Testable quantum effects in the brain?

By Peter Hankins

The idea that quantum mechanics is part of the explanation of consciousness, in one way or another, is supported by more than one school of thought, some of which have been covered here in the past. Recently MLU was quick to pick up on a new development in the shape of a paper by Efstratios Manousakis which claims that testable predictions based on the application of quantum theory have been borne out by experiment.

The claims made are relatively modest compared to those of Penrose and Hameroff, say. Manousakis is not attempting to explain the fundamental nature of conscious thought, and the quantum theory he invokes isn’t new. At its baldest, his paper merely suggests that dominance duration of states in binocular rivalry can be accurately modelled by assuming we’re dealing with a small quantum mechanical system embedded in a classical brain -- although if that much were true, it would certainly raise further issues.

But let’s take it one step at a time. What is binocular rivalry, to begin with? When radically different images are presented to the left and right eye, instead of a blurry mixture of both images, we generally see one fairly clearly (occasionally a composite made of bits of both images); but curiously enough, the perceived image tends to switch from one to the other at apparently random intervals. Although this switching process can be influenced consciously, it happens spontaneously and therefore seems to be a kind of indecisiveness in some unconscious mechanism in our visual system.

Manousakis proposes a state of potential consciousness, with the two possible perceptions hanging in limbo. When the relevant wave function is collapsed through the intervention of another, purely classical brain mechanism, one or other of the appropriate neural correlates of consciousness is actualised and the view through one eye or the other enters actual consciousness. This model clearly requires perception to operate on two levels; one, a system that generates the potential consciousness, and two, another which actualises states of consciousness by checking up every now and then.

Thus far we have no particular reason to believe that the application of quantum concepts is anything more than a rather recondite speculation; but Manousakis has shown that the persistence of one state in the binocular rivalry, and the frequency of switching, can be predicted on the basis of his model: moreover, it explains and accurately predicts another observed phenomenon, namely that if the stimuli in a binocular rivalry experiment are removed and returned at intervals, the frequency of switching is significantly reduced. If I’ve understood it correctly (and I’m not quite sure I have), one of the two images tends to stay around because when you collapse the wave function a second time, there is a high probability of it collapsing the same way. If you remove the images for a while, no new collapses can occur until the images return. It’s as though you were throwing a dice and moving to the other state when you threw a six; if you keep throwing, the changes will happen often, but if you take the dice away for a few minutes between each throw, the changes will become less frequent.

Manousakis has also demonstrated that his theory is consistent with the changes observed in subjects who had taken LSD (a slightly puzzling choice of experiment -- I’m slightly surprised it’s even legal -- but it seems it reflects established earlier findings in the field).

So -- a breakthrough? Possibly, but I see some issues which need clearing up. First, to nail the case down, we need better reasons to think that no mere classical explanation could account for the observations. There might yet be easier ways to account for changes in dominance duration. We also need some explanation of why quantum mechanics only seem to apply in unusual cases of ambiguity like binocular rivalry. A traditional theorist who attributes binocular rivalry to problems with the brain’s interpretative systems has no trouble explaining why the odder effects only occur when we impose special interpretive challenges by setting up unusual conditions; but if a quantum mechanical system is doing the job Manousakis proposes, I would have thought occasional quantum jumps would have been noticeable in ordinary perception, too.

It would help, in addition, to have a clearer idea of how and why quantum mechanics is supposed to apply here. It could presumably be that potential consciousness is generated at a microscopic level where quantum effects would naturally be observable; an account of how that works would be helpful -- are we back with Penrosian microtubules? However, Manousakis seems to leave open the possibility that we’re merely dealing with an analogy here, and that the maths he employs just happens to work for both good old-fashioned quantum effects and for a subtle mental mechanism whose basic nature is classical. That would be interesting in a different way.

It will be interesting, in any case, to see whether anyone else picks up on these results.

Peter Hankins is author of the Conscious Entities weblog.