Representation Of Mechanosensory Forces In Somatosensory Cortex During Object Localization

Our understanding of active touch is still in its infancy. The rodent vibrissal system offers us the perfect model to study touch from mechanosensation to perception. Rodents have whiskers in their mystacial pad that correlate on a 1:1 ratio to a specific column of cells within the somatosensory cortex (S1), known as barrels. The lemniscal pathway is the primary afferent responsible for relaying touch information from each whisker to the cortex, specifically to layer (L) 4 before proceeding to L3 and L5b. We currently know that L4 is highly correlated to touch onset and phase characteristics in whisking. However, knowing just one aspect of touch does not allow us to fully decode ‘when’ the object was touched and most importantly ‘where’ it is in space. This present study seeks to examine how L3 and L5b represent mechanosensory forces to aid in object localization. Mice are trained to locate objects by active whisking while in-vivo juxtacellular loose-seal patch records single neuron spike patterns, and high-speed video (1000Hz) captures whisker movement. Optogenetics is used to differentiate between inhibitory and excitatory neurons. Whisker kinematics and touch forces are quantified with micron and sub-microNewton resolution. Initial analysis reveals firing rates of 3.5 and 70 spikes/second for L3 and L5b, respectively. Excitatory neurons in L3 code for touch onset and offset whereas L5b codes for both mechanosensory forces and whisker motion. These studies will provide insight into how mechanosensory information is transformed in the cortex to aid in object localization.