Effects of attention on primary motor cortex excitability

Nina Majcen (2016) Effects of attention on primary motor cortex excitability. MSc thesis.

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Abstract

The link between basic physiology and its modulation by cognitive states, such as attention, is poorly understood. There have been a large number of studies of the effects of attention on sensory systems but the effects of attention on motor system are not well known. Attention modulates motor system through movement processing, motor learning and motor memory. In healthy people everyday movements and motor actions usually don't require much attention and can happen »automatically«; excessive focus on the details of a task can acutally be associated with poor performance. The effetct of attention on motor system becomes apparent when patients with movement disorders or professional sportsmen describe experiences with changing their attention focus and the fundamental effect that this has on their motor movement. Some people with movement disorders can actually minimize tremors and improve movements when they pay attention to the affected part of the body. The primary motor cortex (M1) lies along the precentral gyrus, and generates signals that control the execution of movements. Attention can affect primary motor cortex through its connections to other brain regions, thorugh connections to basal ganglia pr through diffuse modulatory brain systems. Transcranial magnetic stimulation is a neurophysiological method that allows us to investigate whether attention does have an impact on motor system – by observing changes of electrophysiological parameters of M1 in different conditions. In our study we investigated whether different sensory modalities of selective attention have an influence on M1 excitability (by looking at basic TMS parameters) and whether this influence differs between modalities. Healthy participants had to focus ther attention on three-stimuli oddball tasks while basic TMS measurements were taken. Visual oddball task, auditory oddball task and somatosensory oddball task were compared to control condition (no attention was required). For each condition different TMS parameters were measured: motor evoked potentials, recruitment curve, active recruitment curve, cortical silent period, short interval intracortical inhibition and intracortical facilitation. We concluded that different sensory modalities of selective attention do not have significant influence on primary motor cortex excitability parameters. Preliminary results show that motor control is relatively unaffected by stimuli from environment, if the stimuli is not relevant to the movement.

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