American Journal of Law & Medicine

Is a picture worth a thousand words? Neuroimaging in the courtroom.(Brain Imaging and the Law)


Neuroimaging has advanced our understanding of how the living brain operates, providing structural and functional images of both healthy and diseased brains. This technology pervades today's society, particularly affecting the legal arena. Some judges argue that scientific evidence, which offers insight into the offender's mental state, is crucial because it is the only means of determining whether an offender's punishment is proportional to his crime. (1) Other judges argue that "objective" evidence does not "wholly determine the controversy," and focus instead on their duty as gatekeepers to independently evaluate scientific evidence. If courts use brain images to make their culpability determinations more objective and sound, these images must meet pertinent legal standards and shed light on medical conditions. For neuroimaging to meet these legal and medical standards with scientific integrity, scientists must convincingly correlate the dynamic images in a person's brain with the way the person is thinking or acting at that moment.

With respect to understanding the relationship between the brain and certain behaviors, the state of scientific knowledge is nascent, but promising. The more complex and specific the behavior examined, the more speculative the connection. For example, violence is a multifactorial and socially driven behavior that is not likely reducible to a unitary brain function or region. At present, there is no specific area of the brain to which aggression and violence are singularly ascribed. Brower and Price stated, "The evaluation of research on the neurobiology of violence demands conceptual clarity, along with careful analysis of methods and data to prevent misunderstanding and possible abuse of the results." (2) Currently, attorneys rely on psychologists, psychiatrists, and neurologists to offer integrated expert testimony regarding illness and behavior. This testimony varies among experts. While "scientific" brain imaging appears to offer greater objectivity, (3) current brain imaging techniques, by themselves, may be no more objective than the modalities that came before them.

Some of the problems associated with using new medical technology in the legal arena stem from the different modes of inquiry each discipline uses. Scientists begin by asking questions, collecting as complete a set of relevant information as possible, experimenting with variables, applying statistical odds, and only then drawing conclusions. Because the state of scientific knowledge changes rapidly, sometimes there are multiple contradictory scientific views of a given issue, all of which are potentially credible. These controversies help fuel scientific progress.

Lawyers, unlike scientists, are advocates, and therefore operate within a different paradigm. They gather facts to support a particular theory, attempting to reconcile facts contradictory to that theory in their client's favor. The law counts on legal adversaries to present contrary theories and thereby allow the truth to emerge.

With these cautions in mind, we can still describe the contribution brain imaging may make on certain neurologic illnesses and in the presence of other neurologic data. This Article will review some of the current research on the attempt to use functional imaging to construct a neuropathologic diagnosis for certain behaviors. We will present a continuum, ranging from situations in which neuroimaging may contribute to the explanation of aggressive or criminal behavior, to situations in which neuroimaging is currently too speculative to provide a solid footing.

The goal of this Article is to elucidate the role of neuroimaging in the courtroom from a neurologic perspective. We begin with a brief commentary on historical uses of neurologic evidence in criminal cases and early scientific attempts to create a "science" of criminality. What follows will be a review of the brain anatomy that is relevant to these neuroimages and a simple explanation of the imaging techniques involved. The remainder and bulk of this Article will present instances in which the imaging of certain brain insults may contribute to the understanding of criminal or violent activity. The conditions selected for this section on "solid ground" are a representative sample of such injuries or illnesses, but are not an exclusive list of these conditions. Finally, we will discuss emerging (and as yet theoretical) attempts to use functional imaging to identify brain substrates for specific undesirable traits or activities.


While the brain mediates violent behavior, it is not clear whether there is or ever will be a linear, identifiable relationship between the two. Early religious explanations characterized behavior as the product of spirits, gods, demons, or the devil. (4) These explanations occurred in the context of religious tenets that defined morality and formed a latticework for societal behavioral norms. It was widely accepted that mind and body were a duality, thereby relegating explanations of behavior to an ethereal realm. As recently as a century ago people believed the brain was an organ that, given its gray and unimpressive appearance, could not possibly be responsible for sublime human actions. (5)

These concepts underwent drastic revision both during and after the Enlightenment, and with the decriminalization of anatomical dissection. (6) For instance, Franz Joseph Gall, a physician in the early nineteenth century, challenged the duality of mind and body with his assertion that the brain was the organ of the spirit. (7) Gall did careful and laborious examinations and dissections of the brain and skull, and extrapolated his theories regarding neurologic function from his postmortem findings. (8) He developed a topographical model of the brain based on this research, and asserted that the brain was divided into separate components, each performing a distinct function (see Figure 1). (9)


Gall believed that the brain's components and their functions were reflected in raised areas on the human skull and that one could ascertain brain function by examining these bumps. (11) He posited that these raised areas would reveal how and where an individual's brainpower was allocated; the greater the skull space dedicated to a particular part of the brain, the greater its faculty. (12) Gall extended his study of the skull to the features of the human face and asserted that these features revealed an individual's attributes. (13) Gill's brain studies were an attempt to classify a relatively unknown organ. He was among the first to associate brain anatomy with brain function, and although phrenology eventually became discredited, Gall remained committed to his classification of the human brain and the groundbreaking notion that science could link areas of the brain with the tasks they perform. (14)

Nineteenth-century Italian physician Cesare Lombroso, known as the father of modern criminology, later used phrenology to spearhead a major shift in criminal investigation. (15) In 1872, while performing an autopsy on a notorious criminal, Lombroso was struck with inspiration: "I seemed to see all at once, standing out clearly illumined as in a vast plain under a flaming sky, the problem of the nature of the criminal, who reproduces in civilized times characteristics, not only of primitive savages, but of still lower types as far back as the carnivores." (16) This theory became known as Atavism, or the reemergence of regressed evolutionary traits in modern criminals. (17) It was a radical departure from the thinking of the time and drew heavily from both the work of Charles Darwin and evolutionary theory. (18) Lombroso believed that some individuals were "born" criminals; they were throwbacks to an earlier evolutionary stage, and these individuals could be identified by studying their physical features (see Figure 2). (19)

Lombroso differentiated these "born" criminals from those criminals who committed crimes in a state of passion and believed that the latter could be rehabilitated. (20) However, those with the indelible marks of the born criminal were beyond such help, he posited, and should be adjudicated based on their features rather than their crimes. (21) Lombroso used the "scientific" foundation of his work to marginalize earlier enlightened theories of punishment as "abstract, unscientific, and out of touch with the facts." (22) Lombroso's theories were widely accepted and became the basis for much of Italian law at that time. (23)


As scientific understanding of the human brain progressed, scientists rejected the mind/body duality of the past and instead studied the brain in an effort to understand precisely how this mass of nerve cells produced thought, emotion, and action. Before physicians could image or observe the brain in action, they inferred functional anatomy from observing behavioral changes caused by observable trauma to the brain. The famous index case for this type of injury was that of Phineas Gage. (25) In 1848, Gage, a construction crew foreman, was laying railroad tracks using a three-foot spike to tamp down dynamite. (26) A premature explosion propelled the spike into his face, through his brain, and out the top of his head (see Figure 3). (27) Miraculously he survived, but with a distinct change in his personality. Whereas prior to the accident he was efficient and industrious, afterwards he was behaviorally different. (28) Dr. John Harlow, Gage's personal physician, wrote an extensive account of these changes. Though Gage showed no deficits in speech, movement, or language, he was:

   fitful, irreverent, indulging at times in the grossest profanity 
   which was not previously his custom, manifesting but little 
   deference for his fellows, impatient of restraint or advice when it 
   conflicts with his desires, at times pertinaciously obstinate, yet 
   capricious and vacillating, devising many plans of future 
   operation, which are no sooner arranged than they are abandoned.... 
   A child in his intellectual capacity and 
   manifestations, he has the animal passions of a strong man. (29) 


The case of Phineas Gage established that the brain and personality are intimately related, and that damage to the human frontal cortex can cause a dramatic change in behavior, but not cognition. As his family and peers observed, "Phineas Gage is no longer Phineas Gage." The case began the study of localizing the part of the brain that houses our "humanity."

One hundred and fifty years elapsed between Phineas Gage's elucidating accident and the first use of brain imaging in the courtroom. In 1981, John Hinckley attempted to assassinate President Ronald Reagan. His defense team requested permission to introduce CAT scan images of his brain as part of an effort to establish the presence of mental illness. (31) The judge allowed the jury to see Hinckley's CAT scan, which suggested abnormal brain shrinkage. (32) Thus began the link between brain imaging and the explanation of criminal behavior that is the subject of this Article.


A brief overview of the relevant neuroanatomy will help clarify useful substrates for brain imaging. The Central Nervous System (CNS) is responsible for coordinating a body's interaction with the outside world. It receives sensory input, organizes information, and directs responses. The brain and spinal cord comprise the CNS. The primary cellular building block of the CNS is the neuron. A neuron is a cell that receives chemical communication and converts it into an electrical impulse. That impulse then travels down the length of the neuron to be re-converted into a chemical message that is delivered to the next neuron in the chain. In order to help preserve the electrical impulse that travels down the neuron, the neuron is covered in a sheath called myelin that performs a function similar to the insulation around telephone and cable wires. Much of what we know about function of the brain comes from either animal studies (ablating areas of the rodent or primate brain) or human lesions (either tumors or injuries).

The brain can be rudimentarily divided into the brainstem (responsible for basic functions of life, e.g. respiration), the cerebellum (which primarily coordinates movement), the limbic system, and the cerebrum, which involves both cortical and subcortical components (see Figure 4). (33) The cerebellum, cerebrum, and limbic systems are lateralized, with left and right sides. The two hemispheres of the cerebrum are connected by a dense bridge known as the corpus callosum. The two areas of greatest interest for our purposes are the limbic region and the cerebral cortex, which have been the subject of many advances in understanding the mechanisms of behavior. (34) The limbic region is among the oldest and most primitive evolutionary part of the CNS (see Figure 5). …

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