Sat. Feb 4th, 2023

De afbeelding toont een multimodale menselijke corticale verkaveling van 180 gebieden op de oppervlakken van de linker- en rechterhersenhelft.  Kleuren geven aan in hoeverre de gebieden in rust geassocieerd zijn met auditief (rood), gevoel (groen), visueel (blauw).  (De hersenen, <a href=never ceases to amaze us.)”/>

The image shows a multimodal human cortical parcellation of 180 regions on the surfaces of the left and right hemispheres. Colors indicate to what extent the areas at rest are associated with auditory (red), sensation (green), visual (blue). (The brain never ceases to amaze us.)

The brain can reorganize itself in the event of a traumatic injury or sensory impairment. For example, in deaf mammals, the brain’s auditory processing neurons can be rewired to process other stimuli. But we haven’t been able to find out if this reorganization is task specific – will the circuits be recruited to perform the same tasks? – or more generally.

A recent study published in PNAS suggests that in at least one case these brain circuits are being reused for a similar task. When deaf people were asked to interpret visual rhythms (represented by a flashing light), they used the same auditory processing areas listen rhythms were activated.

This study used fMRI to look at brain activation in both congenitally deaf subjects and people with normal hearing. While inside the fMRI machine, all subjects were asked to differentiate between different rhythms of flashing lights. As a control, all subjects were also asked to look at a light that flashed in a regular, predictable pattern. Hearing subjects were then asked to also distinguish between different auditory rhythms. As a control, these subjects were asked to listen to a similar sound that occurred in a regular, consistent pattern.

The brain scans showed that in deaf subjects, the auditory cortex was activated when looking at rhythmic patterns of flashing lights (as were parts of the visual processing system). In contrast, hearing subjects had activity in the same parts of the visual processing system, but the auditory cortex was not engaged. For hearing subjects, the auditory cortex was not activated until they completed the audible version of this task.

A more robust analysis of the region of interest looked very closely at each voxel (a small 3D pixel). This showed that visual rhythms induced significant activity in the highest processing levels of the auditory cortex for these deaf subjects. In fact, the deaf subjects’ responses to the visual rhythms most closely matched the hearing subjects’ responses to the auditory rhythms. The authors zoomed in and looked at peak activity in the auditory cortex of both groups of subjects. They found very close overlap in peak activation for hearing and deaf subjects, even though the deaf subjects watched the rhythms and the hearing subjects listened to them.

To test whether these results were consistent between deaf subjects, the authors also compared the brain scans of several deaf participants. They found that 80 percent of the auditory cortex activation triggered by visual rhythms overlapped in deaf participants. This highly similar activation within the group was only seen in hearing subjects in response to the auditory stimuli. (In other words, it was not seen in the visual cortex).

In general, the neural responses of the deaf subjects to the visual rhythmic stimuli closely mirrored the neural responses of the hearing subjects to the auditory visual stimuli. These findings are important because although we know that the brain is capable of reorganizing itself, we don’t know what principles govern this reorganization. Here the authors show that the exact same regions that enable hearing people to interpret auditory rhythms are used by deaf people to interpret visual rhythms.

This suggests that brain rewiring can directly assign similar tasks to specific functional units in the brain. While more research is needed, this study adds to our overall understanding of neural rewiring.

PNAS2017. DOI: 10.1073/pnas.1609000114 (About DOIs)

By akfire1

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