Consistency of Angular Tuning in the Rat Vibrissa System

Each region along the rat mystacial vibrissa pathway contains neurons that respond preferentially to vibrissa deflections in a particular direction, a property called angular tuning. Angular tuning is normally defined using responses to deflections of the principal vibrissa, which evokes the largest response magnitude. However, neurons in most brain regions respond to multiple vibrissae and do not necessarily respond to different vibrissae with the same angular tuning. We tested the consistency of angular tuning across the receptive field in several stations along the vibrissa-to-cortex pathway: primary somatosensory (barrel) cortex, ventroposterior medial nucleus of the thalamus (VPM), second somatosensory cortex, and superior colliculus. We found that when averaged across the population, neurons in all of these regions have low (superior colliculus and second somatosensory cortex) or statistically insignificant (barrel cortex and VPM) angular tuning consistencies across vibrissae. Nevertheless, in each region there are a small number of neurons that display consistent angular tuning for at least some vibrissae. We discuss the relevance of these findings for the transformation of inputs along the vibrissa trigeminal pathway and for the detection of sensory cues by whisking animals.