Biomedical subjects

Barry L Whitsel

Publications and source records attributed to Barry L Whitsel.

8 recordsLinked to original sources

PubMed2006

Vibrotactile adaptation enhances spatial localization.

A two-interval forced choice tracking procedure was used to evaluate the effects of a pre-exposure to vibrotactile stimulation ("adaptation") on the capacity of human subjects to spatially localize a subsequent tactile stimulus. A 25 Hz flutter adapting stimulus was presented at a randomly selected position within a 20 mm linear array oriented transversely on the hand dorsum. Two flutter stimuli delivered subsequently were applied to different sites along the linear array; one to the same locus that received the adapting stimulation (the "standard" stimulus), the other to a distant site (the "test" stimulus). Following each trial, subjects were queried as to which of the two stimuli was delivered to the same skin site that received adapting stimulation. A correct response resulted in a reduced distance between the sites contacted by the standard and test stimuli in the following trial. Four subjects participated in 10 sessions each. A session consisted of two sets of 20 trials (one set at 0.5 s and another at 5 s adapting stimulus duration). For every subject, 5 s adaptation resulted in an approximately 2-fold improvement in spatial discrimination performance over that achieved following 0.5 s adaptation. It is proposed that the improved human vibrotactile spatial localization performance following 5 s of 25 Hz stimulation is due to enhanced spatial funneling of the global neuronal population response of primary somatosensory cortex (SI) that has been demonstrated to accompany increases in duration of 25 Hz flutter stimuli delivered to the skin.

Acclimatization↗

PubMed2006

Ipsilateral input modifies the primary somatosensory cortex response to contralateral skin flutter.

We recorded the optical intrinsic signal response of squirrel monkey primary somatosensory cortex (SI) to 25 Hz vibrotactile ("flutter") stimulation applied independently to the thenar eminence on each hand and also to bilateral (simultaneous) stimulation of both thenars. The following observations were obtained in every subject (n = 5). (1) Ipsilateral stimulation was accompanied by an increase in absorbance within the SI hand region substantially smaller than the absorbance increase evoked by contralateral stimulation. (2) The absorbance increase evoked by simultaneous bilateral stimulation was smaller (by approximately 30%) than that evoked by contralateral stimulation. (3) The spatiointensive pattern of the SI response to bilateral flutter was distinctly different than the pattern that accompanied contralateral flutter stimulation: with contralateral flutter, the center of the responding region of SI underwent a large increase in absorbance, whereas absorbance decreased in the surrounding region; in contrast, during bilateral flutter, absorbance decreased (relative to that evoked by contralateral flutter) in the central region of SI but increased in the surround. The results raise the possibility that somatosensory perceptual experiences specific to bimanual tactile object exploration derive, at least in part, from the unique spatiointensive activity pattern evoked in SI when the stimulus makes contact with both hands. It is suggested that modulatory influences evoked by ipsilateral thenar flutter stimulation reach SI via a two-stage pathway involving interhemispheric (callosal) connections between information processing levels higher than SI and subsequently via intrahemispheric (corticocortical) projections to the SI hand region.

Animals↗

PubMed2006

Activation of cat SII cortex by flutter stimulation of contralateral vs. ipsilateral forepaws.

A distinguishing feature of SII cortex is that it receives substantial input from skin mechanoreceptors located on both sides of the body. It remains uncertain, however, if integration of bilateral inputs occurs mainly in those regions of SII that represent near-midline body regions or also occurs to a significant extent in those regions of SII that represent the distal extremities. This issue was addressed using extracellular microelectrode recordings in cat SII in combination with the method of optical intrinsic signal (OIS) imaging. Stimulation of the central pad of either the contra- or ipsilateral forepaw with a 25-Hz sinusoidal vertical skin displacement ("skin flutter") stimulus evoked a prominent OIS response ("activation") in an extensive anteroposterior sector of SII. In the anteriorly located SII region that yielded the maximal OIS response to stimulation of the contralateral central pad, neurons consistently possessed receptive fields that included the stimulated skin site. This "forepaw" SII region also exhibited significant although 75% weaker OIS activation in response to stimulation of the ipsilateral central pad. Stimulation of the central pads of either contra- or ipsilateral forepaws also evoked OIS activation in the posteriorly located 'hindlimb' region of SII--defined as the SII region comprised of neurons with receptive fields on the contralateral hindlimb. The OIS response to ipsilateral central pad stimulation was strongest in the posterior SII region that borders the suprasylvian fringe--a region in which neurons have very large, and frequently bilateral, cutaneous receptive fields. The results indicate that widespread regions within cat SII receive cutaneous inputs from the ipsilateral distal forelimb. It is suggested that the functional role of these ipsilateral inputs may be different in different SII regions.

Action Potentials↗

PubMed2005

Stimulus-dependent spatial patterns of response in SI cortex.

BACKGROUND: Recently we reported that vibrotactile flutter stimulation of a skin locus at different amplitudes evokes an optical response confined to the same local region of the primary somatosensory cortex (SI), where its overall magnitude varies proportionally to the flutter amplitude. In this report, we characterize the impact of the flutter amplitude on the spatial patterns of activity evoked within the responding SI region. RESULTS: In order to characterize the spatial pattern of activity within the responding SI region, images of the flutter-evoked SI optical response were segmented and analyzed with spatial frequency analysis. The analysis revealed that: (1) dominant spatial frequencies in the optical intrinsic signal emerge within the responding SI region within 3-5 sec of stimulus onset; (2) the stimulus-evoked activity is spatially organized in a form of several roughly parallel, anterior-posteriorly extended waves, spaced 0.4-0.5 mm apart; (3) the waves themselves exhibit spatial periodicities along their long axis; and (4) depending on the flutter stimulus amplitude, these periodicities can range from fine 0.15 mm "ripples" at 50 microm amplitude to well-developed 0.5 mm fluctuations at the amplitude of 400 microm. CONCLUSION: The observed spatiointensive fractionation on a sub-macrocolumnar scale of the SI response to skin stimulation might be the product of local competitive interactions within the stimulus-activated SI region and may be a feature that could yield novel insights into the functional interactions that take place in SI cortex.

Animals↗

PubMed2005

Amplitude-dependency of response of SI cortex to flutter stimulation.

BACKGROUND: It is established that increasing the amplitude of a flutter stimulus increases its perceived intensity. Although many studies have examined this phenomenon with regard to the responding afferent population, the way in which the intensity of a stimulus is coded in primary somatosensory cortex (SI) remains unclear. RESULTS: Optical intrinsic signal (OIS) imaging was used to study the evoked responses in SI of anesthetized squirrel monkeys by 25 Hz sinusoidal vertical skin displacement stimulation. Stimuli were 10 sec duration with a 50 sec inter-stimulus interval. Stimulus amplitude ranged from 50 to 400 microns and different amplitudes were interleaved. Control levels of activity were measured in the absence of stimulation, and used to compare with activation levels evoked by the different stimulus amplitudes. Stimulation of a discrete skin site on the forelimb evoked a prominent increase in absorbance within the forelimb representational region in cytoarchitectonic areas 3b and 1 of the contralateral hemisphere. An increase in stimulus amplitude led to a proportional increase in the magnitude of the absorbance increase in this region of areas 3b and 1 while surrounding cortex underwent a decrease in absorbance. Correlation maps revealed that as stimulus amplitude is increased, the spatial extent of the activated region in SI remains relatively constant, and the activity within this region increases progressively. Additionally, as stimulus amplitude is increased to suprathreshold levels, activity in the surround of the activated SI territory decreases, suggesting an increase in inhibition of neuronal activity within these regions. CONCLUSION: Increasing the amplitude of a flutter stimulus leads to a proportional increase in absorbance within the forelimb representational region of SI. This most likely reflects an increase in the firing rate of neurons in this region of SI. The relatively constant spatial extent of this stimulus-evoked increase in absorbance suggests that an increase in the amplitude of a 25 Hz skin stimulus does not evoke a larger area of SI neuronal activation due to an amplitude-dependent lateral inhibitory effect that spatially funnels the responding SI neuronal population.

Animals↗

PubMed2002

Sensory cortical dynamics.

Sensory cortical networks are commonly regarded as stable, changing only in the face of prolonged alteration of sensory input. There is increasing evidence, however, that the functional connectivity of cortical networks changes significantly, but reversibly, in response to conditions of sensory stimulation similar to those encountered in everyday life. In this review, we provide examples of sensory cortical dynamics at the single neuron and neural population levels. The dynamics detected at both levels of experimental observation suggest that a brief exposure (tens of milliseconds to tens of seconds) to sensory stimulation is accompanied by changes in the capacity of cortical networks to process and represent environmental stimuli. Candidate cellular mechanisms and the potential benefits of such stimulus-driven, rapid, and fully reversible sensory cortical dynamics are discussed.

Animals↗

PubMed2002

Optical imaging of intrinsic signals in somatosensory cortex.

The methods of optical intrinsic signal (OIS) imaging and microelectrode mapping of single neuron receptive fields (RFs) were used in combination (in the same squirrel monkey or cat) to characterize the spatial and temporal attributes of the response of contralateral SI cortex to cutaneous flutter stimulation. A change in the location of the stimulated skin site was accompanied by a shift in the locus of the SI optical response. The spatial ordering of the optical responses to independent stimulation of each site in an array of skin sites was consistent with the features of SI topographical organization described in published RF mapping studies. While the single neuron RF mapping observations and the optical response obtained at a given time after onset of flutter stimulation always were positively correlated, the degree of correlation improved progressively with time after stimulus onset (the longest stimulus duration used was 10 s). Analysis of the temporal development of the optical response to cutaneous flutter stimulation revealed that not only does absorbance increase to attain a maximum in the SI region which receives its main input from the stimulated skin site, but at the same time absorbance declines to below-background values in an extensive region of surrounding cortex. The results are interpreted to indicate that the pattern of SI activity evoked by a cutaneous flutter stimulus exhibits increasing spatial contrast (becomes progressively more distinguishable from the activity of surrounding cortex) over periods of continuous stimulation at least as long as 10 s. This time-dependent 'funneling' of the SI spatial activity pattern is proposed to underlie the prominent enhancement of human spatial discriminative capacity which occurs (e.g. Physiol. Behav. 5 (1970) 1431) when oscillatory tactile stimuli are used.

Animals↗

PubMed2002

Stimulus-evoked modulation of sensorimotor pyramidal neuron EPSPs.

Sensory cortical neurons display substantial receptive field dynamics during and after persistent sensory drive. Because a cell's response properties are determined by the inputs it receives, receptive field dynamics are likely to involve changes in the relative efficacy of different inputs to the cell. To test this hypothesis, we have investigated if brief repetitive stimulus drive in vitro alters the efficacy of two types of corticocortical inputs to layer V pyramidal cells. Specifically, we have used whole cell recordings to measure the effect of repetitive electrical stimulation at the layer VI/white matter (WM) border on the synaptic response of layer V pyramidal cells to corticocortical input evoked by electrical stimulation of layer I or layer II/III and emulated by local application of glutamate. Repetitive stimulation (10 Hz for 3 s) at the layer VI/WM border transiently potentiated excitatory postsynaptic potentials (EPSPs) evoked by electrical stimulation of layer II/III by 97 +/- 12% (mean +/- SE). The recovery of EPSP amplitude to its preconditioning value was well-described by a single-term decaying exponential with a time constant of 7.2 s. The same layer VI/WM conditioning train that evoked layer II/III EPSP potentiation frequently caused an attenuation of layer I EPSPs. Similarly, subthreshold postsynaptic responses to local glutamate application in layers II/III and I were potentiated and attenuated, respectively, by the conditioning stimulus. Potentiation and attenuation could be evoked in the same cell by repositioning the glutamate puffer pipette in the appropriate layer. The conditioning stimulus that led to the transient modification of upper layer EPSP efficacy also evoked a slow depolarization in glial cells. The membrane potential of glial cells recovered with a time course similar to the dissipation of the potentiation effect, suggesting that stimulus-evoked changes in extracellular potassium (ECK) play a role in layer II/III EPSP potentiation. Consistent with this proposal, increasing the bath concentration of ECK caused a substantial increase of layer II/III EPSP amplitude. EPSP potentiation was sensitive to postsynaptic membrane potential and, more importantly, was significantly weaker for synaptic currents than for synaptic potentials, suggesting that it involves the recruitment of a postsynaptic voltage-dependent mechanism. Two observations suggest that layer II/III EPSP potentiation may involve the recruitment of postsynaptic sodium channels: EPSP potentiation was strongly reduced by intracellular application of N-(2,6-dimethyl-phenylcarbamoylmethyl) triethylammonium bromide (QX-314) and responses to local glutamate application were potentiated by high ECK in the presence of cadmium but not in the presence of tetrodotoxin. The results demonstrate a novel way in which brief periods of repetitive stimulus drive are accompanied by rapid, transient, and specific alterations in the functional connectivity and information processing characteristics of sensorimotor cortex.

Animals↗