Congenitally Blind "Sight"

I recently read an article in PNAS about how sounds are processed in the brains of humans who are blind from birth (link).  Before this study, it was already known that the brains of people who are blind from birth process sounds in a fundamentally different way than that of sighted people.  In sighted people, a part of the brain known as the visual cortex deals with image processing.  Of course, in blind people, there are no images to process.  Studies have shown that this does not, however, mean that this region of the brain is inactive in congenitally blind people (people blind from birth).  The area has shown to be active instead in the processing of sound, in addition to the normal parts of the brain that deal with sound.  One may hypothesize that this additional activity forms the basis of improved sound perception in congenitally blind people, although such is speculation.

While it has been previously shown that the visual cortex processes sounds in the congenitally blind, this is not all too specific.  Different neural pathways go through the visual cortex.  Relevant to this paper are two pathways.  One is a "what" pathway that is involved in object recognition.  The other is a "where" pathway that is responsible for understanding the spacial relationships between objects.

This study picks up where others have left off, and attempts to determine which pathways are active for different sounds in congenitally blind people.  The authors manipulated the pitches and locations of sounds, carefully recording which pathways became active via fMRI.  The authors found that when pitch was varied, the "what" visual pathway became active.  Given that pitch is one of the descerning properties of sounds, and that the "what" visual pathway more generically analyzes the properties of objects, this result makes sense.  When the location of a given sound was varied, the "where" visual pathway became active.  This is also not a major cognitive leap; the location a sound came from is analogous to where an object is currently located in one's field of vision.

I find it fascinating that there is sufficient plasticity in the brain so that these two similar systems can be mapped so well.  For me, this study presents many more questions than answers.  For example, most of the brain's neuronal connections in the visual cortex are at their adult state by age 11.  This implies that if someone were to become blind after this age, then the brain could not rewire itself in such an elegant or effective way as seen in the congenitally blind.  It is assumed that such people would not be able to achieve better hearing, or at least hearing comparable to the congenitally blind.  It would also be interesting to see the opposite case - a congenitally blind human achieving sight after age 11.  In this case, the brain would have to rewire itself for vision, and it may not be capable of this.  Again, "may" is the operating word; actual studies would need to be conducted to verify such hypothesis.  The plasticity of the brain is fascinating, though it seems that the brain is somehow able to map to related systems when the primary system does not work.  On the same note, this study make it look like the brain attempts to achieve better utilization of existing inputs when some inputs are nonexistent.  Fascinating stuff!