Oliver, R.M.; (2011) The modulation of visuospatial awareness in the human brain using transcranial magnetic stimulation. Doctoral thesis , UCL (University College London).

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Abstract

This thesis describes a series of studies, involving healthy subjects and a carefully selected stroke patient, in which the techniques of Transcranial Magnetic Stimulation (TMS) and Signal Detection Theory (SDT) were combined to explore processing in the posterior parietal cortex (PPC) and the phenomenon of unilateral spatial neglect: 1) A new SDT-based TMS 'hunting' technique was developed and then employed successfully over the right PPC. This revealed a cortical node which could be modulated with 'online' 10Hz-TMS to exert control over subjects' visuospatial perception. 2) By targeting this 'hotspot' and an equivalent area in the left PPC with disruptive 'cTBS' (continuous 'Theta Burst' simulation), neglect-like effects in the healthy brain could be induced and alleviated. These effects were quantified using a newly developed, fully balanced, bihemifield detection paradigm 3) By using TMS to map visuospatial function over healthy right PPC, the 'hotspot' could be enlarged after exposure to excitatory, intermittent TBS (iTBS). 4) cTBS was applied to the left PPC of a patient with a right sided stroke and visuospatial neglect. In doing this, neglect and its alleviation were described for the first time in fully balanced SDT terms. 5) The cerebellum was targeted in healthy subjects with 1Hz inhibitory TMS which induced a shift in their subjective midline for 'imaginary' but not 'real' space, as measured with number or physical line bisection respectively. These TBS studies lend support to Kinsbourne's hemispheric rivalry hypothesis and suggest that the extent of 'spatially eloquent' cortex in the right PPC can be increased. Both strategies could be useful in larger therapeutic studies of patients suffering from USN after right sided brain injury. The final study opens up an additional therapeutic target for patients with imaginal neglect and, for the first time, implicates the cerebellum in number line bisection.

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