The Relationship between Temporal Lobe Epilepsy and Depression: The Test of Functional Involvement of Frontal and Parietal Lobe Hypothesis

Hwang, Seong Hoon; Hahm, Woong

Abstract

OBJECTIVES
Regarding the relationship between the laterality of seizure focus and depression in temporal lobe epilepsy (TLE), previous studies reported inconsistent results. The role of frontal function as moderating variable between laterality and depression had been proposed. We attempted to replicate functional involvement of frontal lobe (FIFL) and, as an effort to extend previous findings, to test the functional involvement of parietal lobe (FIPL) to prove the hypothesis derived from Heller's valencearousal theory of emotion.
METHODS
In study 1, patients with TLE (right 19, left 17) performed MMPI-D as a depression measure, Wisconsin Card Sorting Test (WCST) as a frontal function measure, and block design (BD) as a parietal function measure in the course of pre-operation assessment. Multiple regression model of depression which includes the interaction terms both between laterality and WCST and between laterality and BD were tested. In study 2, patients underwent anterior temporal lobectomy (ATL;right 20, left 25) were assessed and analyzed in the same way as study 1.
RESULTS
In study 1, contrary to the FIFL and FIPL prediction, interaction of laterality with WCST or BD were not significant. In study 2, the interaction with frontal function was significant. Consistent with FIFL prediction, depression came to be evident when seizure focus was lateralized to the left side and simultaneously frontal function declined. But the interaction with BD remained insignificant, which suggests the invalidity of FIPL hypothesis.
CONCLUSION
We replicated the FIFL hypothesis in the depression of ATL patients. The relation of depression with frontal function was more evident in post rather than pre operation sample. This pattern may be due to the inter-hemispheric interference of frontal functions in pre-operation sample and to the release-of-function phenomenon in post-operation sample. On the other hand, we did not succeed in confirming the role of parietal function in depression. Intactness of the parietal function in TLE was considered as the main cause of the negative finding.