1,721,045 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
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
Erratum: Deciphering the spike train of a sensory neuron: Counts and temporal patterns in the rat whisker pathway (Journal of Neuroscience (September 6, 2006) (9216-9226))
No full textDemonstration of discrete place‐defined columns—segregates—in the cat SI
No full textThe SI forelimb area of cats was examined with receptive field (RF) mapping techniques. Arrays of closely spaced, near‐radial microelectrode penetrations were inserted into the crown of postsigmoid gyrus of ketamine anesthetized subjects and minimal RFs were obtained at several depths. The minimal RF was defined as the skin site providing the strongest input to each recorded cluster of neurons. Data analysis showed that all studied cortical territories contained groups of discrete cortical columns, 300–400 μm in diameter. The columns were regarded as topographic entities because no change in minimal RF location could be observed within their boundaries. The boundaries of columns were sharp and could be unequivocally distinguished because the minimal RFs sampled on opposite sides of a boundary occupied displaced, nonoverlapping positions. Pair‐wise comparison of single neuron maximal RFs (defined as the entire skin area providing input to the recorded neuron) further clarified the nature of the SI place‐defined columns: (1) no systematic differences in maximal RF position could be demonstrated for different parts of the same column (even though the maximal RFs in most columns varied extensively in size and skin areas covered), and (2) at the boundary between neighboring columns maximal RFs shifted en masse to center on a new skin locus. These minimal and maximal RF observations strongly support our recent proposal that body surface is represented in SI by a honeycomblike mosaic of discrete place‐defined cortical columns, segregates. Copyright © 1990 Wiley‐Liss, Inc
Information carried by population spike times in the whisker sensory cortex can be decoded without knowledge of stimulus time
Full text linkComputational analyses have revealed that precisely timed spikes emitted by somatosensory cortical neuronal populations encode basic stimulus features in the rat’s whisker sensory system. Efficient spike time based decoding schemes both for the spatial location of a stimulus and for the kinetic features of complex whisker movements have been defined. To date, these decoding schemes have been based upon spike times referenced to an external temporal frame – the time of the stimulus itself. Such schemes are limited by the requirement of precise knowledge of the stimulus time signal, and it is not clear whether stimulus times are known to rats making sensory judgments. Here, we first review studies of the information obtained from spike timing referenced to the stimulus time. Then we explore new methods for extracting spike train information independently of any external temporal reference frame. These proposed methods are based on the detection of stimulus-dependent differences in the firing time within a neuronal population. We apply them to a data set using single-whisker stimulation in anesthetized rats and find that stimulus site can be decoded based on the millisecond-range relative differences in spike times even without knowledge of stimulus time. If spike counts alone are measured over tens or hundreds of milliseconds rather than milliseconds, such decoders are much less effective. These results suggest that decoding schemes based on millisecond-precise spike times are likely to subserve robust and information-rich transmission of information in the somatosensory system
Response to: Ritt et al., “Embodied Information Processing: Vibrissa Mechanics and Texture Features Shape Micromotions in Actively Sensing Rats.” Neuron 57, 599–613
No full textDynamic synaptic modification threshold: computational model of experience-dependent plasticity in adult rat barrel cortex
No full textPrevious electrophysiological experiments have documented the response of neurons in the adult rat somatic sensory ('barrel') cortex to whisker movement after normal experience and after periods of experience with all but two whiskers trimmed close to the face (whisker 'pairing'). To better understand how the barrel cortex adapts to changes in the flow of sensory activity, we have developed a computational model of a single representative barrel cell based on the Bienenstock, Cooper, and Munro (BCM) theory of synaptic plasticity. The hallmark of the BCM theory is the dynamic synaptic modification threshold, θ(M), which dictates whether a neuron's activity at any given instant will lead to strengthening or weakening of the synapses impinging on it. The threshold θ(M) is proportional to the neuron'sactivity averaged over some recent past. Whisker pairing was simulated by setting input activities of the cell to the noise level, except for two inputs that represented untrimmed whiskers. Initially low levels of cell activity, resulting from whisker trimming, led to low values for θ(M). As certain synaptic weights potentiated, due to the activity of the paired inputs, the values of θ(M) increased and after some time their mean reached an asymptotic value. This saturation of θ(M) led to the depression of some inputs that were originally potentiated. The changes in cell response generated by the model replicated those observed in in vivo experiments. Previously, the BCM theory has explained salient features of developmental experience-dependent plasticity in kitten visual cortex. Our results suggest that the idea of a dynamic synaptic modification threshold, θ(M), is general enough to explain plasticity in different species, in different sensory systems, and at different stages of brain maturity
Experience-dependent plasticity of rat barrel cortex: Redistribution of activity across barrel-columns
No full textThe redistribution of neuronal activity across rat barrel cortex following an alteration in whisker usage has been investigated. In adult rats, two mystacial vibrissae - D2 and one neighbor, D1 or D3 were left intact while all other vibrissae on that side of the snout were clipped. Neurons in contralateral barrel cortex were sampled with a microelectrode array 3.5 days later. Stimulation of clipped vibrissae produced a narrow spatial distribution of cortical activity, whereas stimulation of intact vibrissae produced a widened spatial distribution. Simultaneous recordings from multiple cortical barrel-columns suggest that changes in the effective connectivity between barrel-columns may partially account for this redistribution of sensory responses. Evidence is also presented for a second mechanism, a release from inhibition in sensory-deprived cortical areas. A model is therefore proposed where these two mechanisms operate together to regulate the cortical distribution of evoked activity
The role of individual spikes and spike patterns in population coding of stimulus location in rat somatosensory cortex
No full textThis report addresses the nature of population coding in sensory cortex by applying information theoretic analysis to data recorded simultaneously from neuron pairs located in primary somatosensory cortex of anaesthetised rats. We studied how cortical spike trains code for the location of a whisker stimulus on the rat's snout. We found that substantially more information was conveyed by 10 ms precision spike timing compared with that conveyed by the number of spikes counted over a 40 ms response interval. Most of this information was accounted for by the timing of individual spikes. In particular, it was the first post-stimulus spikes that were crucial. Spike patterns within individual cells played a smaller role; spike patterns across cells were negligible. This pattern of results was robust both to the exact nature of the stimulus set and to the precision at which spikes were binned. © 2002 Elsevier Science Ireland Ltd. All rights reserved
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