Spatiotemporal convergence and divergence in the rat S1 “Barrel” cortex

Abstract

The size and response magnitude of receptive fields were evaluated for cells in the rat cortical barrel-field by using standard vibrissal deflections of 1.14 degrees. Such stimuli fell within the plateau region of stimulus-response curves. The response of all neurones to all vibrissae within and surrounding centre-receptive fields were analysed for probability and latency of response. It was found that cells in supragranular layers had small centre-receptive fields (average 1.6 vibrissae) with small excitatory surrounds (1.5 vibrissae) while cells in the granular layers had small, powerful centre-receptive fields (1.4) with moderately large excitatory surrounds (2.6). Neurones in infragranular layers possessed large but weak centre-receptive fields (2.6) with large surrounds (3.5). Sixty-four neurones in layer IV were studied, the precise locations of which were identified by using dye lesioning and cytochrome oxidase staining. There were no differences in receptive field size for cells within septa and barrel hollows, but the latter were twice as likely to produce two or more spikes per stimulus from the principal vibrissa (65% against 33%). Histological analysis showed that the principal vibrissa was synonymous with the appropriate vibrissa for the barrel on 86% (55 of 64) of occasions. A quantitative analysis of convergent input to three neighbouring barrels (E1, E2, and D1) showed considerable graded overlap of receptive field surrounds, although facial hair adjacent to the mystacial pad only influenced cells on the edge of the barrel-field. Individual vibrissae exhibited significant divergent input to adjacent inappropriate barrels, being preferentially directed to distant septal rather than barrel hollow cells. An analysis of latencies showed that 40% of barrel hollow cells and 48% of barrel septal cells responded at short (less than 10 ms) latencies to their appropriate vibrissa. In contrast, responses to inappropriate vibrissae were overwhelmingly of long latency (10-greater than 30 ms), only 2% of inappropriate responses from barrel hollow cells and 13% from septal cells being of short latency. These results suggest that direct inputs largely project to appropriate barrels. The possibility that divergent inputs are generated by intracortical mechanisms is discussed.

The Functional Microarchitecture of the Mouse Barrel Cortex

“…Single-unit recordings from rat and mouse barrel cortex under various conditions have reported that single-whisker deflections evoke approximately one AP [26,27,30,67]. Recent studies using in vivo whole-cell or loose cell–attached recordings reported much lower levels of activity (0.14 AP per whisker deflection for L4 and 0.03 AP per whisker deflection for L2/3); many cells exhibit only subthreshold responses [12,32].…”

“…Cortical maps and the underlying circuits have been studied extensively in the barrel cortex of rodents [25], in which neurons in each cortical column are driven best by the column's principal whisker (PW), and more weakly by surrounding whiskers [26,27]. Neurons in layer (L) 4 are clustered in anatomical barrels, each corresponding to a particular PW.…”

“…Neurons in L5A receive strong input from posterior medial nucleus (POm, “paralemniscal” pathway) and project to L2 [29]. L2/3 cells are therefore key components in some of the earliest stages of intracortical processing [26,27,30–32] (for review, see [33]). L2/3 receptive fields are broader than L4 receptive fields.…”

“…Since L2/3 cells fire few (0–2) action potentials (APs) in response to whisker stimulation [26,27], we developed imaging and analysis methods to detect single APs in individual neurons. Superposed on a coarse map of whisker dominance, we find locally highly heterogeneous response properties.…”

Neocortical Layer 4 to Layer 2/3 Sensory Information Processing Investigated with Digital-Light-Projection Neuronal Photostimulation

“…However, L2/3 pyramidal cell spike firing in response to whisker stimulation is well documented (ie. [11,39,46,[132][133][134][135]), although with lower probabilities than that seen in L4 whisker-responsive cells. The authors of the modeling study acknowledge this discrepancy and suggest several possible solutions, one of which is the existence of spiking synchrony or temporal correlation in L4 which would drive L2/3 neurons with greater strength [52] as is the case with synchronously firing thalamic neurons driving L4 [136].…”