Cognitive Deficits, Effects on Rehabilitation

Cognitive deficits is a generic term, encompassing impairment to essential areas of brain function, but not defined uniquely by low IQ or intellectual disability (ID). ID is defined by the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition as impairment of general mental abilities that affects adaptive functioning in three domains: (1) the conceptual domain (language, reasoning, knowledge, and memory skills), (2) the social domain (interpersonal and communication skills), and (3) the practical domain (skills related to selfmanagement and self-care). To meet the strict definition of ID, symptoms should be chronic and evident before the age of 18 years. Depending on the criteria established, individuals with ID are generally considered those with IQs below 70 on standardized measures. IQs from 70 to 85 are defined as being in the borderline range.

Individuals with specific cognitive deficits, on the other hand, may have IQs in the average range or above average range but commonly manifest symptoms of executive function problems, such as impairments in attention control, strategic goal planning, abstract reasoning, cognitive flexibility, and the ability to organize and adaptively use information contained in working memory. Impairments in executive function have been implicated in aspects of criminal and antisocial behaviors featuring poor impulse control, poor consequential thinking, and problems with emotion management. Unlike intellectual deficits, which must be evident in the developmental period, cognitive deficits can also be acquired impairments resulting from the impact of traumatic brain injury; disease processes, including psychiatric conditions; drug and alcohol abuse; and social and psychological disadvantages, such as poverty and substandard education.

All these conditions have been found to be elevated in offender populations and are risk factors for antisocial behavior. This entry discusses the prevalence of cognitive deficits in offender populations, cognitive deficits as a risk factor for criminal behavior, consideration on how these deficits can affect response to interventions, and supervision and strategies to assist offenders with cognitive deficits.

Prevalence of Cognitive Deficits in Offender Populations. Firm rates of cognitive impairment among offenders have been difficult to estimate, although they are thought to be overrepresented in the criminal justice system. Estimates among incarcerated populations vary based on the assessment tools used and diagnostic and classification criteria applied. Large-scale reviews have found that, when defined strictly by IQ, rates range around 2-3%, broadly in line with rates in the general public. It should be noted, however, that in the criminal justice system, most offenders with severe impairments would be diverted from prison or serve their sentences in specialized secure units, and individuals with very low function would be too limited to become involved in criminal activity. Age-related cognitive decline and lower levels of education among the aged are also rarer in offender populations.

This selection bias, then, restricts the distribution of IQ scores within incarcerated populations relative to the community and probably underestimates the rates of ID among individuals involved in crime. Prevalence rates should also be understood relative to whether the sample constitutes offenders who are incarcerated, awaiting trial, or on parole or probation. Another consideration is whether the prisons incarcerate offenders with particular profiles (e.g., the facility has a disproportionately higher number of high-security offenders, offenders in special treatment units, or offenders allocated to protective custody).

Some subgroups of offenders may be more likely to be identified as having IDs compared with others. For example, violent offenders, sex offenders, and persistent serious offenders are among the profiles associated with lower cognitive function, although, once again, this is not a universal finding. Researchers examining the link between ID and sexual offending, for example, have noted that the evidence for lower IQ appears to be related to the referral source, with offenders referred from child protection agencies and prosecutors’ offices more likely to have scores in the impaired range. Conversely, there is accumulated evidence that higher cognitive function may be a protective factor for the initiation of criminal behavior among at-risk youth and might also be a protective factor for reoffending.

Although there is inconclusive evidence suggesting that offenders have lower intellectual function than nonoffenders (as assessed by standardized IQ measures), there is reliable evidence that offenders are more likely to manifest specific cognitive deficits. In particular, there is evidence of increased rates of learning disabilities and impairments in executive function related to poor planning and impulse control and aggressive and erratic behavior. These symptoms are associated with higher rates of diagnoses for attention-deficit/hyperactivity disorder (ADHD), fetal alcohol spectrum disorder and alcohol-related neurodevelopmental disability, and traumatic brain injury. Given that cognitive deficits are related to alcohol dependence and ADHD, there are considerable levels of co-occurring mental health problems. For example, a significant percentage of offenders with serious alcohol problems have cognitive deficits, as do those with substantial symptoms of ADHD.

In summary, there is an agreement that the rates of cognitive deficits are elevated in offender populations. However, precise estimates of the prevalence of cognitive deficits in offender populations vary widely due to the heterogeneity of the definitions used to describe cognitive impairment, the range of measures used to assess it, and the offender population assessed.