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.