Greenfield's theory of consciousness

Professor Susan Greenfield of the University of Oxford is a noted scientist with an interest in the problem of consciousness. She has proposed that the mind may arise from the activity of brain cells at the level where the cells are connected together (the synapse). Rather than arising from a single isolated region of the brain, she suggests that consciousness arises diffusely from the brain cell connections.

The reasoning, Greenfield argues, is that there is no single complete function that takes place in one region of the brain. It is known, for example, that vision is divided up into many separate components that are connected together to give rise to the conscious experience of seeing, such as colour, motion and form processing, and the function of vision can preoccupy over 30 brain regions. Similarly, any one brain region can participate in more than one function. So brain regions are smaller parts of a wider brain stage and not units that work alone. Thus we know that conscious experience arises from the actions of many different parts at the same time. However, when we break each area of the brain down into its smaller constituents, each area is a complex circuit which is ultimately reduced down to the connections between the cells, or synapses, or in other words the individual wires of the circuits themselves across which electrical signals are passed. This signalling is dependent on a series of different biological products, or proteins, which are themselves products of genes. Therefore, Professor Greenfield has proposed that the neural correlate and in effect the physical substrate of the 'mind' is a process that occurs at the level of the brain connections, or synapses, which are not only highly dynamic but also reflect experience through their strength and extension of connections. She has not been able to propose how actions at the level of the brain cell connections lead to conscious experience. Nevertheless, she also proposes that it is this process, whereby connections so exquisitely mirror what happens to us, which leads to the 'mind'.

According to this theory, consciousness, or our sense of self-awareness, is thought to arise from the interaction of assemblies of neurones involving up to tens of millions of neurones all connected together. It is proposed that at any one time there may be many neuronal assemblies present; however, the largest assembly will dominate and determine that moment of consciousness.

The degree to which cells are recruited and hence the degree of consciousness will be determined by a variety of factors, such as the strength of the input coming into the brain, for example from the eyes and the fingers, as well as pre-existing connections and the degree of competition, as shown by the smaller assemblies starting to form. So let's imagine we are standing on the street, holding something in one hand. An assembly of brain cells related to 'touch' is active, so we are aware of what we are holding. Then suddenly we see something that interests us, for example an accident. We then stop feeling what we are holding and just experience what we are seeing. At that time the activity of the assembly of brain cells related to touch would be overtaken by the new assembly of cells which would have become active in relation to what we have seen. The activity of these cells is in turn determined by the activity of various proteins, which may change in response to other signals, including events that take place in our body, such as hormone changes, immune changes or changes in the levels of the neurotransmitters. So in the same scenario, if we had the 'flu and were feeling very ill, certain chemicals and hormones would be released by our body and immune cells that would also interact with the brain cell networks, so we would feel 'unwell' while seeing the interesting event.

It has thus been suggested that the subtlest influences either from outside or inside the body modulate consciousness at the level of cell synapses in the brain and hence lead to differences in consciousness and that there is always a competitive process going on between different assemblies of cells.