Biomedical subjects

Per Magne Knutsen

Publications and source records attributed to Per Magne Knutsen.

3 recordsLinked to original sources

PubMed2006

Haptic object localization in the vibrissal system: behavior and performance.

Using their large mystacial vibrissas, rats perform a variety of tasks, including localization and identification of objects. We report on the discriminatory thresholds and behavior of rats trained in a horizontal object localization task. Using an adaptive training procedure, rats learned to discriminate offsets in horizontal (anteroposterior) location with all, one row, or one arc of whiskers intact, but not when only a single whisker (C2) was intact on each cheek. However, rats initially trained with multiple whiskers typically improved when retested later with a single whisker intact. Individual rats reached localization thresholds as low as 0.24 mm (approximately 1 degree). Among the tested groups, localization acuity was finest (<1.5 mm) with rats that were initially trained with all whiskers and then trimmed to one arc of whiskers intact. Horizontal acuity was finer than the typical inter-vibrissal spacing (approximately 4.8 mm at contact points). Performance correlated with the net whisking spectral power in the range of 5-25 Hz but not in nonwhisking range of 30-50 Hz. Lesioning the facial motor nerves reduced performance to chance level. We conclude that horizontal object localization in the rat vibrissal system can reach hyperacuity level and is an active sensing process: whisker movements are both required and beneficiary, in a graded manner, for making accurate positional judgments.

Animals↗

PubMed2006

Active construction of percepts about object location.

Mammals acquire much of their sensory information by actively moving their sensory organs. Rats, in particular, scan their surrounding environment with their whiskers. This form of active sensing induces specific patterns of temporal encoding of sensory information, which are based on a conversion of space into time via sensor movement. We investigate the ways in which object location is encoded by the whiskers and decoded by the brain. We recorded from first-order neurons located in the trigeminal ganglion (TG) of anaesthetized rats during epochs of artificial whisking induced by electrical stimulation of the facial motor nerve. We found that TG neurons encode the three positional coordinates with different codes. The horizontal coordinate (along the backward-forward axis) is encoded by two encoding schemes, both relying on the firing times of one type of TG neuron, the 'contact cell'. The radial coordinate (from face outward) is encoded primarily by the firing magnitude of another type of TG neurons, the 'pressure cell'. The vertical coordinate (from ground up) is encoded by the identity of activated neurons. The decoding schemes of at least some of these sensory cues, our data suggest, are also active: cortical representations are generated by a thalamic comparison of cortical expectations with incoming sensory data.

Animals↗

PubMed2004

Tracking whisker and head movements in unrestrained behaving rodents.

Due to recent advances that enable real-time electrophysiological recordings in brains of awake behaving rodents, effective methods for analyzing the large amount of behavioral data thus generated, at millisecond resolution, are required. We describe a semiautomated, efficient method for accurate tracking of head and mystacial vibrissae (whisker) movements in freely moving rodents using high-speed video. By tracking the entire length of individual whiskers, we show how both location and shape of whiskers are relevant when describing the kinematics of whisker movements and whisker interactions with objects during a whisker-dependent task and exploratory behavior.

Animals↗