Introduction
Epilepsy is a prevalent neurological disorder that affects approximately 50 million people worldwide (Meyer et al., 2010). Temporal lobe epilepsy (TLE) is the most common form of localization-related epilepsy in adults. Hippocampal onset accounts for at least 80% of all temporal lobe seizures (Tatum, 2012). The temporal lobe is involved in learning, memory, and affective behavior (Gilliam et al., 2003). Damage to this structure as a result of recurrent spontaneous seizures can result in cognitive impairment (Helmstaedter, 2002), which has been frequently described as a potential comorbidity of TLE (Meador, 2002).
Gamma activity (30–100 Hz) has been linked to memory access (Gruber & Müller, 2005; Gruber et al., 2002; Herrmann et al., 2004; Kaiser et al., 2003). Previous studies have reported suppressed synchronization of gamma frequency in cognition disorders, such as Alzheimer’s disease (Politoff et al., 1996; Stam et al., 2002; Wang et al., 2020). Since gamma alternation occurs early in disease progression, it may be involved in the pathological processes of dementia. Modulation of the gamma band is a promising intervention for cognitive improvement in Alzheimer’s disease (Park et al., 2020; Tian et al., 2021). Increased gamma band power has been reported in idiopathic general epilepsy (Pegg et al., 2020; Willoughby et al., 2003). However, EEG variations in gamma frequency in patients with TLE with cognitive impairment remain poorly understood.
We established a retrospective cohort of patients with drug-resistant TLE with and without cognitive deficits. Using this cohort we evaluated the characteristics of interictal resting-state EEG data in gamma frequency and pathological changes in the resected hippocampus of the patients. Spectral analysis, functional connectivity, and graph theoretical analysis were used in the current study to quantify the brain’s functional system. We observed changes in small-world topology in the gamma band, and elevated amyloid-β (Aβ) and phosphorated Tau (p-Tau) deposition in TLE patients with cognitive dysfunction.