1,721,095 research outputs found
When Outgoing and Incoming Signals Meet: New Insights from the Zona Incerta
No full textIn the sense of touch, it is the motion of the sensory receptors themselves that leads to an afferent signal—whether these receptors are in our fingertips sliding along a surface or a rat's whiskers palpating an object. Afferent signals can be correctly interpreted only if the sensory system receives information about the brain's own motor output. In this issue of Neuron, Urbain and Deschênes provide new insights into the physiological and anatomical interplay between tactile and motor signals in rats
Whisker sensory system–From receptor to decision
No full textOne of the great challenges of systems neuroscience is to understand how the neocortex transforms neuronal representations of the physical characteristics of sensory stimuli into the percepts which can guide the animal's decisions. Here we present progress made in understanding behavioral and neurophysiological aspects of a highly efficient sensory apparatus, the rat whisker system. Beginning with the 1970s discovery of “barrels” in the rat and mouse brain, one line of research has focused on unraveling the circuits that transmit information from the whiskers to the sensory cortex, together with the cellular mechanisms that underlie sensory responses. A second, more recent line of research has focused on tactile psychophysics, that is, quantification of the behavioral capacities supported by whisker sensation. The opportunity to join these two lines of investigation makes whisker-mediated sensation an exciting platform for the study of the neuronal bases of perception and decision-making. Even more appealing is the beginning-to-end prospective offered by this system: the inquiry can start at the level of the sensory receptor and conclude with the animal's choice. We argue that rats can switch between two modes of operation of the whisker sensory system: (1) generative mode and (2) receptive mode. In the generative mode, the rat moves its whiskers forward and backward to actively seek contact with objects and to palpate the object after initial contact. In the receptive mode, the rat immobilizes its whiskers to optimize the collection of signals from an object that is moving by its own power. We describe behavioral tasks that rats perform in these different modes. Next, we explore which neuronal codes in sensory cortex account for the rats’ discrimination capacities. Finally, we present hypotheses for mechanisms through which “downstream” brain regions may read out the activity of sensory cortex in order to extract the significance of sensory stimuli and, ultimately, to select the appropriate action
Spatial and temporal distribution of neural activity in rat barrel cortex and the coding of stimulus location
No full textWhisker vibration information carried by rat barrel cortex neurons
No full textRats can make extremely fine texture discriminations by "whisking" their vibrissa across the surface of an object. We have investigated one hypothesis for the neuronal basis of texture representation by measuring how clusters of neurons in the barrel cortex of anesthetized rats encode the kinetic features of sinusoidal whisker vibrations. Mutual information analyses of spike counts led to a number of findings. Information about vibration kinetics became available as early as 6 msec after stimulus onset and reached a peak at ∼20-30 msec. Vibration speed, proportional to the product of vibration amplitude (A) and frequency (f), was the kinetic property most reliably reported by cortical neurons. Indeed, by measuring information when the complete stimulus set was collapsed into feature-defined groups, we found that neurons reduced the dimensionality of the stimulus from two features (A, f) to a single feature, the product Af. Moreover, because different neurons encode stimuli in the same manner, information loss was negligible even when the activity of separate neuronal clusters was pooled. This suggests a decoding scheme whereby target neurons could capture all available information simply by summating the signals from separate barrel cortex neurons. These results indicate that neuronal population activity provides sufficient information to allow nearly perfect discrimination of two vibrations, based on their deflection speeds, within a time scale comparable with that of a single whisking motion across a surface
Functional principles of whisker-mediated touch perception
No full textIn the progression of events wherein the rodent whisker sensory system constructs a percept of the world around the animal, neurons exercise distinct functional roles; here we review recent progress in our understanding of the principles for response organization in the system. The whisker’s mechanical properties and anchoring to the follicle shape the forces transmitted to specialized receptors. The sensory and motor systems are intimately interconnected, giving rise to two forms of whisker-mediated sensation: generative and receptive. The sensory pathway exemplifies fundamental concepts in computation and coding: hierarchical feature selectivity, sparseness, adaptive representations, and population coding. The central processing of signals can be considered a sequence of filters. At the level of cortex, neurons represent object features by a coordinated population code which encompasses cells with heterogeneous properties
Active sensation: Insights from the rodent vibrissa sensorimotor system
No full textRats sweep their vibrissae through space to locate objects in their immediate environment. In essence, their view of the proximal world is generated through pliable hairs that tap and
palpate objects. The texture and shape of those objects must be discerned for the rat to assess the value of the object. Furthermore, the location of those objects must be specified with reference to the position of the rat’s head for the rat to plan its movements. Recent in vivo and in vitro electrophysiological
measurements provide insight into the algorithms and
mechanisms that underlie these behavioral-based
computations
Ipsilateral and contraletral transfer of tactile learning
No full textWe examined the spatial organization of perceptual learning in a cortex- dependent task. Rats learned a tactile task using four whiskers on one side of the snout, all others being clipped. These trained whiskers were then clipped and prosthetic whiskers were attached. Subsequent performance was found to be determined by the location of the prosthetic whiskers. There was partial transfer of learning to neighbouring whisker positions. In addition, there was partial transfer of learning to whisker positions on the other side of the snout, but only if the prosthetic whiskers were symmetrically opposite the trained whiskers. These findings suggest that neural changes underlying perceptual learning are distributed according to the topographic organization of the sensory cortical map. (C) 2000 Lippincott Williams and Wilkins
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