‘No,’ said he, ‘nor none
Of all these spirits, but myself alone,
Knows anything till he shall taste the blood.
But whomsoever you shall do that good,
He will the truth of all you wish unfold;
Who you envy it to will all withhold.’

Views of the afterlife seem to me to have become markedly more optimistic since ancient times; one of the most depressing versions must surely be the one in the Odyssey, where the dead prove to be mere shadows, devoid of all intelligence until they are provided with revivifying blood.

The idea of blood as the animating feature of the mind has acquired a modern echo of sorts in the theory put forward by Kenneth J. Dillon, namely that red blood cells provide the basic mechanism for a magnetoreceptive system that many animals possess to some degree: in human beings its clarity as a sense is somewhat clouded over, but it plays a vital role in the generation of consciousness.

I ought to admit to begin with that my knowledge of the theory is based purely on this extract from a longer and wide-ranging book, so I may well have missed some of the background: Dillon treats the existence of a magnetoreceptive sense in a wide variety of species, and of a human ability to perceive light with the skin, as established facts which require some explanation, whereas I wasn’t aware that either was particularly well evidenced. However, the idea of thinking, or at least sensing, though the agency of the blood, has some appeal.

It’s probably true that the role of blood in general has been unduly neglected in cognitive science: we know quite well that our emotions and patterns of thought are strongly influenced by hormones and other substances in the bloodstream, but with some honourable exceptions, the fact rarely gets much of a mention in discussions of consciousness. Magnetoreception is a slightly different matter, but after all, the view that phenomenal consciousness arises from an electromagnetic field, while not exactly mainstream, has been put forward by more than one author; if it is so, isn’t it plausible that all those iron-rich red blood cells sweeping round our body have some role in the em field? The brain engrosses a disproportionate share of the body’s blood supply – perhaps there’s another reason for that, and it isn’t just a matter of being a greedy energy consumer.

Dillon suggests that his theory might help to explain blindsight, the phenomenon in which people who are blind so far as conscious vision is concerned, can nevertheless ‘guess’ correctly the location of things they apparently can’t see. Clearly if one had a misty magnetoreceptive sense, it might be able to fill in where your eyes failed you. But blindsight, so far as I know, only occurs in cases of certain kinds of specific, limited damage. A magnetoreceptive sense ought to work irrespective of the visual system, but there’s no blindsight in cases where the eyes are destroyed, and I don’t think it would work even for blindsight patients if they had their eyes covered or closed (though so far as I know, that variation on the experiment has not been carried out). Of course, one of the leading characteristics of blindsight is that it isn’t conscious, so if the red blood cells are supplying it that must presumably be distinct from any direct role they may play in consciousness.

Dillon also thinks that his theory might help with the binding problem, but I’m not convinced about this either. The binding problem is the issue of how the data from different senses gets combined into a smoothly-running, uninterrupted and fully co-ordinated view of reality. The brain never gives us faulty lip-sync or sudden jumps and pauses in our view of events: but exactly how it pulls off this feat is unknown (some would argue that it doesn’t have to, because the problem is misconceived). Now people often suggest, and I suspect this is what Dillon has in mind, various means by which the impressions from different senses could be brought together: but just bringing them together isn’t enough: we need a method of working out what noises and what sights should be associated with the same instants, and of patching them together on the fly in a smooth sequence (and doing it all more or less instantaneously, because a lag of any appreciable size between reality and our view of it would clearly have a significant negative survival value!)

I also see some prima facie problems with the red blood cell theory. If the theory is true, oughtn’t we to be much more aware of magnetic fields in our environment? So far as I know the human body is largely unresponsive to magnets. If we have any kind of magnetoreceptive apparatus, wouldn’t we be sensitive in some way to electric motors, cathode ray tubes, and anything else with a significant magnetic component? Goodness knows what would happen to people undergoing an FMRI scan, since they are likely to be exposed to really whopping magnetic fields for an hour or more. But that point cuts both ways because, of course, FMRI would not be possible if blood didn’t have significant magnetic properties which other tissues lack.

I also wonder why a magnetoreceptive facility would have remained so much in the background? You would think it would be a rather useful ability for an animal to have. It seems particulalry strange that human beings should have it, or have had it, but allow it to remain almost completely dormant. Dillon suggests a number of possible reasons. We might need to be in a more trance-like state for it to work (an odd situation – we need to be less conscious in order to use the system which supports consciousness. Perhaps the role of supporting human-style consciousness is a new adaptation which has spoiled the sensory function.) Or our upright posture, habit of wearing clothes, or tendency to surround ourselves with artificial magnetic fields (ah, so it does have some effect!) has messed things up.

I’m no biologist, but I suspect that magnetoreceptive sensing isn’t common because it doesn’t work as well as some of the more usual senses. The creatures that indisputably have an electrical or magnetic sensory apparatus tend (I think) to need it because they live in murky conditions where vision is no good, or possibly because they want it to sense the earth’s magnetic field as an aid to navigation. Human beings, living in well-lit terrestrial conditions, and not being migratory, wouldn’t actually have much use for such a sense. In fact, I remain sceptical about their ever having had it to any noticeable degree.

I’m not convinced then – but you have to give Dillon credit for boldness and originality, qualities we’re surely going to need before the mystery of consciousness is dispelled.