Brain mechanism underlying the recognition of hand gestures develops even when blind

Does a distinctive mechanism work in the brain of congenitally blind individuals when understanding and learning others’ gestures? Or does the same mechanism as with sighted individuals work? Japanese researchers figured out that activated brain regions of congenitally blind individuals and activated brain regions of sighted individuals share common regions when recognizing human hand gestures. They indicated that a region of the neural network that recognizes others’ hand gestures is formed in the same way even without visual information. The findings are discussed in The Journal of Neuroscience.

Our brain mechanism perceives human bodies from inanimate objects and shows a particular response. A part of a region of the “visual cortex” that processes visual information supports this mechanism. Since visual information is largely used in perception, this is reasonable, however, for perception using haptic information and also for the recognition of one’s own gestures, it has been recently learned that the same brain region is activated. It came to be considered that there is a mechanism that is formed regardless of the sensory modalities and recognizes human bodies.

Blind and sighted individuals participated in the study of the research group of Assistant Professor Ryo Kitada of the National Institute for Physiological Sciences, National Institutes of Natural Sciences. With their eyes closed, they were instructed to touch plastic casts of hands, teapots, and toy cars and identify the shape. As it turned out, sighted individuals and blind individuals could make an identification with the same accuracy. Through measuring the activated brain region using functional magnetic resonance imaging (fMRI), for plastic casts of hands and not for teapots or toy cars, the research group was able to pinpoint a common activated brain region regardless of visual experience. On another front, it also revealed a region showing signs of activity that is dependent on the duration of the visual experience and it was also learned that this region functions as a supplement when recognizing hand gestures.

As Assistant Professor Ryo Kitada notes, “Many individuals are active in many parts of the society even with the loss of their sight as a child. Developmental psychology has been advancing its doctrine based on sighted individuals. I wish this finding will help us grasp how blind individuals understand and learn about others and be seen as an important step in supporting the development of social skills for blind individuals.”

Why do we gesticulate?

If you rely on hand gestures to get your point across, you can thank fish for that! Scientists have found that the evolution of the control of speech and hand movements can be traced back to the same place in the brain, which could explain why we use hand gestures when we are speaking.

Professor Andrew Bass (Cornell University), who will be presenting his work at the meeting of the Society for Experimental Biology on the 3rd July, said: “We have traced the evolutionary origins of the behavioural coupling between speech and hand movement back to a developmental compartment in the brain of fishes.”

"Pectoral appendages (fins and forelimbs) are mainly used for locomotion. However, pectoral appendages also function in social communication for the purposes of making sounds that we simply refer to as non-vocal sonic signals, and for gestural signalling."

Studies of early development in fishes show that neural networks in the brain controlling the more complex vocal and pectoral mechanisms of social signalling among birds and mammals have their ancestral origins in a single compartment of the hindbrain in fishes. This begins to explain the ancestral origins of the neural basis for the close coupling between vocal and pectoral/gestural signalling that is observed among many vertebrate groups, including humans.

Professor Bass said: “Coupling of vocal and pectoral-gestural circuitry starts to get at the evolutionary origins of the coupling between vocalization (speech) and gestural signalling (hand movements). This is all part of the perhaps even larger story of language evolution.”