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S S Hsiao

Publications and source records attributed to S S Hsiao.

18 recordsLinked to original sources
PubMed2005

Vibratory adaptation of cutaneous mechanoreceptive afferents.

The objective of this study was to investigate the effects of extended suprathreshold vibratory stimulation on the sensitivity of slowly adapting type 1 (SA1), rapidly adapting (RA), and Pacinian (PC) afferents. To that end, an algorithm was developed to track afferent absolute (I0) and entrainment (I1) thresholds as they change over time. We recorded afferent responses to periliminal vibratory test stimuli, which were interleaved with intense vibratory conditioning stimuli during the adaptation period of each experimental run. From these measurements, the algorithm allowed us to infer changes in the afferents' sensitivity. We investigated the stimulus parameters that affect adaptation by assessing the degree to which adaptation depends on the amplitude and frequency of the adapting stimulus. For all three afferent types, I0 and I1 increased with increasing adaptation frequency and amplitude. The degree of adaptation seems to be independent of the firing rate evoked in the afferent by the conditioning stimulus. In the analysis, we distinguished between additive adaptation (in which I0 and I1 shift equally) and multiplicative effects (in which the ratio I1/I0 remains constant). RA threshold shifts are almost perfectly additive. SA1 threshold shifts are close to additive and far from multiplicative (I1 threshold shifts are twice the I0 shifts). PC shifts are more difficult to classify. We used an integrate-and-fire model to study the possible neural mechanisms. A change in transducer gain predicts a multiplicative change in I0 and I1 and is thus ruled out as a mechanism underlying SA1 and RA adaptation. A change in the resting action potential threshold predicts equal, additive change in I0 and I1 and thus accounts well for RA adaptation. A change in the degree of refractoriness during the relative refractory period predicts an additional change in I1 such as that observed for SA1 fibers. We infer that adaptation is caused by an increase in spiking thresholds produced by ion flow through transducer channels in the receptor membrane. In a companion paper, we describe the time-course of vibratory adaptation and recovery for SA1, RA, and PC fibers.

Action Potentials↗
PubMed2005

Time-course of vibratory adaptation and recovery in cutaneous mechanoreceptive afferents.

Extended suprathreshold vibratory stimulation applied to the skin results in a desensitization of cutaneous mechanoreceptive afferents. In a companion paper, we describe the dependence of the threshold shift on the parameters of the adapting stimulus and discuss neural mechanisms underlying afferent adaptation. Here we describe the time-course of afferent adaptation and recovery. We found that absolute and entrainment thresholds rise and fall exponentially during adaptation and recovery with time constants that vary with fiber type. slowly adapting type I (SA1) afferents adapt most rapidly, and pacinian (PC) afferents adapt most slowly, whereas rapidly adapting (RA) afferents exhibit intermediate rates of adaptation; SA1 fibers also recover more rapidly from adaptation than RA and PC fibers. We also showed that threshold adaptation is accompanied by a shift in the timing of the spikes within individual cycles of the adapting stimulus (i.e., a shift in the impulse phase). We invoked an integrate-and-fire model to explore possible mechanisms underlying afferent adaptation. Finally, we found that the time-course of afferent adaptation is more rapid than that of its psychophysical counterpart, as is the time-course of recovery from adaptation, suggesting that central factors play a role in the psychophysical phenomenon.

Action Potentials↗
PubMed2001

Neural coding mechanisms underlying perceived roughness of finely textured surfaces.

Combined psychophysical and neurophysiological studies have shown that the perceived roughness of surfaces with element spacings of >1 mm is based on spatial variation in the firing rates of slowly adapting type 1 (SA1) afferents (mean absolute difference in firing rates between SA1 afferents with receptive fields separated by approximately 2 mm). The question addressed here is whether this mechanism accounts for the perceived roughness of surfaces with element spacings of <1 mm. Twenty triangular and trapezoidal gratings plus a smooth surface were used as stimulus patterns [spatial periods, 0.1-2.0 mm; groove widths (GWs), 0.1-2.0 mm; and ridge widths (RWs), 0-1.0 mm]. In the human psychophysical studies, we found that the following equation described the mean roughness magnitude estimates of the subjects accurately (0.99 correlation): 0.2 + 1.6GW - 0.5RW - 0.25GW(2). In the neurophysiological studies, these surfaces were scanned across the receptive fields of SA1, rapidly adapting, and Pacinian (PC) afferents, innervating the glabrous skin of anesthetized macaque monkeys. SA1 spatial variation was highly correlated (0.97) with human roughness judgments. There was no consistent relationship between PC responses and roughness judgments; PC afferents responded strongly and almost equally to all of the patterns. Spatial variation in SA1 firing rates is the only neural code that accounts for the perceived roughness of surfaces with finely and coarsely spaced elements. When surface elements are widely spaced, the spatial variation in firing rates is determined primarily by the surface pattern; when the elements are finely spaced, the variation in firing rates between SA1 afferents is determined by stochastic variation in spike rates.

Action Potentials↗
PubMed2000

Attention modulates synchronized neuronal firing in primate somatosensory cortex.

A potentially powerful information processing strategy in the brain is to take advantage of the temporal structure of neuronal spike trains. An increase in synchrony within the neural representation of an object or location increases the efficacy of that neural representation at the next synaptic stage in the brain; thus, increasing synchrony is a candidate for the neural correlate of attentional selection. We investigated the synchronous firing of pairs of neurons in the secondary somatosensory cortex (SII) of three monkeys trained to switch attention between a visual task and a tactile discrimination task. We found that most neuron pairs in SII cortex fired synchronously and, furthermore, that the degree of synchrony was affected by the monkey's attentional state. In the monkey performing the most difficult task, 35% of neuron pairs that fired synchronously changed their degree of synchrony when the monkey switched attention between the tactile and visual tasks. Synchrony increased in 80% and decreased in 20% of neuron pairs affected by attention.

Action Potentials↗
PubMed1999

Detection of vibration transmitted through an object grasped in the hand.

A tool or probe often functions as an extension of the hand, transmitting vibrations to the hand to produce a percept of the object contacting the tool or probe. This paper reports the psychophysical results of a combined psychophysical and neurophysiological study of the perception of vibration transmitted through a cylinder grasped in the hand. In the first part of the psychophysical study, 19 subjects grasped a cylinder, 32 mm diam, with an embedded motor that caused vibration parallel to the axis of the cylinder. The relationship between threshold and frequency was the traditional U-shaped function with a minimum between 150 and 200 Hz. Except a study by Békésy in which subjects grasped a rod that vibrated parallel to the skin surface, thresholds above 20 Hz were lower and the slopes were steeper than any reported previously. Thresholds were <0.01 microm in some subjects. Data from both the psychophysical and the neurophysiological studies suggest that detection performance at frequencies >20 Hz was based on activity in Pacinian afferents. The extreme sensitivity compared with previous reports may have resulted from differences in contact area, direction of vibration, contact force, and the shape of the stimulus probe. The effects of each of these variables were studied. At 40 and 300 Hz (frequencies near the lower and upper end of the Pacinian range) thresholds were 9.8 and 18.5 dB (68 and 88%) lower, respectively, when subjects grasped the cylinder than when a 1-mm-diam probe vibrated perpendicular to the skin. These differences were accounted for as follows: 1) thresholds at a single fingerpad obtained with the large cylindrical surface were, on average, 20 and 60% lower, respectively, than thresholds with the punctate probe; 2) thresholds at the palm were, on average, 15 and 40% lower, respectively, than at the fingerpads; 3) thresholds obtained when the subjects grasped the cylinder averaged 40 and 20% less, respectively, than when the cylinder contacted only the palm; 4) thresholds with the cylinder contacting two fingers were 10 and 30% lower, respectively, than thresholds with the cylinder contacting a single finger; and 5) thresholds with vibration parallel to the skin surface were, on average, 10 and 30% lower, respectively, than thresholds with vibration perpendicular to the skin. Contact force, which was varied from 0.05 to 1.0 N, had no effect.

Hand↗
PubMed1998

Structure of receptive fields in area 3b of primary somatosensory cortex in the alert monkey.

We investigated the two-dimensional structure of area 3b neuronal receptive fields (RFs) in three alert monkeys. Three hundred thirty neurons with RFs on the distal fingerpads were studied with scanned, random dot stimuli. Each neuron was stimulated continuously for 14 min, yielding 20,000 response data points. Excitatory and inhibitory components of each RF were determined with a modified linear regression algorithm. Analyses assessing goodness-of-fit, repeatability, and generality of the RFs were developed. Two hundred forty-seven neurons yielded highly repeatable RF estimates, and most RFs accounted for a large fraction of the explainable response of each neuron. Although the area 3b RF structures appeared to be continuously distributed, certain structural generalities were apparent. Most RFs (94%) contained a single, central region of excitation and one or more regions of inhibition located on one, two, three, or all four sides of the excitatory center. The shape, area, and strength of excitatory and inhibitory RF regions ranged widely. Half the RFs contained almost evenly balanced excitation and inhibition. The findings indicate that area 3b neurons act as local spatiotemporal filters that are maximally excited by the presence of particular stimulus features. We believe that form and texture perception are based on high-level representations and that area 3b is an intermediate stage in the processes leading to these representations. Two possibilities are considered: (1) that these high-level representations are basically somatotopic and that area 3b neurons amplify some features and suppress others, or (2) that these representations are highly transformed and that area 3b effects a step in the transformation.

Animals↗
PubMed1997

Neural coding mechanisms in tactile pattern recognition: the relative contributions of slowly and rapidly adapting mechanoreceptors to perceived roughness.

Tactile pattern recognition depends on form and texture perception. A principal dimension of texture perception is roughness, the neural coding of which was the focus of this study. Previous studies have shown that perceived roughness is not based on neural activity in the Pacinian or cutaneous slowly adapting type II (SAII) neural responses or on mean impulse rate or temporal patterning in the cutaneous slowly adapting type I (SAI) or rapidly adapting (RA) discharge evoked by a textured surface. However, those studies found very high correlations between roughness scaling by humans and measures of spatial variation in SAI and RA firing rates. The present study used textured surfaces composed of dots of varying height (280-620 micron) and diameter (0.25-2.5 mm) in psychophysical and neurophysiological experiments. RA responses were affected least by the range of dot diameters and heights that produced the widest variation in perceived roughness, and these responses could not account for the psychophysical data. In contrast, spatial variation in SAI impulse rate was correlated closely with perceived roughness over the whole stimulus range, and a single measure of SAI spatial variation accounts for the psychophysical data in this (0.974 correlation) and two previous studies. Analyses based on the possibility that perceived roughness depends on both afferent types suggest that if the RA response plays a role in roughness perception, it is one of mild inhibition. These data reinforce the hypothesis that SAI afferents are mainly responsible for information about form and texture whereas RA afferents are mainly responsible for information about flutter, slip, and motion across the skin surface.

Adaptation, Physiological↗
PubMed1997

Monkey cutaneous SAI and RA responses to raised and depressed scanned patterns: effects of width, height, orientation, and a raised surround.

Monkey cutaneous SAI and RA responses to raised and depressed scanned patterns: effects of width, height, orientation, and a raised surround. J. Neurophysiol. 78: 2503-2517, 1997. The aim of this study was to examine the slowly adapting type I (SAI) and rapidly adapting (RA) primary afferent representation of raised and depressed surface features. Isolated, raised, and depressed squares and small raised squares with a circular surround were scanned across the receptive fields of SAI and RA mechanoreceptive afferents innervating the distal fingerpads of the rhesus monkey. Pattern height ranged from -620 to +620 micron and width ranged from 0.2 to 7.0 mm. The surround radii ranged from 3.0 to 7.0 mm. Previous combined psychophysical and neurophysiological studies have provided evidence that SAI afferent responses are responsible for the perception of spatial form and texture and that RA afferents are responsible for the detection of stimuli that produce minute skin motion (flutter, slip, microgeometric surface features). Our results strengthen these hypotheses. Response properties shared by both SAI and RA afferent types were that both responded only to the edges of the larger raised and depressed patterns, both responded to falling edges half as vigorously as to rising edges, both responded to rising and falling edges with impulse rates that were proportional to the sine of the angle between the edge and the scanning direction, and both had suppressed responses to a small raised surface feature when a raised surround was closer than 6 mm. Response differences consistent with the hypothesis that SAI afferents are specialized for the representation of form were that SAI responses were confined to areas around the features that evoked them in areas that were 40-50% smaller than the comparable RA response areas, SAI responses were more than four times more sensitive to stimulus height than were RA afferents over the range from 280 to 620 micron, and SAI (but not RA) afferents responded 20-50% more vigorously to corners than to edges. Response differences consistent with the hypothesis that RA afferents are specialized for the detection of minute surfaces features were that only RA afferents responded to very small surface depressions, depressed squares 0.8 mm wide, that were detectable by palpation. Mechanisms underlying the many differences in SAI and RA response properties are discussed.

Action Potentials↗
PubMed1996

Marking microelectrode penetrations with fluorescent dyes.

Fluorescent dyes were used to mark and identify the tracks left by extracellular microelectrodes in neurophysiological experiments. Forty-two penetrations were made into the postcentral gyrus of 3 Macaque monkeys with electrodes coated with 1 of 5 fluorescent dyes (DiI, DiO, DiI-C5, PyPO, and Fast Blue). The electrodes were driven at rates ranging from 10 to 1000 microns/min, to a depth of about 4000 microns, where a small electrolytic lesion was made. Histological sections were viewed under fluorescent optics and the electrode tracks were reconstructed from the dye traces. Fluorescent traces (width 50-400 microns) were observed in 41 of 42 penetrations with 24 traces extending to the lesion site. Of the electrodes driven in less than 3 h, those coated with DiI (8/8) and DiI-C5 (8/8) left a trace to the lesion site, while 57% (4/7) of the DiO, 40% (2/5) of the Fast Blue and only 11% (1/9) of the PyPO tracks were fully marked. This method of marking penetrations can be used with any extracellular recording configuration, does not require tissue sections to be processed or stained, does not require electrical lesions, and causes no detectable tissue damage. Because the dyes fluoresce at different wavelengths, closely spaced tracks can be uniquely identified.

Animals↗
PubMed1994

Evaluation of the relative roles of slowly and rapidly adapting afferent fibers in roughness perception.

Previous studies of the neural mechanisms of roughness perception have provided evidence that the magnitude of perceived roughness depends on spatial variation in the afferent population discharge. This paper reviews those studies and provides new data that appear to show that roughness perception cannot depend on activity in cutaneous rapidly adapting afferent fibers when surface element spacings exceed 1 mm. Finer surfaces have not been studied in combined psychophysical and neurophysiological studies. This paper also reinterprets the data of an earlier study, showing that all within-fiber neural coding mechanisms, which include impulse rate codes and codes based on the temporal structure of the afferent signal, can be rejected as the basis for roughness perception when the finger scans a textured surface.

Adaptation, Physiological↗
PubMed1993

Roughness coding in the somatosensory system.

Roughness perception is coded in the somatosensory system by neurons in the type I slowly adapting (SAI) system. When the fingers scan a surface, an isomorphic representation of the surface is encoded in the discharge patterns of SAI afferents. Central neurons in area 3b of primary somatosensory (SI) cortex spatially filter the peripheral image to compute local spatial variation. The outputs from these neurons converge onto neurons in area 1 and onto neurons in secondary somatosensory (SII) cortex which we believe is the critical processing pathway underlying roughness perception.

Afferent Pathways↗
PubMed1993

A tactile stimulator for studying motion processing in the somatic sensory system of primates.

A tactile stimulator was built for studying motion processing in the somatic sensory system of primates. This stimulator is used for assessing the responses of neurons of the somatic sensory system to stimuli moving in any traverse distance (range: 2-20 mm), with a variety of velocities (range: 4-120 mm/s), forces (range: 0-60 gf), and in any scanning direction. The stimulator is highly automated and can be used in combined psychophysical and neurophysiological studies in humans and in behaving monkeys.

Animals↗
PubMed1993

Effects of selective attention on spatial form processing in monkey primary and secondary somatosensory cortex.

1. The effects of selective attention were studied in SI and SII cortex of a rhesus monkey trained to perform two tasks, a tactile discrimination task and a visual detection task. In the tactile task, a letter was displayed on a video screen in front of the monkey and the animal was rewarded for responding when the raised letter (6.0 mm letter height) scanning across its finger (15 mm/s) matched the letter on the screen. In the visual task, three illuminated squares were displayed on the screen, and the animal was rewarded for detecting when one of the squares dimmed. The neural responses evoked by the raised letters were recorded continuously while the animal's focus of attention was switched back and forth between the two tasks. 2. Significant differences between the discharge rates evoked by raised letters in the two tasks were observed in approximately 50% of neurons in SI cortex and 80% of neurons in SII cortex. The effects in SII cortex were divided between increased (58%) and decreased (22%) rates. In SI cortex only increased rates were observed. 3. The attentional effects were expressed not only as changes in overall neuronal activity but also as modifications of the form of the responses evoked by the letters. 4. Whether attentional effects were observed depended upon the behavioral relevance of individual letters. During brief periods in the tactile task when a behavioral response could not yield a reward (time-out and reward periods) the neuronal responses were not significantly different from the responses evoked by the same letters during the visual task.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Neural mechanisms of tactual form and texture perception.

In the last decade or so, there has been rapid movement toward the use of more complex stimuli in the study of perceptual function related to the hand. This review has focused on the neural mechanisms of form and texture perception. Evidence from neurophysiological and psychophysical studies in which static touch, scanning touch, and the Optacon were used indicate that the spatial acuity of the RA system may be as much as three times poorer than the SAI system, evidence that suggests that form perception is dominated by the SAI system. Pattern recognition behavior in a tactual letter recognition task appears to be directly related to the response properties of SAI afferent fibers. Psychophysical studies of roughness perception show that roughness magnitude is related to surface structure in an orderly manner. Because roughness varies along an intensive continuum, mean impulse rate in one or more of the afferent systems is the most obvious coding possibility. No satisfactory relationship between mean impulse rate and roughness has been observed, however. The strongest hypothesis is that tactual roughness perception is based on spatial variation in the SAI population response. The combined evidence from studies reviewed here suggests complementary roles for each of the afferent systems, which are presented as working hypotheses: The SAI system is the primary spatial system and is responsible for tactual form and roughness perception when the fingers contact a surface directly and for the perception of external events through the distribution of forces across the skin surface. The PC system is responsible for the perception of external events that are manifested through transmitted high-frequency vibrations of the kind that are critical in the use of objects as tools. The RA system is responsible for the detection and representation of localized movement between skin and a surface as well as for surface form and texture when surface variation is too small to activate the SAI afferents effectively.

Animals↗
PubMed1991

Human tactile pattern recognition: active versus passive touch, velocity effects, and patterns of confusion.

1. Subjects without any previous experience in a tactile psychophysics task participated in a study of tactile letter recognition employing active and passive touch. In the active task, subjects reached through a curtain and examined embossed letters with horizontal, unidirectional finger strokes. In the passive task, subjects sat with their arms and hands immobilized while a rotating drum stimulator pressed the embossed letters onto the right index finger. The stimulus conditions in the passive task were identical to those used in neurophysiological experiments with monkeys. 2. A survey of 40 naive subjects who were not screened in any way showed a wide range of performance levels. There was no difference between the subjects in the active and passive tasks, either in overall mean percent correct scores, which were 49.0 and 50.7%, respectively or in the percent correct scores for individual letters whose product-moment correlation coefficient was 0.94. The active and passive groups, which contained 25 and 15 members, respectively, had no members in common. 3. Videotapes of the finger movements of eight subjects in the active task showed a characteristic V-shaped velocity profile (velocity vs. lateral position) starting at approximately 100 mm/s at the left-hand edge of the plate containing the embossed letter, decelerating to a minimum when the center of the finger was directly over the letter, and then accelerating away from the letter. The average minimum scanning velocity was 17 mm/s. 4. Scanning velocity had no significant effect on performance in the passive task between 20 and 40 mm/s. An increase to 80 mm/s produced a 16% decline in percent correct identifications. 5. Learning effects were evident across sessions even though subjects were given no feedback or training. The increase in mean percent correct judgments averaged 4% per session, which lasted for approximately 1 h. 6. Data from 64 subjects were pooled for detailed comparison of identification patterns in active and passive touch. The results were analyzed and found to be consistent with the hypothesis that the identification and confusion probabilities are identical in the two modes. We conclude that there is no difference between active and passive touch in form recognition when the stimulus pattern is smaller than a finger pad. 7. Data from all experiments were pooled to produce a single confusion matrix with 324 presentations per letter. The majority of erroneous responses are grouped in a small number of confusion pairs and the majority of those confusion pairs are strongly asymmetric. The probable neural mechanisms of some confusion patterns are discussed.

Adult↗
PubMed1990

Tactile roughness: neural codes that account for psychophysical magnitude estimates.

Hypothetical neural codes underlying the sensation of tactile roughness were investigated in a combined psychophysical and neurophysiological study. The stimulus set consisted of plastic surfaces embossed with dot arrays of varying dot diameter and center-to-center spacing. Human subjects explored each surface with the pad of the index finger and reported their subjective sense of roughness magnitude. The same surfaces were scanned across the receptive fields of cutaneous mechanoreceptive afferents in monkeys while recording the evoked action potentials. Hypothetical neural codes for roughness magnitude were computed from the neural response patterns and tested for their ability to account for the psychophysical data. The psychophysical results showed that subjective roughness magnitude is an inverted U-shaped function of dot spacing that peaks near 3.0 mm spacing, and that increased dot diameter produces decreased roughness sensations at all dot spacings. Hypothetical neural codes that do not bear a consistent relationship to roughness magnitude across all of these stimulus conditions can be rejected as the code for roughness. Four types of neural codes were considered. They were based on (1) mean firing rate, (2) general variation in firing rate, (3) short-term temporal variation in firing rate, and (4) local spatial variation in firing rate. Mean firing rate failed to explain the psychophysical results: surfaces that evoked the same firing rate often evoked very different roughness judgments. In contrast, neural codes based on firing-rate variation, especially in slowly adapting afferents, account for the psychophysical results.

Action Potentials↗
PubMed1988

Spatial pattern representation and transformation in monkey somatosensory cortex.

Embossed letters, used previously in pattern recognition experiments in humans, were used to study the spatial patterns of neural activity evoked in peripheral fibers and cortical neurons in areas 3b and 1 of the primary somatosensory cortex of alert rhesus (Macaca mulatta) monkeys. The object was to investigate the representation and transformation of spatial information during the early stages of peripheral and cortical neural processing. Our method consisted of sweeping each letter of the alphabet across the skin repeatedly and constructing a two-dimensional plot (called a spatial event plot) of the action potentials evoked in afferent fibers and cortical neurons. By using this method, slowly and rapidly adapting primary afferents were shown to transmit isomorphic neural images of the letters. Although the slowly adapting images were more spatially acute, both populations conveyed images of sufficient quality to account for human psychophysical performance. In the cortical areas studied, the slowly adapting neurons of area 3b stood out for the acuity, complexity, and variety of their responses. Some of the spatial event plots for these neurons were isomorphic and at least as acute as those obtained from any primary afferent. Others were highly structured but nonisomorphic. The quality and variety of responses in area 3b slowly adapting neurons suggest that they play an important role in the processing of information underlying tactual pattern recognition. The rapidly adapting neurons of area 3b and all types of neurons in area 1 yield much less structured and differentiated responses.

Animals↗