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Response patterns and force relations of monkey spinal interneurons during active wrist movement
M A Maier1, S I Perlmutter, E E Fetz
1Department of Physiology and Biophysics and Regional Primate Research Center, University of Washington, Seattle, Washington 98195, USA.
Journal of Neurophysiology
|November 18, 1998
Summary
Spinal cord neurons, including motoneurons and interneurons, were studied during wrist torque generation in macaques. Most interneurons showed bidirectional activity, unlike other premotor neurons, suggesting peripheral input influences spinal premotor interneurons.
Area of Science:
- Neuroscience
- Motor Control
- Spinal Cord Physiology
Background:
- Understanding spinal cord neuron activity is crucial for deciphering motor control mechanisms.
- Previous research has characterized various premotor neurons, but spinal premotor interneurons (PreM-INs) remain less understood, particularly their response properties during dynamic tasks.
Purpose of the Study:
- To investigate the activity patterns of C6-T1 spinal cord neurons, including motoneurons (MNs) and different classes of interneurons, during isometric wrist flexion and extension.
- To compare the response properties of spinal PreM-INs with other known premotor neuron populations.
Main Methods:
- Recorded C6-T1 spinal cord neuron activity in three macaques performing visually guided wrist torque tasks.
- Utilized spike-triggered averages (STAs) of electromyographic (EMG) activity from forearm muscles to classify neurons (MNs, PreM-INs, Sy-INs, U-INs).
- Analyzed neuronal firing patterns, including tonic and phasic activity, and their correlation with torque magnitude and rate of change.
Main Results:
- A total of 572 task-related neurons were studied: 29 MNs, 97 PreM-INs, 32 Sy-INs, and 414 U-INs.
- Most interneurons (77%) exhibited bidirectional activity (flexion and extension), contrasting with unidirectional activity in some other premotor neurons.
- Spinal PreM-INs showed a higher proportion of activation after target muscle onset compared to other premotor types, suggesting greater peripheral input influence.
Conclusions:
- Spinal premotor interneurons display distinct response characteristics, including bidirectional activity and sensitivity to peripheral inputs, differentiating them from other premotor neuron populations.
- The findings contribute to a more comprehensive understanding of the neural circuitry underlying voluntary movement control at the spinal cord level.