Brain damage

I wrote here a while ago about some aphasias, linguistic losses due to brain damage that say perhaps surprising things about the way the brain processes language. I’ve been reading about some other losses, not just around language, that again imply interesting things about the way the brain works. Some examples:

Ideomotor apraxia affects the ability to make movements, especially gestures and symbolic movements. Give someone with this condition a hammer and they may be able to make the proper movements, but ask them to demonstrate same without an actual hammer present, and they won’t be able to.

A huge part of the brain processes seeing. Damage to the area of the brain called V4 causes achromatopsia, loss of colour vision, but only on the side opposite to the hemisphere damaged – half of the world becomes B&W. If both sides are badly damaged, the patient loses the ability to even imagine colour.

Damage to the neighbouring V5 is even stranger and rather dangerous: one loses the ability to see motion, and the world jumps from one static state to another in a series of still images.

Damage to V1 can produce a scotoma, a patch of blindness – sufferers will not see anything in some area of their visual field, or at least not consciously – if asked to guess, they tend to be right about what’s there, and are astonished at their own accuracy.

There are a number of sorts of object agnosia, among them: form agnosia, where one can’t link the components into any image of a whole, seeing only a bunch of unconnected fragments – these people may not be able to orientate their hands consciously, for instance for grasping, but can do so unconsciously; simultagnosia, where individual objects can be identified, but not if put together where they overlap visually – such people find safe navigation through rooms easier if they close their eyes; prosopagnosia, where one cannot recognize faces, though one can still discern feelings (extra note: this is consciously – unconscious reactions to familar faces remain). (The flip side of this, the lack of the ability to recognise emotions, is at the root of psychopathy when absent from very early – you don’t see the effects of your emotion on others, so don’t take any account of same.)

Left spatial neglect, caused by damage to the right parietal lobe, is very odd: a sufferer may only dress the right side of their body and eat food only on the right of a plate. This isn’t a blindness, just ignoring the left side.

Damage to the right sensory cortex can cause paralysis of the left side, but this can come with a denial, an inability to remember, that there is a problem. There are a number of interesting effects of brain damage where the sufferer makes up bizarre explanations to account for strange behaviour.