I think there's two, albeit inter-related, issues here:
(1) I have never been totally converted to the 40 Hz way of thinking (it keeps reminding me of the magic number 42 in Hitchiker's Guide..), not least because one of its great revelations, that REM sleep was indistinguishable from waking consciousness, has been known ever since the EEG has been in use. In their enthusiasm at correlating synchronous brain activity with conscious states, neuroscientists omit to distinguish between sufficiency and necessity. My personal gripe is that 40 Hz is the same in rat, cat brains etc right through to humans, but the degree of consciousness varies greatly across species: hence some additional vital physical factor in the brain must be implicated. It might well be that 40Hz synchrony is necessary, but there is no evidence whatsoever that it sufficient. My own view is that different degrees of arousal will correlate with synchronous brain activity, which in turn reflects some large scale process (such as release of modulatory amines) that is important for the brain to configure in a way that is eluctably linked/identifiable wirh consciousness. I agree with Keith that it is not just a matter of stacking up neurons bottom up, which brings us on to (2).
(2) Top-down solutions involving mere feedback or iterative circuits, a la Harth, Edelman or Zeki won't do as they stand because they are two static. More again is needed to explain our changing consciousness and that factors such as stronger stimuli alleviate blindsight or, more typically, drugs such as Prozac can affect consciousness so radically. My favourite top-down concept is that of transient neuronal groupings along the lines of Dennett's metaphorical 'multiple drafts', Penrose's abatracted 'quantum coherence', Freeman's disembodied 'neuroactivity' and my own 'gestalts', where the whole is more than the sum of its parts. Of course 40Hz could, and I think does, play an important part in recruiting the neuronal assemblies. But its only a bit part and shouldn't be placed centre stage.
One final point raised by from Keith's message: I think the biggest job of philsophers at the moment is to continue to bang on about how important it is to account for the subjectivity of consciousness. For most scientists after all, subjectivity is the dirtiest word there is. It is tempting for those raised to prize the objective, to nudge aside for some unmeasurable, non-shareable Thing. We scientists need philosophers to insist that it should be our starting point, not brought in at best as a mere, last minute 'property of the brain'.
Susan Greenfield
jcs-online
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