Neuroscience: My brain made me do it

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Adam Kepecs urges caution in considering the unconscious mind in the justice system.

Incognito: The Secret Lives of the Brain

David Eagleman Pantheon/Canongate: 2011. 304 pp. / 272 pp. $26.95/£20 ISBN: 9780307377333

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A surprising view has been gathering momentum in neuroscience: most of our thoughts and actions are driven by unconscious brain processes that are hidden from conscious introspection. So if consciousness is rarely in the driver's seat, and if we cannot choose our genes or the childhood experiences whose interactions form our brains, then are we responsible for our actions?

In Incognito, accomplished neuroscientist David Eagleman — author of the best-selling short-story collection Sum (Canongate, 2010) — examines this gap between our conscious and unconscious selves. He offers a whirlwind of stories, from visual illusions and sleep-walking killers to ovulating strippers, all carefully chosen to drive home his main point that our brains “neurally preordain” us to make decisions. As is common in books aimed at a general readership, the intriguing and sometimes bizarre case studies create a tension between journalistic musings and more detailed arguments. Although specialists may feel that the balance tilts toward the journalistic, Eagleman's expertise comes through.

Since Sigmund Freud's famous psychological framing of the unconscious in the late nineteenth century, modern neuroscience has shown that most processing in the brain is unconscious. We are unaware of routine processes and have little insight into our choices and preferences. For instance, men unknowingly prefer photographs of women with dilated pupils, presumably because male brains evolved algorithms to recognize pupil dilation as an indicator of sexual arousal. In another experiment, people's descriptions of the strategies they used to make simple economic decisions differed from the rules that they actually used, suggesting that their conscious explanations were formed post hoc and without access to their decision-making process. Through such examples, Eagleman demonstrates that unconscious processes can be clever, adaptive and even outperform the best computer algorithms.


Better understanding of decision-making processes in the brain might predict which perpetrators will offend again.

If our brains can carry out such amazing feats without us knowing, why have consciousness at all? Eagleman answers this question with a metaphor. Consciousness, he says, is like the chief executive of a large company. He or she has little knowledge of the day-to-day operations, yet is indispensable for setting goals and arbitrating between conflicting departments. Similarly, consciousness gets only the abridged, delayed and sometimes contradictory reports from neural subroutines. And, much like a chief executive trying to explain him- or herself to the board of directors, consciousness will “fabricate stories to explain the sometimes inexplicable dynamics of subsystems in the brain”.

Having described the hidden life of our brain circuits, Eagleman moves to an original and provocative discussion of the legal consequences of the unconscious decider within us. Imagine two defendants on trial for murder: one has a large brain tumour next to an area associated with aggression, whereas the other one shows no obvious change in his brain. Most people would not hold the first defendant responsible for his actions. Eagleman argues that as we gain a better understanding of the biology of decision-making, we will be forced to conclude that all crime is caused by faulty brain circuits arising from genetic and environmental interactions over which the perpetrator has no control.

An improved understanding of how subtle changes in the brain generate deviant behaviour would therefore extend the insanity defence — 'my brain made me do it'. Eagleman suggests that a forward-looking legal system should consider biological information to predict how likely a person is to commit a crime again, and take this into account for sentencing. As most criminals commit offences because they are unable to inhibit their impulses, Eagleman proposes that rehabilitative “prefrontal workouts”, aimed at improving self-control, should be a mainstay of the justice system. Crime would still land you in jail, but the focus would be on protecting society, not on punishment.

My feeling is that we need to be extremely cautious in advancing such a brain-centric legal system. A world in which judges are instructed to consider the genetics and neural make-up of defendants, as Eagleman advocates, evokes Phillip K. Dick's short story The Minority Report. If sentencing decisions consider the biological likelihood of recommitting a crime, it is easy to imagine the next step of considering preventive measures before a crime has been committed — a kind of 'Department of Precrime'.

Whether or not one agrees with Eagleman, discussions about these difficult issues at the intersection of neuroscience and society are essential and timely. He should be lauded for his clear exposition of the consequences of our emerging understanding of the brain. Incognito is a smart, captivating book that will give you a prefrontal workout.

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