Early stages of sensory processing responsible for the integration of tactile information across multiple whiskers remains poorly understood despite frequent reports of thalamic and cortical multiwhisker responses. Here we propose to fill two major gaps in the characterization of the synthesis of multiple-whisker receptive field by recording from projection neurons in the rostral region of Spinal Trigeminal Nucleus Interpolaris (SpVir)-a brainstem region which receives primary afferent input from multiple whiskers. First, there has been no characterization of SpVir neuron responses to quantified mechanical stimuli. Second, only one study reported recording from these neurons in the awake animal and this study did not attempt to characterize these neurons. The work proposed here will fill both these gaps. First, to characterize these cells' responses to carefully quantified spatial and temporal mechanical inputs, we will record from SpVir neurons in the anaesthetized animal while presenting a variety of mechanical stimuli to the whiskers. Simultaneously, we will record high-speed video from multiple angles to extract the 3D shape of the whiskers during contact. This will allow us to quantify contact timing and force inputs to all whiskers and compare to neural recordings. Second, we will record from neurons in SpVir while an awake animal performs a series of localization tasks. During awake, naturalistic exploration, the patterns of contact with objects change drastically and top down modulatory inputs may alter receptive field structure. We will record from multiple single neurons simultaneously while the rat performs localization tasks with varying physical stimuli. Using multiple angle high speed video recordings we will determine the patterns of contact during naturalistic investigation of different objects. We will then compare the contact patterns with neural spiking to determine the spatial and temporal structure of the receptive field during awake exploration. These experiments promise to fill the two glaring gaps in our understanding of spatiotemporal integration of tactile information: what are the precise relationships between mechanical input and spiking output in these cells; and what general characteristics do these cells exhibit in the awake, behaving animal.
During active exploration, rats repeatedly brush and tap their whiskers against objects, which generates complex mechanical patterns across multiple whiskers simultaneously. The proposed work will combine neural recordings, high-speed video analysis, and mechanical models of whisker bending to characterize the responses of neurons in Spinal Trigeminal Nucleus Interpolaris (SpVi). We will focus on how the spatiotemporal structure of these neural responses represents the complex, multi-whisker mechanical signals generated during active whisking behavior.
| Bush, Nicholas E; Schroeder, Christopher L; Hobbs, Jennifer A et al. (2016) Decoupling kinematics and mechanics reveals coding properties of trigeminal ganglion neurons in the rat vibrissal system. Elife 5: |
| Bush, Nicholas E; Solla, Sara A; Hartmann, Mitra Jz (2016) Whisking mechanics and active sensing. Curr Opin Neurobiol 40:178-188 |
