| Abstract No.: | B-D2158 |
| Country: | Canada |
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| Title: | ACTIVE AND PASSIVE MOVEMENTS ARE DIFFERENTIALLY ENCODED BY THE CEREBELLUM |
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| Authors/Affiliations: | 1 Jessica Brooks*; 2 Kathleen Cullen;
1 McGill Univeristy, Montreal, QC, Canada
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| Content: | Objectives: Recent work in the vestibular system has found that some neurons in the vestibular nuclei (VN) differentially encode passively applied and actively generated movements. This ability to distinguish between these two types of sensory inputs is necessary for accurate sensory perception and motor control and has been observed in many model systems. Although much is known about the conditions under which these neurons show attenuated sensitivity to vestibular stimuli, the source of the cancellation signal has not yet been identified. The cerebellum integrates convergent information from structures that encode goals, motor commands and movement feedback signals and thus is a likely site to be involved in generating the cancellation signal. More specifically, the rostral fastigial nucleus (rFN), one of the deep cerebellar nuclei, is a good candidate because it receives both vestibular and neck proprioception inputs as well as efference copy signals. Thus, our aim was to answer the following questions: 1)Do rFN neurons differentially encode active and passive movements and 2)If they do, are these signals appropriate to attenuate neurons in the VN?
Materials and Methods: To address these questions, we recorded from single neurons in the rFN in two monkeys. The neurons were further characterized by passively applying motion that activated vestibular sensors, neck muscle proprioceptors or both. The head was then carefully released and the monkey was allowed to generate active head-on-body movements to laser targets for a juice reward. Finally, we passively rotated the animal while it made active head movements.
Results: Based on our passively applied stimuli we could identify 2 types of neurons. The first responded only to vestibular stimulation (V neurons, n=15) and the second responded to both vestibular and neck inputs (V+N neurons, n=13). Despite strong modulation during passively applied vestibular stimulation (0.43 (spikes/s)/(deg/s)), sensitivity of both types of neurons was attenuated by about 70% during actively generated head-on-body movements. During combined active and passive movements these neurons continued to selectively respond to the passive component of the head motion. The estimated sensitivities to each component of the motion remain unchanged when they were applied simultaneously relative to when they were presented alone ((p=0.45 and p=0.19 for passive and active components of the movement respectively)).
Conclusion: Neurons in the rostral fastigial nucleus show attenuated sensitivity to actively generated head-on-body movements compared to passively applied vestibular stimulation whether these active movements occur alone or in combination with passive movements. Furthermore, we demonstrate that although these neurons can contribute to the cancellation of vestibular signals during active movements, the modulation of these neurons alone is not sufficient to attenuate the neurons in the vestibular nuclei during active head-on-body movements.
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