Self-Motion and the Shaping of Sensory Signals

Abstract

Sensory systems must form stable representations of the external environment in the presence of self-induced variations in sensory signals. It is also possible that the variations themselves may provide useful information about self-motion relative to the external environment. Rats have been shown to be capable of fine texture discrimination and object localization based on palpation by facial vibrissae, or whiskers, alone. During behavior, the facial vibrissae brush against objects and undergo deflection patterns that are influenced both by the surface features of the objects and by the animal's own motion. The extent to which behavioral variability shapes the sensory inputs to this pathway is unknown. Using high-resolution, high-speed videography of unconstrained rats running on a linear track, we measured several behavioral variables including running speed, distance to the track wall, and head angle, as well as the proximal vibrissa deflections while the distal portions of the vibrissae were in contact with periodic gratings. The measured deflections, which serve as the sensory input to this pathway, were strongly modulated both by the properties of the gratings and the trial-to-trial variations in head-motion and locomotion. Using presumed internal knowledge of locomotion and head-rotation, gratings were classified using short-duration trials (<150 ms) from high-frequency vibrissa motion, and the continuous trajectory of the animal's own motion through the track was decoded from the low frequency content. Together, these results suggest that rats have simultaneous access to low- and high-frequency information about their environment, which has been shown to be parsed into different processing streams that are likely important for accurate object localization and texture coding.

Encoding and Decoding Cortical Representations of Tactile Features in the Vibrissa System

“…Figure 1B shows an example of the high-velocity transient events experienced by a single vibrissa in a behavioral setting, where the vibrissa motion was tracked using high-speed videography while the animal traversed a linear track lined with periodic textures (Jenks et al, 2010). In this ethologically relevant context, however, high-velocity transients (dotted boxes) are embedded within a highly complex sensory pattern which precludes a simple analysis.…”

“…In an isolated set of non-invasive behavioral experiments in a previously published study (Jenks et al, 2010), adult female rats (Long-Evans; 250g; Charles River Laboratories, Inc., Wilmington, MA) were trained to run back and forth on a linear track. Briefly, we trimmed rows A, B, and E of the vibrissa array to facilitate imaging.…”

“…Figure 4A shows the instantaneous velocity of a single vibrissa in contact with a coarse texture (36 grit sandpaper), as measured through high speed videography (Jenks et al, 2010) – see Methods. The full distribution of instantaneous angular velocity is shown by the black curve in Figure 4B.…”

“…We have recently quantified the degree of variability in vibrissa deflection patterns when the vibrissa array is engaged with various surfaces during free locomotion (Jenks et al, 2010). Head and body movements create a significant amount of variability in the vibrissa deflection patterns for the same surfaces, primarily manifested in the timing and amplitude/velocity of vibrissa contacts.…”

Behavioral study of whisker-mediated vibration sensation in rats

“…barrel cortex | coding R ats use their whiskers to recognize the positions of floors, walls, and objects, particularly in dark surroundings (1)(2)(3)(4). Previous studies have characterized the efficacy of whisker-mediated touch in object localization (5,6), shape recognition (7,8), gap and aperture width detection (9,10), texture discrimination (11)(12)(13)(14), and vibration detection/discrimination (15,16).…”