CHAPTER

The unity of consciousness

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Why do we seem to have only one consciousness? Why is consciousness, as James

puts it, ‘an integral thing not made of parts’ (1890, i, p. 177), when the brain is

such a massively parallel, and complicated, multi-tasking organ? Why do we feel

as though there is just one conscious mind in here that is experiencing a unified

world? This classic problem from philosophy takes on new significance in the con-

text of modern neuroscience (Cleeremans, 2003).

The problem is simple to state. When we look at the brain side of the great divide,

we see nothing but complexity and diversity. At any given time, countless dif-

ferent processes are all going on at once, and in different areas. For example,

right now your visual system is processing multiple inputs and dealing with

colour, motion, and other features in different areas of the eyes and brain. At the

same time, processing is going on in other sensory areas, in memory systems,

and in emotional systems. Thoughts are bubbling along, movements are being

planned and coordinated, and sentences are being constructed. All these diverse

processes are linked through multiple routes and connections, but, as we have

already seen (Chapter 5), there is no single place in the brain where everything is

brought together for someone to watch. All the parts just keep doing their things

all at once.

The parts also take time to do their things. Stuff happens quickly in the brain, but

not instantaneously, and not all at the same speed. Signals travel along neurons at

about 100 m per second, but this varies depending on the width and myelination

of a given neuron, ranging between about 0.5  m per second along the small-

diameter, unmyelinated pain receptors, and up to 120 m per second in the large

myelinated neurons linking the spinal cord to the muscles. Signals also take time

‘consciousness, which is

itself an integral thing

not made of parts,

“corresponds” to the

entire activity of the

brain’

(James, 1890, i, p. 177)