Preparatory Activity in Occipital Cortex in Early Blind Humans Predicts Auditory Perceptual Performance

Abstract

Early onset blindness leads to a dramatic alteration in the way the world is perceived, a change that is detectable in the organization of the brain. Several studies have confirmed that blindness leads to functional alterations in occipital cortices that normally serve visual functions. These reorganized brain regions respond to a variety of tasks and stimuli, but their specific functions are unclear. In sighted individuals, several studies have reported preparatory activity in retinotopic areas, which enhances perceptual sensitivity. "Baseline shifts," changes in activity associated with a cue predicting an upcoming event, provides a marker for attentional modulation. Here we demonstrate that, in early blind subjects, medial occipital areas produced significant blood oxygenation level-dependent (BOLD) responses to a cue signaling an auditory discrimination trial but not to a cue indicating a no-trial period. Furthermore, the amplitude of the BOLD response in the anterior calcarine sulcus of early blind subjects correlated with their discrimination performance on the auditory backward masking task. Preparatory BOLD responses also were present in auditory cortices, although they were more robust in blind than sighted control subjects. The pattern of response in visual areas is similar to preparatory effects observed during visual selective attention in sighted subjects and consistent with the hypothesis that the mechanisms implicated in visual attention continue to modulate occipital cortex in the early blind. A possible source of this top-down modulation may be the frontoparietal circuits that retain their connectivity with the reorganized occipital cortex and as a result influence processing of nonvisual stimuli in the blind.

Psychophysiology and Imaging of Visual Cortical Functions in the Blind: A Review

“…The authors proposed that the medial occipital area in the congenitally blind is recruited for the processing of auditory spatial targets but not during attentional orienting. This apparently contradicts the results of Stevens et al [47], who concluded that preparatory activation in the visual cortex during a cue was positively correlated with selective attention. However, the tasks for these two studies were quite different.…”

“…Stevens, Snodgrass, Schwartz, and Weaver [47] hypothesized that selective attention mechanisms in visual regions of sighted individuals become functionally capable of acting on the reorganized cross-sensory pathways in the blind. The authors presented sighted and early blind participants with an auditory cuing task designed to elicit attention-related responses in much the same way as visual cuing paradigms except via audition.…”

“…This review focuses on recent advances from studies conducted with both blind and sighted participants using imaging [4,6,10,12,21,30,34,35,42,43,47,[50][51][52][53], transcranial magnetic stimulation (TMS) [2,5,7,11,22,26,54,55], and electrophysiological research [1,16-20, 24,25,37-39,41,49]. Pascual-Leone and Hamilton [32] suggested that spatial processing is an implicit function of the visual system, which utilizes spatial information to perform pattern and discriminatory analyses on incoming information from other modalities, such as audition and somatosensation.…”

Corticocortical Connections Mediate Primary Visual Cortex Responses to Auditory Stimulation in the Blind

“…This would explain why resting-state studies (no attentional demands) failed to find coupling (Liu et al, 2007;Yu et al, 2008), whereas activation-based effective-connectivity studies did find enhanced coupling in the blind (Fujii et al, 2009;present study). This hypothesis is also backed by studies that found attentional modulations of visual cortex activity in the blind (Liotti et al, 1998;Stevens et al, 2007).…”

Functional specialization for auditory–spatial processing in the occipital cortex of congenitally blind humans

“…Several studies have reported that the occipital cortex of CB responds quite indifferently to a variety of cognitive tasks, suggesting that some common factors (i.e., attentional) rather than specific cognitive processes may contribute to the unselective occipital activity observed in this population (5)(6)(7)(8). In contrast, other studies do suggest that distinct regions of the visually deprived occipital cortex may show functional specialization that is to some extent comparable to what is known in SI (9).…”