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Default Mode Network patterns and its interactions with memory performance in patients with Temporal Lobe Epilepsy and controls

By Tamires Araujo Zanão, Tátila Martins Lopes, Brunno Machado de Campos, Mateus Henrique Nogueira, Clarissa Lin Yasuda, Fernando Cendes

Posted 18 Oct 2017
bioRxiv DOI: 10.1101/205476

Patients with mesial temporal lobe epilepsy (MTLE) have cognitive dysfunctions not fully explained by the temporal seizure focus. Abnormal functional connectivity in the resting-state default mode network (DMN) appear to be related to these cognitive impairments. Studies showed DMN abnormalities in MTLE, but most combined patients with hippocampal sclerosis (HS) with other underlying etiologies. We enrolled 122 MTLE patients divided into right-HS (n=42), left-HS (n=49), MRI-negative MTLE (n=31) and controls (n=69). All underwent resting-state seed-based connectivity fMRI, with a seed placed at the posterior cingulate cortex, an essential node for the DMN. In addition, patients and 41 controls were tested for verbal and visual memory, estimated intelligence coefficient and delayed recall. Both right-HS and MRI-negative group presented the poorest visual memory scores. Also right-HS and left-HS had a worse performance in verbal memory compared to controls and MRI-negative groups. Overall, the presence of HS in the left hemisphere had more impact on verbal memory, which was not found when the seizure focus is in the left hemisphere in the absence of HS. MTLE patients presented an intricate pattern of increased and decreased connectivity regardless the presence or side of HS. As expected, hippocampus was less connected than controls in all groups of patients. Although EEGs indicated that 64.5% of MRI-negative patients were lateralized to the left, this group showed activations similar to the right-HS. Patients with left and right-HS presented similar, increased and decreased connectivity in the ipsilateral hemisphere; however, left-HS had abnormal decreased connectivity in the contralateral hemisphere.

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