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Neuro-psychological methods in the legal system
Careful use, cognizant of caveats, complements a patient's self-report

Dr. Michael MacIntyre
October 2022

Data from psychological and neuropsychological testing are increasingly used in legal settings. These sorts of tests give useful information through contrast: a respondent’s answers are compared to those from the general population or from specific subgroups (such as those in civil litigation, those in criminal litigation, or those with severe mental illness). The value of the tests is based on the tests’ development and the sample populations used in its construction. Psychological tests may stratify data based on age, level of education, or ethnicity.

For a court (or other forensic evaluator), these tests are valuable because they provide insight into the validity of a patient’s self-report. For example, a test can suggest if the answers given are consistent—or not—with a normal population. Alternatively, a test might reveal a symptom pattern not consistent with any known genuine presentation of mental illnesses. The tests may help show a pattern of personality or behavior consistent with known clinical symptom patterns of mental illness that should be further explored in a psychiatric evaluation.

It is important that data from these tests be used to support any conclusions about a forensic question. Often, the court does not care solely about whether or not there is any mental dysfunction—only whether this dysfunction is relevant to some legal issue. For example, in a personal injury case, is the mental dysfunction due to a specific event? In a criminal case, did the dysfunction prevent a defendant from understanding the difference between right and wrong? The mere presence of dysfunction does not suffice to answer either question. So caution must be used when introducing neuropsychological or psychological tests. They should never be used as the only data point in a decision—doubly so, since they are not absolute but rather provide data on the likelihood that someone’s presentation is valid or consistent with other known populations.

Consider this fictional case study: a person in a car accident becomes involved in litigation in which they claim damages due to impairments in cognitive abilities. The plaintiff may undergo neuro-psychological and cognitive testing. (Litigation is often the first time someone undergoes formal neurocognitive testing.) If the plaintiff has cognitive skills that are in the 10th percentile of similar people, what does this say of the legal question of damages due to the car accident? The results could be due to brain injury or psychological trauma. They could be due to a pre-existing condition. They could represent the person’s baseline abilities. Maybe the evaluee was not giving full effort during the evaluation or was distracted due to anxiety and stress. The results could also be feigned for the legal case (malingering). As often happens in litigation, a combination of causes contributes to abnormal test results.

As another example, neuro-psychological testing of an elderly person may show cognitive dysfunction and a poor memory. This testing may be erroneously used to suggest they do not have testamentary capacity. However, if the person understands the nature and extent of her assets, the act of creating a will, the natural heirs of the property, and the disposition the will is making, then that person has testamentary capacity regardless of any psychological testing result.

While testing may provide data about the validity of one’s symptoms or compare one’s performance to a normalized sample, this data means nothing without a detailed psychosocial history, evaluation, and formulation.

Similarly, neuroimaging might also be introduced to provide evidence of impairment. The same principles of data from neuro-psychological testing should be applied: a resulting image may provide a data point, but it is not conclusive as to any particular legal issue. For instance, a large dark spot in the brain may (erroneously) be suggested to have caused behavioral problems. However, brain lesions often exist without causing behavioral problems—or reside in parts of the brain unrelated to the behavior in question. Brain imaging does not irrefutably prove anything, but it can provide a causal mechanism for impaired behavioral capacities which have already been shown to exist.

There is much more to say about neuroscience and neuroimaging in the courtroom, and I will elaborate in a future article.

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