NON-INVASIVE STIMULATION OF HUMAN CENTRAL NERVOUS SYSTEM

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Recently techniques have become available for the non-invasive stimulation of the human cortex and deep proximal peripheral nerves. Stimulation can be with a high voltage, extremely brief electrical pulse or with magnetic stimulation. One purpose is to use these methods for noninvasive localization of different parts of the human cortex including motor cortex, sensory cortex and language cortex. Another purpose is to study cortical physiology in different disease states. We have established normative data for our own laboratory for measurement of central motor conduction velocities. We have also found that EEGs do not change after a session of cortical stimulation in normal volunteers and patients, which indicates the safety of the procedure. We have succeeded in mapping the hand, arm, leg and mouth areas of the human motor cortex in normal volunteers and correlating these motor maps with the sensory maps as defined by using somatosensory evoked potentials. At this time we are studying changes in these motor maps in patients with mirror movements, stroke, and with different types of amputations. We have found that patients with congenital mirror movements have a bilateral cortical representation of each hand in the motor cortex. Also, that they have physiologically active and fast conducting connections between the motor cortex and ipsilateral muscles in the upper extremity. We have also studied hemispheric dominance for laryngeal muscles finding that there seems to be bilateral projections from both hemispheres to motoneurons controlling muscles in both sides of the larynx and that stimulation of the left hemisphere activates a larger percentage of the motoneuron pool bilaterally. We have mapped sensory cortex by utilizing the phenomenon of blockage of a cutaneous stimulus. We have also used magnetic stimulation to probe the processes in motor cortex during a reaction time task in patients with Parkinson's disease.