Somatosensory stimuli guide and shape behavior, from immediate protective reflexes to longer-term learning and high-order processes related to pain and touch. However, somatosensory inputs are challenging to control in awake mammals due to the diversity and nature of contact stimuli. Application of cutaneous stimuli is currently limited to relatively imprecise methods as well as subjective behavioral measures. The strategy we present here overcomes these difficulties by achieving spatiotemporally precise, remote and dynamic optogenetic stimulation of skin by projecting light to a small defined area in freely-behaving mice. We mapped behavioral responses to specific nociceptive inputs and revealed a sparse code for stimulus intensity: using the first action potential, the number of activated nociceptors governs the timing and magnitude of rapid protective pain-related behavior. The strategy can be used to define specific behavioral repertoires, examine the timing and nature of reflexes, and dissect sensory, motor, cognitive and motivational processes guiding behavior.
bioRxiv Subject Collection: Neuroscience