Brain Scans Go Legal

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                 MICHAEL S. GAZZANIGA

                            magine that you are a judge presiding over the trial of a

                            man named Bill, accused of a grisly murder. The physical
                            evidence is overwhelming, and witnesses have yielded
                            damning testimony. There seems to be no reasonable
                                                                                                 PHANIE Photo Researchers, Inc.

                            doubt that Bill committed the murder. Suddenly, the de-
                            fense asks if it can present images of Bill’s brain, produced
                            by magnetic resonance imaging (MRI). Bill’s attorneys
                            want to introduce the pictures as evidence that their client
                            has a brain abnormality. They will argue that the abnor-
                            mality justifies either a verdict of not guilty (because Bill

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                                   COPYRIGHT 2006 SCIENTIFIC AMERICAN, INC.
Even if most people
   with a given brain
    abnormality en-
 gage in crime, that
      does not mean
  that an individual
 should not be held
     responsible for
  premeditating his
      or her act— for
 intending to harm.

                                                                                                                            MIK A zefa/Corbis

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    lacked the intent to kill or premeditation to com-     forceful, in Bill’s case they come down to a single
    mit murder), or a verdict of not guilty by reason      salient question: Can brain scans reveal a lack of
    of insanity (because Bill lacked control over his      responsibility? We think not. They should not be
    actions), or, at least, a conviction on a lesser of-   allowed as evidence in trials, at least not in the
    fense (because Bill is not fully responsible or pos-   foreseeable future. Never say “never,” but noth-
    sibly just because jurors should feel sorry for        ing close to current technology is trustworthy
    people with brain disorders). The prosecution          enough for legal settings.
    argues that you should not admit the scans, be-
    cause pictures of Bill’s brain and testimony by        What Made Bill Do It?
    revered scientists might influence the jury much            Naive faith in the latest imaging technology
    more than such evidence warrants.                      is misguided at this time. To understand why,

(   Even if Bill’s brain condition causes him to be violent,
      it might not cause ugly premeditated murder.                                                                         )
        Would you, as judge, allow the brain scans         consider the questions one must navigate to de-
    to be exhibited? How would you assess such             cide whether this evidence could be truly infor-
    evidence?                                              mative in a criminal trial.
        This scenario is not merely theoretical. U.S.          First, if a brain scan indicates an abnormality,
    courts have been allowing positron-emission            then the brain really has an abnormality, right?
    tomography (PET) scans of brain metabolism             Wrong. This simple inference overlooks a crucial
    and, more recently, MRI scans of abnormal brain        problem: almost every biomedical test, from
    structures or function. In these cases, attorneys      MRI to the prostate-specific antigen (PSA) test,
    have used the images as evidence of brain dam-         can suggest that a condition is present when in
    age that might impair a defendant’s behavior and       actuality it is not. Such cases are called false pos-
    therefore reduce his or her culpability — the          itives. This problem is not too serious for com-
    degree to which the defendant should be held           mon medical ailments, such as prostate cancer,
    responsible for the crime. Strong editorials have      when doctors can independently confi rm the di-
    been written against these actions. Yet much           agnosis using other tests. The kinds of brain ab-
    of the public as well as participants in the court     normalities that might cause grisly murders,
    system believe that imaging, particularly the          however, are very rare and hard to confirm.
    newer anatomical and functional scans produced         When a condition is rare, even a low rate of false
    by MRI, could provide an independent assess-           positives leaves a relatively large number of er-
    ment of the root cause of a person’s aberrant          rors — not a very reliable means for establishing
    behavior.                                              that the person being scanned has a condition
        As a result, neuroscientists are invading our      that provokes violence. Even if Bill’s scan sug-
    courts. Companies such as No Lie MRI, Inc.,            gests a brain anomaly, it might be very unlikely
    and Cephos Corporation have been started on            that he has any deficit at all.
    the expectation that the legal system will increas-        That is not the only problem. Suppose for
    ingly seek brain scans. Proponents say the im-         the sake of argument that we are absolutely
    ages can detect lying by witnesses, prejudice in       certain that Bill has an abnormality. We still do
    jurors or judges, and mental incapacities among        not know whether that condition caused Bill’s
    defendants. If these prospects pan out, neurosci-      criminal behavior. Some people with this kind of
    ence could greatly influence the direction of our       irregularity might not be violent at all, whereas
    legal system; after all, other forms of advanced       others could become violent on a regular basis.
    scientific technology, such as DNA testing, al-         With this much variability, even if we assume
    ready work well in courts. Opponents object that       that Bill does have an abnormality of the right
    such technology removes the human element that         size in the right place, we cannot know that his
    is essential to law as we know it. They also fear      condition had anything to do with the alleged
    that brain scans will violate precious rights to       illegal behavior. Furthermore, even if Bill’s con-
    privacy and due process.                               dition does cause him to be violent in some way,
        Although the arguments on both sides are           it still might not cause the particular kind of

    w w w. s c i a m m i n d . c o m                                                           SCIENTIFIC AMERICAN MIND   33
                                                COPYRIGHT 2006 SCIENTIFIC AMERICAN, INC.
Responsibility is a social construct , determined by
     a social group, not a medical test result.                                                                                          )
                            attack in question: ugly premeditated murder.           Is Bill Responsible?
                                 To be confident that an abnormality such as             Even if these diagnostic problems can be
                            Bill’s plays a causal role in a particular murder,      solved, a defendant’s medical condition still will
                            researchers would have to have studied many             not prove any legal status. Assume we know for
                            more murderers than anyone has ever studied.            sure that Bill has a certain brain abnormality and
                            The best an expert witness in a courtroom could         that a high percentage of people with that kind
                            do is establish a weak correlation between brain        of irregularity commit violent crimes, including
                            injury and criminal behavior. But without addi-         murder. Bill might still be culpable.
                            tional information, no scientist could be justified          To see why, imagine that most people with a
                            in claiming that Bill’s abnormality caused him to       certain brain condition are thrill seekers. They
                            become a murderer or prevented him from mak-            drive race cars, jump from planes, scale ice cliffs,
                            ing a decision to kill on the day in question.          and so on. These activities are unusual (possibly
                                 The defense might argue that the brain scan        as unusual as violent crimes), but their correla-
                            is just one piece of evidence that when combined        tion with a certain brain condition does not indi-
                            with psychological or psychiatric assessments,          cate that these individuals do not act intention-
                            paints a better picture of Bill’s mental state at the   ally and deliberately or that they suffer a compul-
                            time of the crime. Yet we do not know what the          sion or delusion that makes them unable to
                            relation is between the scan and the other assess-      control themselves. Such thrill seekers plan their
                            ments. What percentage of people with a certain         acts carefully and stop themselves when condi-
                            psychiatric diagnosis will test positive for this ab-   tions are too dangerous. That makes them re-
                            normality? What percentage of those who test            sponsible for what they choose to do.
                            positive for this abnormality will receive that             Similarly, even if most people with a given
                            psychiatric diagnosis? Without such informa-            abnormality engage in unusual criminal activi-
                            tion, we cannot say in the least whether the brain      ties, that abnormality by itself does not indicate
                            scan supports the diagnosis. In this setting, the       that these individuals do not commit their crimes
                            behavioral findings must stand on their own.             intentionally and deliberately. They are still ca-

            When a new
       scientific proce-
    dure is first admit-
     ted in trials, there
      is significant risk
    that lay juries and
       judges will over-
    estimate its value.
     Proponents must
     demonstrate that
            a method is
       accepted by the
    scientific commu-
         nity; scientists
            disagree on
          the validity of
            brain scans.
                                                                                                                                                   G E T T Y I M AG E S

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                       pable of premeditating or planning their acts           defense to use brain scans to dismiss guilt, then        NO RESTRAINT
                       carefully. This means they have the ability to          should prosecutors not also be allowed to use            To absolve guilt,
                       “form malice aforethought”— the mens rea that           brain scans to indicate guilt? If a brain scan of a      a brain scan
                       is a necessary element of the crime of murder—          defendant reveals an abnormality and some peo-           would have to
                       and therefore should not be exculpated during           ple with that aberration become violent, then a          show that a perpe-
                                                                                                                                        trator was unable
                       the guilt phase of a trial. Moreover, if the trial is   prosecutor might use that brain scan to convince
                                                                                                                                        to control his or
                       one based on a plea of not guilty by reason of          a jury that a given defendant is guilty. Yet inno-
                                                                                                                                        her urge. But brain
                       insanity and the evidence is presented in the san-      cent people who suffer from known brain disor-           scans show only
                       ity phase of the trial, such abnormalities would        ders will be even more likely to test positive and       what is, not
                       not justify a verdict of not guilty, because these      be wrongly convicted. Or they might be involun-          what could be.
                       individuals do not necessarily suffer from a com-       tarily committed to mental institutions if the
                       pulsion or delusion. Like thrill seekers, they          brain scan is taken as evidence that they are dan-
                       might well be able to control themselves and            gerous to society. Anyone who has sympathy for
                       make decisions easily.                                  these folks should find this new form of evidence
                           To show that Bill is not responsible, a brain       discomforting.
                       scan would have to indicate not only that Bill has
                       an urge and is likely to commit the crime but also
                                                                                (The Authors)
                       that Bill is unable to control his urge. Brain scans
                       show only what is, however, not what could be.           SCOTT T. GRAFTON, WALTER P. SINNOTT-ARMSTRONG, SUZANNE I.
                       They cannot show that Bill could not have                GAZZANIGA and MICHAEL S. GAZZANIGA have collaborated on projects
                       stopped himself from committing the murder.              involving moral responsibility, cognitive neuroscience, and the interface
                       Because responsibility depends on such abilities,        of law and the mind. Grafton is director of the Brain Imaging Center at
                       brain scans cannot show that Bill is not respon-         the University of California, Santa Barbara. Sinnott-Armstrong is profes-
                       sible for what he did.                                   sor of philosophy and of legal studies at Dartmouth College. Suzanne

                           These stringent standards might seem un-             Gazzaniga is deputy district attorney for Placer County, California (the
                       sympathetic. Shouldn’t we feel compassion for            views expressed herein are hers and not necessarily those of the Placer
                       people with brain disorders and help them get            County district attorney). Michael S. Gazzaniga is professor of psychol-
                       better? Of course, we should. But if we allow the        ogy and director of the Sage Center for the Study of Mind at U.C.S.B.

                       w w w. s c i a m m i n d . c o m                                                            SCIENTIFIC AMERICAN MIND            35
                                                                    COPYRIGHT 2006 SCIENTIFIC AMERICAN, INC.
                 The Truth about Lie Detectors

                        sing brain scans to prove lack of culpability    none of their work comes close to offering the
                        in a courtroom trial is fraught with perils.     precision needed for a scan to be considered
                        Similar issues arise when considering the        conclusive. Besides, a sign of a troubling moral
                 use of imaging as lie detectors to implicate or         judgment could arise simply from defendants
                 exonerate defendants, even though several re-           thinking that they are being wrongly accused. Or
                 search groups and companies say they have per-          they might think that they are doing something
                 fected such techniques [see “Exposing Lies,” by         wrong in volunteering for lie detection or in not
                 Thomas Metzinger; SCIENTIFIC AMERICAN MIND, Oc-         revealing everything they know, which by law they
                 tober/November 2006].                                   are not required to do. The mere fact that they are
                     First of all, despite some wild claims, no lie      making some moral judgment cannot show they
                 detection technology is 100 percent accurate.           are lying.
                 False positives are a persistent problem. Beyond            Third, when people lie in court they often try
                 that is the basic complication of intent. People lie    to lie convincingly. They need to make sure their
                 when they say something they know is false and          lies fit coherently with the facts that have been
                 intend to deceive. To show that someone is lying,       presented in a trial. That assessment takes time
                 then, a brain scan must detect the knowledge            and thought. Brain scans might detect such pat-
                 and the intention. There is no way to do this di-       terns. Yet even if this works in the lab, it is un-
                 rectly. The only way to “show” a lie is to capture      likely to work for defendants. Whether they are
                 some indirect accompaniment of lying. What              lying or not, guilty or not, defendants always need
                 could that be?                                          to make sure that what they say fi ts the larger
                     One possibility is that people get nervous          pattern of information in the case. A small slip
                 when they lie, and brain scans can detect when          can make them look guilty even if they are not.
                 people get nervous. That clearly will not work.             A fourth way that neural lie detection might
                 Even truthful defendants can be nervous when            work is to play on the fact that people have a ten-
                 interrogated.                                           dency to tell the truth. They must therefore sup-
                     A second possibility is that when people            press that tendency when they lie. Perhaps a
                 lie, they make a judgment that they are doing           brain scan could detect that inhibition. But again,
                 something wrong. Perhaps brain scans could tell         even if this holds up in the laboratory it cannot
                 when people make such moral judgments. Re-              work in real cases. When defendants testify, they
                 searchers have progressed in understanding the          do inhibit their natural tendency to blurt out ev-
                 neural underpinnings of moral judgment, but             erything they know. They are circumspect about

                 Who Bears the Burden of Proof?                         procedure involves eye-catching pictures pre-
                     Even without such technological uncertainty,       sented by scientists with impressive credentials.
                 the outcome of a trial often depends on who is         To reduce that risk of error, many jurisdictions
                 responsible for proving what— which is a matter        require defendants who cite new scientific meth-
                 of law, not science.                                   ods to demonstrate that those methods are reli-
                     The burden of proof can differ depending on        able and accepted by the wider scientific com-
                 the kind of proceeding, the phase of a trial and       munity. That kind of proof will be hard to pres-
                 whether the case is before a federal or state court.   ent for brain scans because of their low predictive
                 Usually the burden does lie with the prosecution,      value and the lack of consensus among scientists
                 to prove essential elements of a crime during the      on the validity of these techniques. If the defense
                 guilt phase. But a defendant’s legal team may          cannot carry that burden of proof, then the sci-
                 attempt to introduce a brain scan as evidence          entific evidence should not be admitted into the
                 that negates some element of the crime, such as        guilt phase of a trial.
                 premeditation, or perhaps raises reasonable                Brain scans might instead be cited as evidence
                 doubt. Research shows that when a new scien-           of something like insanity during the sanity
                 tific procedure is fi rst admitted in trials as evi-     phase of a trial. Many jurisdictions give the
                 dence, there is significant risk that lay juries and    defense the burden of proving that a criminal act
                 judges will overestimate the value of that evi-        resulted from an individual’s mental illness
                 dence. This danger is especially high when the         or brain condition. It will be difficult for the de-

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                                                                                                                                     DIM VIEW
                                                                                                                                 Today’s MRI
                                                                                                                                scans cannot
                                                                                                                              reveal whether
                                                                                                                            a person is trying
                                                                                                                                  to deceive.

                             what they say. Many of them also suppress ex-              their lives on the line, as defendants do. Unlike
                             pressions of anger and outrage at accusation.              defendants, the subjects will have been instructed
                             Suppressing natural tendencies is not a reliable           to lie, and they know that their lies will be exposed.
                             indicator of lying, in the context of a trial.             Because these situations are so different, evi-
                                 Defenders of neural lie detection will undoubt-        dence of reliability in controlled experiments can-
                             edly cite tests that indicate their methods are reli-      not be extended to actual trials. It is hard to imag-
                             able and even hold public demonstrations. Still,           ine any procedure that will solve all these problems
                             the subjects in these experiments will not have            anytime soon. — S.T.G., W.P.S.-A, S.I.G. and M.S.G.

                                fense to carry this burden, for the same reasons          along that will someday make brain scans reli-
                                just given.                                               able enough to determine the legal implications
                                    The questions of where to place the burden of         of a brain abnormality. The problems might be
                                proof, which evidence to allow and which dis-             solved with time, but we are nowhere close today.
                                abilities are severe enough to preclude punish-           Brain scans of this kind are, after all, only 15
                                ment are all considerations for society. And these        years old. Neuroscientists need much more basic
                                decisions must indeed be made by society, not by          research, experience and thought about imaging
                                neuroscientists. Data about an individual’s brain         before it invades our courts. Until then, brain
                                cannot alone settle whether that person should            scans have too little predictive value to be applied
                                be held responsible. Responsibility is a social           in criminal trials. M
                                construct, determined by a social group, not by
3D4MEDICALCOM Getty Images

                                a medical or scientific test result. If society choos-      (Further Reading)
                                es to use forms of brain testing as evidence to
                                                                                           ◆ Neuroscience and the Law. Edited by Brent Garland. Dana Press, 2004.
                                assess responsibility, then it needs to make these
                                                                                           ◆ Neuroimaging Studies of Aggressive and Violent Behavior:
                                decisions in light of complete and accurate infor-
                                                                                             Current Findings and Implications for Criminology and Criminal Justice.
                                mation about the pitfalls of the various methods             J. L. Bufkin and V. R. Luttrell in Trauma, Violence and Abuse, Vol. 6, No. 2,
                                being proposed.                                              pages 176–191; April 2005.
                                    We cannot predict the future. Better informa-          ◆ Law and the Brain. Edited by Semir Zeki and Oliver Goodenough.
                                tion, techniques and equipment might come                    Oxford University Press, 2006.

                                w w w. s c i a m m i n d . c o m                                                                  SCIENTIFIC AMERICAN MIND               37
                                                                             COPYRIGHT 2006 SCIENTIFIC AMERICAN, INC.

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Tags: Brain, Scans, Legal
Description: Imagine that you are a judge presiding over the trial of a man named Bill, accused of a grisly murder. The physical evidence is overwhelming, and witnesses have yielded damning testimony. There seems to be no reasonable doubt that Bill committed the murder. Suddenly, the defense asks if it can present images of Bill’s brain, produced by magnetic resonance imaging (MRI). Bill’s attorneys want to introduce the pictures as evidence that their client has a brain abnormality. They will argue that the abnormality justifi es either a verdict of not guilty
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