A vegetative state is caused when parts of the brain called the cerebral hemispheres are extensively damaged – but another part of the brain, called the brainstem, is undamaged or only partially damaged.
The cerebral hemispheres
The cerebral hemispheres are responsible for all the higher functions of the brain, such as:
- thought
- emotion
- memory
- comprehension
- perception
- purpose
- being aware of your surroundings
If the cerebral hemispheres suffer extensive damage then a person will lose all the functions listed above. They will be unable to think and have no sense of awareness and experience.
In addition, they will be unable to feel any pain or sensations such as hunger or thirst. However, due to the possibility that the condition may be misdiagnosed, a person who is in a vegetative state will never be subjected to any unnecessary pain and every effort will be made by the hospital to ensure that they are as comfortable as possible.
The brainstem
The reason that people in a vegetative state will still carry out some actions is because another part of the brain, called "the brainstem", is undamaged.
The brainstem is responsible for regulating most of the automatic functions of the body that are essential for life, such as:
- breathing
- heartbeat
- blood pressure
- swallowing
As the brainstem is still intact, a person who is in a vegetative state will have some basic, but random, physical movements and behaviour. For example, they may be able to:
- chew
- swallow
- grind their teeth
- make random eye movements
- make random limb movements
- make random facial movements, such as smiling or grimacing
- make grunting or moaning noises
The may have a normal pattern of sleeping and waking.
The brainstem also controls some basic automatic reflexes. This means that someone in a vegetative state will automatically react to some types of stimulation. For example:
- They may gag if something is placed in their throat.
- They may grip an object or another person hand if placed in their hand.
- Their pupils will widen if a light is shone into their eyes.
- They may blink or turn their head briefly if they hear a sudden, loud noise.
- They may grimace if they smell something unpleasant.
Read about how vegetative state is diagnosed.
