Abstract
Understanding the mechanisms by which sensory experiences are stored remains a compelling challenge for neuroscience. Previous work has described how the activity of neurons in the sensory cortex allows rats to discriminate the physical features of an object contacted with their whiskers. But to date there is no evidence about how neurons represent the behavioural significance of tactile stimuli, or how they are encoded in memory. To investigate these issues, we recorded single-unit firing and local field potentials from the CA1 region of hippocampus while rats performed a task in which tactile stimuli specified reward location. On each trial the rat touched a textured plate with its whiskers, and then turned towards the Left or Right water spout. Two textures were associated with each reward location. To determine the influence of the rat's position on sensory coding, we placed it on a second platform in the same room where it performed the identical texture discrimination task. Over 25 percent of the sampled neurons encoded texture identity – their firing differed for two stimuli associated with the same reward location – and over 50 percent of neurons encoded the reward location with which the stimuli were associated. The neuronal population carried texture and reward location signals continuously, from the moment of stimulus contact until the end of reward collection. The set of neurons discriminating between one texture pair was found to be independent of, and partially overlapping, the set of neurons encoding the discrimination between a different texture pair. In a given neuron, the presence of a tactile signal was uncorrelated with the presence, magnitude, or timing of reward location signals. These experiments indicate that neurons in CA1 form a texture representation independently of the action the stimulus is associated with and retain the stimulus representation through reward collection.
Highlights
Whisker-mediated tactile perception in rats has been the object of intense investigation[1,2,3,4,5,6,7,8,9]
In spite of progress in understanding the coding of physical features, little is known about how tactile events are encoded in memory and how neurons represent the meaning of tactile stimuli in the context of behavior
Touch-guided Behavior This study set out to identify how neurons in rat hippocampus represent tactile stimuli and the behavior associated with those stimuli
Summary
Whisker-mediated tactile perception in rats has been the object of intense investigation[1,2,3,4,5,6,7,8,9]. In spite of progress in understanding the coding of physical features, little is known about how tactile events are encoded in memory and how neurons represent the meaning of tactile stimuli in the context of behavior. To address these issues, we have investigated the CA1 region of hippocampus. We isolated tactile signals by presenting 3 or 4 textures, 2 of which were associated with one reward location; because two stimuli were always associated with the identical action and reward location, any difference in activity must reflect the coding of touch rather than some aspect of explicit behavior
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