The speed of technology in neuroscience as it impacts ethical and just decisions in the legal system needs to be understood by lawyers, judges, public policy makers, and the general public. The Massachusetts General Hospital Center for Law, Brain, and Behavior is an academic and professional resource for the education, research, and understanding of neuroscience and the law. Read more

Neuroscience Experts on the Stand

The use of neuroscience in the courtroom has a long and controversial history (Baskin, Edersheim, & Price, 2007). Some observers will recall introduction of computerized tomography (CT) scans to support a diagnosis of Schizophrenia at the John Hinckley Jr. trial for his attempted assassination of President Reagan (United States v. Hinckley, 1982). In subsequent years, much has changed in neuroscience and the law. Recent advances in technology and methods for collecting and analyzing imaging data, coupled with decreasing costs and greater availability of training, has resulted in an explosion of neuroscientific research (Rosen & Savoy, 2012). The ability to track fluctuating brain activity (i.e., functional data), as opposed to examining structural or anatomical images, has allowed for research in a wide-array of applied fields.

It is not surprising that techniques that could presumably measure thought patterns, identify lying, detect psychopathology, and assess for violence and impulsivity, incite interest in the legal community (Jones, Wagner, Faigman, & Raichle, 2013). The MacArthur Foundation Research Network on Law and Neuroscience has tracked peer-reviewed publications in the field of neurolaw (application of neurosciences to legal questions). Between 2003 and 2013, the total number of articles skyrocketed from less than 100 to more than 1,100 (Jones et al., 2013). A debate has ensued about the appropriate use of neuroscience research in the courtroom. Many researchers urge strong caution in applying this nascent field to complicated psycho-legal questions (Appelbaum, 2009; Rushing & Langleben, 2011).

Despite the controversial nature of this topic, attorneys have attempted to bring in neuroscience experts on a wide-range of criminal and civil issues (Jones et al., 2013). In general, the courts have been conservative about allowing in neuroscientific findings. For some issues, such as deception, there are consistent state and federal precedents in rejecting any neuroscientific findings (dating back to Frye v. United States, 1929). However, in other areas of the law, neuroscientific data and expert testimony has been allowed (e.g., in areas of competency, insanity, diminished capacity), particularly during the sentencing phases. Some defendants have argued that failure to exhibit or obtain brain-imaging data amounts to ineffective assistance of counsel (Ferrell v. State, 2005). Thus, it seems likely that admissibility of neuroscientific data and testimony is likely to continue being debated.

Impressions of Neuroscience

One concern about neuroscience testimony is that the jury or judge may be unfairly prejudiced. One study has found that simply placing unrelated pictures of the brain next to complicated explanations made those explanations seem more “scientific” (McCabe & Castel, 2008). Other findings indicate that psychological phenomena are determined to be “good” when accompanied by neuroscientific explanations (Weisberg et al., 2008). In part, this research has raised concerns about unrealistic expectations that triers of fact may have about neuroscientific research.

A few studies have sought to understand what the public thinks neuroscience can do. Wardlaw and colleagues (2011) asked laypeople (n=660) and experts (n=303) to complete an online survey about the uses of neuroimaging. About half of the non-expert respondents (47%) were at least “a little” aware about the potential uses of neuroimaging, with 10% being “very aware.” The majority (84%) of the public responders believed that neuroimaging could diagnose brain diseases such as tumors “very well.” In contrast, fewer had confidence that neuroimaging could be used to identify mental illness (64% responded “to some extent” and 17% answered “very well”). With respect to deception, 62% believed that neuroimaging could be used to detect lying to “some extent” and 5.6% endorsed “very well.” Neuroscience experts, a group that included psychologists, psychiatrists, and neuroscientists, did not believe that current adaptions of neuroimaging could be used to detect deception or understand criminal behavior. When experts were asked about the frequency that such tools were used in United State courts, approximately three fourths believed it to be fewer than 30 times in the past five years. In contrast, the authors reported that it had been used in excess of 100 times (actual numbers are unavailable).

These findings are concerning. The public appears to harbor beliefs that current neuroimaging technology is able to answer psycho-legally relevant questions, in marked contrast to experts’ beliefs. Equally important is the misconception that neuroscience experts have that there are fewer applications of neuroimaging in court-related matters than there actually are.

Impact of Neuroscience on Juror Decision-Making

Researchers have explored how neuroscientific images and data may impact juror decision-making. The findings are equivocal. There appeared to be an initial consensus that neuroimages (and potentially testimony) sway jury decision-making. However, recent studies have qualified this finding and offered a more nuanced view about what may actually influence the jury.

McCabe, Castel, and Rhodes (2011) examined how neuroscientific explanations, with and without descriptions about the limitations of imaging tools, would impact legal judgments. Undergraduates (N=330) read a vignette about a defendant who allegedly killed his wife and her lover. Participants were randomly assigned to one of six groups based on the type of testimony offered about the defendant lying. The groups were: polygraph, fMRI, fMRI with its validity questioned, thermal imaging (TI), TI with its validity questioned, and no testimony. No neuroimages were presented. Respondents were more likely to find the defendant guilty in the fMRI (no description of the limitations) condition than any other group. There were no significant differences between any of the other conditions, including between the control group and that of fMRI and TI with validity questioned groups. This study highlights the point that a comprehensive and accurate portrayal of the limitations of neuroscientific tools may reduce prejudicial impact of such evidence.

Schweitzer and Saks (2011) also examined the impact of neuroscience testimony, specifically as it compared to other types of testimony and neuroimages. The authors devised a six-by-four experiment comparing types of evidence to verdict type. The participants (N=1,170) were asked to read trial proceedings about a defendant who punched his victim unconscious. Evidence was presented by the defense to show that the defendant was suffering from a mental illness that resulted in aggression and inability to control his behavior. The six groups of evidence were: neurologist’s testimony and a brain image, neurologist’s testimony and a neuro-graph (bar graph of frontal lobe function), neurologist’s testimony, neuropsychologist’s testimony, clinical psychologist’s testimony, and control (no testimony or images). The four types of verdicts were based on mental state at the time of the crime defenses. There was a main effect for the type of evidence proffered.. Individuals in the neuroimaging condition (testimony by a neurologist and a neuroimage) were significantly more likely to find the defendant as Not Guilty by Reason of Insanity or Guilty but Mentally Ill (53.2%) than the control group (12%) and the clinical psychology group (43.2%) condition. There were no significant differences between the other three types of conditions, all of which were around the 50% mark. Respondents were also queried about what type of evidence that they had not seen would be most helpful to them in deciding the case. Those who did not see the neuroimage asked for it, while those that did see it asked for clinical psychology testimony.

This study suggests that any scientific explanation, with and without testimony, is likely to be more powerful to the jury than its absence (i.e., control group). Further, this research highlights that it is not the neuroimages themselves per se that impact decision making, because there were no difference between evidence types with and without neuroimages. However, it is potentially the testimony, an explanation by the expert, behind the neuroscientific findings that makes the deciding difference. The most surprising aspect of this research was that the only testimony significantly less likely to result in NGRI/GBMI finding was that of a clinical psychologist (the nature of whose testimony was the same as that of a clinical neuropsychologist).. It is possible that the jury believed that brain-related explanations necessitated an expert trained in neurological bases or simply one that had the word “neuro” in the title.

Cautionary notes

Jones, Wagner, Faigman, and Raichle (2013) offer advice to neuroscience experts about testifying in legal proceedings. The authors emphasize that certain issues may be particularly problematic to neuroscientists. For example, they describe “two fonts of confusion” about wording used in testimony. First, neuroscientists and lawyers may have different meanings for the same terms. Second, neuroscientists and lawyers may use terms that are specialized in one field while general in the other. More broadly, Jones et al suggest that like other types of expert witnesses, neuroscientist will need to become familiar with legal terms and process. Jones and colleagues outline what will be important basics about neuroscience that will need to be relayed to decision-makers. The expert will need to distinguish specifically between structural and functional data, explain that research data and images are amalgamations of multiple brain images from multiple individuals, highlight that neuroimages are not analogous to brain x-rays, and finally, that like mental states, individuals’ brains change with time.

Note: A version of this post was submitted as a chapter entitled “The Credibility of Witnesses” by Stan Brodsky Ph.D. and Ekaterina Pivovarova Ph.D. for an upcoming book by Springer Publications, The Witness Stand and Lawrence S. Wrightsman Jr. 


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Frye v. United States, 293 F. 1013 (D.C. Cir. 1923).

Ferrel v. State, 918 So. 2d 163 (S.C FL 2005).

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