in the phonatory control system. The motorcortical larynx area is strongly connected with areas lying within as well as along the Sylvian fissure, from the anterior prefrontal cortex back to the posterior parietal cortex. These areas seem to be responsible for different stages of vocal processing, reaching from planning (prefrontal cortex) via motor preparation and execution (premotor and motor cortex) to proprioceptive (parietal cortex) and auditory feedback control (superior temporal cortex). The marked projections to the mediofrontal cortex probably serve the initiation of vocal behaviour. Several of these areas have been shown with modern brain imaging techniques (PET, fMRI) to be activated during speech. The lack of a direct connection of the motorcortex with the laryngeal motoneurones, in contrast to humans, suggests that this connection has evolved in the last few million years and might represent one of the factors that made speech evolution possible. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://elib.tiho-hannover.de/servlets/MCRFileNodeServlet/etd_derivate_00002638/simonyank_2003.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
