The computer in our heads[SATURDAY, MARCH 15, 2003 07:49:35 AM]
Life is an unending series of events. No wonder we are perplexed, surprised, shocked, delighted, pleased, saddened...It is all in the mind, we are told. All of this is controlled by the brain.
The brain is the most important part of animals and humans, though only humans can think, plan, speak, imagine, etc. Apart from carrying out vital jobs including breathing, the brain connects and directs all our organs. The brain, spinal cord and peripheral nerves make up a complex, integrated information processing and control system.
Modern science tells us that humans evolved from lower life forms by a process of natural selection from randomly occurring changes. The human brain seems to have evolved in three stages. Its oldest and primitive part is the innermost core or reptilian brain. We share it with all other animals, which have a backbone. This is called the pons and it controls body functions such as breathing and other vital activities that sustain life. At this level sexual and other behaviour is instinctive and our responses are automatic. The instincts include acquiring and defending territory by force and feeling that ‘Might is Right’. The spinal cord, the medulla and the pons form a system that constitutes nearly all of the brain of a fish or an amphibian.
At the next stage, as mammals evolved from reptiles, the mammalian brain evolved with the capability for new functions. It automatically controls functions such as digestion, maintains fluid balance, blood pressure, etc. It records new experiences as they occur and creates memories. This helps in recognition of danger and provides responses according to past experience. It generates some conscious feelings about events. As a result, mammals are more conscious of their relationship to the environment. The behaviour of mammals is less rigidly controlled by instincts. Feelings such as attachment, anger and fear emerged with associated behavioural response patterns of care, fight or flight.
The last part of the brain to evolve was the neocortex. It envelopes most of the earlier brain and amounts to about 85 per cent of the human brain mass. This is known as the grey matter. The brain is divided into two symmetrical hemispheres by a prominent groove. At the base of this groove lies the thick bundle of nerve fibres, which enable these two halves of the brain to communicate with each other. The left hemisphere usually controls movement and sensation in the right side of the body, while the right hemisphere controls the left side. It is the neocortex, which makes us behave like human beings. These three brains interact with each other resulting in human behaviour. The ability to organise speech and the ability to speak are predominantly localised in the left side of the brain. Appreciating spatial perceptions depends more on the right hemisphere. However, on receiving a stimulus, both hemispheres are activated and recognise the nature of visual stimuli as well as spoken words.