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The Deceptive Brain

Why might deception be of interest to a clinical readership? Is it not a moral issue, more relevant to legal or theological discourse? How can we determine, scientifically, whether another human being is lying to us? Should we want to? 
 
The answers to all of these questions might depend on the clinical setting envisaged. The significance of a lie about adherence to a treatment will depend on the clinical necessity of that treatment. In the forensic arena, a lie about plans for future conduct might have profound consequences: will the paedophile avoid playgrounds? In psychiatry, neurology, medicolegal practice and perhaps certain other areas of medicine, doctors are called upon to judge the veracity of their patient’s account (even though this may not be made explicit). Doctors commonly imply veracity in the terms that they use. 
 
Consider the distinction between feigned physical symptoms (‘malingering’) and those ascribed to conversion disorder (‘hysteria’). These diagnoses have very different meanings, yet what objective grounds are there for differentiating between them?1 Notwithstanding the findings of brain imaging experiments,2 it would seem that, phenomenologically, there is little objective evidence that would favour one above the other, and the diagnosis reached may be influenced by circumstantial factors and the physician’s opinion of the patient’s personality or background. Also, the subtle ‘tricks’ used to elicit hysterical motor inconsistency (e.g. the unintentional movement of the ‘paralysed’ limb) might just as well be used to indicate deception.1,3 The point is not that these disorders are equivalent, rather that they lack objective differentiation. Yet, when recording these diagnoses, the physician implies whether the patient is to be believed.1 
 
Are doctors especially good at detecting deception? This seems unlikely. When psychologists have studied various groups trying to decide whether others are lying to them, doctors have performed at the level of chance;4,5 with the possible exception of security personnel, it seems to make little difference whether the putative ‘lie detector’ is a judge, a police officer or a doctor. 
 
However, there is a more subtle aspect to deception that emerges when human behaviour is conceptualized in terms of its higher, executive, control processes. For it would appear that deception ‘behaves’ as if it is a skill—something that must be worked at, for which attention is required, and in which fatigue may lead to inconsistency or unintended confession.5 
 
The question of whether lying relies upon higher brain systems is important because such systems may be differentially affected in neuropsychiatric disorders. In the case of some of the most difficult patients with whom psychiatrists interact (such as ‘psychopaths’ and sex offenders), deception may be a feature of that interaction. A psychopath who is a skilled liar may be demonstrating preserved, or possibly superior, executive brain function. This may have profound implications for our understanding of responsibility and mitigation.