Characterizing the Complete Mechanosensory Input to the Rat Vibrissal Array

It is easy for you to reach into your pocket and – without looking – identify your keys, a coin, or a paperclip. Somehow, your brain transforms the patterns of mechanical input to your fingertips into the robust perception of an object. How is this tactile feat accomplished? The first step towards answering this question is to quantify the patterns of mechanical input that your brain must interpret.

Our laboratory uses the rat vibrissal (whisker) system as a model to understand how the sense of touch is integrated with movement to enable tactile perception. Rats rhythmically brush and tap their whiskers against objects to tactually extract features such as shape and texture. The neural pathways that carry mechanical information from the rat’s whiskers through its brain are in many ways analogous to the neural pathways that carry information from your fingertips through your brain. In this talk I will describe our laboratory’s recent advances in quantifying the complete mechanosensory input to the rat vibrissal array during natural exploratory behaviors, and discuss implications of these results for neural processing in both rats and humans.

Our laboratory has recently identified the primary mechanical variables sufficient for three-dimensional feature extraction by the whiskers. Based on this analysis, we have developed inexpensive arrays of artificial (“robotic”) whiskers that can determine obstacle distance and perform 3-dimensional extraction of object shape. In addition, we have developed a laser light sheet to visualize vibrissae-object contact patterns as an awake rat explores an object. This technique has shed light on the relative contributions of head and vibrissal movements to the mechanosensory patterns of input. Finally, we have quantified the morphology of the rat vibrissal array and begun to examine its influence on the vibrissae-object contact patterns generated during exploration of an object.

We are now combining results from all these experiments – robotic, behavioral, and morphological – to develop a simulation environment that permits full dynamical simulations of vibrissal-object contact. The simulations aim to integrate realistic vibrissal dynamics with behaviorally-measured head and vibrissal kinematics to model the rat's sampling strategies for various objects in the environment. Ultimately, the simulation system will be used to predict the contact patterns in terms of forces and moments at each vibrissa base for a given exploratory sequence, and thus predict the input to the brain.  Supported by NSF IOS-0818414, IOS-08090000.