Marsden, Jonathan Frank; (2001) Oscillatory activity in the human motor system in health and neurological disease. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The central nervous system structures involved in the genesis of oscillatory activity within the motor system and their functional role were investigated in humans. Assessment of the common modulation of motor unit firing patterns in various muscle groups reveals that the pattern of descending oscillatory drives to distal hand and axial muscles differs in healthy subjects. Such oscillatory drives can be affected by neurological disease. In rotational torticollis oscillatory drives to the affected muscles are of lower frequency compared to controls and tend to synchronise the firing of motor units between the affected muscles possibly contributing to the symptoms of dystonia. In Parkinson's disease, whilst off dopaminergic medication, there is a decrease in high frequency (15-30 Hz) coherence between distal upper limb muscles. Following clinically effective stimulation of the subthalamic nucleus or the administration of dopaminergic medication the 15-30 Hz coherence is increased. Direct recordings of local field potentials from a macroelectrode inserted into the subthalamic nucleus simultaneously with muscle and electroencephalography over the sensorimotor cortex demonstrate that the subthalamic nucleus is part of a circuit that is entrained in oscillations extending between 7-45 Hz. Significant coherence between signals recorded from the ventralis intermedius nucleus of the thalamus, sensorimotor cortex and contralateral muscle has also been detected in patients surgically treated for the alleviation of tremor. The coherence, which extends up to 28 Hz, may be decreased in the presence of a cerebellar lesion. Recording contralateral muscle and electrocorticographic activity from sites whose functional properties had previously been defined by electrical stimulation further revealed that spatially disparate cortical sites could be coherent and synchronised with each other and with contralateral muscle. This supports the hypothesis that oscillatory activity may have a role in binding together neural activity in functionally related neuronal pools.

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