Evoked slow and unit responses of the cerebral cortex following repetitive stimulation

¹ Department of Anatomy and Physiology, University of Kentucky, Lexington, Kentucky

Unit and slow primary responses have been compared in the sensorimotor cortex of the cat to stimulation of the radial nerve. As frequency of stimulation is increased, the amplitude of the primary decreases but remains constant at a given frequency. The evoked positive and negative phases of the primary usually disappear at frequencies below 30/sec. Unit responses, however, can still be found in a region where the primary is absent. As frequency of stimulation is raised, the unit responses begin to fail intermittently with complete disappearance of the spikes at about 60/sec. but firing can be encountered at much higher frequencies. In some preparations intermittent unit firing occurs at rates of stimulation between 500 and 1000/sec. The relationship of these findings to cortical mapping is discussed. It is concluded that these data do not support the method of mapping which depends upon the use of the evoked slow potentials.