Abstracts

Rationale: Mood disorders are a common psychiatric comorbidity of mesial temporal lobe epilepsy (MTLE). This comorbidity has led to suggestions that certain forms of epilepsy and psychiatric symptoms share a common neurobiologic substrate involving the amygdala. It is well-known that the amygdala is composed of functionally distinct nuclei that contribute to emotion processing in specific ways through interactions with other brain structures. To date, no studies have investigated functional connectivity (FC) emerging from amygdala subdivisions in MTLE to determine if these networks differ from normal controls (NC), and are associated with psychiatric symptoms, and perhaps bear preferential relationships with anxiety or depression. Methods: We collected resting-state in fMRI in 11 left and 11 right MTLE patients, and 19 age-matched NCs. We tested if distinct FC patterns can be detected across 3 amygdala subdivisions: laterobasal (LB), centromedial (CM), and superficial (SF). Using each of them as a seed, we compared the associated functional network between each group, using 2-sample t-tests. Then, we investigated if these FC abnormalities were correlated to the anxiety and depression levels in the patients. The ‘Anxiety' (ANX), ‘Anxiety-Related Disorders' (ARD) and ‘Depression' (DEP) scales of the Personality Assessment Inventory were used to assess these symptoms. Results: No significant differences emerged between the left MTLE and the NCs. In contrast, and regardless of the side of the seed, we observed increased FC between each seed and contralateral regions in the right MTLE group, compared with NCs. The NCs showed increased FC in the hemisphere ipsilateral to the seed compared to the RMTLE group. Based on these results, we revealed 3 significant relations with psychiatric symptoms in the RMTLE group. We found that higher level of ARD was associated with increased FC between the left CM amygdala and a region of the left cerebellum (p=0.008, Spearman r=0.86). In contrast, higher levels of both DEP (p=0.001) and ANX (p=0.002) were associated with reduced FC between the left LB amygdala and a right inferior temporal region (Fig. 1). Conclusions: Overall, these results indicate that MTLE alters FC in areas outside the epileptogenic temporal lobe, in ways that correlate with key psychiatric symptoms common in these patients. We highlight that right MTLE differentially affects the FC emerging from each amygdala's subdivision, indicating these distinct FC patterns mediate different emotional networks. Our data show that seizure pathology, and its effect on FC, impacts psychiatric symptoms in important ways that vary with the pathologic hemisphere. More generally, pathology in the emotion-dominant right hemisphere appears more closely related for the expression of emotion networks. To our knowledge, this is the first description of FC alterations in MTLE involving a specific limbic structure that have relevance to the emotional problems of these patients.