Ridding, M. C.; (1996) Corticocortical connections in man. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Anatomical and electrophysiological evidence suggests that there is a dense network of intrinsic interneurones in the motor cortex. Many of these neurones appear to have an inhibitory action. The experiments described in this thesis examine the importance of a subset of these intracortical inhibitory neurones in motor control. Using the relatively new technique of transcranial magnetic stimulation it is now possible to study the motor system in awake human subjects. This painless, non-invasive technique allows us to study the functioning of the motor cortex in humans both during rest and while making natural movements, something that has been impossible until recently. By employing a double pulse magnetic stimulation technique it is possible to study the efficacy of intracortical inhibitory actions. The experiments described in this thesis examine the role of the inhibitory system in normal subjects at rest and during voluntary contraction. The results are compared with those from two groups of patients and controls. The first group consisted of patients suffering from disorders of movement (myoclonus, dystonia and Parkinson's disease). The second group consisted of subjects who had suffered either temporary (normals with ischaemic blocks) or permanent (traumatic amputees) deafferentation. The results suggest that the observed inhibition has an important role in the functioning of the motor cortex. In the conditions studied, when there are disorders of motor control there are also clear abnormalities in cortical inhibition. It appears that abnormalities in inhibition in the motor cortex may be caused by either intrinsic pathology (e.g. as seen in cortical myoclonus) or provoked by pathology elsewhere in the central nervous system (e.g. the basal ganglia in Parkinson's disease or focal dystonia). It is possible that the disordered cortical inhibition may contribute to some of the symptoms seen in these conditions.

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