What moves when mice move a single whisker to touch? Individuality and stereotypy in behavior

Abstract

A key function of the brain is to move the body through a rich, complex environment. When rodents engage with their environment, they move their whiskers as they extract tactile information. Even though the study of whisking has a long history, the details of individual whisker movements bilaterally, of nose movement, of stereotypy and variability in an active whisking to touch task are unknown. Here we trained head fixed mice in a simple go-cue task to move a whisker on one side of the face to touch a sensor and tracked facial movements. Our analysis shows that mice specifically control movement of the whisker they use to touch and that as they move their whiskers, they move their nose and apply forces on the head-post in a manner that reflects the behavioral epoch, i.e. whether go cue triggered movement had begun, or a whisker was touching the sensor. Importantly, mice control the setpoint, amplitude and frequency of movement of whiskers bilaterally and individually. Additionally, even though mice achieved the goal of the task -- to touch the sensor within 2 seconds -- how they coordinated movement of the nose and forces on head post with movement of individual whiskers was stereotyped and related to the distance they needed to move a whisker to touch the sensor. Our work shows how stereotyped mouse behavior can be, and it emphasizes both the level of fine motor control mice can exert over individual whiskers and the extent of facial movements in a goal-directed whisking-to-touch task. SignificanceRecent work shows that facial movements are reflected in the activity of a surprisingly large number of brain areas. But what aspects of the face do mice move when they move a whisker to actively touch an object? Our work shows that while mice control the movement of a whisker they use to touch, they also move their nose, apply forces on the head-post and move adjacent whiskers and whiskers on the other side of the face. Additionally, our analysis shows that from day-to-day, this behavior can be surprisingly stereotyped, and that small changes in how far mice move a whisker during tactile behavior fundamentally changes the relationship between the movement of a single whisker and other facial movements.