Neuroscience and behavioral genetics in US criminal law: an empirical analysis

Abstract

The goal of this study was to examine the growing use of neurological and behavioral genetic evidence by criminal defendants in US criminal law. Judicial opinions issued between 2005-12 that discussed the use of neuroscience or behavioral genetics by criminal defendants were identified, coded and analysed. Criminal defendants are increasingly introducing such evidence to challenge defendants' competency, the effectiveness of defense counsel at trial, and to mitigate punishment.

Keywords: IAC; Neuroscience; behavioral genetics; capital punishment; criminal law; neurobiology.

Graph 1.

Judicial opinions discussing neurobiological introduced by criminal defendants 2005–12. (Homicide (capital) are murder cases in which the prosecutor sought the death penalty. Homicide (not capital) are some degree of homicide (murder, manslaughter) cases in which the death penalty was not at issue. Other felony cases are those in which the defendant was not charged with homicide.) © Author, 2016. This image/content is not covered by the terms of the Creative Commons licence of this publication. For permission to reuse, please contact the rights holder.

Graph 2.

Degree to which neurobiological evidence is discussed in Judicial opinion. (Mention is in a list of information. Some is less than one paragraph of the opinion. Substantive is one paragraph or more of the opinion discussing the neurobiological evidence introduced by a criminal defendant.) © Author, 2016. This image/content is not covered by the terms of the Creative Commons licence of this publication. For permission to reuse, please contact the rights holder.

Graph 3.

Most serious offense charged with when neurobiological evidence raised in non-capital cases, 2005–12. An evaluation of the most serious criminal charge (per case) that the defendant was charged with to illustrate the range of felony cases impacted by neurobiological evidence. © Author, 2016. This image/content is not covered by the terms of the Creative Commons licence of this publication. For permission to reuse, please contact the rights holder.

Graph 4.

Neurological testing discussed in criminal opinions 2005–12. (The number of opinions per year in which each time of neurobiological testing is discussed. Interview+ = neuropsychological testing/evaluation, as well as medical or other history of head/brain trauma; Scan+ = some form of brain scanning evidence, neuropsychological testing/evaluation, as well as medical or other history of head/brain trauma; History only = medical or other history of head/brain trauma but no other form of testing discussed in opinion; No neurotesting = no discussion of any form of neurological testing introduced in opinion.) © Author, 2016. This image/content is not covered by the terms of the Creative Commons licence of this publication. For permission to reuse, please contact the rights holder.

Graph 5.

Distribution of neuroimaging discussed in Judicial opinion 2005–12. (In the opinions where neuroimaging was introduced, the type of neuroimaging. SPECT = single-photon emission computed tomography; qEEG = quantitative electroencephalography; fMRI = functional magnetic resonance imaging; Unknown = brain scanning discussed but type not mentioned; BEAM = sometimes known as qEEG, brain electrical activity mapping; CAT = computed tomography; EEG = electroencephalography; MRI = magnetic resonance imaging; PET = positron emission tomography.) © Author, 2016. This image/content is not covered by the terms of the Creative Commons licence of this publication. For permission to reuse, please contact the rights holder.

Graph 6.

Distribution of neurobiological evidence-based claims in capital and non-capital cases, 2005–2012. (The denominator is all claims raised in the study sample. The numerator is the specific type of claim. E.g. for mental retardation, 1% of the claims raised in the study sample were for a claim of mental retardation in a non-capital case.) © Author, 2016. This image/content is not covered by the terms of the Creative Commons licence of this publication. For permission to reuse, please contact the rights holder.

Graph 7.

Nature of competency claims raised when neurobiological evidence introduced by criminal defendants. © Author, 2016. This image/content is not covered by the terms of the Creative Commons licence of this publication. For permission to reuse, please contact the rights holder.

Graph 8.

Case outcome in adult trials when neurobiological evidence is introduced by defendant. + means the defendant achieved a positive outcome on appeal, whether as a reversal, remand, or modification of a component of the trial courts’ decision. – means the defendant did not achieve any positive outcome on appeal.

Graph 9.

Case outcome in juvenile trials when neurobiological evidence is introduced by defendant. Favorable means the defendant achieved a positive outcome on appeal, whether as a reversal, remand, or modification of a component of the trial courts’ decision. Unfavorable means the defendant did not achieve any positive outcome on appeal.