Functional connectivity between somatosensory and visual cortex in early blind humans

Area of Science:

• Neuroscience
• Sensory processing

Background:

• Crossmodal plasticity involves sensory system reorganization after sensory loss.
• In congenital blindness, the visual cortex responds to somatosensory input, like Braille reading.
• The neural pathways for this crossmodal processing are not fully understood.

Purpose of the Study:

• To investigate the cortico-cortical pathways connecting the somatosensory cortex to the visual cortex in humans.
• To determine if these pathways are utilized differently in early versus late blindness.

Main Methods:

• Used repetitive transcranial magnetic stimulation (rTMS) over the primary somatosensory cortex (S1).
• Combined rTMS with positron emission tomography (PET) to measure regional cerebral blood flow.
• Studied sighted controls, individuals with early-onset blindness, and individuals with late-onset blindness.

Main Results:

• Regional cerebral blood flow in the occipital cortex was highest in early blind and lowest in late blind individuals.
• Only the early blind group exhibited significant activation in early visual areas (V1) when S1 was stimulated.
• This activation was significantly greater in early blind compared to late blind individuals.

Conclusions:

• Findings support the hypothesis that tactile information reaches early visual areas in early blind individuals via cortico-cortical pathways.
• This pathway may underlie enhanced tactile processing and Braille reading abilities in the early blind.
• The degree of crossmodal plasticity in the visual cortex is dependent on the age of blindness onset.