Insights into motor performance and muscle fatigue based on transcranial stimulation of the human motor cortex

1. Direct cortical stimulation of motor and sensory areas of the cortex in experimental animals and some neurosurgical patients has provided much useful physiological information. Some of the benefits of this approach can be provided in awake volunteer subjects using new techniques which activate the motor cortex thorough the skull (i.e. transcranial electrical or magnetic stimulation). 2. Both electrical and magnetic transcranial stimulation produce complex descending corticospinal volleys which usually contain a direct component (via corticofugal axons) and an indirect trans-synaptic component. Changes in cortical 'excitability' can affect the evoked corticofugal volleys and the electromyographic responses which they involve. 3. Apart from its diagnostic applications to patients with neurological disorders, transcranial stimulation has been applied to the study of a range of aspects of human motor control ranging from apparent cortical 'plasticity' to the changes in cortical behaviour produced by exercise.