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The laryngeal motor cortex: its organization and connectivity
1Department of Neurology, Icahn School of Medicine at Mount Sinai, New York, NY 10029, United States; Department of Otolaryngology, Icahn School of Medicine at Mount Sinai, New York, NY 10029, United States.
The human laryngeal motor cortex (LMC) in primary motor cortex controls speech and song. In monkeys, LMC in premotor cortex does not affect vocalizations, suggesting evolutionary divergence for human vocal control.
Area of Science:
- Neuroscience
- Comparative Anatomy
- Evolutionary Biology
Background:
- The laryngeal motor cortex (LMC) modulates complex laryngeal behaviors like speech and song.
- Human LMC is in area 4 of the primary motor cortex, with direct/indirect connections to motoneurons.
- Primate LMC is in area 6 of the premotor cortex, with indirect connections and minimal impact on vocalizations.
Purpose of the Study:
- To investigate the evolutionary differences in LMC location and connectivity between humans and monkeys.
- To understand the functional implications of these differences for vocal control.
Main Methods:
- Comparative cytoarchitectonic analysis of LMC in humans and monkeys.
- Tracing of neural connections from LMC to laryngeal motoneurons in both species.
Main Results:
- Human LMC located in primary motor cortex (area 4) with direct and indirect projections.
- Monkey LMC located in premotor cortex (area 6) with only indirect projections.
- LMC destruction in monkeys did not affect species-specific vocalizations.
Conclusions:
- The distinct location and connectivity of the human LMC suggest an evolutionary shift from a phylogenetically older to newer motor cortex.
- This evolution likely enabled the voluntary motor control of complex human vocalizations, including speech and song.
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