MRI has limited applicability in assessing sanity


Sophisticated brain imaging, like an MRI, has limited applicability in assessing a defendant’s sanity, investigators say.

The bottom line of an insanity defense is the defendant’s inability to distinguish right from wrong at the time of the crime, something which neuroimaging cannot help do, they say in a review article in the journal Neuroethics.

“MRIs and other brain scans are good for many things but they really have limited use when you talk about truly determining if someone was criminally responsible or not,” says Dr. Michael J. Vitacco, forensic psychologist in the Department of Psychiatry and Health Behavior at the Medical College of Georgia at Augusta University.

“The key element of an insanity defense is you have to be unable to tell right from wrong,” Vitacco says. “It’s that functional deficit that is critical. It’s a very high bar.”

It’s also an important distinction that means the difference between a defendant going to jail or to a hospital, says the article’s corresponding author.

And, it’s one that advanced brain imaging technology, like functional MRIs and positron emission tomography, or PET scans, which provide images of brain structure and insight into how the brain is functioning, typically cannot help defendants seeking a not guilty by reason of insanity verdict achieve.

But it’s use is growing. Particularly in the last decade, brain imaging, which routinely provides valuable, objective information to a medical diagnosis, has been increasingly used in criminal and civil cases.

It even has a name, “neurolaw,” with neurolaw centers sprouting up across the country and beyond, Vitacco says.

“The problem is nobody talks about the limitations of these images,” says Vitacco who, along with colleagues at the Medical University of South Carolina, Emory University and University of Southern Mississippi, decided to take a look at research and evidence out there.

No published studies they found showed the ability of brain imaging to provide insight and evidence beyond the usual exhaustive clinical evaluations of defendants, says Vitacco.

These evaluations may include talking with the defendant, with friends and family members, possibly personality testing and medical record reviews looking for patterns of behavior and for evidence that supports or contradicts an insanity defense.

Another issue is that brain images are taken well after the crime, sometimes even a year or more after, and the dynamic brain function images they display indicate what is happening at that moment, not at the time of the crime, he says.

Scans can show evidence of serious mental health problems like chronic depression and schizophrenia, as well as brain tumors or brain damage.

While problems like these may qualify defendants for an insanity evaluation, a very small percentage of these individuals will meet the high bar of not being able to distinguish right from wrong, Vitacco says.

As an example, pedophilia has been associated with tumors in the front of the brain in areas involved with emotion and memory, but they don’t necessarily mean the offender did not know right from wrong, Vitacco and his colleagues write.

Even sociopaths typically know right from wrong but choose to ignore it, Vitacco says.

What may better provide insight on many defendants is social media, notes Vitacco.

He and Dr. Ashley B. Batastini, director of the Correctional and Forensic Psychology Research Laboratory at the University of Southern Mississippi, recently coauthored the book Forensic Mental Health Evaluations in the Digital Age: A Practitioner’s Guide to Using Internet-Based Data.

It’s also an important distinction that means the difference between a defendant going to jail or to a hospital, says the article’s corresponding author.

They found these often multi-daily posts about detailed thoughts and actions on social media can provide that retrospective picture of what was happening in the mind of the defendant at the time of the crime in the defendant’s own words, says Vitacco.

“It really is powerful evidence, that tells you a lot about their function, says Vitacco.

He notes, for example, a Georgia case when the defendant was pleading insanity but his social media accounts at the time of the crime included an instant message to a friend that he had done something bad.

“This kind of evidence can speak directly to knowing right from wrong at the time a crime happens,” Vitacco says.

While there is no accurate measure of how often the defense of not guilty by reason of insanity is used, it is a controversial issue both in the legal and general community, Vitacco and his colleagues write.

An insanity verdict is reached in less than 1% of cases, he notes.

Insanity evaluations are court ordered and experts like Vitacco only make recommendations to judges and juries. “Insanity evaluations are never easy, mainly because they are retrospective,” he says.

A 2013 University of Denver study of 165 defendants who each had multiple evaluations by either a forensic psychologist or forensic psychiatrist found unanimous agreement about legal sanity among evaluators only 55% of the time.

While recent years have seen a surge in brain imaging in an insanity defense, its usage dates back much further, including the 1982 trial of John Hinckley Jr., who shot President Reagan, and whose defense team said had an abnormal CT scan that suggested “organic brain disease.” Hinkley was found not guilty by reason of insanity.

Insanity evaluations are among the most complex and controversial mental health assessments that psychiatrists and psychologists perform1,2.

A forensic evaluator is expected to perform a retrospective evaluation of the defendant’s state of mind at the time of crime, to ascertain the presence of a mental disease or defect and to further verify the existence of a possible relationship between that state of mind and the criminal behavior.

In case such a relationship exists, its impact on the defendant’s responsibility is further evaluated, and the conclusions will be used by the judge to assess the defendant’s legal responsibility.

Depending on the jurisdiction, the psychiatrist’s task and the threshold for satisfying legal criteria for insanity, as well as the definition of insanity itself, may vary.

In Western countries, the legal standards for insanity often rely on the presence of cognitive and/or volitional impairment of the defendant at crime time3.

In the Anglo-American systems the most acknowledged standards are the M’Naghten Rule (M’Naghten’s Case, 10 Cl. & Fin. 200, 8 Eng. Rep. 718 (H.L. 1843)), and the The Model Penal Code’s test, also known as the American Law Institute (ALI) standard4.

The M’Naghten Rule focuses on the cognitive component, and states that a defendant is not found responsible if, due to a mental disorder, he did “not know the nature and quality of the act he was doing; or if he did know it, that he did not know what he was doing was wrong”.

The Model Penal Code, meanwhile, comprises a cognitive as well as a behavioral component, and states that “a person is not responsible for criminal conduct if at the time of such conduct as a result of mental disease or defect he lacks substantial capacity either to appreciate the criminality (wrongfulness) of his conduct or to conform his conduct to the requirements of the law”.

In those cases where insanity is ascertained, the defendant would be adjudicated either not guilty by reason of insanity (NGRI or NGI) or guilty but not criminally responsible, depending on the legal system5.

A negative attitude toward the insanity defense has been reported, and it has been found to be associated with juror judgments6,7.

A common perception by the lay public is that the insanity defense is overused and might allow criminals to avoid punishment, a belief that appears to entail an implicit distrust regarding the underlying forensic mental health evaluations610.

Such a perception, however, might be inaccurate in view of the existing data. For instance, in a dated pioneering study, it was found that insanity pleas are raised in about 1% of felony cases and proving successful only in about 28% of those cases11.

Nevertheless, a more recent study from our group showed 42% of insanity judgments among evaluated defendants12. These differences are mainly due to different legal thresholds for admitting psychiatric evidence in criminal cases that vary broadly.

A possible source of distrust lies however in the frequent disagreement among experts, with a recent meta-analysis showing that forensic evaluators disagreed 25–35% of the time13. This may be associated with the intrinsic limits of psychiatric diagnosis, the different and non-standardized evaluation methodologies2,14, and with the longitudinal variability of psychiatric symptoms, implying that evaluations carried out at different times can lead to different conclusions on the same case.

As a consequence, expert evaluation has often been considered a “battle of the experts” rather than accurate, objective, and reliable testimony on the defendant’s criminal responsibility—in particular in adversarial legal systems15.

The absence of biological markers available to guide forensic psychiatric evaluations, and the relative scarcity of reliable and diagnostic tools to guide such assessments, might also account for discrepancies between expert testimonies.

In addition, the paucity of research on insanity evaluations implies poor empirical support underlying such assessment2. Finally, the dialectic of the criminal trial must be acknowledged, where different parties plead their case, which entails the possibility of different opinions, which the court or jury weighs.

At the same time, we should be cautious in interpreting this finding13, since this analysis concerns those cases that went to trial. In some jurisdictions, when the experts agree, the cases may not go to trial.

Efforts have been made to guide and structure criminal responsibility evaluations, for example the American Academy of Psychiatry and Law published practice guidelines for insanity defense evaluations5, which mainly deal with the steps and information needed to perform them.

Among the forensic assessment instruments to assist the criminal responsibility evaluation, are the “Mental State at the Time of the Offense Screening Evaluation” (MSE)16 and the “Rogers Criminal Responsibility Assessment Scales” (R-CRAS)17,18.

The MSE is a semi-structured interview to screen out defendants whose criminal conduct clearly was not caused by significant mental abnormality19. The R-CRAS was developed from the American Law Institute’s criteria for the insanity defense, and is composed of 25 items organized into 5 scales assessing: reliability (including malingering), organic factors, psychopathology, cognitive control, and behavioral control18.

In addition, some theoretical models have been proposed to guide the insanity evaluation2024. However, to the best of our knowledge, a valid instrument that could be useful to guide mental health experts in criminal responsibility assessments in different jurisdictions, is lacking. This is a lacuna that deserves to be addressed, considering the significant forensic and procedural implications of psychiatric evaluations. Basically, two types of errors may occur:

  1. An (insane) defendant who is mistakenly considered to be accountable for a crime, despite the presence and influence of a significant psychiatric disorder on his criminal behavior, will find himself/herself punished for a crime for which he should not be held responsible. No justice is being done. Moreover, he could enter the penitentiary system with fewer possibilities to be treated for his disease.
  2. A (sane) defendant who is erroneously acquitted because considered insane at the moment of the crime will not be punished for a crime he/she should have been held responsible for. No justice is being done. In addition, he/she will enter a forensic psychiatric system, by using treatment resources that are usually limited.

Differences in methodology used in insanity assessments may also have consequences for the principle of equal rights for all citizens before the law, which should be guaranteed in the European Union.

Furthermore, the availability of a tool that can be used in forensic psychiatric practice could facilitate the exchange of empirical data in research across different jurisdictions and disciplines, thus implementing the evidence that could be of empirical support.

Some efforts to shed light on the processes underlying forensic evaluators’ decision-making during the insanity assessment have already been made12,25,26.

The aim of this study was to develop the Defendant’s Insanity Assessment Support Scale (DIASS), an instrument, which can be useful to support, structure, and guide the insanity assessment across different jurisdictions, in order to improve reliability and consistency of such evaluations.

Medical College of Georgia at Augusta University



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