Efferent optic nerve fibers mediate circadian rhythms in the Limulus eye.

When the horseshoe crab is kept in constant darkness, the lateral eye produces larger electroretinographic and optic nerve responses at night than during the day. These circadian rhythms are mediated by synchronous bursts of efferent impulses in the optic nerve trunk. The endogenous efferent activity appears to increase both the gain and the quantum catch of the photoreceptors.

A longitudinal study of somesthetic perceptual disorders in an individual with a unilateral thalamic lesion.

Several aspects of tactile, thermal and pain perception were evaluated in an individual (R.S.) with a hemorrhagic lesion centered in her left lateral thalamus. Over a 4-year period, psychophysical evaluations were undertaken every 6-8 months, and five magnetic resonance (MR) studies were conducted. Early tests (1991-1992) revealed large contralateral deficits in R.S.'s perception of touch, innocuous temperature, and mechanically evoked cutaneous pain--more so for the upper versus the lower extremity. R.S. showed a similar pattern for heat pain sensitivity, but a more modest deficit than for mechanically evoked pain. She showed a deficit for cold pain sensitivity on her foot, but not for her hand. Thresholds for all types of stimuli ipsilateral to the lesion were within a normative range. Late in 1993, R.S. demonstrated improvements in sensory capacity for touch and mechanically evoked pain contralaterally, although deficits were still evident. During the same period, heat pain sensitivity improved contralaterally, and strikingly, a permanent, ipsilateral hypersensitivity to heat pain developed in her hand. Throughout the entire testing period, R.S.'s ratings of perceived unpleasantness matched the patterns of perceived pain intensity. Thus, the discriminative and the affective dimensions of her pain would change in tandem. However, perceptible innocuous thermal stimuli evoked no affective response when applied contralaterally, despite being described as pleasant when presented ipsilaterally. Throughout the testing period, R.S. reported a persistent numbness on her right hemi-body. Only during a 3-month period in 1995 did she experience spontaneous pain, which was referred to her right foot. The only change in psychophysical performance related to her right foot was a transient but intense thermal allodynia several months prior to her spontaneous pain. The MR studies over this 4-year period showed changes in the extent of edema, gliosis and/or ischemia that could be related to perceptual changes. Thus, the conspicuous observations in this thalamic lesion case were: (i) differential effects upon the various pain modalities (mechanical, heat and cold); (ii) development of thermal allodynia without mechanical allodynia, including an ipsilateral effect; (iii) a deficit in positive affective responses to temperature; and (iv) the different time courses for changes in evoked somesthetic capacity versus spontaneous paresthesias and pathological pain.

Passive, active and intra-active (self) touch.

A series of experiments are described in which magnitude estimates of the perceived size of steel balls were made when the balls were actively rolled between the fingertip and several other body sites (thumb, thenar eminence, forearm). This movement, called scripting, involves actively moving an object by a touching surface over another surface of the body which is passively being touched. We define this active/passive activity as "intra-active touch" and the results show that the perceptual size of the balls is dependent upon the body part passively being activated. An additional series of experiments decoupled the actively generated and passively received tactile information by having subjects either perform the scripting on another individual's body site or by having the other individual roll the balls on the subject's various sites. The latter experiments showed that the passive body can contribute to the overall impression of the size of the balls, but only when the intra-active touching involved the glabrous skin of the hands. Intra-active touch between the active finger and the passively touched hairy skin of the forearm showed no effect of the touched surface on the perceived size of the balls. The results suggest that the mechanisms of intra-active touch are different when glabrous skin activates glabrous skin than when glabrous skin activates hairy skin.

Some characteristics of tactile channels.

The four information-processing channels of glabrous skin have distinct tuning characteristics which appear to be determined in the periphery at the level of sensory receptors and their afferent nerve fibers. The four-channel model [J Acoust Soc Am 84 (1988) 1680] has been updated to include measurement over a wider frequency range of tuning of the P and NP I channels, psychophysically determined by forward-masking and adaptation tuning curve methods. In addition to differences in their tuning, the P and NP channels differ in the following ways: (1) the P channel, but not NP channels, has been found to be capable of temporal summation, which operates by neural integration; (2) the capacity for spatial summation is also an exclusive property of the P channel; (3) sensitivity declines with age at a greater rate in the P channel than in the NP channels; (4) the masking or adaptation of a channel has no effect on the sensitivity of the other channels, although the channels interact in the summation of the perceived magnitudes of stimuli presented to separate channels.

Contourless stimuli produce binocular brightness summation.

Absolute magnitude estimates by 16 observers reveal that complete binocular brightness summation occurs for flashed Ganzfeld conditions. In other words, the view using both eyes appears twice as bright as with one. However, using the same technique, but with 2 degrees fields, no such summation is found. In addition to showing that, on the average, human observers can act as photometers, the results suggest that either complete summation or averaging of the monocular brightness can occur, depending upon the presence of contours.

Perceptual "blankout" of monocular homogeneous fields (Ganzfelder) is prevented with binocular viewing.

The loss of visual perception or "blankout" which occurs when a homogeneous field (Ganzfeld) is presented monocularly is prevented when the same field is viewed binocularly. Thus, blankout cannot be retinal; and contours or transients in time and space are unnecessary for the continuous maintenance of visual perception. Experiments are reported in which blankout ensues only if the two eyes receive luminance disparities ca 0.75 log I. Furthermore, blankout is only marginally affected by stimulus intensity, nor is it dependent on stimulus hue. However, equally luminant but disparate hues presented to the two eyes produce perceptions reminiscent of blankout, with the darkness of blankout replaced with that of color. It is hypothesized that the underlying mechanisms have a commonality in the phenomena of blankout and binocular rivalry but several noncongruent features require explanation.

Low cost Video Scaler and Gray Scale Integrator.

A hybrid digital/analog device capable of making high-resolution linear and area measurements from a standard monochromatic video image is described. The device is capable of dynamic as well as static data acquisition when used in conjunction with standard NTSC video recording equipment. Digital output allows for computer interfacing. Linear dimensions are obtained by electronically superimposing two horizontal and two vertical scaling lines on a video monitor. Each linear dimension has an eight-bit resolution and is displayed on the front panel with seven segment LED's. Eight-bit, digital-to-analog converters are also used to provide analog outputs. A measurement of the temporal deformation pattern of the accessory capsule surrounding a mechanoreceptor (Pacinian corpuscles) in response to vibratory displacements is demonstrated. Area measurements are obtained via a window comparator, a 6-MHz clock, and a 16-bit digital-to-analog converter. Data is only valid within the zone set by the scaling lines, allowing data regions to be isolated from noise, etc. The 16-bit digital signal measuring the area of interest is then converted for analog output. The measurement of the consensual pupillary reflex in response to full-field illumination (Ganzfeld) is given as an example.

Assessment of vibrotactile sensitivity in patients with carpal tunnel syndrome.

The effectiveness of using vibrotactile threshold measures to aid in the diagnosis of carpal tunnel syndrome (CTS) was evaluated. Thresholds for detecting 1-, 10-, and 300-Hz vibratory stimuli were measured on the fingertips of 24 CTS patients and 20 healthy control subjects. There were no significant differences in threshold for 1- and 300-Hz between the two groups. Although there were significant differences for 10-Hz stimuli, the mean patient threshold was within 1 standard deviation of the mean threshold for the control group. These results indicate that threshold testing is not a suitable diagnostic tool for CTS. Additionally, we examined whether thresholds were elevated in the presence of pain. Seven patients reported experiences of pain and no pain sessions. No significant differences in threshold were found between the two pain conditions, indicating that the presence of pain related to CTS does not affect threshold.

Intensity and frequency characteristics of pacinian corpuscles. III. Effects of tetrodotoxin on transduction process.

This is the third in a series of three papers dealing with intensity and frequency characteristics obtained on pacinian corpuscles isolated from the cat mesentery (8, 9). The experimental results show that tetrodotoxin (TTX) affects not only regenerative action potentials but also the measured receptor (generator) potentials. Extracellularly recorded receptor and action potentials were simultaneously recorded in response to sinusoidal displacement stimuli. Receptor potentials measured in this manner responded with a time course similar to the driving frequency. Since the duration of the action potentials is long relative to the cycle period at high stimulus frequencies, the underlying receptor potentials can become obscured. To prevent this, TTX was applied through superfusion at a concentration of 6.0 microM. After about 30 min, the neural spikes were fully eliminated but the receptor potentials were also decreased in amplitude. Intensity characteristics relating receptor-potential amplitudes to probe displacement amplitudes showed that the percentage decrease in amplitude due to the application of TTX was constant regardless of stimulus intensity. Frequency characteristics relating probe displacement amplitudes to vibration frequency for a constant-response criterion showed an increase in the displacement amplitude required for the criterion response, across frequency, when TTX was applied. On average, the increase was a power function of vibration frequency.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of stimulus duration on frequency-response functions in the Pacinian (P) channel.

Psychophysical experiments on human observers and physiological measurements on Pacinian corpuscles (PCs) isolated from cat mesentery were performed to explain certain discrepancies in the psychophysical-physiological model (Bolanowski et al., 1988) for the sense of touch in the vibrotactle Pacinian (P) channel. The model was based on correlations among the psychophysical frequency response obtained on human glabrous skin and physiological frequency-response functions measured on two PC preparations: PC fibers innervating human glabrous skin (Johansson et al., 1982) and PCs isolated from cat mesentery. The three frequency-response functions were qualitatively similar. However, the low-frequency slope for the human PC fibers differed from the slopes for the psychophysical and cat mesentery PC functions by being 3 dB/octave less steep. This discrepancy can be explained theoretically by differences in methodology involving the effect of stimulus duration and the property of temporal summation known to exist in the P channel (i.e., a 3-dB increase in sensitivity per doubling of stimulus duration). To test this, experiments were performed using two methods of stimulation: (1) a constant stimulus duration for different test frequencies, as generally used in this laboratory; and (2) a constant number of stimulus cycles (n = 5) for each test frequency as used by Johansson et al. The method of least squares was used to calculate the low-frequency (50 to 150-Hz) slopes of individual psychophysical and physiological functions. The mean slopes that resulted from using the two methods of stimulation were consistent with the theoretical expectations.

The effects of skin temperature on the psychophysical responses to vibration on glabrous and hairy skin.

Psychophysical detection thresholds for vibration were measured at the thenar eminence and volar forearm using a 0.008-cm2 (1.0-mm-diam) contactor. Measurements were made at 14 sinusoidal frequencies between 12 and 500 Hz at six skin temperatures between 15 degrees and 40 degrees C. The results are consistent with the hypothesis that three functionally discrete non-Pacinian afferent systems mediate vibrotactile responses. It was possible to identify the response characteristic of the rapidly adapting (Meissner) system, but it was not possible to isolate the responses of two slowly adapting (SAI, SAII) systems.

Effects of stimulus duration on the response properties of Pacinian corpuscles: implications for the neural code.

Based on physiological and psychophysical data, it has been suggested that the neural code for threshold detection in the P channel, mediated by Pacinian corpuscles (PCs), may be 2-4 neural impulses/stimulus (Bolanowski et al., 1988). To further test the efficacy of this code, responses from PCs were measured at different vibratory burst durations. Since it is known that the P channel has the capacity to summate vibratory stimuli temporally within the central nervous system, the effect should also be present in the physiological results. Temporal summation predicts a decrease in threshold at a rate of -3 dB/doubling of stimulus duration. Responses from single PCs were integrated by counting neural spikes over the entire burst duration. Furthermore, real-time responses were integrated with a low-pass filter, more accurately modeling the central process. For the spike-counting scheme, a criterion of 4 impulses/stimulus showed a decrease in stimulus amplitude for increases in duration similar to that obtained psychophysically. The amplitude-duration function obtained with the low-pass filter, however, resulted in a function which did not follow that obtained psychophysically, regardless of the number of impulses/stimulus. Since the P channel is known to have a central integrator, it has been concluded that activity of a single PC afferent probably is not sufficient to signal threshold in the P channel.

Intensity and frequency characteristics of pacinian corpuscles. I. Action potentials.

The mechanisms by which pacinian corpuscles, isolated from cat mesentery, transduce mechanical stimuli have been measured for directly applied sinusoidal deformations. Stimulus-response relationships were measured as follows: intensity characteristics, which relate the receptor-potential magnitude or the neural firing rate to stimulus intensity; amplitude-frequency characteristics, which relate the stimulus amplitude to stimulus frequency for a given response criterion; and phase-frequency characteristics, which relate the phase angle between the stimulus and the receptor response to stimulus frequency. This report, the first in a series of three, deals with the characteristics reflected in the neural firing rate. The two reports that follow deal with the receptor potential, which, if of sufficient amplitude, generates the propagated action potential. In the majority of the pacinian corpuscles investigated, the intensity characteristics for neural firing rates were steep at low stimulus intensities and plateaued at submultiples and multiples of the stimulus frequency as stimulus intensity was increased. Poststimulus time and interval histograms reveal that the plateaus occur as a result of phase locking to the stimulus. The submultiples and multiples of stimulus frequency at which phase locking was found and the length of the plateaus depended on stimulus frequency. These plateaus were eliminated with the use of narrow-band noise stimuli. The amplitude-frequency characteristics obtained with either a criterion of constant firing rate or that of a constant number of neural spikes per stimulus cycle were U-shaped functions. Their positions along both the intensity and frequency continua are affected by response criterion. For example, the mean (n = 19) amplitude-frequency characteristic generated with a constant firing rate criterion of 1 spike/s has a maximum sensitivity of about -37.0 dB re 1-micron peak and a best frequency (BF, stimulus frequency where maximum sensitivity occurs) of 465 Hz. The bandwidth, measured by Q3 dB, is 1.02. Alternatively, the average (n = 16) amplitude-frequency characteristic obtained with a response criterion of 1 spike per stimulus cycle has a maximum sensitivity of about -25.0 dB re 1-micron peak, a BF of 270 Hz and Q3 dB value of 1.16. Spontaneous activity (SPA; activity in the absence of controlled stimuli) was found in 13.6% of the pacinian corpuscles. Intensity characteristics and frequency characteristics of these corpuscles show features similar to those of corpuscles without spontaneous activity except that the intensity characteristics asymptote to SPA levels at low stimulus intensities.(ABSTRACT TRUNCATED AT 400 WORDS)

Intensity and frequency characteristics of pacinian corpuscles. II. Receptor potentials.

Intensity characteristics that relate receptor- (generator) potential amplitude to vibration amplitude and frequency characteristics that relate either the stimulus intensity required for a criterion response or the phase angle between the stimulus and the receptor potential to vibration frequency have been obtained from isolated pacinian corpuscles removed from cat mesentery. The intensity characteristics of signal-averaged receptor potentials in response to sinusoidal displacements were found to be linear at low stimulus levels and to saturate at higher ones. At the higher levels, an asymmetric full-wave rectification was often found, the degree of which varied among receptors. The receptor-potential waveforms showed a time-dependent hysteresis in response to every stimulus cycle at moderate and high stimulus levels. An average intensity characteristic is given. The measured amplitude-frequency characteristics for a constant magnitude of the receptor potential below the neural spike threshold were found to be U-shaped functions. The averaged (n = 7) amplitude-frequency characteristic generated at a constant criterion response had a best frequency of 370 Hz and a bandwidth of Q3 dB equal to 0.8. The phase-frequency characteristics of the receptor potentials below spike threshold exhibited two populations of responses. Both populations underwent phase changes of about 300 degrees as the vibration frequency was increased from 20 Hz to 1.0 kHz but were separated by 180 degrees. An average (n = 8) phase-frequency characteristic is shown. For a constant neural firing rate, the relationship between receptor-potential amplitude and stimulus frequency was also U-shaped. Several qualitative physiological models are presented in relation to previously reported anatomical evidence (14, 18, 19, 32, 45). For the intensity domain, it is suggested that the cytoplasmic extensions that protrude from the unmyelinated portion of the corpuscle axon into the hemilamellar clefts are responsible for the asymmetric full-wave rectification and the response polarity in the phase-frequency characteristics. It is the asymmetric full-wave rectification and consequent receptor-potential waveforms that produce the 2 spikes/stimulus cycle plateaus in the characteristics relating firing rate to stimulus intensity described in the preceding paper (5). An additional model, based on the recovery of spike threshold, suggests how the plateaus in the firing rate-intensity characteristics (5) are produced. For the frequency domain, three filters in cascade can account for the frequency characteristic obtained with a constant firing rate criterion (see Ref. 5).(ABSTRACT TRUNCATED AT 400 WORDS)

Semi-serial electron-micrographic reconstruction of putative transducer sites in Pacinian corpuscles.

The Pacinian corpuscle (PC) is composed of an afferent neurite surrounded by an accessory capsule formed by concentric layers of lamellae. Projecting from the neurite, which is elliptical in cross-section, are "filopodia" or axonal, spike-like extensions. These filopodia are the putative sites of transduction. It has been proposed that two populations of filopodia organized in morphofunctional opposition exist, and that this arrangement is responsible for the bidirectional sensitivity of PCs as seen in receptor potential recordings. In order to explore this possibility, PCs obtained from cat mesentery were processed for electron microscopy, and semiserial reconstructions were made. We evaluated the extensions' (n > 110) locations, inclusions, shapes, and sizes. The filopodia were found to project along the major elliptical axis of the neurite, their density being approximately 2.8 per micron. The filopodia were found to contain filaments, vesicles, and amorphous ground substance, and dense accumulations of mitochondria were found at their bases. Measurements of their size (i.e., length, width, and height) suggest that there are two different types of filopodia. No other obvious relations among filopodial type, location along the neurite, and landmarks for transduction were found. The presence of the two filopodial types may be the basis for the bidirectional sensitivity of the PC.

Heat-induced pain diminishes vibrotactile perception: a touch gate.

The gate control theory of pain (Melzack and Wall, 1965) suggests that tactile stimuli can decrease the perception of pain. We have found the reverse effect: Heat at levels that induce pain can substantially suppress tactile sensitivity, independently of shifts in attention or arousal. Ten human observers were stimulated by a tonic, pain-producing heat stimulus and vibrotactile stimuli (1, 10, and 100 Hz) coincidentally presented to the right thenar eminence. Vibrotactile thresholds were assessed with the skin at a normative temperature of 31 degrees C and at higher temperatures producing pain. Increases in vibrotactile thresholds (mean change = 7.3 dB) occurred at skin temperatures just below and above those that induced pain. Furthermore, absolute-magnitude estimates of suprathreshold vibrotactile stimuli determined during the same experiments showed decreased sensitivity and psychophysical recruitment. The changes are not attributable to attentional or arousal shifts, since they were not associated with changes in auditory thresholds. Furthermore, the changes occurred just below the subjects' pain thresholds (where nociceptors are presumably activated). This over-twofold diminution of vibrotactile sensitivity suggests that heat stimuli capable of inducing pain can significantly diminish taction, perhaps through a "touch gate" in a manner similar to the gate control theory proposed for pain.

Hairy skin: psychophysical channels and their physiological substrates.

Experiments were conducted in which threshold-frequency characteristics were measured on the hairy skin of the forearm of human observers. Thresholds were measured with two stimulus probe areas (2.9 and 0.008 cm2) at three skin-surface temperatures (15 degrees, 30 degrees, and 40 degrees C). The results suggest that whereas glabrous skin uses four distinct channels of information, only three channels may be involved in mediating the sense of touch for hairy skin. The three channels are defined as Ph, (Pacinian, hairy skin), NPh low (non-Pacinian, hairy skin, low frequencies) and NPh mid (non-Pacinian, hairy skin, middle frequencies). In addition, it is proposed that the neural substrates for the three psychophysically characterized channels are, respectively, the Pacinian corpuscle (PC) nerve fibers, the slowly adapting type II (SAII) fibers, and the rapidly adapting (RA) fibers.

Relationship between oral pain and ethanol concentration in mouthrinses.

Previous reports have indicated that certain mouthrinses, even when used as directed can induce oral pain. In order to help determine the causal agent(s), various commercially available mouthrinses, as well as control solutions, were tested in a psychophysical study in which subjects rated categories of pain during and after mouthrinsing. More specifically, the studies tested the effects of ethanol concentration on induced pain. The results show that there is a direct relationship between ethanol content and the amount of induced pain. Furthermore, the amount of pain was found to increase with time of rinsing, and to slowly decrease after cessation of rinsing. Lastly, comparison of ethanol/water controls with a marketed product (Clear Choice) matched for ethanol content showed that, while ethanol was the key factor in mouthwash-induced oral pain, other presently unidentified agents can also add to the effect.

The frequency selectivity of information-processing channels in the tactile sensory system.

The frequency selectivity of the P, NP I, and NP II channels of the four-channel model of mechanoreception for glabrous skin was measured psychophysically by an adaptation tuning curve procedure. The results substantially extend the frequency range over which the frequency selectivity of these channels is known and further confirm the hypothesis that the input stage of each of these channels consists of specific sensory nerve fibers and associated receptors. Specifically, the frequency characteristics of Pacinian nerve fibers, rapidly adapting (RA) nerve fibers, and slowly adapting Type II (SA II) nerve fibers were found to be the peripheral neurophysiological correlates of the P, NP I, and NP II channels, respectively. The finding that the tuning characteristic for a test stimulus of 250 Hz delivered through a small (0.008 cm2) contactor depended dramatically on the duration of the test stimulus whereas the detection threshold did not, provides new evidence in support of the hypothesis that separate NP II and P channels exist.

The effects of static indentation on vibrotactile threshold.

Vibrotactile thresholds were measured on the thenar eminence and the volar forearm at different static depths of skin indentation. Three stimulus frequencies (1, 20, and 200 Hz) were delivered through either a 0.008- or a 2.9-cm2 contractor. The indentation depths ranged from 0 to 1 mm (0.25-mm steps) relative to the point of skin contact with the stimulator. There was a significant effect of indentation in all stimulus combinations of contactor size, location, and frequency. These results resolve an apparent discrepancy in the literature regarding threshold reduction with increasing contactor size observed on the forearm at low frequencies.