Tactile Object Familiarity in the Blind Brain Reveals the Supramodal Perceptual-Mnemonic Nature of the Perirhinal Cortex

Abstract

This study is the first to investigate the neural underpinnings of tactile object familiarity in the blind during both perception and memory. In the sighted, the perirhinal cortex (PRC) has been implicated in the assessment of visual object familiarity-a crucial everyday task-as evidenced by reduced activation when an object becomes familiar. Here, to examine the PRC's role in tactile object familiarity in the absence of vision, we trained blind participants on a unique memory-guided drawing technique and measured brain activity while they perceptually explored raised-line drawings, drew them from tactile memory, and scribbled (control). Functional magnetic resonance imaging (fMRI) before and after a week of training revealed a significant decrease in PRC activation from pre- to post-training (i.e., from unfamiliar to familiar) during perceptual exploration as well as memory-guided drawing, but not scribbling. This familiarity-based reduction is the first evidence that the PRC represents tactile object familiarity in the blind. Furthermore, the finding of this effect during both tactile perception and tactile memory provides the critical link in establishing the PRC as a structure whose representations are supramodal for both perception and memory.

Keywords: blindness; familiarity; perirhinal cortex; tactile memory; tactile perception.

FIGURE 1

The experimental functional magnetic resonance imaging (fMRI) design, stimuli, and setup. (A) Three-task blocked experimental design, repeated twelve times (twice per stimulus). Auditory cues signaled the beginning of each block. (B) Raised line-drawing stimuli. (C) A participant operating our multimodal MRI-compatible drawing device. PE, Perceptual Exploration; MD, Memory Drawing; S, Scribble.

FIGURE 2

Hand-drawn medial temporal lobe regions of interest (ROIs) in the left hemisphere (LH) in one participant. The collateral sulcus (CS) is shown in the other hemisphere as a point of reference. PRC, perirhinal cortex; ERC, entorhinal cortex.

FIGURE 3

Representative examples of pre- and post-training drawings. Note the substantial improvement from pre-training (middle column) to post-training (last column) in resembling the original stimulus (first column) after just 5 days of the Cognitive-Kinesthetic training.

FIGURE 4

Functional magnetic resonance imaging results. ROI analysis results for pre- and post-training are shown (A) separated by hemisphere and (B) collapsed across hemisphere. Error bars represented standard error of the mean of the difference scores (post-pre). (C) Pre-training > post-training difference z-score map in one participant (#2), with the PRC ROI outlined in blue. PRC, perirhinal cortex; PE, Perceptual Exploration; MD, Memory Drawing; S, Scribble; ^∗p < 0.05, ˆp < 0.10.