“My brain made me do this!” – This is what in 2012 alone over 250 defendants  in the United States argued in their judicial opinions. From 2007 to 2012 the number of criminal cases that take into account nonscientific evidence has more than doubled, suggesting a dramatically increasing trend. But how exactly are neurobiological data used in court? And more importantly, is neuroscience ready to improve the dispensation of justice or do criminals take advantage of misinterpreted neurological evidence?

Neuroscience is more than just brain scans

A recent study by Farahany and colleagues who analyzed judicial opinions issued between 2005 and 2012 revealed interesting findings about the use of neuroscientific evidence in US criminal law. Although neuroscience is typically associated with neuroimaging, only in 15 per cent of the cases where neurobiological evidence was raised, brain scans played a role. In the other cases, neuroscientific evidence was introduced in other forms, for example medical history such as brain damage or neuropsychological testing.

These different types of neurological evidence can for instance be used in pretrial proceedings when the subjective mental state and the competency of the defendant can be contested. In 15 per cent of the cases in the current study, the defendants claimed that abnormalities in their brains cause an incompetency to stand trial. In a prominent case in 2007, where a young man was charged with murdering his mother, the defendant underwent neuropsychological testing. As experts diagnosed the young man with a severe language disorder, the judge concluded that the defendant was unable to assist in his own defense, and thus set aside the jury verdict.

In a substantial proportion of cases, where neuroscientific findings are discussed in pretrial proceedings, impaired defendants obtain a favorable finding of incompetent to proceed. The success of defendants who attempt to use neuroscientific evidence to prove their innocence is far more limited.

My brain made me do this

In around 7 per cent of the judicial opinions, defendants argued that their neurobiology made them commit the crime involuntarily. In one case, when a police officer was about to arrest an accused, the situation turned into a high-speed car chase. Later, the defendant argued that he had suffered from head injury 8 weeks before which made him act unconsciously in a state of shock during the police chase. Experts concluded that the present MRI scan did not support any states of unconsciousness.

In general, these attempts seem to be rather unpromising, because in criminal law a strong presumption exists that defendants act voluntarily. Only if the defendant’s actions directly resulted from a reflex or convulsion arising from unconsciousness or sleep, the defense of involuntariness might be recognized (see this article)  for a very special case of a man who murdered his wife while sleeping).

The aforementioned examples show that neuroscientific evidence is often used by defendants in order to show that they are not able to stand trial or that they were not responsible for their actions. Nonetheless, such two-sided evidence can also be used against them, when prosecutors demonstrate defendants’ future dangerousness. But apart from this, is neuroscience of any use to judges, advocates and prosecutors?

From brain scans to mindreading

A field that could potentially benefit from neuroscientific insights is eye witness testimony. When eyewitnesses describe what they observed while a crime happened or when they are asked to identify a suspect, they often report inaccurate information. Unfortunately, human memory is not foolproof and under certain conditions prone to several types of errors, especially in stressful situations. As no behavioral methods exist that can reliably distinguish true from false memories, the possibility that brain imaging techniques could contribute to this sounds exciting.

In such studies, typically a list of items, for example words, is presented and participants are instructed to remember these items. Afterwards, a new list of items is presented and participants have to indicate whether these items were part of the first list. Neuroimaging methods, such as functional magnetic resonance imaging or event-related potentials, have shown that brain regions involved in true and false memories largely overlap, but that true memories tend to cause greater activity in sensory areas compared to false memories. This is in line with behavioral findings that suggest that true memories are associated with retrieval of more detailed sensory and perceptual information. Although in some studies, researchers were able to successfully distinguish between true and false memories, there are several reasons against the idea that the legal system could rely on neuroscientific evidence. 

Challenges that neuroscience has to face

One compelling argument is that everyday situations are far more complex than the simple tasks used in neuroimaging studies, which makes the transfer of results from those studies to court life difficult, if not impossible. Moreover, in research the delays between study and test are typically very short, whereas in real life, witnesses report their observations days, weeks or even months later. Whether neuroimaging can distinguish true and false memories over such long delays is completely unclear. On top of that, the reliability and accuracy of such measures are really important. Although the question of which level of accuracy is good enough is an entire topic on its own, it is obvious that in the current situation accuracy rates are far from being ethically acceptable.

These are only a few of a large number of obstacles, neuroscience has to deal with before being freely applied in court (take a look at this study  for an interesting review). These problems do not only apply to the issue of true and false memories, but to all other related aspects as well, such as lie detection or the examination of alleged brain dysfunctions. So, can neuroscience actually contribute anything in court? And if so, how should all these issues be resolved?

 Prospects and duties

What most researchers would agree on is that for being able to use fMRI to detect false memories or lies, there is still much work to be done (read also this study about lie detection). Whether and when neuroscience will be ready to provide waterproof facts in these areas remains to be seen in the future. For some, this may sound disappointing, but there is much more potential in neuroscience to contribute to jurisdiction.

An essential point that should not be underestimated is that neuroscience can inform us about how our memory works. It is important for judges to understand that our memory does not work like a video recording that can be displayed to remember any information. The fact, that our memory is prone to errors and illusions, should always be taken into account when eyewitnesses give their testimony.

Neuroscientists should be much more involved in trials, to inform lawyers and judges about these facts and to give advice how different types of neurological evidence should be used in court. In many cases when defendants tried to argue that their brains were dysfunctional, structural brain scans were used to show abnormal anatomical features. However, for examining whether the normal brain function is disrupted, functional imaging or neuropsychological testing would be much more appropriate. This clearly shows the need for specialists to avoid the misapplication of neuroscientific evidence.

Neurological evidence should definitely be used with precaution, nonetheless neuroscience carries a high potential to contribute to informed decisions. It can either help defendants to demonstrate their abnormal brain function or support the prosecutors’ claim that criminals were aware of their own actions. In other words, by being reasonably applied, neuroscience can help both sides equally in their struggle for justice.