Abstract
Deafness leads to brain modifications that are generally associated with a cross-modal activity of the auditory cortex, particularly for visual stimulations. In the present study, we explore the cortical processing of biological motion that conveyed either non-communicative (pantomimes) or communicative (emblems) information, in early-deaf and hearing individuals, using fMRI analyses. Behaviorally, deaf individuals showed an advantage in detecting communicative gestures relative to hearing individuals. Deaf individuals also showed significantly greater activation in the superior temporal cortex (including the planum temporale and primary auditory cortex) than hearing individuals. The activation levels in this region were correlated with deaf individuals' response times. This study provides neural and behavioral evidence that cross-modal plasticity leads to functional advantages in the processing of biological motion following lifelong auditory deprivation.
Highlights
An increasing number of studies suggest that early sensory loss leads to the enhancement of the other intact sensory modalities [1]
Activation of the superior temporal gyrus (STG), including the primary auditory cortex and the planum temporale, has been observed across tasks requiring to recognize emblems, pantomimes, and meaningless gestures [14,34,37] despite the absence of behavioral differences in terms of accuracy or reaction time between deaf signers and hearing individuals. These findings suggest that lifelong deafness and/or sign language use could lead to alterations in the neural networks recruited to interpret manual communication, even when it is not linguistically structured
The results showed a significant difference in signal strength between the right and the left STG, both in the combined biological motion condition (Emblems + Pantomimes), (t (16) = -8.42, p < .0001 (Right: M ± SD = 2.31 ± 1.07; Left: M ± SD = 1.00 ± .91)) as well as in the emblems condition (t (16) = -5.31, p < .0001 (Right: M ± SD = 2.31 ± .99; Left: M ± SD = 1.22 ± .85))
Summary
An increasing number of studies suggest that early sensory loss leads to the enhancement of the other intact sensory modalities [1]. Several behavioral studies have shown that early-deaf people possess enhanced abilities for visual localization and visual motion detection [2]. According to functional neuroimaging studies, the visual enhancements in early-deaf individuals are generally attributed to the recruitment of the deafferented auditory cortex [3,4,5,6]. The visual crossmodal activity of the auditory cortex is typically defined as compensatory, meaning that deaf people rely more on their intact visual system to encode their environment in comparison to hearing individuals [7]. Some tactile [8,9,10,11] and language abilities (i.e., sign language and/or lip-reading) [12,13,14,15,16,17] are associated with the recruitment of the auditory cortex in deaf people [1] and support the compensatory reorganization of the brain after early auditory deprivation.
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