News Release: Research, School of Medicine
Feb. 11, 2009
Brain's Visual Cortex Tied to Tactile Discrimination in the Blind
Dr. Krish Sathian with a patientResearchers have found that in blind individuals, the brain’s visual cortex is engaged in tactile discrimination—unlike in the sighted.
The finding, recently published in the Journal of Vision, implies that the visual cortex in the blind does not lie fallow but is recruited for other tasks, such as tactile perception.
"The present study explored whether tactile sensory processing recruits visual cortical activity. The answer is definitely affirmative," says lead author Krish Sathian, MD, PhD, professor of neurology, rehabilitation medicine and psychology at Emory University, and medical director of the Atlanta Veterans Affairs Rehabilitation R&D Center of Excellence.
"Knowing this may help people design better tactile interfaces for the blind that capitalize on the abilities of the visual cortex. Such tactile interfaces include navigational and virtual reality devices," says Sathian.
Although blindness changes how the brain processes non-visual tasks, previous studies did not clearly indicate how purely perceptual tasks are processed, he says. The current study showed that the visual cortical regions in the blind interacted mainly with one another as well as with cortical regions that govern tactile sensation, according to Gopikrishna Deshpande, who conducted the connectivity analyses.
The researchers used functional magnetic resonance imaging (fMRI) to examine the neural processing underlying a task involving fine tactile discrimination versus a task involving tactile temporal discrimination.
The former task incorporated an embossed plastic three-dot pattern. The central dot was offset to the left or right by a variable distance. Participants were asked to determine whether the central dot was offset to the left or right. The latter task also involved a three-dot relief pattern but without an offset of the central dot. The pattern was applied to participants’ fingerpads; they indicated whether the contact duration was long or short.
The sensory processing in the tasks is analogous to that necessary for Braille reading.
"We were specifically interested in determining whether the relevant sensory processing, independent of linguistic or other cognitive factors, evoked activity in visual cortical areas and whether this differed as a function of the age at which subjects became blind. Thus, we explored the effect of the age of blindness and whether there were particular regions of the brain whose degree of activation predicted tactile spatial activity," says Randall Stilla, first author of the study.
The present study showed no significant acuity differences between early blind and late blind subjects, between use of the left and right hand, or between the Braille-reading or non Braille-reading hand. Interestingly, the level of activity in both somatosensory and visual cortex predicted individual acuity in the blind, whereas in the sighted an earlier study from the Sathian lab had shown such predictive activity in a different brain region, the posterior parietal cortex. This means that a lot of the circuitry underlying fine tactile perception is quite different between blind and sighted people.
"Although visual cortical activity is clearly involved in tactile perception, the underlying reasons for this remain uncertain, since such activity also characterizes a host of cognitive process including language processing, verbal memory and attention. There may be a common denominator underlying all these tasks, and if so, it’s most likely a high-level cognitive factor. This issue remains open for future research," says Sathian.
This work was supported by the National Institutes of Health and the Veterans Administration.
Reference: Stilla, R., Hanna, R., Hu, X., Mariola, E., Deshpande, G., and Sathian, K. (2008). Neural processing underlying tactile microspatial discrimination in the blind: A functional magnetic resonance imaging study. Journal of Vision, 8(10):13, 1-19, http://journalofvision.org/8/10/13/, doi:10.1167/8.10.13.
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