Response of Anterior Parietal Cortex to Cutaneous Flutter Versus Vibration

Abstract

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...

Optical Imaging of SI Topography in Anesthetized and Awake Squirrel Monkeys

“…In the anesthetized animal, a prominent activation site is observed in area 3b. Consistent with previous reports (Tommerdahl et al, 1998(Tommerdahl et al, , 1999(Tommerdahl et al, , 2002Chen et al, 2001Chen et al, , 2003Friedman et al, 2004), activation in area 1 of the anesthetized animal is often weak or absent.…”

“…For the 3 d shown in Figure 2, the stimulus-induced activations in area 3b fall in the 0.01-0.1% range [0.077 Ϯ 0.01% ( A), 0.083 Ϯ 0.007% ( D), and 0.075 Ϯ 0.019% ( G); no significant differences between each pair of days; all t tests; p Ͼ 0.05]. The signal amplitudes were consistent with the changes in reflectance reported previously in the anesthetized squirrel monkey (Tommerdahl et al, 1998(Tommerdahl et al, , 1999(Tommerdahl et al, , 2002Chen et al, 2001Chen et al, , 2003Friedman et al, 2004). Thus, signal amplitudes did not change appreciably from day to day or decline during the 2 year period.…”

Brain Activations in Response to Vibrotactile Tooth Stimulation: a Psychophysical and fMRI Study

“…This localization and lateralization was then compared with the response to analogous mechanical stimulation of the digit tip as found in our previous study (Francis et al 2000), and the frequency response to tooth stimulation was also compared with that of finger tip stimulation. In previous work in humans (Sleigh et al 2001), a significant increase in activity in SII and the posterior insular, and a decrease in activity in SI, was found to occur as the frequency of a vibrotactile stimulus applied to the digit tip was increased, corroborating the findings of Tommerdahl et al (1999). These authors, using nearinfrared optical intrinsic signal (OIS) imaging, found that 25 Hz flutter stimuli applied to various sites on the squirrel monkey limbs consistently evoked a pattern of increased optical absorbance (neural activation) in SI which was wellmaintained for the duration of stimulation.…”

“…The fMRI frequency results to vibrotactile stimulation of the first upper left incisor show a differing trend of brain activity in SII to that of vibrotactile stimulation of the fingertip, where activity in SII has been shown to increase, while activity in SI decreases, as a function of increasing stimulus frequency (Sleigh et al 2001;Tommerdahl et al 1999).…”

Transient and steady-state responses to mechanical stimulation of different fingers reveal interactions based on lateral inhibition

“…A comparable interaction effect with continuous frequency stimulation has been described in cats using optical imaging (Tommerdahl et al 1999). In that study the effect of combined flutter (up to 50 Hz) and vibration (50 Hz and higher) stimulus was investigated.…”