Correlation – not Causation: Traumatic Brain Injury and Aggressive Behavior in Detainees

Correlation – not Causation: Traumatic Brain Injury and Aggressive Behavior in Detainees

In a sample of Dutch inmates, a history of traumatic brain injury (TBI) was found to be related to aggressive behavior and verbal aggression. However, a TBI history did not differentially affect behavior in detainees and a control group of non-incarcerated individuals. This is the bottom line of a recently published article in The Journal of Forensic Psychology Research and Practice. Below is a summary of the research and findings as well as a translation of this research into practice.

Featured Article | Journal of Forensic Psychology Research and Practice | 2020, Vol. 20, No. 5, 395-412

Traumatic Brain Injury and Its Relationship to Previous Convictions, Aggression, and Psychological Functioning in Dutch Detainees


Jochem Jansen, Institute for Criminal Law & Criminology, Leiden University


Objective: Higher prevalence of traumatic brain injury (TBI) has been reported for detained individuals. TBI may result in erroneously interpreting situations in everyday life, impair problem- solving abilities through dialogue, or negotiation, which may increase aggressive behavior. Knowledge of TBI and its consequences in Dutch penitentiaries is lacking, as virtually no screening, supervision, or treatment is currently provided. Method: The current manuscript assesses differences in self reported aggression, impulsivity, indication for mild intellectual disability, history of childhood trauma, and emotion regulation in detainees (n = 283) and non-incarcerated controls (NIC; n = 51), with and without a history of TBI. Result: A total of 45.2% of detainees reported a TBI, compared to 29.4% in the NIC group. ANCOVA results revealed no interaction between group and TBI history, indicating that TBI history did not affect behavior in detainees and NIC differently. The main effects revealed higher levels of aggression in detainees compared to NICs, and in participants with TBI compared to those without. Separate ANCOVA’s per group reveal that TBI history in detainees was associated with more aggression – also when correcting for violence as the cause of TBI. A logistic regression revealed that detainees with TBI have a higher chance (odds ratio = 3.3) of having at least one prior conviction. Conclusions: TBI history was related to aggressive behavior in Dutch inmates, future studies should assess if TBI history is predictive of in-prison infractions and recidivism rates, and if screening and providing neuro-rehabilitative measures or improved supervision may improve TBI related deficits.


Acquired brain injury, prisoners, violence, convictions

Summary of the Research

“Traumatic brain injuries (TBI) can have prolonged and detrimental effects on behavior and social functioning during adulthood…TBI is defined as an alteration in brain function, or other evidence of brain pathology, caused by an external cause…Patients who have experienced a TBI may show deficits in various domains, including emotion processing, self-control, impulsivity, IQ, and aggression…Reduced emotion regulation abilities following TBI have received relatively little attention but seems to be impaired after TBI…A decrease in such functions may result in erroneously interpreting situations in everyday life, and may impair problem-solving abilities through dialogue or negotiation, which in turn may increase the chance of violent and aggressive behavior…” (p.395-396).

“An overrepresentation of people with TBI within the criminal justice system has been reported…a recent review estimates that between 40% and 60% of inmates have suffered at least one TBI and that having experienced multiple TBIs occurs relatively frequent…Detainees with a history of TBI have a higher risk of recidivism…have been convicted more often…and have increased risk of in-prison infractions…Despite the problems related to drawing causal conclusions, and comparisons between detained and non-incarcerated control (NIC) groups, the association between TBI and violent behavior justifies addressing this issue upon (re)entering the criminal justice system…this manuscript, therefore, aims to answer the following issues: (1) describe the prevalence and causes of TBI within Dutch penitentiaries, (2) evaluate if TBI is more prevalent in detainees (DN) compared to non-incarcerated controls (NIC), (3) assess if DN with TBI have higher rates of aggressive behavior, more previous convictions, longer or more sentences, deficits in emotion regulation, impulsivity, or lower scores on a screener for intellectual disability compared to those without TBI, (4) assess whether the number of experienced TBIs is related to any of the above” (p. 396-397).

“A total of 281 male detainees were recruited from six different geographically dispersed penitentiaries in the Netherlands. Only detainees from the general prison population and houses of custody were eligible for participation…Additionally, 51 male non-incarcerated controls were recruited…The results show that 45.2% of the detainees have a history of TBI and that this is related to higher levels of aggression, especially more anger, verbal, and physical aggression…Although we did not find a significant difference in the prevalence of TBI or the amount of TBIs suffered, between NIC and detainees, the difference in prevalence did border on significance…” (p.405-406).

“Detainees with a TBI history report higher levels of aggression, specifically higher levels of anger, verbal and physical aggression…It may also be related to increased risk of in-prison infractions…However, we did show that when correcting for violence as the cause of TBI, detainees with a TBI history were still more aggressive…Additionally, the results indicate that detainees with a TBI history are more likely to have a prior conviction compared to detainees without TBI history…but are not more likely to have a prior prison sentence…having experienced multiple TBIs did not correlate to current sentence length or the number of previous prison sentences/convictions…Although previous studies have shown that TBI might result in higher levels of impulsivity…lower intelligence…and impaired emotional processing or control…no differences were found in the current study…” (p.406-407).

Translating Research into Practice

“…Since this [aggressive] behavior has a neurological origin, neuro-rehabilitation measures may improve various underlying executive functions and thereby decrease aggressive and offending behavior…Treatment of TBI is often focused on healing the wound and less so on rehabilitation and supervising the adjustment to the (possibly) acquired impairments…Neuro-rehabilitation measures may vary from experience-dependent learning, neurophysiological stimulation, or a combination of these concepts…and should be adapted to the specific needs and abilities of the detainee. Although detainees may benefit from such rehabilitative measures, the prison setting brings some unique challenges, such as restrictions in autonomy, confidentiality, validity of (neuro)psychological testing and possible stigmatization by staff and other detainees…which should be addressed when such measures were to be developed or studied… Future studies should assess TBI in detainees residing in psychiatric and/or maximum security wards…” (p. 407-408).

Other Interesting Tidbits for Researchers and Clinicians

“…the detainees report less TBIs which were the result of falling, but more TBIs resulting from (traffic) accidents and violence compared to NIC…the trauma underlying the reported TBIs might be more severe for TBI resulting from violence or (traffic) accidents compared to falling. Therefore, TBIs reported by detainees are possibly more severe, compared to the NIC group…The detainees showed higher levels of impulsivity and lower intelligence when compared to non-incarcerated controls, but these differences are likely not the result of experienced TBI. Other (childhood) risk factors, including neglect during childhood, paternal mental health issues like substance abuse or antisocial personality disorders, or growing up with a disadvantaged socioeconomic background may explain these differences between the detainee and NIC groups…” (p.406-407).

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Authored by Amber Lin

Amber Lin is a clinical psychology doctoral student at Fairleigh Dickinson University. Her research interests include forensic assessment, competency to stand trial, and the refinement of instruments used to assess the psychological states of criminal defendants.

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