Task-specific reorganization of the auditory cortex in deaf humans

Abstract

The principles that guide large-scale cortical reorganization remain unclear. In the blind, several visual regions preserve their task specificity; ventral visual areas, for example, become engaged in auditory and tactile object-recognition tasks. It remains open whether task-specific reorganization is unique to the visual cortex or, alternatively, whether this kind of plasticity is a general principle applying to other cortical areas. Auditory areas can become recruited for visual and tactile input in the deaf. Although nonhuman data suggest that this reorganization might be task specific, human evidence has been lacking. Here we enrolled 15 deaf and 15 hearing adults into an functional MRI experiment during which they discriminated between temporally complex sequences of stimuli (rhythms). Both deaf and hearing subjects performed the task visually, in the central visual field. In addition, hearing subjects performed the same task in the auditory modality. We found that the visual task robustly activated the auditory cortex in deaf subjects, peaking in the posterior–lateral part of high-level auditory areas. This activation pattern was strikingly similar to the pattern found in hearing subjects performing the auditory version of the task. Although performing the visual task in deaf subjects induced an increase in functional connectivity between the auditory cortex and the dorsal visual cortex, no such effect was found in hearing subjects. We conclude that in deaf humans the high-level auditory cortex switches its input modality from sound to vision but preserves its task-specific activation pattern independent of input modality. Task-specific reorganization thus might be a general principle that guides cortical plasticity in the brain.

Limitations of compensatory plasticity: the organization of the primary sensorimotor cortex in foot-using bilateral upper limb dysplasics

“…In these cases, the roles of association sensory cortex regions appear to be defined not by their commonly-driving sensory modality ("visual cortex"), but by their computational role. This was demonstrated in vision (17)(18)(19)(20)(21)(22)(23) for domain selectivity for complex perceptual and functional categories, such as objects, body parts and scenes (23) as well as for functional tasks such as spatial localization (22) and motion perception (24), and has been extended also to functional tasks for audition (25,26). Such selectivity is retained, albeit via different sensory inputs, even in the absence of original dominant sensory experience.…”

Functional selectivity for face processing in the temporal voice area of early deaf individuals

“…In humans, however, there is only limited evidence that specific nonauditory inputs are differentially localized to discrete portions of the auditory-deprived cortices. For example, Bola et al have recently reported, in deaf individuals, cross-modal activations for visual rhythm discrimination in the posterior-lateral and associative auditory regions that are recruited by auditory rhythm discrimination in hearing individuals (5). However, the observed cross-modal recruitment encompassed an extended portion of these temporal regions, which were found activated also by other visual and somatosensory stimuli and tasks in previous studies (2,3).…”

Whether the hearing brain hears it or the deaf brain sees it, it’s just the same

“…This proposition implies that following hearing loss, auditory areas switch their sensory modality but maintain a relation to its typical function. Following the same thread, another study recently published in PNAS by Bola et al (13) showed an analogous outcome. Using similar groups of deaf and hearing subjects, we explored how the deaf's auditory cortex processes rhythmic stimuli.…”

“…Overall, these two studies demonstrate that the high-level auditory cortex in the deaf switches its input modality from sound to vision but preserves its task-specific activation pattern independent of input modality (2,13). These findings mean that that task-specific reorganization is not limited to the visual cortex, but might be a general principle that guides cortical plasticity in the brain.…”

“…Impressive experiments, some of them involving reversible inactivation of auditory cortex with cooling loops, have shown that a distinct auditory area supports peripheral visual localization and visual motion detection in deaf cats, and that the same region supports these functions in the auditory modality in hearing cats (11,12). However, human evidence, in contrast, has been relatively scarce (13).…”