So, taking your idea of a turbo charged brain as acting similarly to a brain in an epileptic fit state, that is, receiving too many inputs, your classic interpretation of an epileptic fit is a frontal lobe seizure or overload. That's the strange twitching, postures, loss of voluntary muscle control etc.
Assuming that what you mean by the idea of turbocharging a brain and then the idea of damage left afterwards might follow a similar pattern, and using some very vague neuroscientific knowledge gained from my own head injury, here's what I think you might expect those people to feel afterwards.
Damage to the Frontal Lobe:
From Headway - the brain injury charity
- Changes in personality.
- Difficulties with attention and taking in information.
- Emotional responses may be reduced.
- Difficulties with motivation (Apathy) or getting things started
- Changes in the ability to control behaviour (Disinhibition). This
means that the person may be more impulsive. They may say or do
things without considering the consequences.
- Reduced self-awareness (Anosagnosia). Poor judgment and
- Difficulty planning things and meeting goals. ‘Black and white’
thinking (Concrete Thinking).
- Irritability and less tolerance of frustration.
The frontal lobe is also often indicated in dementia, and is the area that is severed in a lobotomy, giving rise to the idea of a zombified human. As the frontal lobe also controls voluntary movement, damage to this could damage your ability to make voluntary and purposeful movements, meaning you would possibly be able to catch or at least fend off the ball headed straight for your face, but not to pick it up and throw it back.
As your memories would be intact, you might have some awareness of the change in your personality and definitely an awareness of the change in your physical skill, which is distressing and frustrating.
Damage to the Temporal Lobe:
The temporal lobe contains the hippocampus, and is essentially the seat of memory.
Again, from Headway
- Difficulty in recognising faces, things or places.
- Difficulty understanding or remembering what people say.
- Difficulty reading.
- Difficulty recognising objects.
- Short-term memory difficulties.
- Changes in sexual behaviour.
- Increased aggression
I can offer the personal experience here after a really nasty head injury centred on my temporal lobe, that the effects of this are distressing. Acutely, I kept finding myself in places with no idea how i'd got there. I would get trapped on the sides of roads because the car headlights were too confusing to me to understand, I got absolutely furious with everyone around me because there were concepts that felt very important to communicate that I had absolutely no way of telling. Mine was mixed in with some temporal lobe damage so in addition to slurring the words I could remember, I also fell over a lot. Fun times!
Damage to the Parietal Lobes:
The parietal lobes are your sensing and touching lobes essentially, from Headway, once more.
- Difficulty naming objects (Anomia).
- Difficulty in distinguishing left from right.
- Difficulties with hand-eye coordination.
- Difficulty making sense of what we see even if we do not have a
visual impairment (Visual Perceptual difficulty).
- Difficulty knowing the function of an object.
- Problems with reading (Alexia), writing (Agraphia) or maths
- Difficulty knowing where things are in relation to our own bodies;
for example, how close an object is to us (Spatial Awareness
- Reduced self-awareness (Anosognosia).
- Visual Neglect.
Outside of the ordinary unpleasant symptoms of an injury or effect of something messing up your parietal lobes, this one I think has the propensity to be the most horrifying. The parietal lobes are sort of one major part of what tells you if something is going to be sharp or hot or dangerous or otherwise something to be avoided. Without that collision avoidance you can and would walk merrily into a big old rusty metal spike and not notice it was a bad thing until the pain arrived from your extremities. If there's any damage at all to that nerve function, suddenly you've got a massive wound you know nothing about until you happen to glance down.
Damage to the Occipital Lobe:
There's no helpful list for this one, but it controls your visual cortex primarily. Damage to the occipital lobe might make you blind, or might give you visual disturbances, or a bit of both. It could be partial blindness, and it's not the sort that can be fixed with glasses because there's nothing necessarily wrong in the eyes.
Damage to the Cerebellum:
Not strictly a lobe but as its in your picture i've included it.
Damage to the cerebellum affects your motor skills and balance, in cats with a condition called cerebellar hypoplasia, they have what's called a "drunken sailor" walk. (also available in other mammals).
Damage to the cerebellum could entail:
- loss of coordination of motor movement (asynergia)
- the inability to judge distance and when to stop (dysmetria)
- the inability to perform rapid alternating movements
- movement tremors (intention tremor)
- staggering, wide based walking (ataxic gait)
- tendency toward falling
- weak muscles (hypotonia)
- slurred speech (ataxic dysarthria)
- abnormal eye movements (nystagmus)
Based on those classifications for what happens when damage occurs to the lobe, you could reasonable construe those are the sorts of things that might happen when a demon took up residence in there. So in your example of a frontal lobe, a demon could potentially puppeteer the person whilst they remained aware of it, changing their personality but not their perceptions necessarily.
There's a reasonable argument to say that amount of time spent in residence successfully could be linked to electrical activity in those regions of the brain. Certainly there isn't, so far as we can currently tell, consistent blood flow and electrical activity to all areas of the brain all the time, but the brain is, incredibly difficult to study. You might argue that by dint of being smaller physically the smaller lobes get less blood flow and can thus generate less electricity and so would last a shorter time? But honestly it's an argument for which there is currently no right (scientifically backed) answer.