Abstract
Temporal lobe epilepsy (TLE) is increasingly becoming considered a network disease, whose effects spread beyond the temporal lobes to strongly interconnected cortical areas. However, little is known about how connectivity in extratemporal regions is manifested in newly diagnosed TLE, and how this relates to memory functions. The aim of the present study was to explore the presence of connectivity alterations in the parieto-frontal network in patients with newly diagnosed TLE, and to examine whether this is associated with their episodic memory impairments. The reason for choosing this network is two-fold. First, parieto-frontal regions are strongly connected to the medial temporal lobes (MTL), making it likely that they will be affected by connectivity disruptions stemming from the seizure focus. Second, research is increasingly indicating the important role played by frontal and parietal regions in the reconstructive processes underlying episodic memory function. The parieto-frontal network of newly diagnosed TLE patients (N = 21) was assessed through electroencephalograph (EEG) effective connectivity and compared to that of controls (N = 21). Further, we assessed the subjects on the phenomenological aspects of episodic memory, in addition to verbal and visual memory functions. Last, we explored the associations between effective connectivity measures and neuropsychological memory scores. Based on previous research, we predicted that patients would have connectivity and memory disruptions, and that higher connectivity would correlate positively with better episodic memory function. Our results show that patients have altered connectivity in the parieto-frontal network, as well as decreased episodic and visual memory functions. In addition, we found a negative correlation between left parieto-frontal connectivity in controls, and the inverse pattern in patients. Thus, the results support the notion of TLE as a connectivity disorder. The positive correlation in patients are discussed in relation to reorganization or maladaptation, whereas the negative correlation is speculated to reflect the specific electrophysiological underpinnings of EEG.