Question: what does the brain look like when someone is deaf, blind or has synithsezia?

Rebecca Dewey answered on 18 Jun 2015:

It probably doesn’t look very different. The things that make someone deaf or blind usually aren’t happening in the brain, they happen in the ears or eyes. After a while the part of the brain that deals with sounds (called the auditory cortex) or vision (called the visual cortex) can change, so it can sometimes get smaller or lose its connections to other parts of the brain, but sometimes it doesn’t, and these changes are often not noticeable just by looking at an image of the brain.

What does change is which areas of the brain *use up oxygenMATOMO_URL So the imaging methods I use are based on measuring how much oxygen or blood or oxygenated blood is travelling to certain bits of the brain. In a hearing person, when the hear a sound, the auditory cortex starts using up oxygen and demands a greater supply of oxygenated blood. This doesn’t happen if the person is deaf. Likewise, in a sighted person, when they look a something, the visual cortex starts demanding more blood, and this doesn’t happen in a blind person.

During synaesthesia, there is a lot of extra communication between the two senses that are working together (vision and touch, or vision and sound, or sound and touch, or less commonly other combinations involving smell or taste). This could probably be detected by looking for areas of the brain that are working together a lot – I would expect to see the vision and touch areas demand more oxygenated blood at the same time as each other. This can be done by looking for correlations (mathematical similarities) between the oxygen flow to the two areas over time, and is called functional connectivity.