M Echanisms of Active Sensing

Active sensing and sensorymotor loops Sensation is an active process whereby sensory organs continuously and actively sample the external world, usually by physical movements. Thus, to acquire meaningful information about the surrounding, the brain must integrate sensory signals with information about the active movement that induced them. We study how sensor motion and sensory signals interact to produce perception, focusing on the rat vibrissal system. Rats generate activelycontrolled sweeping movements of their facial whiskers (“whisking”) to locate and identify objects in their immediate environment. Their whiskers are embedded in nested sensory-motor loops at several levels of the brain, from the brainstem up to neocortex (figure 1), whereby rhythmic whisking behavior is exquisitely modulated by sensory feedback, allowing precise positioning of the vibrissae in a manner that maximizes information uptake. Sensory processing of active vibrissal touch Using artificial whisking in anesthetized rats, we found that whisker information is carried from the whisker follicle via the trigeminal ganglion and to the thalamus by three parallel afferent pathways: the paralemniscal pathway, processing self-generated motion of the whiskers, extralemniscal pathway, processing contact signals which contain information about object location, and the lemniscal pathway, integrating whisking and touch information, perhaps for processing object identity (Szwed et al., 2003; Szwed et al., 2006; Yu et al., 2006). These three pathways begin to integrate in the primary and secondary somatosensory cortices (S1 and S2) (Derdikman et al., 2006; Yu et al., unpublished). Specifically, the deeper layers of S2, which are the major anatomical target of the extralemniscal and paralemniscal pathways, contain a Sebastian Haidarliu,