Processing of vibrissa sensory information within the rat neocortex

Abstract

Neuronal response properties were compared among different layers of the urethan-anesthetized rat vibrissa cortex. Measurements were made of the receptive-field (RF) size, the degree of directional selectivity, the latency of driving, the velocity threshold, and the tuning-curve slope. The RF size was defined by the number of whiskers that, when deflected individually, activated a neurons. For the center whisker of the RF (usually whisker C3), the response to deflection in the most preferred direction was compared with that in the opposite direction to classify the neuron as either strongly directional, weakly directional, or nondirectional. For the most preferred direction of the center whisker, the minimum velocity of deflection required to drive the unit was defined as the velocity threshold, the latency of driven response to a standard supramaximal velocity was measured, and finally, using exponential ramp-and-hold deflection, the threshold amplitude was determined at different values of time constant to construct a tuning-curve slope. Cortical layer IV neurons, as a whole, have the lowest threshold velocity. Layer Vb neurons stand on the opposite extreme in having the highest mean velocity threshold value. Although this difference is consistent with the generally held view that the "barrels" in layer IV represent the input stage of cortical information processing, the lack of laminar differences in latency and RF size support the idea that neurons of other cortical layers also receive direct thalamocortical inputs. The population of cortical neurons thus appears quite homogeneous across different layers as far as the results of examination with short-pulsed stimulation are concerned. Correlation of pairs of parameters (RF, directionality, velocity threshold, and latency) was tested in the two layers (layer IV and layer Vb). The latency and velocity threshold are highly correlated within both layers. Also, most of correlation coefficients of the corresponding pairs of the two layers are similar. However, the use of exponential ramp-and-hold deflection of whiskers revealed a difference in tuning-curve slope between layer IV and layer Vb (also layers II-III); layer IV neurons show flatter tuning-curve slopes (more oriented for detection of the amplitude component of whisker deflection) than neurons of layer Vb and layers II-III, which are more oriented for velocity detection. During the hold phase of whisker deflection, layer IV neurons tend to show sustained discharges, whereas layer Vb (also layers II-III) neurons mainly exhibit transient responses.(ABSTRACT TRUNCATED AT 400 WORDS)

Synaptic Responses to Whisker Deflections in Rat Barrel Cortex as a Function of Cortical Layer and Stimulus Intensity

“…Therefore, although at all stimulus intensities Gr cells had the earliest and steepest response, the dV/dt of IGr cells was the most sensitive to changes in velocity-acceleration. This result is consistent with the high velocity thresholds reported for layer 5 neurons (Ito, 1985(Ito, , 1992.…”

“…In the rodent barrel system, neurons are exquisitely sensitive to velocity (Gibson and Welker, 1983;Ito, 1985;Shoykhet et al, 2000;Deschenes et al, 2003;Temereanca and Simons, 2003;Lee and Simons, 2004) and acceleration (Temereanca and Simons, 2003) at which the corresponding principal whisker in the mystacial pad is deflected. As rodents explore, their whiskers repetitively move back and forth at 5-15 Hz (Welker et al, 1964;Carvell and Simons, 1995;Berg and Kleinfeld, 2003) contacting surfaces and objects, causing small angular deflections at the base of the whiskers.…”

Functional neocortical microcircuitry demonstrated with intrinsic signal optical imaging in vitro

“…6,25 However, other studies have failed to find a difference in RF size in layer IV and have concluded that RF size is independent of the laminar location of the recorded neuron. 18 Interestingly, hourglass-shaped IOS patterns were observed in the present study following layer IV and V stimulation, but not following stimulation delivered at the layer VI/WM border, a location usually chosen for allowing the most physiological stimulation of cortex. The difference between functional hourglass and columnar patterns recorded in vivo could be due to differences in anesthetic or stimulus conditions among studies.…”

Spatiotemporal Characteristics of Neuronal Sensory Integration in the Barrel Cortex of the Rat

“…For example, a peak of supralinear summation was found in layers II/III (Shimegi et al 1999), and facilitatory interactions were also found in layer V (Ghazanfar and Nicolelis 1997). In parallel, anatomical data have confirmed the lack of intracortical horizontal connections between barrels in layer IV and their predominance in nongranular layers, where they could be the basis for multi-whisker integration (Gottlieb and Keller 1997;Ito 1985;Lübke et al 2000;Petersen and Sakmann 2000). These last observations, as well as electrophysiological recordings and optical imaging studies investigating functional circuitry (Goldreich et al 1999;Laaris and Keller 2002;Petersen and Sakmann 2001;, have contributed massively to the idea that barrels in layer IV function independently of one another, i.e., activity from one barrel does not spread directly to an adjacent barrel.…”