| Abstract No.: | C-D3137 |
| Country: | Canada |
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| Title: | CONTROL OF POSTURE IN MOTOR CORTEX |
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| Authors/Affiliations: | 1 Sergiy Yakovenko*; 1 Trevor Drew;
1 Université de Montréal, QC, Canada
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| Content: | Objectives: Two postural objectives must be achieved during reaching from a standing position: 1) the disturbance of the center of mass must be minimized by producing appropriate anticipatory postural adjustments (APAs) before the movement and; 2) the postural support and equilibrium of the body must be assured during the movement. Here, we tested the hypothesis that the motor cortex contributes to the execution of the first of these objectives.
Materials and Methods: Three cats were trained to reach and press a lever with either forelimb in response to an auditory cue in an instructed delay task. The cats were then implanted with a chamber over the motor cortex to allow us to record from identified pyramidal tract neurones (PTNs) with conventional microelectrodes. Electromyographic activity was recorded from selected muscles in all four limbs. Kinematics and ground reaction forces (GRFs) for each limb were also recorded.
Results: We recorded 175 neurones that showed increased discharge activity during the movement of either the contralateral or ipsilateral limb. Of these cells, 81/175 showed a short latency change in activity that was time-locked to the Go signal and preceded the onset of movement. This activity preceded or coincided with the short-latency changes in activity of the muscles that contribute to the APA. Moreover, the activity of all of these Go-related neurones was temporally correlated with APA-related changes in GRFs and/or the composite anterio-posterior and medio-lateral components of the centre of vertical pressure (CoVP).
Neurones with Go-related activity included those with receptive fields on the distal paw as well as those with receptive fields around the shoulder. The former population frequently showed non-reciprocal changes of activity during reaches with either limb. Microstimulation at the site of the recording frequently evoked activity in elbow flexor and wrist dorsiflexor muscles. As such, we suggest that this population might play a role in stabilising the distal limb during the APA. The cells with receptive fields around the shoulder more frequently discharged during movements of one or the other limb; they were most frequently facilitated during movement of the ipsilateral limb and decreased during movement of the contralateral limb. Microstimulation at these sites most frequently activated proximal musculature. This is consistent with a role for these cells in stabilising the body during the APA.
Conclusion: These results provide support that the motor cortex contributes not only to the control of the reaching movement but also to the anticipatory postural adjustments that precede the movement and which are essential for its successful completion.
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