The most sensitive inputs to cutaneous representing regions of primary somatosensory cortex do not change with behavioral training

Abstract

Learning a sensory detection task leads to an increased primary sensory cortex response to the detected stimulus, while learning a sensory discrimination task additionally leads to a decreased sensory cortex response to the distractor stimulus. Neural responses are scaled up, and down, in strength, along with concomitant changes in receptive field size. The present work considers neural response properties that are invariant to learning. Data are drawn from two animals that were trained to detect and discriminate spatially separate taps delivered to positions on the skin of their fingers. Each animal was implanted with electrodes positioned in area 3b, and responses were derived on a near daily basis over 84 days in animal 1 and 202 days in animal 2. Responses to taps delivered in the receptive field were quantitatively measured each day, and receptive fields were audiomanually mapped each day. In the subset of responses that had light cutaneous receptive fields, a preponderance of the days, the most sensitive region of the field was invariant to training. This skin region was present in the receptive field on all, or nearly all, occasions in which the receptive field was mapped, and this region constituted roughly half of the most sensitive region. These results suggest that maintaining the most sensitive inputs as dominant in cortical receptive fields provide a measure of stability that may be transformationally useful for minimizing reconstruction errors and perceptual constancy.

Keywords: Implant; map plasticity; receptive field; somatosensory.

Figure 1

An example site. Each graph shows the averaged neural responses from one cortical location in one day's recordings. Responses to three different amplitude taps are overlaid, and are shown for each of four different days. On the right, the contour of the most sensitive region of the receptive field on that day is shown.

Figure 2

(A) Receptive fields from one electrode. Contour lines over the hand trace the most sensitive skin inputs to one position in primary somatosensory cortex, 25 samples over 31 days. The heatmap net to each hand shows the probability of i different locations being present on any 1 day. Samples were from animal 1. (B) A similar set of plots from one location in animal 2, with 121 receptive fields over 202 days. (C) A third example, from animal 2, with 43 receptive fields over 146 days.

Figure 3

Center of mass movement. The lines joined by circles plot the movement of the x coordinate of the receptive field center of mass, while the lines joined by x plot the y coordinate. Each position is normalized with zero as the initial position, and 1 means the center of mass moved the mean receptive field range in that coordinate.

Figure 4

(A) Ratio of receptive fields’ intersection to union. Pairwise samples from single locations in animal 1 were used to calculate receptive field intersection to union ratios. Values averaged above 0.5 if pairs were sampled 1 day apart, and decreased for longer time differences. (B) Data from animal 2.