Australasian Science: Australia's authority on science since 1938

The Crimes of Sleepwalkers

By Tim Hannan

Sleep experts and lawyers are wrestling over the criminal responsibility of sleepers.

For a person to be convicted of a crime, it must be demonstrated that the act was committed (actus reus) and that it was intended (mens rea). Yet in several rare but well-publicised cases, the accused person has claimed to be asleep or sleepwalking at the time of the event, and thus to have lacked conscious awareness of its nature and implications. In these cases, the court must determine whether the person was in a state of automatism, and thus not responsible for the acts that occurred. A forum at last month’s annual conference of the Australasian Sleep Association explored the complexities of the interaction of sleep medicine and the law in this area, and identified several difficult questions for both practitioners and courts.

Recent cases in Australia and overseas have highlighted the contribution of sleep disorders to tragic accidents or violent acts. Some cases found that fatal motor vehicle accidents resulted from excessive sleepiness brought on by obstructive sleep apnoea or some other primary sleep disorder. In other cases, the accused has claimed that violent acts such as physical or sexual assaults and homicide occurred while in an abnormal sleep state.

In law, for a conviction to be made it is necessary that the act of the accused person is voluntary: it must be determined both that the accused was conscious of its nature and that he or she exercised a choice to commit the act. If it is found that the accused acted without control or direction of the will, it is said to be an act done in a state of automatism, and no criminal responsibility is attached. When a person is asleep, it may usually be taken that the person is incapable of acting with control or direction of the will.

A particular state in which the question commonly arises is sleepwalking, one of a number of parasomnias – unusual behaviours, emotions or movements occurring while asleep. Most parasomnias take place during non-rapid eye movement (NREM) sleep, and the person has no recollection of events on waking. Other NREM parasomnias include sleep terrors and sleep-related eating disorders. The terms “sleepsex” or “sexsomnia” have recently been coined to refer to the less common occurrence of sexual behaviour during sleep.

The nature of the neuropsychological functions present during sleepwalking and related states is not fully clear, but it is generally agreed that the sleeper is not acting with the direction of the will. As Dr Peter Buchanan, a sleep physician from the Woolcock Institute of Medical Research in Sydney, put it: “The parts of brain which subserve visuospatial functions such as orientation and locomotion are functioning, but higher cortical centres which subserve executive function, contextual information and moral judgement are asleep”. The person is observed to perform various behaviours, but these are not judged to be intentional or directed.

Even aggressive behaviours towards others are assumed to be unintended. Dev Banerjee, the Medical Director of the Woolcock Institute’s clinical sleep services, noted that when sleepwalkers engage in violent behaviour this is usually triggered by provocation by or close proximity to another person, and does not reflect an act of the will.

From the legal perspective, another speaker at the Australasian Sleep Association conference queried the presumption that the automatism defence should formally be understood as the claim that the action was not under the control and direction of the will. Ms Hayley Kormann, a Senior Associate at the legal firm of Clayton Utz Perth, argued that automatism is better conceptualised as the claim that the behaviour of a sleeping person should not even be regarded as physical “acts” at all (actus reus) for the purpose of assigning criminal responsibility.

It should be added that the willingness of a court to acknowledge the contribution of sleep disorders to accidents does not mean that the accused will be acquitted. In evaluating responsibility, courts usually examine decisions made by the person before falling asleep. For example, the driver who is aware of his sleepiness may be held responsible for the risks taken in driving, and the tragic consequences of that choice.

Tim Hannan is an Associate Professor of Clinical Psychology at Charles Sturt University, and the Past President of the Australian Psychological Society