Tactile-channel interactions in the somatosensory system (original) (raw)
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Integration of vibrotactile frequency information beyond the mechanoreceptor channel and somatotopy
Scientific Reports
A wide variety of tactile sensations arise from the activation of several types of mechanoreceptorafferent channels scattered all over the body, and their projections create a somatotopic map in the somatosensory cortex. Recent findings challenge the traditional view that tactile signals from different mechanoreceptor-channels/locations are independently processed in the brain, though the contribution of signal integration to perception remains obscure. Here we show that vibrotactile frequency perception is functionally enriched by signal integration across different mechanoreceptor channels and separate skin locations. When participants touched two sinusoidal vibrations of fardifferent frequency, which dominantly activated separate channels with the neighboring fingers or the different hand and judged the frequency of one vibration, the perceived frequency shifted toward the other (assimilation effect). Furthermore, when the participants judged the frequency of the pair as a whole, they consistently reported an intensity-based interpolation of the two vibrations (averaging effect). Both effects were similar in magnitude between the same and different hand conditions and significantly diminished by asynchronous presentation of the vibration pair. These findings indicate that human tactile processing is global and flexible in that it can estimate the ensemble property of a largescale tactile event sensed by various receptors distributed over the body. Touching an object produces a unique skin deformation reflecting mechanical interactions between the object and skin. The spatiotemporal features of skin deformation are neurally encoded in the activation patterns of multiple mechanoreceptor-afferent channels with distinct spatiotemporal tuning characteristics 1-5 , forming the basis of the content information ('what') of touch. The channels' responses at each skin location are sent to the central nervous system (the contralateral side of the cortex) with the somatotopic organization preserved 6, 7. The somatotopy forms the basis of the location information ('where') of touch. Given this structure, the fundamental question in tactile processing is how the brain processes these multi-channel inputs from multiple skin locations to compute final touch perception. Specifically, we are interested in whether inputs from different channels and those from different skin locations contribute to the final perception in an independent manner or in an integrated one. With regard to the inputs from different mechanoreceptor channels, a conventional view prefers independent processing, with each channel contributing to different aspects of the touch sensation 8-10. Psychophysically, the detection sensitivity of each channel is not affected by adaptation or masking of the other channels 2, 11-13. Physiologically, different tactile channels appear to be segregated from the periphery to, at least, the first stage of cortical processing, i.e., the primary somatosensory cortex (S1) 14-16. However, while the psychophysical evidence for integration of multiple channels for vibrofrequency perception is still equivocal and not decisive 17-19 , recent physiological studies have shown that singles neurons receive peripheral inputs from multiple channels even in S1 20-22. Regarding interactions of peripheral signals from different skin locations, several studies have suggested interactions beyond strict somatotopic mapping. Physiologically, some neurons in S1 or higher areas have multi-finger/ hand receptive fields, take projections from multiple peripheral neurons, and show inhibition/facilitation effects among them 23-29. Psychophysical masking occurs even when similar input signals are presented to skin locations
Some characteristics of tactile channels
Behavioural Brain Research, 2004
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.
Brain Sciences
Nerve paresthesia is a sensory impairment experienced in clinical conditions such as diabetes. Paresthesia may “mask” or “compete” with meaningful tactile information in the patient’s sensory environment. The two objectives of the present study were: (1) to determine if radiating paresthesia produces a peripheral mask, a central mask, or a combination; (2) to determine if a response competition experimental design reveals changes in somatosensory integration similar to a masking design. Experiment 1 assessed the degree of masking caused by induced radiating ulnar nerve paresthesia (a concurrent non-target stimulus) on a vibrotactile Morse code letter acquisition task using both behavioral and neurophysiological measures. Experiment 2 used a response competition design by moving the radiating paresthesia to the median nerve. This move shifted the concurrent non-target stimulus to a location spatially removed from the target stimuli. The task, behavioral and neurophysiological measure...
PhD Thesis, 2020
Response characteristics of single tactile afferent fibers and their target neurons of the dorsal column nuclei (DCN: somatosensory nuclei located at the junction between the spinal cord and the medulla oblongata) were investigated in anaesthetised cats. To examine this, we developed an experimental paradigm based upon paired, simultaneous recordings from individual afferent fibers in an intact peripheral nerve fascicle, and from their central target neurons of the DCN. Purely dynamically-sensitive tactile neurons of the DCN can be divided into two classes, one responsive to a range of low-frequency (20-80Hz) tactile input, associated with the Meissner corpuscle (RAI), and the other with a higher-frequency range (3-400Hz) of tactile sensitivity associated with the Pacinian corpuscle (RAII). The following research focuses on the transmission characteristics of the RAII class of tactile afferent, one of the main tactile receptors in the fingertips and palms. Intraneural microstimulati...
Cortical processing of near-threshold tactile stimuli: An MEG study
Psychophysiology, 2010
In the present study we tested the applicability of a paired-stimulus paradigm for the investigation of near-threshold (NT) stimulus processing in the somatosensory system using magnetoencephalography. Cortical processing of the NT stimuli was studied indirectly by investigating the impact of NT stimuli on the source activity of succeeding suprathreshold test stimuli. We hypothesized that cortical responses evoked by test stimuli are reduced due to the preactivation of the same finger representation by the preceding NT stimulus. We observed attenuation of the magnetic responses in the secondary somatosensory (SII) cortex, with stronger decreases for perceived than for missed NT stimuli. Our data suggest that processing in the primary somatosensory cortex including recovery lasts for o200 ms. Conversely, the occupancy of SII lasts !500 ms, which points to its role in temporal integration and conscious perception of sensory input.
The neural signal for the intensity of a tactile stimulus
The Journal of neuroscience : the official journal of the Society for Neuroscience, 1984
The effect of indenting the skin at different rates on the perceived intensity of the stimulus was studied by indenting the skin of the fingertip with two triangular waveforms, given as a pair. The subjects were asked to judge which member of the pair was more intense. Perceived intensity was found to increase both with the depth and the speed of the indentation. In contrast, changes in the rate of skin indentation had little influence on perceived skin indentation depth. This suggests that intensity and depth are different attributes of tactile sensibility. Since the skin is viscous, a rapid indentation is more forceful than a slow indentation of the same depth, raising the possibility that perceived intensity is related to stimulus force. Even though intensity judgments were more closely correlated with the force of a stimulus than with the indentation it produced, a rapidly increasing force was felt as more intense than one that increased more slowly but attained the same final m...
Visuo-tactile cross-modal associations in cortical somatosensory cells
Proceedings of the National Academy of Sciences, 2000
Recent studies show that cells in the somatosensory cortex are involved in the short-term retention of tactile information. In addition, some somatosensory cells appear to retain visual information that has been associated with the touch of an object. The presence of such cells suggests that nontactile stimuli associated with touch have access to cortical neuron networks engaged in the haptic sense. Thus, we inferred that somatosensory cells would respond to behaviorally associated visual and tactile stimuli. To test this assumption, single units were recorded from the anterior parietal cortex (Brodmann's areas 3a, 3b, 1, and 2) of monkeys performing a visuo-haptic delay task, which required the memorization of a visual cue for a tactile choice. Most cells responding to that cue responded also to the corresponding object presented for tactile choice. Significant correlations were observed in some cells between their differential reactions to tactile objects and their differentia...