ANTERIOR PARIETAL CORTICAL RESPONSE TO TACTILE AND SKIN-HEATING STIMULI APPLIED TO THE SAME SKIN SITE

1. The response of anterior parietal cortex to skin stimuli was evalua ted with optical intrinsic signal imaging and extracellular microelect rode recording methods in anesthetized squirrel monkeys, 2. Nonnoxious mechanical stimulation (vibrotactile or skin tapping) of the contrala teral radial interdigital pad was accompanied by a decrease in reflect ance (at 833 nm) in sectors of cyoarchitectonic areas 3b and 1. This i ntrinsic signal was in register with regions shown by previous recepti ve field mapping studies to receive low-threshold mechanoreceptor inpu t from the radial interdigital pad, 3. A skin-heating stimulus applied to the contralateral radial interdigital pad with a stationary probe/ thermode evoked no discernable intrinsic signal in areas 3b and 1, but evoked a signal within a circumscribed part of area 3a. The region of area 3a responsive to skin heating with the stationary probe/thermode was adjacent to the areas 3b and regions that developed an intrinsic signal in response to vibrotactile stimulation of the same skin site. Skin heating with a stationary probe/thermode also evoked intrinsic si gnal in regions of areas 4 and 2 neighboring the area 3b/1 regions act ivated by vibrotactile stimulation of the contralateral radial interdi gital pad. 4. The intrinsic signal evoked in area 3a by a series of he ating stimuli to the contralateral radial interdigital pad (applied wi th a stationary probe/thermode) increased progressively in magnitude w ith repeated stimulation (exhibited slow temporal summation) and remai ned above prestimulus levels for a prolonged period after termination of repetitive Stimulation, 5. Brief mechanical stimuli (''taps'') appl ied to the contralateral radial interdigital pad with a probe/thermode maintained either at 37 degrees C or at 52 degrees C were accompanied by the development of an intrinsic signal in both area 3a and areas 3 b/1. For the 52 degrees C stimulus, the area 3a intrinsic signal was l arger and the intrinsic signal in areas 3b/1 smaller than the correspo nding signals evoked by the 37 degrees C stimulus. 6, Spike discharge activity was recorded from area 3a neurons during a repetitive heating stimulus applied with a stationary probe/thermode to the contralatera l radial interdigital pad. Like the area 3a intrinsic signal elicited by repetitive heating of the same skin site, the area 3a neuron spike discharge activity also exhibited slow temporal summation and poststim ulus response persistence. 7. The experimental findings suggest i) a l eading role for area 3a in the anterior parietal cortical processing o f skin-heating stimuli, and 2) the presence of inhibitory interactions between the anterior parietal responses to painful and vibrotactile s timuli consistent with those demonstrated in recent cortical imaging a nd psychophysical studies of human subjects.