The paper reviewed here is ‘Theory of Mind Deficits in Patients with Acquired Brain Injury’ by Martin-Rodriguez and colleagues. As the title suggests, the researchers are looking at how adult acquired brain injury influences ‘Theory of Mind’ (ToM). ToM is an important component in various models of social cognition. For those not familiar with ToM, this concept refers to the model that a person has of another person’s mind. In other words it is about empathy, the insight into either one’s own or another person’s mind. Disorders of ToM have been associated with Autistic Spectrum Disorders (ASD). However, we can say that ToM is a function of mind which in turn is a function of brain. Indeed in the introduction, the researchers refer to three regions associated with ToM
- Prefrontal Cortex
- Posterior Cingulate Cortex
- Bilateral Temporo-Parietal Junction
If this is the case then we can also say that an adult without an autistic spectrum disorder could acquire a disorder of theory of mind after developing a brain injury affecting the relevant brain region(s). This could occur for instance after traumatic brain injury or in the course of a neurodegenerative disease (for instance there is discussion and emerging evidence of altered empathy in frontotemporal dementia e.g see here and here).
In the abstract the authors write that
‘The severity of ToM impairment was influenced by ratio of patients with frontal lobe lesion, ratio of patients with right hemisphere injury, type of belief task, and heterogeneity of the sample’s etiology‘
The researchers used the PsychInfo and Medline databases between the years 1995 and 2008. I didn’t look through all of the returned results but on using the search term “Theory of Mind” in PubMed for the years 1900-1998, 537 abstracts were retrieved. Although these were not all relevant, there might have been additional useful references if the search period had been extended. The researchers combined ‘Theory of Mind’ as a search term with ‘brain damage’, ‘brain injury’ and ‘head injury’. I looked at some alternative search terms such as trauma and accident but these didn’t seem to produce distinct results although this was only a brief inspection. Studies that used the following tests were included
- ‘FOTOM’ (first order ToM)
- ‘SOTOM’ (second order ToM)
- ‘Understanding IS’ (indirect speech e.g sarcasm)
- Detecting faux pas
Studies needed to compare subjects with demographically matched healthy controls for inclusion. The number of correct responses on the above tasks provided a simple quantitative measure of ToM. The mean difference between controls and subjects was standardised using Cohen’s D. The researchers applied a Hedge’s D correction to produce an unbiased estimator. They coded a number of other variables including other demographic variables as well as subcomponents of the tasks described above. The analysis was performed using ‘Comprehensive Meta-analysis Version 2‘ as well as macros for SPSS. The statistical analysis was more involved than described here and the researchers also calculated the number of unpublished studies that would be needed to nullify the statistically significant published results using Rosenthal’s approach and a specified threshold.
Unbiased effect sizes for the four types of tasks were as follows
- FOTOM – Unbiased d = 0.52
- SOTOM – Unbiased d = 0.60
- Faux pas – Unbiased d = 0.70
- Understanding IS – Unbiased d = 0.87
The results of a meta regression analysis for the subtest components and demographic variables were tabulated. From this table I could identify three results that were statistically significant at below the 5% level
FLP ratio – R-Squared 0.86 slope 0.93 for Faux Pas (p=0.02)
RHP ratio – R-Squared 0.85 slope -0.92 for Faux Pas (p=0.04)
RHP ratio – R-Squared 0.68 slope 0.82 for IS (p<0.01)
Results for additional variables were also included. Sample sizes required to nullify the effects within the different subtest components were all over n=100.
From these results the researchers drew a number of conclusions as per the abstract excerpt quoted above. The researchers acknowledge that they could not factor in the effects of other variables that influence outcome after brain injury. Indeed one point I was not clear on was the longitudinal nature of the performance on the ToM tasks. For instance, premorbid performance would have been useful although there are comparator groups for the included studies. There was no mention of whether a period of stability had been achieved for performance on ToM tasks and whether this was cross-sectional data. There were differences in the effect sizes for FOTOM and SOTOM tasks and these effect sizes were increased with the use of the false belief tasks. The moderating effect of frontal lobe lesions on faux pas tasks weren’t too surprising but in their discussion the researchers focus on specific regions within the frontal cortex.
In conclusion, this is a complex paper with more involved results and conclusions than are discussed here although a number of the more interesting findings are described above. The involvement of the frontal cortex in performance on ToM tasks such as the faux pas task are consistent with other parts of the research literature and I found the relationship between the ratio of right hemisphere involvement in participants to Faux pas and IS tasks quite interesting. It would be interesting to take some of these findings and use them to generate hypotheses in a longitudinal assessment of fronto-temporal dementia.
Martin-Rodriguez J F and Jose Leon-Carrion.Theory of mind deficits in patients with acquired brain injury: A quantitative review. Neuropsychologia. Vol 48. Issue 5. April 2010. pp1181-1191.
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