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.

Multiple sclerosis (MS) pathology can cause disruptions in central auditory processing. Here, we applied quantitative magnetic resonance imaging (MRI) techniques to investigate the impact of global neurodegenerative processes on dichotic listening performance in MS. We studied 28 subjects with clinically definite MS and 26 healthy controls using 3T MRI and a dichotic digits task (DDT) performed in the scanner. Subjects with MS displayed increased white matter lesions, prolonged water proton longitudinal relaxation time constants in normal appearing white matter, reduced gray matter volumes, and reduced corpus callosum areas compared with controls. No group differences were found for any of the DDT performance measures. In subjects with MS, corpus callosum area was strongly correlated with DDT performance. This relationship remained present after controlling for other measures of neuropathology, suggesting that callosal atrophy directly impacts dichotic listening performance in MS.