Jackson, Andrew; (2002) Synchrony in the primate motor system. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Synchronised neuronal activity is widespread throughout the cortex, and can give rise to oscillations observed in local field potentials (LFPs). Such organised firing patterns are of interest in understanding how populations of neurons interact, but the mechanisms responsible for generating this activity and its consequences for neural processing are poorly understood. This thesis aims to address these issues with specific focus on the motor system. The corticomotoneuronal (CM) pathway is particularly important for skilled control of the hand, and synchronous oscillation is evident in the cortical drive descending via the pyramidal tract (PT) to motoneurons in the cervical spinal cord. To investigate the networks underlying this activity, multiple single units and LFPs from primary motor cortex and EMG from hand muscles were simultaneously recorded from monkeys performing a precision grip task. Synchrony between pairs of CM neurons was related to each cells output effects as revealed by spike-triggered averaging of EMG, and evidence was found for synchronised networks of cells with shared CM projections. Furthermore, stimulation of the PT revealed that rhythmicity within these motor cortex networks arises from intrinsic connectivity rather than a separate oscillatory drive. Firing rates and the strength of LFP oscillation were compared across different load conditions presented in blocked or randomised sequences. These results were incorporated into a model of rhythm generation within the motor cortex which showed that oscillatory activity is associated with a low gain motor state. Finally, recordings made simultaneously in the cerebellum and motor cortex revealed evidence for oscillatory coupling between the two areas. However, differences in the nature of these oscillations suggest that separate circuits are responsible for their generation. Taken together, this research shows how synchrony, as revealed by multiple electrode recordings in the awake brain, can help to describe the functional architecture of the motor system.

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