The contribution of executive function to theory of mind and speech comprehension deficits following TBI

Background and aims: Theory of mind (TOM) is critical to effective communication in individuals with traumatic brain injury (TBI). TOM abilities are mediated by frontal brain structures that also mediate executive functioning. There is much debate in the research literature, however, about whether TOM is dependent on executive function or not. The issue is complicated by the fact that many TOM tasks use complex stories requiring a significant capacity to understand. This study aimed to determine whether TOM is dependent on executive function or whether these abilities are, in fact, modular.

Method: Twenty-four individuals with severe TBI (18 males; mean age: 47.5±12.3 years), recruited from Sydney brain injury units, and 24 match controls participated in the study. Videotaped vignette segments were used across four conditions containing both low and high TOM tasks. These conditions included: (1) low cognitive load; (2) high flexibility load, (3) high working memory load, (4) high inhibition load.

Results: Individuals with TBI were more impaired than controls in high TOM tasks. Significant group differences remained even after controlling for working memory load. In contrast, poor performance on ToM appeared to be fully accounted for by poor inhibitory control. This indicates that whereas TOM may not be dependent on working memory demands, it may be dependent on inhibition demands. No group differences were found for the flexibility tasks.

Conclusions: The results indicate that TOM does not uniquely contribute to communication comprehension ability, and that TOM ability is selectively dependent on inhibition demands, in individuals with TBI.