Cross modal plasticity
Cross modal plasticity is the adaptive reorganization of
Plasticity in the blind
Even though the blind are no longer able to see, the
For example, blind individuals show enhanced perceptual and attentional sensitivity for identification of different auditory stimuli, including speech sounds. The spatial detection of sound can be interrupted in the early blind by inducing a virtual lesion in the visual cortex using transcranial magnetic stimulation.[3]
The
Experience dependence
There is evidence that the degree of cross modal plasticity between the somatosensory and visual cortices is experience-dependent. In a study using tactile tongue devices to transmit spatial information, early blind individuals were able to show visual cortex activations after 1 week of training with the device.
Plasticity in the deaf
Cross modal plasticity can also occur in
Deaf individuals lack auditory input, so the auditory cortex is instead used to assist with visual and language processing. Auditory activations also appear to be attention-dependent in the deaf. However, the process of visual attention in the deaf is not significantly different from that of hearing subjects.[17] Stronger activations of the auditory cortex during visual observation occur when deaf individuals pay attention to a visual cue, and the activations are weaker if the cue is not in the direct line of sight.[18] One study found that deaf participants process peripheral visual stimuli more quickly than hearing subjects.[19] Deafness appears to heighten spatial attention to the peripheral visual field, but not the central one.[20] The brain thus seems to compensate for the auditory loss within its visual system by enhancing peripheral field attention resources; however, central visual resources may suffer.[21]
Improvements tend to be limited to areas in the brain dedicated to both auditory and visual stimuli, not simply rewriting audio-dedicated areas into visual areas. The visual enhancements seem to be especially focused in areas of the brain that normally process convergence with auditory input. This is specifically seen in studies showing changes in the posterior parietal cortex of deaf individuals, which is both one of the main centers for visual attention but also an area known for integrating information from various senses.[22]
Recent research indicates that in attention-based tasks such as object tracking and enumeration, deaf subjects perform no better than hearing subjects.
Sign language
Deaf individuals often use sign language as their mode of communication. However, sign language alone does not appear to significantly change brain organization. In fact, neuroimaging and electrophysiology data studying functional changes in visual pathways, as well as animal studies of sensory deprivation, have shown that the enhancement in attention of peripheral visual processing found in deaf individuals is not found in hearing signers.[26]
The peripheral visual changes are seen in all forms of deaf individuals – signers, oral communicators, etc.[27] Comparative fMRIs of hearing speakers and hearing early signers, on the other hand, show comparable peripheral activation. The enhancement in attention of peripheral visual processing found in deaf individuals has not been found in hearing signers. It is therefore unlikely that signing causes the neurological differences in visual attention.[28]
Cochlear implants
Another way to see cross modal plasticity in the deaf is when looking at the effects of installing
Plasticity after olfactory deficit or whisker trimming
Cross-modal plasticity can be mutually induced between two sensory modalities. For instance, the deprivation of olfactory function upregulate
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