1,721,011 research outputs found
Spatial and temporal distribution of neural activity in rat barrel cortex and the coding of stimulus location
No full textActive 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
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
Enhanced response of neurons in rat somatosensory cortex to stimuli containing temporal noise
No full textWhisker 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
Whisker 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
Vibrissal texture decoding
No full textTexture is a central component of touch. To learn how contact with a surface gives rise to a sensation of texture, many laboratories have examined the vibrissae system of rodents—a highly efficient sensory system with well-studied structural organization [by Kleinfeld et al. (Current Opinion in Neurobiology 16(4): 435–444, 2006)]. Vibrissal texture decoding summarizes current knowledge about how whisking on surfaces leads to texture sensation. The vibrissae system of rats presents a unique opportunity for investigating how sensory receptors generate signals through their interaction with the environment, and how the brain reads and interprets the afferent signals
Behavioral study of whisker-mediated vibration sensation in rats
No full textRats use their vibrissal sensory system to collect information about the nearby environment. They can accurately and rapidly identify object location, shape, and surface texture. Which features of whisker motion does the sensory system extract to construct
sensations? We addressed this question by training rats to make discriminations between sinusoidal vibrations simultaneously presented to the left and right whiskers. One set of rats learned to
reliably identify which of two vibrations had higher frequency (f1 vs. f2) when amplitudes were equal. Another set of rats learned to
reliably identify which of two vibrations had higher amplitude (A1 vs. A2) when frequencies were equal. Although these results indicate that both elemental features contribute to the rats’ sensation, a further test found that the capacity to discriminate A and f
was reduced to chance when the difference in one feature was counterbalanced by the difference in the other feature: Rats could
not discriminate amplitude or frequency whenever A1f1 = A2f2. Thus, vibrations were sensed as the product Af rather than as separable elemental features, A and f. The product Af is propor-
tional to a physical entity, the mean speed. Analysis of performance revealed that rats extracted more information about
differences in Af than predicted by the sum of the information in elemental differences. These behavioral experiments support the predictions of earlier physiological studies by demonstrating that rats are “blind” to the elemental features present in a sinusoidal whisker vibration; instead, they perceive a composite feature, the speed of whisker motion
Whisking and whisker kinematics during a texture classification task
No full textRats explore objects by rhythmically whisking with their vibrissae. The goal of the present study is to learn more about the motor output used by rats to acquire texture information as well as the whisker motion evoked by texture contact. We trained four rats to discriminate between different grooved textures and used high-speed video to characterize whisker motion during the task. The variance in whisking parameters among subjects was notable. After whisker trimming, the animals changed their behaviour in ways that appear consistent with an optimization of whisker movement to compensate for lost information. These results lead to the intriguing notion that the rats use an information-seeking 'cognitive' motor strategy, instead of a rigid motor programme. Distinct stick/slip events occurred during texture palpation and their frequency increased in relation to the spatial frequency of the grooves. The results allow a preliminary assessment of three candidate texture-coding mechanisms-the number of grooves encountered during each touch, the temporal difference between groove contacts and the spatial pattern of groove contacts across the whiskers
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