brain lesions and criminal behavior 2009

Brain Lesions and theirImplications in CriminalResponsibility

Shelley Batts, Ph.D.*

For over 200 years, Western courts have considered pleas of‘‘not guilty by reason of insanity’’ (NGRI) for defendants inpossession of a mental defect rendering them unable tounderstand the wrongfulness of their act. Until recently,determining the mental state of a defendant has fallenlargely upon the shoulders of court psychologists andexperts in psychiatry for qualitative assessments relatedto NGRI pleas and mitigation at sentencing. However,advances in neuroscience—particularly neurological scan-ning techniques such as magnetic resonance imaging(MRI), functional magnetic resonance imaging (fMRI),computed tomography scanning (CT), and positron emis-sion tomography scanning (PET)—may provideadditional, pertinent biological evidence as to whether anorganically based mental defect exists. With increasingfrequency, criminal defense attorneys are integrating neu-roimaging data into hearings related to determinations ofguilt and sentencing mitigation. This is of concern, sincenot all brain lesions and abnormalities indicate a com-promised mental state that is relevant to knowing whetherthe act was wrong at the time of commission, and juriesmay be swayed by neuroscientific evidence that is notrelevant to the determination of the legal question beforethem. This review discusses historical and modern casesinvolving the intersection of brain lesions and criminality,neuroscientific perspectives of how particular types oflesions may contribute to a legally relevant mental defect,and how such evidence might best be integrated into acriminal trial. Copyright # 2009 John Wiley & Sons, Ltd.

Behavioral Sciences and the Law

Behav. Sci. Law 27: 261–272 (2009)

Published online in Wiley InterScience

(www.interscience.wiley.com) DOI: 10.1002/bsl.857

*Correspondence to: Shelley Batts, Ph.D., Neuroscience Program, The University of Michigan, U.S.A.E-mail: [email protected]

Copyright # 2009 John Wiley & Sons, Ltd.

NEUROSCIENCE AND THE LAW:THE TWAIN HAVE MET

The development of noninvasive techniques to observe blood flow (either directly or

indirectly, as with glucose uptake) and structures in the functioning human brain has

been a boon to advancing knowledge of how damage to particular neural structures

can correlate with shifts in behavior. As important determinations in criminal

proceedings rely on judgments of a defendant’s state of mind at the time of the crime,

it may have been only a matter of time before neuroimaging evidence found its way

into the courtroom. An influential instance where structural neuroimaging evidence

was presented in a criminal proceeding was in 1991, in the second-degree murder

case involving 64-year-old defendant Herbert Weinstein. During a heated argument

with his wife, the advertising executive strangled her to death and then threw her

body from the window of their apartment to make it appear a suicide (Rojas-Burke,

1993). Weinstein’s lawyer claimed that his client was not responsible for his actions

due to a mental defect: a large cyst located in the membranous casing of the brain

(the arachnoid membrane) had increased the pressure on his frontal cortex, creating

metabolic imbalances in the region, which decreased his ability to tell right from

wrong (Figure 1). Expert testimony from a forensic psychologist for the prosecution

was presented arguing that arachnoid brain cysts were often benign and that no

established correlation existed connecting such cysts to criminal actions. However,

at a pretrial hearing, the judge ruled that the jury could hear that Weinstein had a

brain cyst, but not that such cysts or abnormal brain metabolism increase violent

tendencies. Weinstein pled guilty to the reduced charge of manslaughter.

Prior to the Weinstein case, neuroimaging evidence had been presented in a few

rare cases. In 1981, the attorneys for John Hinckley, Jr. tried to introduce a CAT

scan of Hinckley’s brain through expert witness Dr. David Bear as part of an NGRI

defense (Dumit, 1999). Both the defense and prosecution said such evidence had

never been admitted as evidence in an American courtroom, and the judge decided

to dismiss the jury, during which time he heard arguments about the CAT scan’s

Figure 1. PET and MRI images from defendant Herbert Weinstein, performed by Dr. Abass Alavi at theUniversity of Pennsylvania Hospital in 1991. Left: MRI scan reveals the neural architecture of Weinstein’sbrain, with the large black area representing the cyst in the frontal temporal area of the brain. Right: FDG-PET scan of Weinstein’s brain, showing altered (lowered) glucose metabolism in the brain areas around

the cyst. Adapted from The Journal of Nuclear Medicine, 34(1), Jan 1993

Copyright # 2009 John Wiley & Sons, Ltd. Behav. Sci. Law 27: 261–272 (2009)

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262 S. Batts

relevancy. The expert explained to the judge that the CAT scan illustrated that

Hinckley had widened sulci—the ridges in the brain formed by its folds (Taylor,

1982). Histopathological studies consistently reveal that people with schizophrenia

are more likely to have widened sulci than normal controls, with an estimated one-

third of the schizophrenic population exhibiting this particular brain defect while less

than one in 50 normal controls show the same abnormal structures (Dumit, 1999).

After several rounds of arguments, the CAT scan was eventually admitted into

evidence and was considered alongside more traditional neuropsychological

evidence and testimony, despite the unknown significance of widened sulci to the

ultimate issue of Hinckley’s sanity. Ultimately, Hinckley was acquitted and

committed to St. Elizabeths Hospital.

In a similar case, defense attorneys in the embezzlement trial of a former United

Way executive William Aramony used an MRI scan to argue a ‘‘shrinking brain’’

defense for their client; the scan also showed widened sulci (Chandrasekaran &

Miller, 1994). Due to Aramony’s supposed diminished mental capacity, it was

argued he was unable to form the requisite criminal intent to commit the crime of

embezzlement. Both Weinstein and Aramony were plead guilty to lesser charges,

suggesting that the impact of neuroimaging—with or without merit—is not a trivial

one.

Neuroimaging evidence is by no means a guarantee of a successful NGRI or

mitigation defense though. In 2002, in United States v. Mezvinsky the defense

argued following his indictments on 66 counts of fraud (2002) that the defendant

suffered from mental illness, specifically bipolar disorder and frontal lobe damage.

Defense attorneys wanted to present PET scans to support the claim that the

defendant was incapable of deception, the requisite mens rea for the fraud charges,

but this request was denied because the judge considered the evidence more

prejudicial than probative.

Neuroimaging has also been presented as evidence for mental illness and

sentencing mitigation, as in the case where a PET scan saved mass murderer Barry

Wayne McNamara from the death penalty in 1985 (Emmons, 1989), although the

presentation of neurological evidence as part of a criminal defense or sentencing

mitigation is more common (Snead, 2007). However, it is yet to be determined what

the proper impact and role of such evidence should be in legal proceedings: how

neuroscience can best assist the law without encouraging bias or allowing

rationalization of crime. Furthermore, while neurological scans are invaluable in

medical diagnoses and neuroscientific studies of brain regions, their use in

connecting data about brain lesions to criminal behavior should not be over-

estimated. The usefulness of neurological scans may be limited to the detection of

lesions rather than a tool to explicate brain states, and this should be considered a

caveat of any discussion of brain lesions and behavioral changes (Morse, 2006).

In comparison to the multi-faceted descriptions of behavior in psychology, the

viewpoint of the courts is simpler. To the law, human behavior generally exists in a

dichotomy of guilty and not guilty. Between these ‘‘black and white’’ extremes lie

pleas of ‘‘not guilty by reason of insanity’’ as well as various intermediate mental

defenses and arguments for sentencing mitigation (e.g. mens rea defense). These rest

upon the notion that impaired mental states should reduce criminal liability. The

legal system’s analysis of behavior is aimed at creating a fair judicial system that

discourages and punishes actions deemed socially malevolent by dispensing


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Brain lesions and criminality 263

punishments that deprive criminal offenders of freedom (and in the extreme, life).

The behavioral and biological sciences, including the neurosciences, consider

human behavior in a fundamentally different way than the law, by engaging in the

scientific study of the organic, neural roots of normal and abnormal human behavior.

To the neurosciences, it is the causality of behavior that is of the highest interest,

considered to be the result of a combination of complex genetic and environmental

factors, which affect brain development and function. Conversely, to the law, it is the

effect of a particular behavior that is considered the most important fact.

In the United States, criminal sentencing is punitive as well as rehabilitative, with

a person being considered fully responsible for voluntary acts unless forced to

commit a crime (i.e. under duress) or if the person is found to possess a serious

mental defect in rationality compromising the ability to know right from wrong. This

precedent was solidified in the M’Naghten case of 1843, where a Scotsman who

assassinated an English civil servant was recognized to be delusional and therefore

not responsible. Most states allow for an insanity test that is a version of either the

M’Naghten insanity standard or that of the American Law Institute (ALI). Both

the M’Naghten and ALI standards include a cognitive prong including knowledge

(M’Naghten) or appreciation (ALI) at the time of the criminal act that the act was

wrong. Conditions constituting a defective ability to know or appreciate the

wrongfulness of the act typically include mental illness and mental retardation

(Dalby, 2006). Other conditions such as voluntary intoxication with the requisite

cognitive deficit at the time of the act may allow for conviction of a lesser included

charge or a mitigated sentence but not a full acquittal based on insanity. A brain

lesion, depending on its size, location, and resulting implications in psychological

function, could in principle serve as a mental defect for purposes of the insanity

defense or other mental defense.

Additionally, juvenile crime is, to varying degrees, judged differently than adult

crime, as maturity is seen to affect moral judgment and knowledge of how behavior

conforms to societal norms (Loeber, Farrington, Stouthamer-Loeber, & Van

Kammen, 1998). Neuroscience has informed this determination, to a degree. A brief

filed by the American Medical Association in Roper v. Simmons (2005), the case in

which a divided Supreme Court struck down the death penalty for those under 18

years of age, argued that since ‘‘adolescent brains are not fully developed’’ in the

prefrontal regions they are less able than adults to control their impulses and should

not be held fully accountable ‘‘for the immaturity of their neural anatomy’’ (Rosen,

2007).

If one accepts that the brain causes all mental states, and mental states do come to

bear on criminal responsibility and the appropriate punishment, then an increased

understanding of the biological nature of relevant mental states—and any organic

disruptions to the brain that might exist—would provide an increasingly precise and

truthful account of a defendant’s capacity to knowingly and purposefully commit

crime. To be clear, this is not to excuse criminal behavior or to provide a wedge for

brain scans to become a ‘‘get out of jail free card.’’ Indeed, the law should view

purported ‘‘brain abnormalities’’ with caution and confine precedent-setting

decisions regarding lesions to those that are solidly informed by published,

reproducible studies. The purpose of considering the relevance of brain lesions to the

law would be to provide additional relevant evidence which could come to bear on

judging whether a mental defect exists, whether it is of abnormal neurological origin,


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264 S. Batts

and whether it is possible that the defect either increased the likelihood of

committing a crime or reduced the ability to exert control and moral judgment.

FOCAL LESIONS CAN PRODUCE SPECIFICALTERATIONS IN BEHAVIOR

It is important to assess whether a neurological lesion could provide a reasonable

foothold for arguing that a particular cognitive faculty had been compromised. The

brain is an immensely complex organ presenting unique challenges for those who

wish to reduce it simply. However, the dominant paradigm of current neuroscientific

studies suggests that localized areas of the brain are responsible for some discrete

behaviors, and when impaired through injury or disease may explain aberrant

behaviors. For example, the motor and pre-motor cortices have neural regions that

precisely correspond to the movement of particular parts of the body. Strokes or head

trauma in this region can result in the loss of movement in just one or two isolated

body parts, depending on the size and location of the damage. Complex cognitive

processing can be focally damaged as well. The neural structures responsible for

understanding, processing, and producing language are lateralized to the left

hemisphere in the vast majority of people, with two small regions called Broca’s and

Wernicke’s areas completely dedicated to this function (Figure 2). Injuries that result

in the destruction of Broca’s area, responsible for language processing and speech

production, leave the person unable to effectively communicate in fluent,

Figure 2. Map of relevant human brain regions mentioned, including the prefrontal area, Broca’s andWernicke’s areas, and the primary motor cortex. Retrieved October 13, 2008, from Review of the Universe,

www.universe-review.ca


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grammatical sentences although they can understand what is being said and transmit

halting speech that has content. Conversely, the destruction of Wernicke’s area

results in a completely different type of deficit—a person can no longer understand

or meaningfully use language, and while the person can produce copious speech, it is

‘‘word salad,’’ a perfectly grammatical jumble of nonsense. These specific deficits

illustrate how the loss of a particular brain region due to injury can result in

substantial changes in behavioral output, of which the neurologically damaged

person may or may not be aware. Equally, focal lesions have been described in

regions of the brain noted to be involved in components of intentional action,

regulation of emotion and aggression, self-control, and the ability to judge and act

morally. Some of the case studies and investigations involving the better-established

and most relevant lesions will be discussed, beginning with a case that has shaped the

field of neuroscience.

PREFRONTAL CORTEX: MORAL ACTIONAND SELF CONTROL

For hundreds of years before modern medicine, the frontal lobes had been

considered the seat of intelligence, individual personality, and decision-making—

but it was the published medical case of Phineas Gage that solidified the theory. On

September 13, 1848, railroad worker Phineas Gage suffered a devastating brain

injury when a three-and-a-half foot long tamping iron packed with gunpowder

blasted through the left side of his face, shattering his upper jaw and destroying his

left ventromedial frontal cortex (Figure 3). Despite this incredible injury, he was

coherent and conscious for the ride into town to see physicians Edward H. Williams

and John Martyn Harlow, who marveled that their patient had survived seemingly

Figure 3. Rendered computer generated image (CGI), using a standard human skull as reference,plotting how the tamping iron entered Gage’s skull at a diagonal angle and destroyed a large part ofhis prefrontal cortex. Retrieved October 21, 2008, from National Institute of Neurological Disorders and

Stroke (NINDS) public domain website: www.ninds.nih.gov/health_and_medical/pubs/tbi.htm


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266 S. Batts

with faculties intact, and saw fit to publish articles about Gage’s injury and

subsequent recovery. Although Harlow’s initial report did not emphasize

psychological changes that occurred as a result of Gage’s injury, a later article in

1868 described the now-classic case of a severe personality disruption associated

with damage to the prefrontal cortex (Harlow, 1848, 1868). Harlow contrasted a

hard-working, polite, and well liked Gage prior to the injury, with a Gage now:

. . .fitful, irreverent, indulging at times in the grossest profanity (which was notpreviously his custom), manifesting but little deference for his fellows, impatient ofrestraint or advice when it conflicts with his desires, at times pertinaciously obstinate, yetcapricious and vacillating, devising many plans of future operations which are no soonerarranged than they are abandoned. . . A child in his intellectual capacity andmanifestations, he has the animal passions of a strong man (Macmillan, 2000, p. 52).

Harlow’s account was further embellished over the years by others in the popular

and medical press, until by the early 20th century the long-dead Gage came to

represent a Dr. Jeckyll/Mr. Hyde persona whose every fault could be attributed to his

amazing injury (Macmillan, 2000). However, it is now accepted that, while the exact

extent of personality change due to Gage’s lesion cannot be quantified, some real

qualitative, negative change in Gage’s ability to make moral decisions did occur

following the damage—mirroring other modern cases of prefrontal damage. And

beneath the tall tales and fish stories, a basic truth is embedded in Gage’s story that

has played a tremendous role in shaping modern neuroscience: that the brain is the

physical manifestation of the personality and sense of self, and that focal damage to

brain areas can results in focal changes in behavior and personality while leaving

other aspects of the self unchanged.

More than a century after Phineas Gage had died, the involvement of the

ventromedial frontal cortex in moral action was further explored by neuroscientist

Antonio Damasio in the case study of EVR, a 35 year old man whose left and right

orbital and lower mesial cortices (including the prefrontal area) were removed after the

diagnosis of a cancer called orbitofrontal meningioma (Eslinger & Damasio, 1985).

Prior to the cancer, EVR had been described as a paragon of morality, loved by his

friends, his wife, and his two children. Following his surgery to remove the cancerous

lesion in his brain, while his intelligence and memory remained unchanged, his ability to

act appropriately and morally had been dramatically compromised. A string of poor

decisions led to his financial ruin, the loss of his family and job, and a marriage to a

prostitute who he divorced six months later (Damasio, Tranel, & Damasio, 1990).

Interestingly, Damasio’s further work with EVR parsed out that, while his ability to

morally judge situations was not largely impaired, his ability to act effectively in

‘‘ethically charged’’ situations was now extremely poor (Bechara, Damasio, & Damasio,

2000). When removed from a situation, EVR could report what the proper moral

response would be in certain circumstances. However, when forced to perform, EVR

and similar patients chose actions that resulted in immediate gratification even when

they knew that the long-term outcome could be disastrous or objectively immoral.

The prefrontal cortex is known to provide essential neurological inhibition to

many cognitive processes, and several types of human mental illness, such as

schizophrenia, bipolar disorder, and ADHD, have abnormal patterns of activation in

the prefrontal cortex (Krawczyk, 2002). Recent brain imaging studies have also

found that reduced prefrontal volume, abnormal activity, and fewer interconnec-

tions from the frontal lobes to the rest of the brain are common in depressed people


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(Ongur, Drevets, & Price, 1998), people who are under constant stress (Miner et al.,

2006), suicide victims (Rajkowska, 1997), incarcerated criminals (Yang et al.,

1999), sociopaths (Barkataki, Kumari, Das, Taylor, & Sharma, 2006), and female

cocaine users (Li, Kosten, & Sinha, 2006). Additionally, the prefrontal cortex

receives input from many sensory and non-sensory areas of the brain, and integrates

them into a unified informational set which informs choices and decisions. A severely

damaged prefrontal cortex would suggest that more cognitive processes, many of

which would normally be repressed or delayed, could translate into action despite a

person being aware that an action was wrong or unwise. Essentially, many types of

available information will never even enter the scope of the decision-making process.

These case studies and others suggest that the prefrontal cortex plays an important

role in self-control and the ability to effectively act morally, as well as in the delay of

immediate gratification in order to achieve a more rational or eventually more

rewarding long-term goal.

THE AMYGDALA: AGGRESSION, EMPATHYAND EMOTIONAL INTELLIGENCE

The amygdala is part of the limbic system, implicated in a variety of emotional and

motivational behaviors including aggression. In animals the amygdala also supports

perceptual vigilance—in humans, it may influence the likelihood that certain events

of affective importance reach awareness, segregating the neural representations of

the significant from the mundane. Neuroscientific studies also suggest that increased

stimulation of the amygdala can result in increased feelings of aggression and fear.

One famous historical instance of a brain lesion potentially contributing to

uncontrollable and unexplained violence is the case of a 25-year-old University of

Texas (UT) student, Charles Whitman (Lavergne, 1997). Whitman, an Eagle Scout

who joined the Marines, was an intelligent scholarship student at UT who began to

suffer from excruciating headaches, disturbing thoughts, and a compulsion for

writing. His behavior, once exemplary, changed drastically for the worse until he was

court-martialed, lost his scholarship, began hitting his wife, and noted an increasing

desire to ‘‘take a deer rifle and start shooting people’’—a fear that he related to a

campus psychologist along with the worry that something was wrong with him. In

1966, two weeks after that encounter with the psychologist, Whitman brutally killed

his wife and his mother, leaving notes expressing his bewilderment as to why he had

done it as well as how much he loved them. He then methodically shot and killed

14 people, wounding 31 others, while holed up with a small arsenal atop a 32-story

UT campus building. Whitman was killed by Austin police, and a subsequent

autopsy (which he requested in his suicide note, to determine if anything could

explain the disturbing thoughts and severe headaches he had developed) revealed

something surprising: he had a glioblastoma brain tumor the size of a walnut in the

hypothalamus region of his brain. The tumor was impacting the hypothalamus and

compressing his amygdala, hypothetically causing over-stimulation, although even

after autopsy experts were not in agreement that the lesion changed his behavior. At

that time there were no imaging analyses available that could have detected the

presence of the tumor when Whitman was alive.

As over-stimulation of the amygdala may result in uncontrollable, violent

emotions, lesions of the amygdala that impair its function result in a person with flat


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affect unable to assign the proper emotional response or meaning to memories and

actions (Volavka, 2002[SH1]). This may be relvant to NGRI or as a mitigating factor

at sentencing, since a person’s behavior might not follow from a proper emotional

response—such as being unaware that someone is in severe distress, or over-reacting

with extreme violence in response to a minor insult. Patients with amygdala lesions

exhibit normal subjective and psychophysiological responses to aversive word types

(i.e. galvanic skin response) but do not show the normal retention advantage

associated with these words (Anderson & Phelps, 2001). Damage to the human

amygdala impairs the initial perception of stimuli which have emotional significance,

suggesting that identifying emotional events is problematic for these people

(Anderson & Phelps, 2001). Normally, the amygdala enhances the perception and

memory consolidation of stimuli that have a strong emotional link (for example, the

birth of one’s child or a scene where one witnessed a murder), due to its role as neural

mediator between the limbic system and brain structures involved in memory

processing. The amygdala is also found to be activated when someone is exposed to a

linguistic threat (Isenberg et al., 1999). A patient (S.P.) with a bilateral amygdala

lesion was found to have no enhanced perception for aversive stimulus events or

emotionally charged words, where normal controls both remembered and reacted

strongly to items with emotional content (Anderson & Phelps, 2001). However, the

left amygdala seems particular important—an examination of patients with either a

left or right amygdala lesion shows that the enhanced perception of aversive words is

specifically related to the left amygdala, and fMRI confirmed that the left amygdala is

activated with the presentation of emotional, linguistic stimuli. The amygdala is also

divided into several regions with different functions, and lesions of particular areas

may result in different deficits. For example, whereas the lateral amygdala exerts

excitatory influences on the hypothalamus, the medial amygdala exerts inhibitory

influences. This means that the amygdala can exert direct excitatory/inhibitory

influence on hunger, thirst, sexual arousal, rage as well as hormonal, endocrine, and

other functions associated with the hypothalamic nucleus (Dreifuss & Murphy,

1968; Gloor, 1975; Joseph, 1992).

As these scientific and case studies illustrate, there exist many types of organic

brain lesion that can have drastic and direct effects on judgment, aggression, and

self-control. The observations from these case studies hold up when very large

numbers of subjects are included, as illustrated in a longitudinal study of 279

Vietnam War veterans who experienced frontal lobe lesions (Grafman et al., 1996).

Subjects who had frontal lobe lesions in the ventromedial area demonstrated

measures of violence and aggression that were significantly higher than those of

controls, suggesting that this type of lesion increases the risk for aggression and

violence. The presence and severity of such lesions, as judged by medical experts,

could provide additional information as to the causes of mental defects, although the

proper way to wield this information remains to be worked out.

THE ROLES OF NEUROIMAGING DATAIN THE COURTROOM

Although there are many discretely-functioning parts of the brain, the brain is also

known for its redundancy of function (i.e., more than one area of the brain may be

involved in a behavior), its interconnectivity between areas, and its plasticity.


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Essentially, while brain injury or lesions may impair decision-making or influence

violent tendencies, there is no one ‘‘moral’’ region of the brain. As the case of Phineas

Gage shows, it is possible to suffer an extremely traumatic frontal lobe brain injury—

even one that results in drastic personality changes—and still refrain from engaging

in anything inherently criminal or violent. We must resist the urge to be entirely

deterministic. While neuroscience has contributed a vast amount to understanding

of the brain, there is still no consensus as to what constitutes normal variation in the

size of regions, whether a lesion actually indicates that a region of the brain is

impaired, and whether impairment of a particular region provides a direct link to

behavior. Currently, the best neuroscience has to offer may be the bolstering of an

already established case for mental defect—to provide another piece of the puzzle

rather than stand alone evidence.

Additionally, neuroimaging evidence might provide insight for parole hearings,

especially if a tumor or lesion that had been argued to be affecting behavior had been

surgically removed. If the behavior had been judged to be improved, the chance of re-

offending might be low. This observation is reflected in the case of a 40 year old man

who experienced sudden and uncontrollable pedophilia which was later thought to

be caused by an egg-sized tumor in the orbitofrontal cortex (Burns & Swerdlow,

2003). After the tumor was successfully removed, the urges disappeared and he

successfully completed a therapy program. When the tumor began to re-grow, the

behavior once again returned, and when the tumor was again removed, so did the

urges. Consistent with other reports of prefrontal damage, the man knew that the

urges and behavior was morally wrong, yet he was still unable to stop himself. This

leads to another question: should people who are biologically unable to control their

behavior, or predisposed to anti-social behavior, be released from custody if the

behavior can return as a result of the disorder? Surgical interventions, such as

orchidectomy, could conceivably be considered as factors for determining parole and

sentence length. However the Texas orchidectomy law attempts to dissociate

castration from legal consequences in order to preserve the voluntary nature of

offenders’ decisions to undergo the procedure (Voluntary Castration for Sex

Offenders, 2007). Neurological follow-up visits could become mandatory for

offenders who suffered from a lesion that could recur.

It is important that the integration of neuroimaging evidence into legal

proceedings occur in a way that is scientific, logical, and free of bias. The alternative

could be a legal system overwhelmed with criminal defense lawyers attempting to

rationalize away any crime as the result of neurological disease, and juries

overwhelmed by the vividness and ‘‘scientific’’ nature of such data. Recent research

suggests that presenting neuroimaging evidence at trial may sway juries’ beliefs about

a defendant’s culpability. In one study, ‘‘mock jurors’’ were asked to render a verdict

in staged insanity trials where various types of evidence, including neuroimaging

evidence such as MRI data, was presented. The jurors were more likely to find the

defendant not guilty by reason of insanity if the defendant had a history of brain

injury, had been diagnosed with a psychotic disorder, or could prove the existence of

a brain lesion via MRI. Furthermore, the jurors who stated that the neuroimaging

data had influenced them were nearly six times as likely to render a not guilty verdict

(Gurley & Marcus, 2008). This is illustrated in the previously mentioned 1989 trial

of Barry Wayne McNamara, whose sentencing of life in prison (as opposed to the

death penalty) was handed down due to mitigation from mental illness (Emmons,


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1989). Following the hearing, jurors acknowledged that the neuroimaging visual aids

were given considerable credence in mitigating the sentence. How is the average jury,

comprised of laypeople not well versed in neurological deficits, supposed to judge a

normal, functioning brain from a damaged, abnormal one? Even expert

neuroscientists may be unable to testify that, with reasonable medical certainty, a

brain lesion caused a defendant’s behavior at the time a crime was committed.

However, between 60 and 77% of all defendants found not guilty by reason of

insanity are diagnosed with a psychosis, and at least 10% of these individuals have a

diagnosis of neurologically based psychosis (Cochrane, Grisso, & Frederick, 2001;

Warren et al., 2006). This suggests that, while neuroimaging evidence might

currently pose unfair bias in some criminal trials, the evidence is certainly relevant to

many cases and should not be excluded wholesale. Mediating how and when to

introduce such evidence will require that judges, and likely juries, become educated

to some degree about the relevant neurological disorders that may impact

responsibility or contribute to legal insanity. It is not difficult to foresee a future

where law schools teach relevant areas of neuroscience, creating a new type of

‘‘neurolaw’’ expert capable of bridging this gap. Clinical neuroscientists interested in

how neuroimaging impacts the law might empirically explain how many people who

have high-risk lesions do not exhibit criminality. Of particular importance for the

medical community is the determination of what constitutes the legally significant

threshold for structural damage to a brain structure and the extent of behavioral

impairment required for mitigation or NGRI to be justified. Ideally, neuroimaging

information could be integrated into the milieu of evidence about defendants’ mental

functioning, and, along with psychiatric and neuropsychological testing, provide a

more complete picture without eclipsing the other facts in the case.

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