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TBI and Mental Illness

What if a defendant commits a crime because of being affected by either an acute brain injury or an acquired or inherited brain disease? This is called the “brain defense.” In criminal cases, defense attorneys are increasingly using clinical evidence of brain injury to either establish their client’s innocence or mitigate their punishment during sentencing. In several studies by Duke University, they found that approximately 1,600 judicial opinions in the U.S. Court system between 2005 and 2012 mentioned neurobiological evidence being used in this manner. Since these studies were done, the use of the “brain defense” has doubled to 400-500 per year.

This same principle may also be applied to civil cases. Neuroscience is being used by personal injury lawyers to assess damages for their clients. Traumatic brain injury may be suffered in many ways such as blunt force trauma, car accidents, or job injuries. The extent to which these injuries will affect the client and the ultimate need for further medical and psychological care can be assessed by a cost analysis.

The medical disciplines of neurology, psychology, and psychiatry all focus on issues involving the brain. And all illnesses have both a psychological and physiological component. Therefore, motor and sensory processes as well as cognition and behavior all come into play when evaluating someone for any type of illness or injury to the brain. Physical and psychological symptoms can be related and manifest in conjunction with each other such as:

  • Physical illness with a psychological reaction;
  • Psychological illness with physical symptoms;
  • Physical disease with secondary psychological reaction; and
  • Physical disease giving rise to psychological manifestations.

For example, a dementia patient may have confusion and disorientation but so can a person with a traumatic brain injury. Therefore, it is essential to obtain a fully accurate medical and event history in order to make an accurate diagnosis; distinguishing between a pre-existing physiological or psychological disease and an acute brain injury. There are four major categories of neurological disorders that describe their psychiatric presentations along with their possible acute pathologies.

  • Tempo – Acute pathologies such as those caused by trauma, drugs, infections, etc., are associated with confused states such as “delirium”, but a chronic brain syndrome such as dementia may present itself similarly.
  • Site – Certain brain regions are associated with particular presentations of psychological and behavioral problems. Lack of oxygen in the right hemisphere of the brain can either be from a stroke or TBI and can cause mania. Damage to the orbitofrontal cortex can be associated with disinhibited behavior which is also a symptom of many mental illnesses.
  • Neurotransmitter system – Neurotransmitters are chemicals in the brain that assist with transmitting signals. These are norepinephrine, acetylcholine, dopamine, and serotonin. These neurotransmitters can be affected by either TBI or mental illness. Medications are available to treat issues with these transmitters.
  • Individual differences – Age, sex, education level, and prior psychiatric history may all influence the likelihood that someone will manifest psychological symptoms.

Pre-existing Conditions

In the event of an injury, we need to be cognizant of the fact that the injured person may have pre-existing conditions that were either inherited or acquired during their lifetime. The list of possibilities is long and include:

Psychological problems TBI from a prior incident or accident Central nervous system degenerative disorders
Vascular disorders Inflammatory or infective disorders, such as multiple sclerosis Neoplastic and paraneoplastic disorders (tumors/cancer)
Metabolic/endocrine disorders Deficiency disorders such as Wernicke’s Structural disorders
Narcolepsy Disorders of consciousness REM sleep behavior disorder
Attention issues Visual attention disorder Executive function ability problems
Memory issues Transient global amnesia Reduplicative paramnesia
Perception problems Charles Bonnet syndrome characterized by visual hallucinations Peduncular hallucinosis
Capgras delusion Fregoli delusion Language disorders
Praxis Alien hand syndrome Mood and emotional problems
Thought disorders Behavior/personality disorders

Acute Injuries

Irrelevant of a historical injury, anybody who has recently suffered an impact to their head may have an acute injury to the brain that can demonstrate neuropsychiatric symptoms. In some situations an acute injury will be apparent from the history of the present illness, but in other cases it may be difficult, or even impossible, to differentiate. If the person does indeed have an injury such as a chronic subdural hematoma, they may present with delirium, insidious cognitive decline or odd behavior and not be able to properly convey their medical history. There may also be a delayed presentation of hours or days. In this case, the medical personnel should do a thorough evaluation and appropriate testing as well as attempt to contact a close family member, in order to obtain an accurate diagnosis.

Chronic Injuries

A condition known as chronic traumatic encephalopathy (CTE) has been found in football players and has been associated with psychiatric symptoms, including suicidal ideation, depression, and poor behavior resulting in domestic violence and criminal behavior. Unfortunately, this condition cannot be diagnosed until autopsy, which makes using it for criminal defense only a “theory.” Combat veterans are coming home with depression and personality changes that can be linked to traumatic brain injuries and post-traumatic stress disorder. Their traumatic brain injuries may or may not be a direct result of being “struck” but may be an indirect injury from being in the vicinity of a blast. In addition, research among adolescents regarding their brain development and its role in decision making and impulsive behavior has determined that their brains are not fully developed until about 25 years of age, therefore confirming that an adolescent does not always have the tools to make sound judgements or control their impulsive behaviors.

How does this relate to criminal cases?

Neuroscientific evidence can be a valuable tool for attorneys. PET scans and MRI scans that measure brain activity are both generally accepted as evidence in death penalty sentencing hearings. Of course, there is a need to definitively tie this brain activity or lack thereof to the behavior of the defendant.

Any of these issues could be present in any person that presents with a possible traumatic brain injury and therefore should be ruled out by the medical provider by taking an extensive medical history from the victim and the family of the victim. Doing so may be critical in developing your case.


Works Cited

Butler, C., & Zeman, A. (2005). Neurological syndromes which can be mistaken for psychiatric conditions. Journal of Neurology, Neurosurgery, & Psychiatry, 76(1), i31-i38. doi:

Lindley, R. (2017, July 30). Columbian College of Arts & Sciences: The George Washington University – History News Network. Retrieved October 29, 2020, from History News Network:


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