Quantifying whisking behaviour and its neural encoding during active somatosensation

Abstract

A key problem in neuroscience is to understand what inputs enter a sensory system and how they are encoded. The somatosensory system is fundamentally an active system, however, due to experimental constraints to measure tactile organ behaviour, the literature has focused on the study of anaesthetised animals, suppressing the active components of somatosensation. Therefore, these questions remain largely unanswered for this system, hence, this study was conducted in the mouse whisker system. Specifically, this project aimed to accurately describe mouse whisking behaviour and characterise how mechanical inputs are represented in barrel cortex in awake, behaving mice. To this end, Chapter 2 describes the development of a method to track whisker shape and kinematics in three dimensions from awake, behaving animals. Whiskers were simultaneously recorded with high-speed video cameras from two vantage points. The whisker tracker algorithm automatically reconstructed 3D whisker information directly from the 'stereo' video data, tracking multiple whiskers in parallel with a low error rate. The output of the tracker was used to produce a 3D description of each tracked whisker, including its 3D orientation and 3D shape, as well as bending-related mechanical forces. Chapter 3 details the development of a computational model (GLM) to predict neural activity in the barrel cortex in awake, behaving mice from whisker contacts and mechanical sensory inputs as bending and twisting moment. To this end, extracellular recordings from layer 5 obtained during a tactile detection task were used to characterise the sensory inputs using the method developed in Chapter 2. Recorded units conformed a heterogenous population showing sensitivity to touch or one of the mechanical variables. The results suggested that changes in both bending and twisting moments are encoded in cortical neurons, providing a mechanosensory basis for somatosensation during active touch. In Chapter 4, the features of sensory adaptation which can be observed during active sensation were investigated. For this, extracellular recordings from cortical neurons obtained during a detection task (Chapter 3) were analysed and the simultaneous whisking behaviour was described using the method developed in Chapter 2. Single- and multi-unit activity was sensitive to whisker contacts, whose responses were modulated by both behaviour dynamics and neural adaptation. Stimulus-Specific Adaptation was observed for whisker identity, and more weakly for bending direction. These results suggest that encoding of behaviourally relevant stimuli are modulated by sensory adaptation and its effects can be studied and measured in awake, behaving animals. In conclusion, these results show that a comprehensive analysis of sensorimotor behaviour is critical to understand neural activity and shed light on the dynamic computations performed in barrel cortex in awake, behaving animals.

Date of Award	1 Aug 2021
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Rasmus Petersen (Supervisor) & Mark Humphries (Supervisor)