Forensic Neurology and the Role of Neurologists in Forensic Evaluations

Making Complex Neuropsychiatric Diagnoses

Many neuropsychiatric diseases are complex and require a careful clinical interview, evaluation of collateral data, and integration of advanced and quickly evolving diagnostic testing. While forensic psychiatrists will be familiar with this general process in making psychiatric diagnoses in forensic cases, the specific work-up for certain neuropsychiatric disorders may extend beyond the typical expertise of a forensic psychiatrist.

Regarding the clinical history, some symptoms may lead experts inexperienced with neuropsychiatric disorders toward the wrong diagnosis. For example, a patient demonstrating disinhibition may lead to a diagnosis of bipolar disorder, whereas the presence of concurrent onset of apathy, hyperorality, and perseverative motor behaviors in a middle-aged adult without prior psychiatric symptoms would instead direct a well-trained behavioral neurologist toward the diagnosis of behavioral-variant frontotemporal dementia (bvFTD).¹⁴ Similarly, in patients with episodic spells involving loss of awareness, derealization, or sudden onset panic, the possibility of seizures can be overlooked in favor of a psychiatric diagnosis (e.g., panic disorder or dissociative disorders) or malingering.²² While many psychiatrists might be familiar with these presentations, behavioral neurologists have specific training in diagnosing patients with complex symptomatology and in probing for both psychiatric and neurological symptoms that may be relevant for diagnosis.

The neurological examination is also crucial for making certain neurological diagnoses. For example, the diagnosis of Parkinson’s disease can be made clinically based entirely on the neurological examination showing cardinal features of rigidity, bradykinesia, tremor, abnormal gait, and masked facies.²³ It is also important to differentiate Parkinson’s disease from related disorders such as progressive supranuclear palsy (PSP) or corticobasal degeneration (CBD), types of frontotemporal lobar degenerations with different exam findings, or from Lewy Body dementia (DLB), which has different clinical symptoms, time-course, and progression.

Increasingly, neurodiagnostic testing is used to make certain diagnoses. In some cases, the diagnosis may be obvious from the imaging, such as tumors or acute ischemic strokes or hemorrhages. In other cases, neuroimaging findings may be subtle. For example, cortical atrophy on MRI can support the diagnosis of Alzheimer’s disease or frontotemporal dementia but may be subtle and difficult to identify in those lacking experience diagnosing and treating patients with those diseases.^24,25 Some imaging findings are inherently nonspecific and must be interpreted carefully when considering differential diagnosis. For example, white matter hyperintensities are common findings on MRI that can be found in a range of diagnoses, including traumatic brain injury (TBI), vascular disease, migraine, or multiple sclerosis. Imaging might also be inappropriately applied to establish a neurological diagnosis. For example, diffusion tensor imaging (DTI) is often used in medicolegal cases to establish a diagnosis of mild TBI despite many recommendations and guidelines that DTI is not currently indicated for clinical use in this circumstance.²⁶ Without experience in the appropriate use and potential misuse of such neuroimaging modalities, inappropriately presented evidence may go unchallenged. These examples highlight a crucial benefit of including behavioral neurologists in cases involving neuroimaging by integrating any neuroimaging findings with clinical diagnostic and behavioral assessments, a step beyond expert opinions provided by neuroradiologists.

Beyond neuroimaging, other diagnostic tests are increasingly necessary for neuropsychiatric diagnoses. For example, EEG abnormalities in persons with suspected seizures strongly support the diagnosis of epilepsy, but care must be taken when interpreting the specific EEG abnormalities, as both nonspecific abnormalities and a normal EEG can be misinterpreted. Specialized tests of biomarkers in Alzheimer’s disease and Parkinson’s disease are quickly becoming incorporated into diagnostic algorithms, such as testing for amyloid and tau using positron emission tomography (PET), cerebrospinal fluid, or blood biomarkers as advocated for in the recently proposed National Institute on Aging and Alzheimer’s Association criteria for the diagnosis of Alzheimer’s disease.²⁷ Importantly, these guidelines and available diagnostic tests are rapidly evolving and their implementation and interpretation may be challenging for psychiatrists without continued training in behavioral neurology.

Localizing Neuropsychiatric Symptoms

Beyond diagnosis, behavioral neurologists can help to strengthen opinions regarding alterations to mental states using the process of localization. Localization seeks to provide a neuroanatomical explanation for an individual’s unique set of cognitive, behavioral, and neuropsychiatric symptoms, providing a scientifically grounded link between a neuropsychiatric diagnosis and possible mental states. The process of localization is therefore useful in forensic contexts, where neuropsychiatric diagnoses must be shown to have affected a person’s mental state in a specific manner to have relevance.

Like the diagnostic work-up for neuropsychiatric diseases, the approach to localization in behavioral neurology is advancing rapidly. While the classical approach to neurological localization (e.g., overlapping lesions causing similar symptoms to identify brain regions involved in a particular process) has been fruitful, it has been difficult to localize complex neuropsychiatric symptoms using these methods. For example, many different brain regions have been associated with the development of criminal behavior, including ventromedial prefrontal cortex (vmPFC), orbitofrontal cortex (OFC), the dorsolateral prefrontal cortex (dlPFC), the anterior cingulate cortex (ACC), anterior insula (AI), the anterior temporal lobes, the amygdala, and the nucleus accumbens or ventral striatum.^28,–,31 Alternative approaches to understanding these complex neuropsychiatric symptoms by localizing symptoms to brain networks or circuits, rather than brain regions, has significantly advanced our understanding of behaviors ranging from delusions^{13,15,17,–,20,32} and hallucinations^12,33 to disordered free will perception^10,21 to even new-onset criminal behavior itself.^30,31,34 The strong theoretical basis for understanding certain symptoms as “disconnection syndromes,”^35,–,39 combined with methodological advances to test for functional disconnection syndromes using the human connectome,^15,33,40 have provided exciting new approaches toward localizing neuropsychiatric symptoms relevant for forensic evaluations.

As a recent example, studies in neurological patients have begun to investigate the brain-behavior relationships between damage to specific parts of the brain and the development of criminal behavior.^30,31 Seventeen cases of lesions causing new-onset criminal behavior were found to occur in different parts of a common frontotemporal brain network involved in moral decision-making, a finding replicated in 23 cases where the causal relationship between lesion onset and criminal behavior was less clear (because it was unknown whether the brain lesion occurred before or after the criminal behavior).³⁰ This localization was specific, as lesions that did not cause criminal behavior fell outside of this network.³⁰ While this should not suggest that all or even most patients with lesions to this network will develop criminal behavior, it does suggest that damage to this network may predispose patients to developing criminal behavior, and could be used to provide a neuroanatomical basis for an opinion as to whether a neuroimaging abnormality could conceivably have contributed to a criminal defendant’s behavior. Further, the study found that the network associated with acquired criminal behavior was involved in moral decision-making, and specifically in the processes of value-based decision-making (e.g., tasks of reward and punishment and neuroeconomics) and theory of mind, suggesting capabilities that may be important when considering whether criminal behavior is related to a neuropsychiatric disorder. Antisocial behaviors are also increased in patients with other diseases causing damage to this network, including frontotemporal dementia,^41,–,50 Huntington’s disease,^51,–,55 and Parkinson’s disease patients’ developing impulsive and compulsive behaviors after receiving dopamine agonists.^31,34,56

An important caveat is that this process of localization, while beneficial, cannot provide direct evidence regarding a person’s mental state at the time of a crime.⁵⁷ At best, neuroimaging and localization can provide a basis for establishing and supporting certain neuropsychiatric deficits that, in the right context, could contribute to a criminal act in a manner that is forensically relevant. A related challenge is establishing causality between the neuroimaging findings and the resulting behavior. Ideally, more definitive evidence of causality between a neurological disease and criminal behavior would require historical evidence of a time when both the neurological disease and problematic behaviors were absent, with antisocial behavior only emerging after the onset of disease. Such a history may be absent or challenging to establish. For example, the causal relationship between TBI and criminal behavior is often difficult to determine.³¹ Antisocial behavior, drug and alcohol use, and risky, impulsive behaviors are all risk factors for having a TBI,⁵⁸ making it difficult to establish that criminal behavior following a TBI was caused by the injury and was not related to these preexisting factors. It is also possible that the neuropsychiatric effects of a TBI could exacerbate or add to preexisting risk factors for crime, again adding complexity to the process of localization.

Legal Relevance of Neuropsychiatric Symptoms

Even if a brain lesion is determined to causally contribute to a defendant’s criminal behavior, the implications for criminal responsibility determinations may be more complicated and nuanced. For instance, a focal brain lesion that reduces a defendant’s capacity for weighing moral considerations during decision-making may meet the moral incapacity test found in some jurisdictions’ legal insanity criteria. Defendants with frontal lobe diseases may have preserved knowledge that their criminal behavior was illegal and wrong by societal moral standards (i.e., objective moral wrongfulness), but may lack an ability to recognize this wrongfulness in the moment, to appreciate moral wrongfulness as an emotionally negative experience, or to consider this wrongfulness appropriately when reasoning about moral decisions. In such contexts, the defendant might only be eligible for meeting insanity criteria in jurisdictions that permitted subjective moral wrongfulness standards. Determining whether the legal insanity criteria refer to subjective versus objective moral wrongfulness or both will in many cases be a question for the trier of fact to decide, as many jurisdictions in the United States do not specify which type of wrongfulness is to be applied.⁵⁹ For a forensic psychiatrist, determining a defendant’s appreciation of moral wrongfulness will likely prove more challenging with a defendant with a frontal lobe syndrome than with a defendant with a primary psychotic disorder experiencing irrational delusions and hallucinations. A behavioral neurologist can be beneficial in such cases by carefully delineating the type of socioemotional dysfunction mediated by frontal lobe injuries (e.g., loss of social semantic knowledge, emotion recognition, empathy, perspective taking, hyper-reward, deficits in loss aversion, loss of context-specific reward cues, limbic reactivity, etc.) and relating these deficits to the legal standard in a given case.

Similarly, the factors related to competency to stand trial in persons with possible dementia are likely quite different than in persons with psychotic disorders. For instance, memory impairment may be common, but the severity and extent of memory impairment may vary from person to person. Thus, experience in evaluating persons with memory disorders, what types of memories are or are not affected in persons with dementia, the expected time-course for memory disorders, and whether certain facts in the case are consistent with the proposed time-course, are crucial when determining whether a defendant is competent to stand trial. Similarly, evaluating for the possibility of malingering requires careful consideration of how the defendant’s reported abilities to confer with counsel are consistent or inconsistent with functional abilities in other situations, other time-points, and with other pieces of diagnostic evidence like neuroimaging. Beyond cognition, neurologists are also trained to evaluate for inconsistencies on the other portions of the neurological examination that are suggestive of malingering, which could provide additional support for deception.

Forensic Training for Behavioral Neurology

Unlike psychiatry, neurology has no established training or professional group aimed at educating neurologists in how to address legal questions in criminal cases. Thus, neurologists with such expertise are extremely rare. Forensic expertise for neurologists comes from direct experience agreeing to work on forensic cases, or from collaboration and guidance from attorneys or forensic psychiatrists. While valuable, the above mechanisms are clearly inadequate, and greater effort should be made to provide forensic training to behavioral neurologists. For example, educational opportunities designed for forensic psychiatrists, such as the AAPL annual meeting, AAPL forensic review course, Virtual AAPL, AAPL Ethics Guidelines, and AAPL Forensic Practice Guidelines, can provide a strong starting point and might easily be adapted for neurologists interested in forensic work. Exposure to forensic topics in neurology residency, or in behavioral neurology and neuropsychiatry fellowship, is another mechanism for advocating for involvement of behavioral neurologists in forensic evaluations.

Neurology Training for Forensic Psychiatry

In parallel, increased efforts to provide education on recognizing and assessing neurological disorders and responding to neurological evidence would be valuable additions to forensic psychiatry education and training. Such training could become a part of all forensic psychiatry fellowship programs, or specific programs might opt for a unique neuropsychiatry track focusing on these topics. Psychiatrists completing a fellowship in behavioral neurology or neuropsychiatry would be eligible to pursue a second fellowship in forensic psychiatry. Neurologists completing the identical fellowship in behavioral neurology or neuropsychiatry, however, would not be eligible to pursue a forensic psychiatry fellowship or join AAPL because unlike the behavioral neurology and neuropsychiatry fellowship, which is open to both neurologists and psychiatrists, forensic psychiatry does not currently allow for other physicians to participate. More inclusive membership in AAPL could lead to improvements in the cross-training between forensic psychiatry and behavioral neurology.

Using a Team-Based Approach

Behavioral neurologists may be identified who are interested in forensic work but lack prior experience addressing legal questions. In such cases, collaboration with experts who do have this experience and skill, such as forensically trained psychiatrists, can be an appropriate strategy. For instance, a behavioral neurologist may provide an expert opinion regarding the individual’s diagnosis and resulting cognitive, behavioral, and neuropsychiatric impairments, whereas a forensic psychiatrist might rely on such opinions to inform an opinion regarding the specific legal question at hand (e.g., relying on the neurologist’s interpretation of EEG and neuroimaging findings and diagnosis of temporal lobe epilepsy in a case involving postictal violence). In other circumstances, both a neurological disease and a primary psychiatric illness may be present and pertinent to the legal question, requiring separate but overlapping opinions from a behavioral neurologist and forensic psychiatrist. A forensic psychiatrist may benefit from consultation with a behavioral neurologist or integrating a behavioral neurologist’s findings in cases where opposing experts appear to be misrepresenting, distorting, or exaggerating data from neuroimaging, EEG, biomarkers, neurological examination, or neuropsychological evaluation.

Additionally, there are instances in which forensic psychiatrists may determine that the legal question being asked falls outside of their scope of expertise and would be best referred to a behavioral neurologist. For example, in cases involving focal brain lesion from tumors and strokes and where the question arises whether these lesions caused new-onset criminal behavior or whether this mental defect meets insanity criteria for a particular jurisdiction, psychiatrists may yield to behavioral neurologists unless they have advanced training and expertise in these areas. Similarly, although forensic psychiatrists may be comfortable making the diagnosis of behavioral variant frontotemporal dementia (bvFTD), they may refer retaining attorneys to behavioral neurologists for criminal responsibility questions relating the extent of brain atrophy and severity of the disease to deficits in social cognition, emotion regulation, motivation, and moral decision-making.

Forensic psychiatrists may rely on opinions from neuropsychologists regarding evidence such as performance-based tests of cognitive functions and response-based measures of psychopathology, in a similar manner as they may rely on opinions from neurologists regarding neurological examination findings and diagnostic testing evidence. In competency to stand trial evaluations in which a bona fide doubt is raised because of concerns of dementia, there can be synergistic value in independent evaluations and opinions from a forensic psychiatrist, neuropsychologist, and behavioral neurologist utilizing each discipline’s distinct skill sets. Similarly in cases of criminal responsibility or mitigating circumstances, having a multidisciplinary approach with a forensic psychiatrist, behavioral neurologist, and neuropsychologist when neurological evidence is relevant will best maximize objective truth-telling as it relates to the legal question at hand. While such a team-based approach is useful to provide a broader range of expertise and allows experts to integrate important findings from other disciplines, care must be made to ensure that opinions remain independent between different experts, and that the behavioral neurologist, with less forensic experience, does not simply take the position of the forensic psychiatrist, and vice versa.

U.S. v. Robert Brockman

On October 1, 2020, Robert Brockman, a 79-year-old wealthy businessman, was accused of hiding over $2 billion dollars from the IRS in the largest tax evasion case in U.S. history.⁶⁰ Shortly thereafter, on December 8, 2020, his defense team filed a motion requesting a competency hearing based on the claim that Mr. Brockman experienced dementia.

To evaluate these claims, both the defense and the prosecution hired experts in psychiatry, neuropsychology, neuroradiology, and neurology. Evidence included MRI scans, FDG-PET scans, EEG studies, sleep studies, laboratory tests, amyloid PET scans, dopamine transporter (DAT) scans, neuropsychological evaluation, and neurological examinations. The neurologists in the case served several important purposes. First, the neurological examinations provided the basis for the diagnosis of Parkinson’s disease, which had important implications for the etiology of various reported symptoms. Second, the neurologists guided the ordering and interpretation of various diagnostic studies, based on expertise in which studies would help to address both the diagnostic question but also the forensic questions in the case. Third, the neurologists used their expertise in the presentation and evolution of neurodegenerative disorders to support opinions about whether the defendant’s reported symptoms and demonstrated capacities were consistent or inconsistent with the known and expected disease course, helping to support or refute claims of malingering. Fourth, the neurologists used their skills matching the severity and localization of neuroimaging findings with the reported extent and severity of Mr. Brockman’s claimed cognitive impairment to help inform opinions regarding plausibility and possible malingering. These roles complemented the role of the forensic psychiatrists, who focused on the question of malingering, and of the neuropsychologists, who used neuropsychological measures to support or refute claims of dementia and symptom and performance validity tests to help support or refute questions of malingering. Ultimately, the court ruled that while Mr. Brockman had a diagnosis of Parkinson’s Disease and mild cognitive impairment, he was competent to stand trial, citing evidence presented by the neurologists in support of this opinion.

U.S. v. Robert Bowers

On October 27, 2018, Robert Bowers committed the deadliest attack against the Jewish community in U.S. history, killing 11 and wounding six others.⁶¹ It was never disputed that he was the killer, and the jury found him guilty on all 63 charges on June 16, 2023. The real trial, however, began at the sentencing phase to answer the question posed by his defense team: did Mr. Bowers have brain damage that made him unable to control his behavior, and were the antisemitic beliefs that motivated the attack delusions?

Evidence presented during the trial included MRI scans, PET scans, EEG tests, and neuropsychological testing, and neurological examination findings looking at the structure, function, physiology, and performance of Mr. Bowers’s brain. Contrasting narratives were produced by the defense and prosecution regarding what neurological disorders were present, whether there were any behavioral, cognitive, or neuropsychiatric symptoms related to those behaviors, and ultimately what affect these symptoms had on his specific criminal actions. Behavioral neurologists testified for both the defense and the prosecution regarding not only the interpretation of neuroimaging and other diagnostic testing, but also regarding frontal lobe or limbic syndromes that could affect Mr. Bowers’s ability to conform his behavior to the requirements of the law, as well as possible neurological basis for any potential delusions he may have held. This testimony was importantly distinguished from the testimony of retained forensic psychiatrists and psychologists in the case, who focused on the question of schizophrenia, and the role of neuroradiologists, nuclear radiologists, and research neuroscientists in the case, who focused on analysis of the neuroimaging but did not perform evaluations of Mr. Bowers, make diagnoses, or link neuroimaging findings to his behavior or conduct. Mr. Bowers was ultimately sentenced to death on August 2, 2023.⁶² Several of the mitigating factors the jury was asked to consider were directly related to the expert neurologist’s testimony, such as the question of whether Robert Bowers has brain abnormalities.⁶³