Todd F. Heatherton and Dylan D. Wagner, ‘Cognitive Neuroscience of Self-Regulation Failure’, Trends in Cognitive Sciences, 15 (2011), 132-9.
Ilia N. Karatsoreos and Bruce S. McEwen, ‘Psychobiological Allostasis: Resistance, Resilience and Vulnerability’, Trends in Cognitive Sciences, 15 (2011), 576-84.

Heatherton and Wagner are interested in why sometimes we lose self-control. After being subjected to a , dieters eat more than non-dieters, one lapse disabling all their restraint. Neuroimaging suggests that brain regions pertaining to rewards, on the one hand, and self-control on the other, are involved in a sometimes precarious balance. Self-regulation exercises help; drinking alcohol does not. Further research could get further into the way that external stimuli and internal control mechanisms interact.
      Karatsoreos and McEwen develop the idea of ‘allostasis’, an adaptive resilience to changes and challenges, as an alternative to the more negative-seeming ‘stress response’. In addition to exploring how allostasis work at a molecular level, they discuss the effect of sleep-deprivation on the ability to adapt. When their circadian rhythms are compromised, mice do badly in changed mazes; jet lag shrinks the medial temporal lobes of air crews. Karatsoreos and McEwen end up wondering about modern life, where sleep-deprived humans face an unprecedentedly hectic environment.

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Tragic dramas are often thought of as intensely psychological, in a loose sense at least. And in tragedies, adaptive resilience (or indeed, stress), and self-control, might both come into play. The point of this post is to ask what a literary work – Macbeth, in this case – might offer to anyone trying to understand such things. I want to start with two quirky, detailed connections, before suggesting something more substantial.

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‘That Which Hath Made Them Drunk Hath Made Me Bold’
This is what Lady Macbeth says about wine: it has given her courage, and removed her inhibitions. She turns to the same idea when berating her husband: ‘Was the hope drunk / Wherein you dress’d yourself?’ Later in the play, a drunken porter takes his time opening the door; at a (surely not teetotal) banquet, Macbeth sees a ghost. Alcohol loosens minds at several key points in the play. This feature of the play, part of an atmosphere in which self-regulation fails and disaster breeds, looks a little different after reading Heatherton and Wagner.
      The play turns to self-regulation in the long scene set in England (4.3). Malcolm tests Macduff by claiming to have boundless appetites: ‘my more-having would be as a sauce / To make me hunger more’. This is just a ruse, the point being to make sure Macduff is on the side of right, not just against Macbeth. However, it brings the psychology of restraint back into focus, in a play where Macbeth, having fallen once, is capable of further, escalating violence.

‘Sleep No More’
We cannot blame the wine for the murders in Macbeth. It would be even harder to blame disrupted circadian rhythms for its atrocities. Nonetheless, the play makes an issue of sleeplessness:

      Methought I heard a voice cry ‘Sleep no more!
      Macbeth does murder sleep’, the innocent sleep,
      Sleep that knits up the ravell’d sleeve of care,
      The death of each day’s life, sore labour’s bath,
      Balm of hurt minds, chief nourisher in life’s feast, —

‘What do you mean?’ asks Lady Macbeth of her husband, when he speaks these lines. . By the end of the play she and her husband both suffer from bad sleep:

      I have almost forgot the taste of fears;
      The time has been, my senses would have cool’d
      To hear a night-shriek; and my fell of hair
      Would at a dismal treatise rouse and stir
      As life were in’t: I have supp’d full with horrors;
      Direness, familiar to my slaughterous thoughts
      Cannot once start me.

Macbeth is remarking on his indifference to horror, which might be thought of as a distortion of adaptive resilience, if not a failure. Having murdered sleep, he has wrecked allostasis. In the light of Karatsoreos and McEwen, this aspect of the play resonates a little more specifically and acutely. The wine and the sleeplessness together look like fragments of psychological insight. They don’t come together to form coherent conclusions (or even knowledge) about the mind, but they suggest ways in which discoveries in details, as well as in the thematic mainstreams, could be thought-provoking.

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I would like to suggest a way in which Macbeth offers something more structured. Heatherton and Wagner end up by recognising that failures in self-regulation involve external factors (such as the nature of the tempting stimuli) and internal factors (such as the neurological make-up of an individual). They wonder how the contributions of external and internal are to be figured in each individual case. In Macbeth, there are equivalents to these external factors (opportunities and circumstances; the workings of the witches) and internal ones (what we are told, and what we have to infer, of his character).
      Some readers would privilege external or internal in their interpretation of the play. I would suggest that Shakespeare does not resolve the question, that in Macbeth’s unique and extreme case, the interaction between causes of different origins is something like alchemy, a mixing of ingredients that produces an extreme result. The play proposes that disentangling the contributions of internal and external may not be possible; that many things about human beings happen in the feedback loops between internal and external; and that seems like a believable (and appropriately tragic and horrifying) answer to the emerging scientific question.