Episodic Memory Dysfunction and Effective Connectivity in Adult Patients With Newly Diagnosed Nonlesional Temporal Lobe Epilepsy

Aftab Bakhtiari; Agnes Balint Bjørke; Pål Gunnar Larsson; Ketil Berg Olsen; Marianne C Johansen Nævra; Erik Taubøll; Kjell Heuser; Ylva Østby

doi:10.3389/fneur.2022.774532

Episodic Memory Dysfunction and Effective Connectivity in Adult Patients With Newly Diagnosed Nonlesional Temporal Lobe Epilepsy

Front Neurol. 2022 Feb 10:13:774532. doi: 10.3389/fneur.2022.774532. eCollection 2022.

Authors

Aftab Bakhtiari¹, Agnes Balint Bjørke^{2

3

4}, Pål Gunnar Larsson⁵, Ketil Berg Olsen⁵, Marianne C Johansen Nævra⁵, Erik Taubøll^{2

3}, Kjell Heuser², Ylva Østby¹

Affiliations

¹ Department of Psychology, Faculty of Social Sciences, University of Oslo, Oslo, Norway.
² Division of Clinical Neuroscience, Department of Neurology, Oslo University Hospital, Rikshospitalet, Oslo, Norway.
³ Division of Neurology, Rheumatology and Habilitation, Department of Neurology, Drammen Hospital, Vestre Viken Hospital Trust, Drammen, Norway.
⁴ Faculty of Medicine, Institute of Clinical Medicine, University of Oslo, Oslo, Norway.
⁵ Section of Clinical Neurophysiology, Division of Clinical Neuroscience, Department of Neurosurgery, Oslo University Hospital-Rikshospitalet, Oslo, Norway.

Abstract

Objective: Epilepsy is associated with both changes in brain connectivity and memory function, usually studied in the chronic patients. The aim of this study was to explore the presence of connectivity alterations measured by EEG in the parietofrontal network in patients with temporal lobe epilepsy (TLE), and to examine episodic memory, at the time point of diagnosis.

Methods: The parietofrontal network of newly diagnosed patients with TLE (N = 21) was assessed through electroencephalography (EEG) effective connectivity and compared with that of matched controls (N = 21). Furthermore, we assessed phenomenological aspects of episodic memory in both groups. Association between effective connectivity and episodic memory were assessed through correlation.

Results: Patients with TLE displayed decreased episodic (p ≤ 0.001, t = -5.18) memory scores compared with controls at the time point of diagnosis. The patients showed a decreased right parietofrontal connectivity (p = 0.03, F = 4.94) compared with controls, and significantly weaker connectivity in their right compared with their left hemisphere (p = 0.008, t = -2.93). There were no significant associations between effective connectivity and episodic memory scores.

Conclusions: We found changes in both memory function and connectivity at the time point of diagnosis, supporting the notion that TLE involves complex memory functions and brain networks beyond the seizure focus to strongly interconnected brain regions, already early in the disease course. Whether the observed connectivity changes can be interpreted as functionally important to the alterations in memory function, it remains speculative.

Keywords: autobiographical memory; electroencephalography; hemispheric differences; memory disorders; network; newly diagnosed epilepsy; temporal lobe epilepsy.