American Journal of Law & Medicine

A double-edged sword: the role of neuroimaging in federal capital sentencing.(Brain Imaging and the Law)


H.L.A. Hart has stated that certain mental conditions have an "excusing" effect on punishment, whereby "It]he individual is not liable to punishment if at the time of his doing what would otherwise be a punishable act he is ... the victim of certain types of mental disease." (1) The Supreme Court, (2) however, upheld a state statute allowing for increased "punishment," (3) in the form of civil commitment, for sexually violent predators who suffer from a "mental abnormality." (4) Thus, American jurisprudence is faced with a paradoxical role of mental conditions: serving to both aggravate and mitigate sentences. This dual purpose of mental conditions becomes a pressing legal issue as mental conditions associated with brain structure or function become more detectable with the emergence of neuroimaging. (5)

In federal capital sentencing, judges are obligated to consider aggravating and mitigating factors before imposing a death sentence. (6) There are aggravating and mitigating factors that could be implicated by mental conditions, including future dangerousness, (7) and impaired capacity, (8) respectively. As a result, the academic question arises: What if a brain dysfunction, detectable by neuroimaging, indicates both future dangerousness and impaired capacity? Unfortunately for the law, such an area of the brain already has been identified: the frontal lobes.

This Note has two limitations: its scope of brain-imaging and its scope of the judicial system. First, the focus is on damage to the frontal lobe, where much research has been conducted linking this area of the brain both to violent and aggressive behavior, (9) and to the inability to completely control one's actions. (10) Second, this note will limit the cases examined to federal capital cases for homicide, as federal courts are statutorily required to consider mitigating and aggravating circumstances. (11) Additionally, federal cases have articulated future dangerousness as an aggravating factor, and federal statutes list impaired capacity as a mitigating factor.

In Part II, this Note will provide background information on both frontal lobes and the effects damage to the frontal lobes can have on one's behavior. Part III will examine current federal procedure for capital cases, the roles of aggravating and mitigating evidence, and how frontal-lobe dysfunction can fit into each category. Part IV explains the danger that neuroimaging evidence can pose: in the same case, serving to both aggravate and mitigate defendant's sentence. Part V discusses the obligations of defense counsel in neuroimaging cases, such as when defendant can raise an ineffective assistance of counsel claim for counsel's failure to introduce neuroimaging evidence and when defendant is legally entitled to psychiatric expert assistance. Part VI focuses on the mental health expert and the care, caution, and limitations that must surround expert testimony on neuroimaging evidence. Part VII considers outside areas to shed light on this discussion, such as civil commitments, juveniles, and philosophical bases for punishment. Part VIII concludes this Note with a recommendation on how potentially dualistic neuroimaging evidence should be treated in the American legal system.


Neuroimaging detects frontal-lobe dysfunction either through computer-generated visual representations of the brain's structure or of its function. (12) Structural neuroimaging is conducted by either computerized tomography scanning ("CT") or magnetic resonance imaging ("MRI"), and generates images of the brain's soft-tissue structure. (13) Functional neuroimaging is conducted by positron emission tomography scanning ("PET"), and captures the brain while in action, measuring cognitive activity. (14) Brain activity is actually inferred from the presence of high metabolic rates in structures involved in the cognitive process. (15) A hybrid of structural and functional neuroimages is functional MRI ("fMRI"), which combines structural representations with information about brain activity extracted from functional scans. (16) Another tool is an electroencephalogram ("EEG"), which uses electrodes to measure electrical impulses of brain activity, detecting structural brain abnormalities. (17)


Frontal lobes are anatomical masses of the brain located at the anterior of the skull behind the forehead. (18) Frontal lobes regulate socially appropriate behavior and suppress impulses; therefore, damaged frontal lobes may cause emotionally impulsive actions. (19) Frontal-lobe dysfunction, mainly caused by trauma, tumor, or stroke, (20) effectively removes from the sufferer the segment of the brain that says, "Don't do that! Don't say that! It's not appropriate! There are going to be consequences!" (21) Thus, a brain image of one's frontal lobes may offer a biological glimpse into one's behavior. (22)

One syndrome of frontal-lobe injury is pseudopsychopathic behavior, characterized as impulsive. (23) Early-onset frontal-lobe damage leads to impairment in the development of moral rules and social conventions. (24) Thus, damage to the frontal lobe will impair one's ability to identify violations of social norms. (25) The implication of this association is that because a mitigating factor in federal capital cases is "the defendant's capacity to appreciate the wrongfulness of the defendant's conduct," (26) a defendant with shown, frontal-lobe dysfunction may be unable to appreciate the wrongfulness of his criminal conduct.


Neuroimaging studies of aggressive and violent subjects have "consistently found frontal lobe abnormalities." (27) In one study, inmates charged with murder or manslaughter with deviate frontal lobe activity were more likely to be affective, impulsive, and emotionally aggressive. (28) A meta-analysis concluded that "clinically significant frontal lobe dysfunction is associated with aggressive dyscontrol." (29) "Frequently, increased levels of aggression and aberrant behaviour (sic) are reported both when the lesions [to the frontal lobe] are acquired early in life and when they occur in adulthood." (30) Moreover, federal courts have recognized frontal-lobe dysfunction as a cause for "impulsive" behavior. (31) In fact, a psychiatrist studying murderers has posited that "most murderers are shaped by the combination of damage to the brain, particularly to the frontal lobes, which control aggression and impulsiveness, and the even more complex damage visited by repeated, violent child abuse." (32)

Empirical research strongly suggests that frontal-lobe dysfunction is correlated with potentially criminal behavioral tendencies. (33) However, while the presence of frontal-lobe dysfunction "may be related to violence, it is probably only a biological predisposition factor, requiring environmental, psychological and social factors for the emergence of severe violent behaviour (sic) in an individual." (34) Similarly, this correlation may "represent a predisposition to affective (emotional) states relevant to aggressive behavior, without necessarily signifying an incapacity to avoid actual violent acts." (35) Therefore, damage to the frontal lobe will not result, at least for purposes of this Note, in mental impairment so severe that one's mental state will be relevant in the guilt-phase of a capital case. (36)


The federal death penalty system is bifurcated into a guilt-phase and sentencing-phase. (37) In the sentencing phase, the court is to consider both statutory and nonstatutory aggravating and mitigating factors. (38) Under the Federal Death Penalty Act of 1994 (the "FDPA"), (39) the court may impose death only if there is at least one statutory aggravating factor (40) and the aggravating factor(s) "sufficiently outweigh all the mitigating factors." (41)


There are sixteen statutory aggravating factors that the FDPA requires the jury or judge to examine when determining whether "a sentence of death is justified" for homicide. (42) Beyond these enumerated aggravating factors for homicide, the FDPA is permissive, allowing the judge or jury to consider "whether any other aggravating factor for which notice has been given exists." (43) However, for the defendant to be eligible for the death penalty, the judge or jury must find that there exists at least one statutorily defined aggravating factor. (44) With this eligibility finding, the prosecution then introduces nonstatutory aggravating circumstances to apprise the sentencing judge or jury of other relevant factors helpful in crafting an appropriate sanction. (45) Under 18 U.S.C. [section] 3593(c), a nonstatutory aggravating circumstance "may be excluded if its probative value is outweighed by the danger of creating unfair prejudice, confusing the issues, or misleading the jury." (46)

One nonstatutory aggravating factor under the FDPA is future dangerousness. (47) The standard for ascertaining future dangerousness is whether "the defendant is likely to commit criminal acts of violence in the future which would be a continuing and serious threat to the lives and safety of others." (48) The Supreme Court, in Jurek v. Texas, (49) found that the likelihood that a defendant will commit future crimes is a "constitutionally acceptable criterion for imposing the death penalty," (50) because prediction of future behavior and dangerousness is not impossible. (51) While proving future dangerousness is "difficult," the Court maintained that it is possible if aided with the testimony of psychiatrists. (52)

In a recent case involving the FDPA, however, a district court cast doubt on the provability of future dangerousness. (53) The court held that "[d]evelopments in the law and more recent scientific research suggest that expert testimony on future dangerousness would be inadmissible under the Federal Rules of Evidence and is also too unreliable to be admitted in the penalty phase of a capital case under the balancing test established by [the FDPA]." (54) The court offered empirical justification for this proposition, stating that "the scientific community virtually unanimously agrees that psychiatric testimony is, to put it bluntly, unreliable and unscientific." (55) Specifically, the court cited a survey that concluded:

   For nearly twenty years we have known that psychiatrists cannot 
   predict whether a person who has committed a violent act will be 
   violent in the future. … 

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