Scholars of psychiatry of all generations will be cheered that Peter McKenna has chosen to disregard the wise counsel which states that, ‘there can be no acceptable definition of a delusion – all we are left with is a shambles’. For in his latest book, Delusions – understanding the un-understandable, the student is provided with a veritable hitchhiker's guide to the symptom complex which is surely most central to the concept of insanity.
True, delusions can never be defined, that is to say demarcated, differentiated. Boundaries are fuzzy. Worse still, there is the endless play of signifiers (words) and signified (meanings). But McKenna gently steers the student away from the world of robotic, tick-box psychiatry to classical phenomenology; phenomenology as a method (the listening ear) as art (the unambiguous expression of conscious experience) and as a therapeutic process (being understood).
McKenna's text re-calibrates the phenomenological radar, the listening ear, the faculty of discernment. He guides us through the whole landscape of false belief, pointing out the main forms that stand above the chaos; from outrageous, bizarre delusions, which appear to violate basic common sense, to paranoia, overvalued ideas, obsessions, conspiracy theories, witch-hunts and cults. Science and medicine are certainly not immune from false belief, psychiatry especially so. Indeed, the history of psychiatry suffers no lack of shared illusions, irrational groupthink and factions that value loyalty above everything else.
McKenna directs his gaze to modern schools of thought, who is claiming to understand how delusions emerge, have attracted large numbers of adherents, ‘theory of mind’ and ‘jumping to conclusions’ being the most prominent constructs. Conveying a sense of drama, the appeal, the intuitive ‘rightness’ of each construct is elevated – until, casting a forensic eye over the empirical evidence, McKenna dislodges a vital support and the whole edifice comes crashing down in ruins. There is no escape either, for so-called ‘biological’ schools. The glutamate theory, 25 years in construction at an industrial scale, is judged to be in ‘existential crisis’ – and the evidence seems to justify McKenna's bleak appraisal.
The text is not all destruction and iconoclasm. McKenna offers his own construction (or perhaps re-construction; his materials are those of classical phenomenology), by separating delusions into two classes. Firstly, there are ‘referential delusions’, in which the outside world is charged with double meanings, ‘on the street he is stared at, strange people follow him, look at one another, make signs to one another’, or a mood of foreboding, ‘the environment is somehow different – not to a gross degree – perception is unaltered in itself but there is some change which envelops everything…an indefinable atmosphere’.
The second class of delusion is purely ideational; there is no attribution of unfounded significance to any external event, ‘If it comes into someone's head that he is Christ, that is a single process’. McKenna suggests the term ‘propositional delusion’ for this class. (Perhaps a simpler term would suffice. ‘Propositional’ is a lofty, technical term with authority, but one that is already trapped within a web of meanings in contemporary philosophy.)
McKenna's separation of referential from propositional delusions is a major seam throughout the book and his purpose becomes clear as he turns to the most imposing construct of all – the hyper-dopamine/aberrant-salience hypothesis – imposing to the extent that, a few years back, adherents attempted to usurp ‘schizophrenia’ with a new syndrome, ‘salience dysregulation disorder’. Aberrant salience maps onto McKenna's referential class of delusions, particularly the delusional mood sub-type, ‘My senses seemed alive’, ‘I felt that there was some overwhelming significance in this’ (Kapur, Reference Kapur2003). For McKenna, this presents a fairly easy first strike. Self-evidently, not all delusions are preceded by a delusional mood (or delusions of reference) – some delusions are purely ideational, McKenna's propositional class.
A main pillar of the hyper-dopamine/aberrant-salience hypothesis is that, by causing a huge increase in extracellular dopamine, stimulant drugs induce a paranoid psychosis McKenna is alert to the flaw in the argument, ‘the immediate effects of stimulant drugs are euphoria and increased alertness, psychosis is something that occurs later…’ Indeed, Sigmund Freud, in his Über Coca of 1884, famously described the feelings of mental and physical well-being which accompany an immediate, drug-elicited hyper-dopaminergia, ‘an exhilaration no different from the normal or healthy person…you perceive an increase of selfcontrol… possess more vitality and capacity for work’. Of course, without doubt, stimulant addiction can lead, over time, to a paranoid psychosis, but paradoxically – and this is the important point – by that stage stimulant drugs evoke a relatively meagre dopamine release, compared with the initial exhilarating/vitalizing doses. For the hyper-dopamine/aberrant-salience construct, this double dissociation between the acute versus the chronic pharmacology/phenomenology of stimulants is problematic. A supporting pillar, which has been robust for decades, actually shows distinct cracks.
McKenna picks at two other aspects of the hyper-dopamine/aberrant-salience hypothesis. Firstly, the blood-flow signature of salience, as measured by fMRI, actually appears to be lower in psychotic patients compared to controls, which is in the opposite direction to the prediction; troubling perhaps for the aberrant salience hypothesis, although whether fMRI signals reveal much about neuronal processing is a moot point. Secondly, McKenna examines those studies which have used radiotracers in the hope of finding the long-sought hype-rdopaminergia.
There have been several finds of elevated dopamine components in psychotic patients. But any differences from controls tend to be slight, and disappear entirely as more data accrue. Worse still, treatment with antipsychotics actually causes many dopamine components, including the enzymes which synthesize dopamine, to up-regulate – a most inconvenient confound. One solution to this problem, is to search for hyper-dopamanergia in prodromal psychosis, before treatment is initiated, and McKenna highlights some very encouraging findings from this approach, although yet again the differences between groups are marginal, with considerable overlap. Data from larger samples is needed; the long-sought hyper-dopaminergia may rise triumphant, or disappear completely, and herald the crumbling of another pillar of the hyper-dopamine/aberrant-salience hypothesis.
Towards the end, McKenna appears to be in construction mode. He looks to the horizon and the landscape of dynamic neural networks, setting up the closing section with, ‘Perhaps the time has come to broaden the argument to brain mechanisms of learning and memory, as achieved by synaptic plasticity’. But instead of further exploration, McKenna turns back abruptly to phenomenology, leaving the student with a few sign-posts but no map, and apparently unaware that others have already wandered into the territory he refers to (Morrison & Murray, Reference Morrison and Murray2009). So, on this occasion, we do not hear about how a range of components; glutamate, dopamine, lipids, peptides, immune mediators, even gases; coalesce in harmony to strengthen, stabilize, weaken or remove individual connections, as the neural network is wired-up by experience. Students of psychiatry will be hopeful that McKenna returns to explore such landscapes – he is a knowledgeable and entertaining guide.
