CASE: Self-reported TBI
When charged with raping a 19-year-old woman, Mr. P, age 32, pleads not guilty by reason of insanity (NGRI). He has a self-reported history of traumatic brain injury (TBI) and claims that since suffering a blow to the head 8 years before the rape, he has experienced episodes of personality changes, psychosis, and violent behavior. Mr. P is adamant that any wrongdoing on his part was beyond his control, and he argues that consequences of the brain injury, such as hallucinations and aggressive behavior, had recently emerged. The court asks that a forensic psychiatrist evaluate Mr. P.
An only child, Mr. P was raised by his mother in an inner city area. His father was dependent on alcohol and cocaine and abandoned the family shortly after Mr. P’s birth. Mr. P abuses alcohol, as evidenced by previous driving under the influence charges, but denies illicit drug use. He graduated from high school with average grades and denies a history of disciplinary action at school or home. Although Mr. P was charged with misdemeanors in his late teens, the sexual assault is his first felony charge. Mr. P describes himself as a “charmer.”
After high school, Mr. P worked full-time in construction, where he claims he suffered a traumatic blow to the head. Despite this injury, he continued to work and socialize and never sought treatment at a mental health clinic.
The authors’ observations
Although defendants may legitimately suffer from TBI and resultant complications, many individuals capitalize on a history of minor head injury to support their NGRI defense.1 Forensic psychiatrists must retain a healthy degree of clinical suspicion for malingering in defendants who claim NGRI as a result of complications from brain injury, especially when the injury and complications are not documented and simply patient-reported.
TBI is a CNS injury that occurs when an outside force traumatically injures the brain and can cause a variety of physical, cognitive, emotional, and behavioral effects ( Table 1 ).2 Cognitive deficits include:
- impaired attention
- disrupted insight
- poor judgment
- thought disorders.
Reduced processing speed, distractibility, and deficits in executive functions such as abstract reasoning, planning, problem solving, and multitasking have been documented. Memory loss—the most common cognitive impairment among head-injured people—occurs in 20% to 79% of people with closed head trauma, depending on injury severity.3 People who have suffered TBI may have difficulty understanding or producing spoken or written language, or with more subtle aspects of communication, such as body language.
TBI may cause emotional or behavioral problems and personality changes. Mood and affect changes are common. TBI predisposes patients to obsessive-compulsive disorder, substance abuse, dysthymia, clinical depression, bipolar disorder, phobias, panic disorder, and schizophrenia.4 Frontal lobe injuries have been correlated with disinhibition and inappropriate or childish behavior, and temporal lobe injuries with irritability and aggression.5
Table 1
TBI symptoms correspond to area of injury
| Area of injury | Motor/sensory | Psychiatric/behavioral | Cognitive |
|---|---|---|---|
| Brain stem | Decreased vital capacity in breathing, dysphagia | Sleep difficulties | Inability to categorize objects, difficulty with organization |
| Frontal lobe | Aphasia, praxis | Disinhibition, personality changes | Impaired executive function |
| Cerebellum | Nystagmus, tremor | Labile emotions | Inability to process information |
| Parietal lobe | Apraxia | Personality changes | Neglect |
| Occipital lobe | Visual field cuts; diminished proprioception | Visual hallucinations | Color agnosia; inability to recognize words; difficulty reading, writing, and recognizing drawn objects |
| Temporal lobe | Seizure | Libido changes, humorless verbosity, aggression, olfactory perceptual changes | Prosopagnosia, aphasia, agnosia, memory loss, inattention |
| TBI: traumatic brain injury | |||
| Source: Reference 2 | |||
TBI and the insanity defense
The M’Naghten Rule of 1843 requires that for an insanity defense, the defendant must have a mental disease or defect that causes him not to know the nature and quality or the wrongfulness of his act.6 TBI is an abnormal condition of the mind leading to a mental disease that can substantially affect control of emotions and behaviors.
Nevertheless, TBI-induced criminality remains controversial.7 Theories on the etiology of impulse dyscontrol resulting from TBI have suggested structural damage to the brain and altered neurotransmitters. In TBI, the amygdala—which is located within the anterior temporal lobe and adjoins emotions to thoughts—often is injured. Damage to this structure leads to poor impulse control and violent behavior. Damage to specific neurotransmitter systems that causes elevated norepinephrine and dopamine levels and reduced serotonin levels have also been implicated as a cause of impulse dyscontrol in TBI patients.8
In theory, TBI patients potentially could have enough cognitive impairment to have a substantial lack of appreciation of the criminality or wrongfulness of an act. TBI-related impulsivity and cognitive impairment can lead to recklessness and negligence.9 The U.S. Supreme Court has acknowledged that CNS dysfunction affects judgment, reality testing, and self-control.10