Deficits in comprehension of speech acts after TBI: The role of Theory of Mind and Executive Function

Background: An important facet of social cognition that is often impaired in people with traumatic brain injury (TBI) is theory of mind (TOM) - the ability to make inferences about another person’s beliefs or intentions. Critical to effective communication, TOM is mediated by frontal brain structures that overlap with those that mediate executive function. While some studies have found relationships between ToM and executive function, others have found no such relationship. Many TOM tasks also use complex stories that require significant capacity to understand. Consequently, the issue of whether TOM uniquely contributes to pragmatic understanding or whether it is mediated by reduced cognitive capacity and executive skills remains unclear. This study aimed to disentangle this issue.

Method: Participants included 24 individuals with severe TBI (18 males; age: M = 47.5±12.3 years) recruited from brain injury units in metropolitan Sydney and 24 age, gender and education-matched Controls. Participants completed comprehension tasks consisting of videotaped vignettes with low TOM (answering questions about causal or logical inferences) and high TOM requirements. These were performed across four conditions with varying executive function demands, including: (1) low cognitive load; (2) high flexibility; (3) high working memory; and (4) high inhibition.

Results: Individuals with TBI were more impaired than controls in high TOM tasks in the working memory and inhibition conditions. When controlling for executive function demands, significant group differences remained in the working memory task, but not the inhibition task. This indicates that TOM is dependent on inhibition demands but not working memory. No group differences were found for the flexibility tasks.

Conclusions: Although TOM is an important facet of social cognition the present results suggest that it does not uniquely contribute to communication comprehension ability in individuals with TBI.