Legal responses to neuroscience

Neuroscientific and Genetic Evidence in Criminal Cases: A Double-Edged Sword in Germany but Not in the United States?

Aim of the Study

The study examines how neurobiological and genetic explanations of psychopathy influence decision-making of German law students about legal and moral responsibility and sentencing of a defendant in a case of manslaughter. Previous studies from the United States and Germany have been criticized because they partly contradict legal analyses of real-world criminal cases. With a modified design, which integrates the main criticism, we re-examined the impact of biological explanations for psychopathy on decision-making in the courtroom.

Methods

We developed an improved quasi-experimental design to probe three case vignettes presenting different explanations of psychopathy in a criminal case of manslaughter. All three vignettes present the same information about a forensic expert's testimony that is said to report compelling evidence for the diagnosis of "psychopathy." The independent variable being manipulated is the type of information supporting the expert diagnosis: either no biological explanation of "psychopathy" versus a neurological explanation (brain injury) versus a genetic explanation (MAOA gene). The outcome measure is a questionnaire on legal and moral responsibility, free will, the type of custody, and the duration of the sentence. The study is adequately powered. We openly publish the data and all statistical analyses as reproducible R scripts.

Results

The answers of German law students (n = 317) indicate that the omission of a neurobiological explanation is significantly associated with higher ratings of legal responsibility while compared to no biological explanation. However, there was no significant difference on the prison sentencing and type of custody assigned. Furthermore, there was no difference in the self-reported impact of the explanation of psychopathy on the participants' decision-making.

Conclusion

Our findings from German law students corroborates previous research on German judges but is markedly distinct from studies on United States judges. Whereas in the United States, biological information seems to have a mitigating effect, it seems to increase the rate of involuntary commitment to forensic psychiatric hospitals in Germany.

Forensic psychiatry and neurolaw: Description, developments, and debates

Neuroscience produces a wealth of data on the relationship between brain and behavior, including criminal behavior. The research field studying the possible and actual impact of neuroscience on the law and legal practices, is called neurolaw. It is a new and rapidly developing domain of interdisciplinary research. Since forensic psychiatry has to do with both neuroscience and the law, neurolaw is of specific relevance for this psychiatric specialty. In this contribution, I will discuss three main research areas in neurolaw - revision, assessment, and intervention - and explore their relevance for forensic psychiatry. I will identify some valuable possibilities as well as some notable challenges - both technical and ethical - for forensic psychiatry regarding neurolaw developments.