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Investigating Object Representations in the Macaque Dorsal Visual Stream Using Single-unit Recordings
Published on: August 1, 2018
Muscle representation in the macaque motor cortex: an anatomical perspective
Jean-Alban Rathelot1, Peter L Strick
1Research Service, Veterans Affairs Medical Center, Department of Neurobiology, University of Pittsburgh School of Medicine, W1640 Biomedical Science Tower, 200 Lothrop Street, Pittsburgh, PA 15261, USA.
Summary
Neurons directly controlling muscles in the primary motor cortex (M1) are widespread, not focal. This suggests a neural basis for diverse muscle synergies, challenging previous representations of muscle control.
Area of Science:
- Neuroscience
- Motor Control
- Cortical Mapping
Background:
- The precise distribution of neurons directly influencing motoneurons in the primary motor cortex (M1) remains a key question in motor control.
- Understanding this organization is crucial for deciphering how voluntary movements are generated.
Purpose of the Study:
- To map the distribution of cortico-motoneuronal (CM) cells that directly innervate motoneurons of specific thumb and finger muscles in macaques.
- To investigate whether M1 exhibits a focal representation for individual muscles or a more distributed organization.
Main Methods:
- Utilized retrograde transneuronal transport of rabies virus from single muscles in macaque monkeys.
- Identified and mapped CM cells making monosynaptic connections with motoneurons of injected digit muscles.
Main Results:
- CM cells for digit muscles are located in the caudal M1, within the central sulcus, and show a widespread mediolateral distribution.
- Cortical territories for CM cells of different digit muscles overlap extensively, with no evidence of focal representation.
- A significant proportion (15-16%) of CM cells originate from somatosensory area 3a.
- CM cells encompass a range of sizes, including those characteristic of both fast and slow pyramidal tract neurons.
Conclusions:
- The widespread and overlapping distribution of CM cells suggests a neural substrate for generating a wide repertoire of muscle synergies, rather than a precise somatotopic map for individual muscles.
- The inclusion of cells from area 3a and the range of CM cell sizes challenge existing views on the function and organization of the cortico-motoneuronal system.
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