Gilbertson, TP; (2006) Oscillatory activity in the human motor system. Doctoral thesis , UCL (University College London).

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Abstract

The human motor system is characterised by fast oscillatory neural activity at around 20 cycles per second. This so-called beta rhythm is commonly observed in the primary motor cortex and is transmitted via the spinal cord to muscle. The functional significance of this cortico-muscular coherence is uncertain. Recent theories of the pathophysiology of Parkinson's disease have lead to the idea that the exaggerated expression of this oscillatory activity may in some way contribute to the symptoms of slowed movements (bradykinesia) and rigidity. In this thesis I provide evidence to argue that these oscillations may produce a transient impairment in the ability of healthy humans to produce effective ballistic speed associated with voluntary movements. Using a simple reaction time task in which the timing of movements was biased to coincide with transient increases in beta oscillatory activity, the ballistic acceleration of the movement could be impaired. Direct recording of local field potentials (ECOG) from the sensorimotor cortex in two patients during a similar reaction time task further confirmed that cortical beta activity was associated with a state of impaired ballistic motor performance. The properties of this neural state are further explored using a variety of neurophysiological techniques. In particular, beta oscillations were found to be associated with a state of enhanced responsiveness to sensory inputs relevant to motor control. Transcortical reflexes and the cortical components of the somatosensory evoked potential (SEP) were shown to be enhanced when preceded by periods of oscillatory activity.

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