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Reacquisition deficits in prism adaptation after muscimol microinjection into the ventral premotor cortex of monkeys
1Department of Physiology, Tohoku University School of Medicine, Sendai 980-8575, Japan.
Abstract:
A small amount of muscimol (1 microl; concentration, 5 microg/microl) was injected into the ventral and dorsal premotor cortex areas (PMv and PMd, respectively) of monkeys, which then were required to perform a visually guided reaching task. For the task, the monkeys were required to reach for a target soon after it was presented on a screen. While performing the task, the monkeys' eyes were covered with left 10 degrees, right 10 degrees, or no wedge prisms, for a block of 50-100 trials. Without the prisms, the monkeys reached the targets accurately. When the prisms were placed, the monkeys initially misreached the targets because the prisms displaced the visual field. Before the muscimol injection, the monkeys adapted to the prisms in 10-20 trials, judging from the horizontal distance between the target location and the point where the monkey touched the screen. After muscimol injection into the PMv, the monkeys lost the ability to readapt and touched the screen closer to the location of the targets as seen through the prisms. This deficit was observed at selective target locations, only when the targets were shifted contralaterally to the injected hemisphere. When muscimol was injected into the PMd, no such deficits were observed. There were no changes in the reaction and movement times induced by muscimol injections in either area. The results suggest that the PMv plays an important role in motor learning, specifically in recalibrating visual and motor coordinates.
Insights
The ventral premotor cortex (PMv) is crucial for motor learning. Injections of muscimol into the PMv impaired monkeys' ability to adapt to visual prism displacement, highlighting its role in recalibrating sensorimotor transformations.
Area of Science:
- Neuroscience
- Motor Control
- Cognitive Neuroscience
Background:
- Motor learning involves adapting to sensory feedback.
- The premotor cortex is involved in planning and executing movements.
- Sensorimotor recalibration is essential for accurate goal-directed actions.
Purpose of the Study:
- To investigate the role of the ventral premotor cortex (PMv) and dorsal premotor cortex (PMd) in motor learning.
- To determine the specific contribution of the PMv to sensorimotor recalibration during a visually guided reaching task.
Main Methods:
- Monkeys performed a visually guided reaching task with prism goggles.
- Muscimol was injected into the PMv and PMd to temporarily inactivate these areas.
- Adaptation to prism-induced visual field displacement was assessed before and after injections.
Main Results:
- Muscimol injection into the PMv impaired the monkeys' ability to adapt to prism-induced visual field shifts.
- This deficit was specific to contralateral target locations.
- Inactivation of the PMd did not affect prism adaptation.
- Reaction and movement times remained unchanged.
Conclusions:
- The PMv plays a critical role in motor learning, particularly in recalibrating visual and motor coordinates.
- The PMv is essential for adapting to changes in the visual environment during reaching tasks.
- These findings elucidate the specific functions of premotor cortex subregions in sensorimotor control.