The human brain is the highest point attained by evolution of matter. Physically it weighs about 1.5 kilograms, which is heavier than most human organs. Its surface is wrinkled like a walnut and has a colour and consistence resembling cold porridge. It is, however, extremely complex biologically. It contains a vast number of cells (neurons), possibly numbering 100 billion in total. But even this is dwarfed when we discover that each neuron is embedded in a mass of smaller cells called glia, which serves to support the neurons.

The brain is largely composed of the cerebrum, which is divided into two equal parts. The surface area is known as the cortex. The size of the cortex distinguishes humans from all other organisms. The cerebrum is split into regions or lobes, which correspond roughly to particular body functions and in processing sensory information. Behind the cerebrum lies the cerebellum, which supervises all the tiny muscular movements of the body. Below these parts is a thick stalk or brain stem, which is the continuation of the spinal cord. This carries the nerve fibres from the brain through the spinal cord and throughout the body’s nervous system, bringing everything into communication with the brain.

The increased brain size, which decisively sets humans apart from other animals, is mainly accounted for by the enlargement of the thin outer layer of nerve cells known as the neocortex. However, this expansion did not take place uniformly. The frontal lobes, associated with planning and foresight, expanded much more than the rest. The same is true of the cerebellum, at the rear part of the skull, which is associated with the ability to acquire automatic skills, a host of everyday actions which we perform without thinking, such as riding a bike, changing gear while driving or doing up pyjama buttons.

The brain itself contains a circulatory system that brings nutrients to regions distant from a blood supply. It receives a large proportion of blood, which carries vital oxygen and glucose. Although the adult brain makes up only 2 per cent of body weight, its oxygen consumption is 20 per cent of the total – and as much as 50 per cent in an infant. Twenty per cent of the body’s glucose consumption occurs in the brain. Fully one fifth of the blood pumped by the heart passes through the brain. The nerves transmit information electrically. The signal that passes down a nerve does so as a wave of electricity; a pulse which passes from the cell body to the end of the nerve fibre. So the language of the brain is composed of electrical impulses, not only the amount but the frequency. “The information upon which such predictions are based,” writes Rose, “depends on the arrival of data at the body surface in terms of light and sound of varying wavelengths and intensities, fluctuations in temperature, pressure on particular points of the skin, concentration of certain chemical substances which are detected by nose or tongue. Within the body this data is transformed into a series of electrical signals passing along particular nerves to the central brain regions where the signals interact with one another producing certain types of response.”

The neuron is composed of a whole number of properties (dendrites, cell body, axon, synapses), which carry out this relay of information (messages arrive at the synapses from the axon). In other words, the neuron is the unit of the brain system. Thousands of motor neurons are involved in any coordinated muscular action. More complex actions will involve millions – though even a million represents only about 0.01 per cent of the total available in the human cortex. But the brain cannot be understood as an assemblage of separate parts. While analysis of the detailed make up of the brain is vital, Rose explains it can only go so far.

There are many levels at which one can describe the behaviour of the brain. One can describe the quantum structure of atoms, or the molecular properties of the chemicals which compose it; the electron-micrographic appearance of the individual cells within it; the behaviour of its neurons as an interacting system; the evolutionary or developmental history of these neurons as a changing pattern in time; the behavioural response of the individual human whose brain is under discussion; the familial or social environment of that human, and so on.[55]

In order to understand the brain, it is necessary to grasp the complex dialectical interrelations of all its parts. It is necessary to bring together a whole host of sciences: ethology, psychology, physiology, pharmacology, biochemistry, molecular biology, and even cybernetics and mathematics.

  1. Rose, S. The Conscious Brain, p. 28.