Chewing gum and walking is not multi-tasking. They are using muscle memory for repetitive motions. The brain can use many different muscles at the same time. Muscle control is a very rudimentary brain function.

Athletes can train to use many different muscles at the same time. Same goes for musicians, especially piano players and such. These are also memorized movements. It is like learning to ride a bike. Once the brain has memorized the movements and synchronized them to balance inputs, the task is easy.

But, cognitive thought and even subconscious processing of stimuli such as tactile, auditory, visual, olfactory (smell) can fill up the brain's bandwidth, especially in a compromised brain.

I used to be able to drive, eat, and listen to the radio while looking at my map book to find a customer's house, and in San Jose's busy traffic. Now, if I am riding and my wife is driving, I need her to pull over, turn off the radio and maybe even the air conditioner if it is blowing loud just so I can read the map.

My brain could quickly switch between tasks, while ignoring muscle memory tasks like driving.

Recently published research has determined that the brain's effort to switch quickly between multiple tasks is detrimental to good brain health. Even the computer processor designers have discovered this same limitation. That is why they have developed multi-core/multi-processor computer CPU's.

The brain has a unique ability to allocate processing power between sensory systems. If vision is only using a small bandwidth, the brain can allow the extra bandwidth to be used by hearing or other sensory systems.

It is a zero sum game except for the injured brain where the sum is so much smaller that there is not enough to share between active senses. It is why closing your eyes and wearing ear plugs can improve cognitive abilities. The small sum remaining functional can almost all be allocated to the cognitive task at hand. Allowing that small bandwidth to be used without congestion or chaos helps it to slowly recover more bandwidth.

Enough bandwidth for tonight.

My best to you.