Cross modal plasticity
Cross modal plasticity is a type of neuroplasticity and often occurs after sensory deprivation due to disease or brain damage.
Studies found that the volume of white matter (myelinated nerve connections) was reduced in the optic tract, but not in the primary visual cortex itself.
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.
Cross modal plasticity reworks the network structure of the brain, leading to increased connections between the somatosensory and visual cortices.
[5] With this cross-modal networking the early blind are able to react to tactile stimuli with greater speed and accuracy, as they have more neural pathways to work with.
The dorsal stream is used by the sighted to identify spatial information visually, but the early blind use it during tactile sensation of 3D objects.
Early or congenitally blind individuals have stronger cross modal connections the earlier they began learning Braille.
[8] An earlier start allows for stronger connections to form as early blind children have to grow up using their sense of touch to read instead of using their sight.
Perhaps due to these cross modal connections, sensory testing studies have shown that people who are born blind and read braille proficiently perceive through touch more rapidly than others.
In the case of auditory deprivation, some of these compensations appear to affect visual periphery processing and movement detection in peripheral vision.
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.
In terms of cellular mechanisms, the coordinated plasticity between cortical excitatory and inhibitory neurons is associated with these upregulations of sensory behaviors.
