Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Neuroscience

Supervisor

Dr. Derek Mitchell

Abstract

Recent lesion studies have indicated that regions of the human prefrontal cortex play a critical role in empathy; however, these lesion studies often include patients with severe head injuries. The present study utilizes a cohort of 84 patients with cerebrovascular disease with mild-to-moderate strokes to examine the neural regions involved in empathy. We hypothesized that dissociable areas of the prefrontal cortex are involved in empathy. We predicted that lesions to the inferior prefrontal cortex would result in deficits in empathy compared to superior prefrontal lesions, non-prefrontal lesions, and those with no detectable lesions. To measure empathy, caregiver ratings were obtained on the empirically validated Interpersonal Reactivity Index. No significant differences were found among groups. A voxel-based lesion-symptom mapping analysis was conducted on segmented lesion images to create a statistical map of the neural regions involved in empathy; no significant results were found. Our findings indicate that mild-to-moderate stroke lesions may not be severe enough to produce observable deficits in empathy.

Summary for Lay Audience

Lesion studies have a crucial role in neuroscience for examining relationships between brain regions and emotional or cognitive processes. When a stroke occurs, it creates lesions within the brain and prevents the affected area from functioning properly. These lesions allow researchers to examine brain regions and their function by what deficits occur. Stroke can cause various deficits, and it is reported that stroke affecting the prefrontal cortex can disrupt empathy. Empathy has two facets, emotional and cognitive. Emotional empathy refers to our ability to understand what others are feeling. Cognitive empathy involves the ability to understand the thoughts and intentions of others. Research examining the neural regions involved in empathy have implicated areas of the prefrontal cortex and temporal lobes, although these studies often involve lesions from severe brain injuries. By examining lesions to the prefrontal cortex and empathy in individuals who have mild-to-moderate size strokes, we have the opportunity to examine specific areas involved in these processes. To do this we obtained data from the Ontario Neurodegenerative Disease Research Initiative, which included 155 participants who were classified as having cerebrovascular disease. Imaging volumetric data was obtained and participants who had lesions greater than 10% in the brain regions of interest were included in this analysis. Participants were separated into groups based on lesion location: superior prefrontal cortex, inferior prefrontal cortex, non-prefrontal cortex and no detectable lesions. To measure empathy, we used caregiver ratings of the Interpersonal Reactivity Index (IRI). We predicted that individuals in the inferior prefrontal cortex group would have lower scores on the IRI compared to the superior, non-prefrontal cortex and no detectable lesion groups. However, our study found no significant differences among these groups. A lesion mapping analysis was also conducted in this study. This analysis creates a statistical map of the lesions that are most related to the behavioural deficit, however, this did not demonstrate a significant result in our study. Future research should seek to examine this in a larger cohort of individuals with chronic stroke lesions.

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