Theatre of the Mind by Ingram Jay

Author:Ingram, Jay [Ingram, Jay]
Language: eng
Format: epub
ISBN: 9781443402316
Publisher: HarperCollins Canada
Published: 2012-05-15T00:00:00+00:00

While it is unlikely that any one part of the brain will turn out to be the “hub” of consciousness, the thalamus would come close. Myriad circuits of neurons are routed through it, and it controls not only the flow of neural traffic up to the all-powerful cerebral cortex, but also its activity.

The thalamus is the shape of a quail’s egg, and about the size of two walnuts held together. It is a mass of neurons, millions of them, buried in the middle of the brain just under the cerebral hemispheres. Not only is it the place where most sensory infor mation makes a final stop before moving upward to the cerebral cortex, but it also transmits signals from the cortex to the muscles and controls the flow and intensity of information to and from the cortex. The thalamus has been called the brain’s switchboard, a metaphor that dramatically understates its role.

Cutting the fibres of one small part of the thalamus, the cluster of neuron groupings called the intralaminar nuclei, causes coma.* There are very few brain areas that, when damaged, have such a dramatic and direct effect on consciousness. They not only participate in the thalamic control of neuronal traffic flow, but also appear to tweak the activity level of the cerebral hemispheres. They play a generalized role: they’re not responsible for the traffic of specific sensations or ideas, but you can’t be aware without them. If you are startled by the sudden appearance of a threat, all your senses are heightened, your brain on alert, thanks in part to the intralaminar nuclei.

But the thalamus isn’t all there is to it. Some scientists argue that recordings of electrical activity from the human brain can be used to differentiate conscious brain activity from its unconscious counterpart, and that if such electrical patterns were recorded from animal brains as well, it would at least suggest the presence of consciousness. For instance, conscious brains are characterized by bursts of simultaneous activity in widespread areas of the brain, often linked to incoming sensory information. Such patterns are easily distinguished from unconscious brain states like that of slow-wave sleep, which, as the name implies, is a steady, slow and repetitive electrical pattern, largely unresponsive to the senses and producing no sudden neuronal flare-ups.

Seth, Edelman and Baars are saying, look for brains that have dense connections between the thalamus and the cortex (or the structures most like them) or brains that exhibit electrical activity typical of awareness. There you might find consciousness. The best part of this approach is that it encourages casting the consciousness net very wide. Finally we can talk about some animals other than the great apes! Seth, Edelman and Baars point out that the fundamental circuitry running from thalamus to cortex—circuitry that is necessary (but perhaps not sufficient) for consciousness—has been in place since mammals first appeared in the evolutionary record, more than 100 million years ago. That is a startling thought: there have been very few suggestions that animals in the age of dinosaurs were thinking, aware, conscious creatures.

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