Effects of Repetitive Peripheral Stimuli on Evoked Potentials of Somatosensory Cortex

¹ From West Haven Veterans Administration Hospital, West Haven, Connecticut

Evoked potentials were recorded with a macroelectrode at somatic area I of cerebral cortex of cats under pentobarbital sodium anesthesia. Repetition rate (interstimulus interval) of trains of brief electrical pulses to the skin varied from 0.30–3.00 seconds. Average amplitude of response did not reach a maximal, stable level until repetition rates of 2.00 seconds and longer were used. When repetition rate was fixed and responses were studied as a function of the serial number of a stimulus in a train, amplitude slowly declined to a stable level as more stimuli were given. Besides these monotonic effects, a cyclic component appeared in both the repetition rate and serial number functions. All results are explained by assuming that the recovery function set off by one stimulus in a train starts later, or is slower than, the recovery function produced by the preceding stimulus; this progressive slowing of recovery ceases when equilibration is reached. Temporal interaction between successive stimuli at somatosensory cortex clearly lasts for several seconds, as other workers find at visual cortex.