Correlated physiological and perceptual effects of noise in a tactile stimulus

Abstract

We investigated connections between the physiology of rat barrel cortex neurons and the sensation of vibration in humans. One set of experiments measured neuronal responses in anesthetized rats to trains of whisker deflections, each train characterized either by constant amplitude across all deflections or by variable amplitude ("amplitude noise"). Firing rate and firing synchrony were, on average, boosted by the presence of noise. However, neurons were not uniform in their responses to noise. Barrel cortex neurons have been categorized as regular-spiking units (putative excitatory neurons) and fast-spiking units (putative inhibitory neurons). Among regular-spiking units, amplitude noise caused a higher firing rate and increased cross-neuron synchrony. Among fast-spiking units, noise had the opposite effect: It led to a lower firing rate and decreased cross-neuron synchrony. This finding suggests that amplitude noise affects the interaction between inhibitory and excitatory neurons. From these physiological effects, we expected that noise would lead to an increase in the perceived intensity of a vibration. We tested this notion using psychophysical measurements in humans. As predicted, subjects overestimated the intensity of noisy vibrations. Thus the physiological mechanisms present in barrel cortex also appear to be at work in the human tactile system, where they affect vibration perception.psychophysics | somatosensory cortex | vibration | whisker | finger A n effective approach to uncover how neuronal activity leads to sensation is to vary stimulation parameters while correlating changes in firing with changes in the percept (1-5). In the present work, we measured changes in neuronal activity in rat somatosensory ("barrel") cortex induced by variation in vibration parameters and correlated these changes with perceptual reports from human subjects. The stimuli in the two cases were trains of whisker and skin vibration, respectively.Isolated neurons respond more robustly to unpredictable (noisy) patterns of electrical stimulation than to repeating, periodic patterns (6) or constant inputs (7). Synaptic transmission also can be enhanced by noise (8). In a recent study of the effects of stimulus noise in rat barrel cortex, we found that whisker vibration trains containing temporal noise (irregularity in the sequence of interdeflection intervals) evoked a larger and more synchronous cortical response than did periodic vibration trains (9). In the present work, to verify that response amplification by noise is a general property of the sensory system, we explored another stimulus feature: We compared cortical responses to trains that had constant amplitude vs. trains that had varying amplitude. We then investigated the perceptual impact of noise using psychophysical experiments in humans. We predicted that noise, by enhancing neuronal firing rates and/or firing synchrony in somatosensory cortex, would produce a systematic bias in the perceived intensity of noisy vibrations compared with noise-free vibrations. Resu...

Neuronal Reward and Decision Signals: From Theories to Data

“…during visual categorization (288). Tactile responses in mouse barrel cortex require 200 ms to become differential (300). Similar multicomponent responses are seen with reward coding.…”

Behavioral study of whisker-mediated vibration sensation in rats

“…In both cases, subjects overestimated the intensity of the noisy vibrations compared with nonnoisy vibrations with the same mean values. When the same stimuli were applied to rat whiskers, barrel cortex neurons' firing rates were boosted by the presence of noise (40,41). The precise match of noise effects on barrel cortex firing rate and noise effects on perceived vibration intensity in human subjects again suggests that in the neuronal representation of a vibration, firing rate is the most salient firing property.…”

“…A different study showed that human subjects' judgment of vibrotactile intensity was affected by introducing temporal irregularity (frequency noise) and irregularity in deflection magnitude (amplitude noise) (40). In both cases, subjects overestimated the intensity of the noisy vibrations compared with nonnoisy vibrations with the same mean values.…”

Tactile perception and working memory in rats and humans

“…First, in pilot studies, rats attended to noisy stimuli better than to periodic stimuli and were more likely await the go cue before withdrawing. Second, noisy vibrissal stimuli evoke a more robust cortical response (37,38), an advantage for future neurophysiological studies. Third, the structure of the noise stimulus is well suited to reverse correlation methods (39) and will provide rich data for studying the kinematic features extracted by sensory neurons (40,41).…”