Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Psychology

Supervisor

Johnsrude, Ingrid

Abstract

Individuals with focal epilepsy whose seizures are poorly managed with medication will often undergo extensive investigations to determine surgical candidacy. These investigations make use of various methodologies to localize normal and pathological brain tissue. Temporal lobe epilepsy (TLE), the most common type of medically refractory epilepsy, can often be detected through structural and functional changes to the affected temporal lobe. On neuropsychological assessment, this dysfunction may be inferred from material-specific memory deficits, with left TLE associated with reduced verbal memory and right TLE associated with reduced visual memory. Although, simple, artificial stimuli may be useful when a clearly lateralizing pattern emerges on testing, other memory deficits may be more subtle or recruit both temporal lobes. Our primary goal with this work was to investigate the utility of a brief, engaging audiovisual film clip to assess temporal-lobe dysfunction in TLE. The first two investigations offer an evaluation of the psychometric properties of a memory test designed to investigate various aspects of memory for the movie. In the first investigation, we used a variety of recall- and recognition-based measures derived from the movie-memory test, whereas the second investigation focused on temporal memory, memory for the temporal context of events in the movie. Both chapters demonstrate the sensitivity of movie-based measures to detect cognitive deficits in TLE. In fact, movie measures appear to be more sensitive than some commonly used standardized tests. The third investigation integrated structural and movie-driven functional neuroimaging measures with performance on the movie-memory test to investigate the combined utility of these methodologies in studying temporal-lobe dysfunction in TLE. Measures of hippocampal volume and connectivity could sensitively distinguish participants with TLE from controls, and abnormal neuroimaging markers could be directly related to cognitive measures to better understand their behavioural consequences. In summary, the current investigations suggest a promising role for movie-based assessment tools in TLE, and motivate their further validation as potential clinical tools to inform surgical planning in TLE.

Summary for Lay Audience

Epilepsy is a seizure disorder that can often be treated with medications. However, when medications do not adequately control seizures, brain surgery can be an effective alternative. Surgery consists of removing the part of the brain that is causing seizures, which, in many cases, involves the temporal lobes of the brain. The temporal lobes are important for memory, so although memory may already be affected by epilepsy itself, surgery in this area may cause more substantial memory difficulties. In planning this surgery, different health professionals are asked to identify the part of the brain from which the seizures originate and to consider how a surgery in this area could affect cognitive skills like memory. Neuropsychologists, for example, administer and interpret cognitive tests to make inferences about how well different parts of the brain are functioning. Memory testing typically involves asking the person to learn and remember a series of words or designs. Since everyday memory is more complex, we wanted to investigate whether asking people to remember something more complex and realistic could also be used to assess memory deficits in epilepsy.

We asked people with epilepsy (whose seizures originated in the temporal lobe) and people without any neurological disorder to watch a short, suspenseful movie while they underwent a functional brain scan, and then to complete a memory test for the movie. Their memory for the movie was assessed in different ways, like asking them to state as much as they could remember or asking them to recognize scenes from the movie. We also compared their performance on the memory test with how different parts of the brain were communicating with each other while they watched the movie. We found that the memory test captured memory difficulties in the epilepsy group, the brain scan identified brain differences in the epilepsy group, and together, the memory test and brain scan could be used to clarify how different brain differences manifest as memory difficulties. Future studies can expand on these findings to better understand how tests like these can complement the more traditional tests of memory in presurgical assessments of epilepsy.

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