1. The response of anterior parietal cortex to skin stimuli was evaluated with optical intrinsic signal imaging and extracellular microelectrode recording methods in anesthetized squirrel monkeys. 2. Nonnoxious mechanical stimulation (vibrotactile or skin tapping) of the contralateral radial interdigital pad was accompanied by a decrease in reflectance (at 833 nm) in sectors of cytoarchitectonic areas 3b and 1. This intrinsic signal was in register with regions shown by previous receptive field mapping studies to receive low-threshold mechanoreceptor input 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 1 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 signal in regions of areas 4 and 2 neighboring the area 3b/1 regions activated by vibrotactile stimulation of the contralateral radial interdigital pad. 4. The intrinsic signal evoked in area 3a by a series of heating stimuli to the contralateral radial interdigital pad (applied with a stationary probe/thermode) increased progressively in magnitude with repeated stimulation (exhibited slow temporal summation) and remained above prestimulus levels for a prolonged period after termination of repetitive stimulation. 5. Brief mechanical stimuli ("taps") applied 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 3b/1. For the 52 degrees C stimulus, the area 3a intrinsic signal was larger and the intrinsic signal in areas 3b/1 smaller than the corresponding 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 contralateral 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 poststimulus response persistence. 7. The experimental findings suggest 1) a leading role for area 3a in the anterior parietal cortical processing of skin-heating stimuli, and 2) the presence of inhibitory interactions between the anterior parietal responses to painful and vibrotactile stimuli consistent with those demonstrated in recent cortical imaging and psychophysical studies of human subjects.

Response of anterior parietal cortex to different modes of same-site skin stimulation. J. Neurophysiol. 80: 3272-3283, 1998. Intrinsic optical signal (IOS) imaging was used to study responses of the anterior parietal cortical hindlimb region (1 subject) and forelimb region (3 subjects) to repetitive skin stimulation. Subjects were four squirrel monkeys anesthetized with a halothane/nitrous oxide/oxygen gas mixtures. Cutaneous flutter of 25 Hz evoked a reflectance decrease in the sectors of cytoarchitectonic areas 3b and/or 1 that receive input from the stimulated skin site. The intrinsic signal evoked by 25-Hz flutter attained maximal intensity

The response of anesthetized squirrel monkey anterior parietal (SI) cortex to 25 or 200 Hz sinusoidal vertical skin displacement stimulation was studied using the method of optical intrinsic signal (OIS) imaging. Twenty-five-Hertz ("flutter") stimulation of a discrete skin site on either the hindlimb or forelimb for 3-30 s evoked a prominent increase in absorbance within cytoarchitectonic areas 3b and 1 in the contralateral hemisphere. This response was confined to those area 3b/1 regions occupied by neurons with a receptive field (RF) that includes the stimulated skin site. In contrast, same-site 200-Hz stimulation ("vibration") for 3-30 s evoked a decrease in absorbance in a much larger territory (most frequently involving areas 3b, 1, and area 3a, but in some subjects area 2 as well) than the region that undergoes an increase in absorbance during 25-Hz flutter stimulation. The increase in absorbance evoked by 25-Hz flutter developed quickly and remained relatively constant for as long as stimulation continued (stimulus duration never exceeded 30 s). At 1-3 s after stimulus onset, the response to 200-Hz stimulation, like the response to 25-Hz flutter, consisted of a localized increase in absorbance limited to the topographically appropriate region of area 3b and/or area 1. With continuing 200-Hz stimulation, however, the early response declined, and by 4-6 s after stimulus onset, it was replaced by a prominent and spatially extensive decrease in absorbance. The spike train responses of single quickly adapting (QA) neurons were recorded extracellularly during microelectrode penetrations that traverse the optically responding regions of areas 3b and 1. Onset of either 25- or 200-Hz stimulation at a site within the cutaneous RF of a QA neuron was accompanied by a substantial increase in mean spike firing rate. With continued 200-Hz stimulation, however, QA neuron mean firing rate declined rapidly (typically within 0.5-1.0 s) to a level below that recorded at the same time after onset of same-site 25-Hz stimulation. For some neurons, the mean firing rate after the initial 0.5-1 s of an exposure to 200-Hz stimulation of the RF decreased to a level below the level of background ("spontaneous") activity. The decline in both the stimulus-evoked increases in absorbance in areas 3b/1 and spike discharge activity of area 3b/1 neurons within only a few seconds of the onset of 200-Hz skin stimulation raised the possibility that the predominant effect of continuous 200-Hz stimulation for >3 s is inhibition of area 3b/1 QA neurons. This possibility was evaluated at the neuronal population level by comparing the intrinsic signal evoked in areas 3b/1 by 25-Hz skin stimulation to the intrinsic signal evoked by a same-site skin stimulus containing both 25- and 200-Hz sinusoidal components (a "complex waveform stimulus"). Such experiments revealed that the increase in absorbance evoked in areas 3b/1 by a stimulus having both 25- and 200-Hz components was substantially smaller (especially at times >3 s after stimulus onset) than th...

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Skin brushing stimuli were used to evoke spike discharge activity in single skin mechanoreceptive afferents (sMRAs) and anterior parietal cortical (SI) neurons of anesthetized monkeys (Macaca fascicularis). In the initial experiments 10-50 presentations of each of 8 different stimulus velocities were delivered to the linear skin path from which maximal spike discharge activity could be evoked. Mean rate of spike firing evoked by each velocity (MFR) was computed for the time period during which spike discharge activity exceeded background, and an across-presentations estimate of mean firing rate (MFR) was generated for each velocity. The magnitude of the trial-by-trial variation in the response (estimated as CV; where CV = standard deviation in MFR/MFR) was determined for each unit at each velocity. MFR for both sMRAs and SI neurons (MFRsMRA and MFRSI, respectively) increased monotonically with velocity over the range 1-100 cm/s. At all velocities the average estimate of intertrial response variation for SI neurons (CVSI) was substantially larger than the corresponding average for sMRAs (CVsMRA). Whereas CVsMRA increased monotonically over the range 1-100 cm/s, CVSI decreased progressively with velocity over the range 1-10 cm/s, and then increased with velocity over the range 10-100 cm/s. The position of the skin brushing stimulus in the receptive field (RF) was varied in the second series of experiments. It was found that the magnitude of CVSI varied systematically with stimulus position in the RF: that is, CVSI was lowest for a particular velocity and direction of stimulus motion when the skin brushing stimulus traversed the RF center, and CVSI increased progressively as the distance between the stimulus path and the RF center increased. In the third series of experiments, either phencylidine (PCP; 100-500 microg/kg) or ketamine (KET; 0.5-7.5 mg/kg) was administered intravenously (iv) to assess the effect of block of N-methyl-D-aspartate (NMDA) receptors on SI neuron intertrial response variation. The effects of PCP on both CVSI and MFRSI were transient, typically with full recovery occurring in 1-2 h after drug injection. The effects of KET on CVSI and MFRSI were similar to those of PCP, but were shorter in duration (15-30 min). PCP and KET administration consistently was accompanied by a reduction of CVSI. The magnitude of the reduction of CVSI by PCP or KET was associated with the magnitude of CVSI before drug administration: that is, the larger the predrug CVSI, the larger the reduction in CVSI caused by PCP or KET. PCP and KET exerted variable effects on SI neuron mean firing rate that could differ greatly from one neuron to the next. The results are interpreted to indicate that SI neuron intertrial response variation is 1) stimulus tuned (intertrial response variation is lowest when the skin stimulus moves at 10 cm/s and traverses the neuron's RF center) and 2) NMDA receptor dependent (intertrial response variation is least when NMDA receptor activity contributes minimally to the response, and increases as...