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Birznieks I, Vickery RM (2017) Spike timing matters in novel neuronal code involved in vibrotactile frequency perception. Current Biology, 27(10):1485-1490    
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• Temporal spike patterns may shape frequency perception regardless of spike count • Periodicity is not the most salient temporal cue for vibrotactile frequency • Tactile frequency is determined by duration of the silent gap between spike bursts • This new code is well suited to signal naturalistic complex vibratory patterns By controlling spike timing in tactile afferents, Birznieks and Vickery demonstrate that temporal spiking patterns may shape frequency perception regardless of spike count. The most salient temporal feature for vibrotactile frequency was the duration of the silent gap between bursts of neural activity and not the periodicity as previously expected
Abstract
Skin vibrations sensed by tactile receptors contribute significantly to the perception of object properties during tactile exploration [1; 2; 3 ; 4] and to sensorimotor control during object manipulation [5]. Sustained low-frequency skin vibration (<60 Hz) evokes a distinct tactile sensation referred to as flutter whose frequency can be clearly perceived [6]. How afferent spiking activity translates into the perception of frequency is still unknown. Measures based on mean spike rates of neurons in the primary somatosensory cortex are sufficient to explain performance in some frequency discrimination tasks [7; 8; 9; 10 ; 11]; however, there is emerging evidence that stimuli can be distinguished based also on temporal features of neural activity [12 ; 13]. Our study’s advance is to demonstrate that temporal features are fundamental for vibrotactile frequency perception. Pulsatile mechanical stimuli were used to elicit specified temporal spike train patterns in tactile afferents, and subsequently psychophysical methods were employed to characterize human frequency perception. Remarkably, the most salient temporal feature determining vibrotactile frequency was not the underlying periodicity but, rather, the duration of the silent gap between successive bursts of neural activity. This burst gap code for frequency represents a previously unknown form of neural coding in the tactile sensory system, which parallels auditory pitch perception mechanisms based on purely temporal information where longer inter-pulse intervals receive higher perceptual weights than short intervals [14]. Our study also demonstrates that human perception of stimuli can be determined exclusively by temporal features of spike trains independent of the mean spike rate and without contribution from population response factors