Somatosensory Neurons: Spike Timing
A long-standing controversy in neural coding has been about whether the timing of individual action potentials (spikes) conveys information and is behaviorally relevant or whether information is instead transmitted simply by neurons’ firing rates. Both peripheral and cortical somatosensory neurons in primates can exhibit precisely timed action potentials in response to tactile stimuli, and there is a growing consensus that not only is some tactile information exclusively represented by such temporal codes but also that spike timing can shape tactile perception.
Precisely Timed Responses of Cutaneous Mechanoreceptors to Skin Vibrations
Peripheral Responses During Object Manipulation
Another temporal code might be active during object manipulation. When grasping an object, one needs to rapidly adapt grip forces depending on object properties to prevent slip or overgrasping. Information about object curvature and similar properties is encoded mostly by SA1 and RA afferents. It has been shown that in addition to firing rates, the first-spike latencies of SA1 and RA afferents are highly informative about object features. A neural code based on first-spike latencies could explain how tactile feedback is rapidly integrated into motor commands (grip force adjustments can occur within 100 ms) (Johansson and Birznieks 2004; Saal et al. 2009).
Spike Timing in Somatosensory Cortex
Spike Timing and Attention
Spike timing across a population of neurons can also carry information. Specifically, attention modulates the synchrony of spikes of cortical somatosensory neurons (Steinmetz et al. 2000). Such a mechanism might enhance the saliency of attended stimuli by increasing the number of coincident spikes across the neural population.