Probability distributions of whisker–surface contact: quantifying elements of the rat vibrissotactile natural scene

Abstract

Analysis of natural scene statistics has been a powerful approach for understanding neural coding in the auditory and visual systems. In the field of somatosensation, it has been more challenging to quantify the natural tactile scene, in part because somatosensory signals are so tightly linked to the animal's movements. The present work takes a step towards quantifying the natural tactile scene for the rat vibrissal system by simulating rat whisking motions to systematically investigate the probabilities of whisker-object contact in naturalistic environments. The simulations permit an exhaustive search through the complete space of possible contact patterns, thereby allowing for the characterization of the patterns that would most likely occur during long sequences of natural exploratory behavior. We specifically quantified the probabilities of 'concomitant contact', that is, given that a particular whisker makes contact with a surface during a whisk, what is the probability that each of the other whiskers will also make contact with the surface during that whisk? Probabilities of concomitant contact were quantified in simulations that assumed increasingly naturalistic conditions: first, the space of all possible head poses; second, the space of behaviorally preferred head poses as measured experimentally; and third, common head poses in environments such as cages and burrows. As environments became more naturalistic, the probability distributions shifted from exhibiting a 'row-wise' structure to a more diagonal structure. Results also reveal that the rat appears to use motor strategies (e.g. head pitches) that generate contact patterns that are particularly well suited to extract information in the presence of uncertainty.

Spatiotemporal Patterns of Contact Across the Rat Vibrissal Array During Exploratory Behavior

“…For the results shown in Figure 6 , an anatomically accurate model of the rat head and vibrissal array was used to simulate vibrissal contact and detach patterns with a vertical wall (Knutsen et al, 2008 ; Towal et al, 2011 ). Whisking kinematics were governed by equations from Knutsen et al ( 2008 ), as in previous work (Hobbs et al, 2015 , in press ). Briefly, the simulated rat was placed in the same position and orientation as the rat in the behavioral video.…”

Whisking mechanics and active sensing

“…Second, studies on orienting behavior have shown that rats tend to position their heads so as to maximize the number of whiskers in contact with a surface, given the expected orientation of the surface [74,75]. The tendency to maximize the number of whisker-object contacts suggests that the integration of information across multiple whiskers will play an important role during contour extraction.…”

Whisker Vibrations and the Activity of Trigeminal Primary Afferents in Response to Airflow

“…For rodents, the whiskers (vibrissae) are a particularly important sensory modality, and the brain structures associated with the whiskers are correspondingly expanded (Woolsey and van der Loos, 1970;Welker and Woolsey, 1974). Although the rodent whisker system is a premier model for studying active touch (Knutsen et al, 2006;Kleinfeld and Deschênes, 2011;O'Connor et al, 2013;Maravall and Diamond, 2014;Hobbs et al, 2015;Chakrabarti and Schwarz, 2018), we still lack a full understanding of the stimuli that guided the evolution of vibrissaerelated neural structures.…”