Functional and structural MRI connectivity associated to autobiographic memory in temporal lobe epilepsy with uni and bilateral  hippocampal sclerosis

Thesis supervisor: Antoni Rodríguez Fornells

ABSTRACT

Structural damage associated with hippocampal sclerosis (HS) is the most common cause of temporal lobe epilepsy (TLE). TLE patients with persistent paroxysmal activity during seizures have structural and functional brain connectivity disturbances with abnormalities in the wider cortico-subcortical network. The majority of lesion studies report that mesial temporal lobe (MTL) is associated with impairment of autobiographic memory (AM), namely the memory for experiences that occurred in a specific time and place, probably because the human hippocampus known to be a crucial node in the neural network supporting AM. In addition, there are many other factors that may influence the pattern and extent of retrograde memory loss after a temporal lobe lesion, such as the impact of lesion side, or the method of assessing and/or scoring memory performance.

We extensively reviewed the literature about the neurofunctional changes elicited by TLE, bilateral mesial TLE (BMTLE), and surgical treatment on AM, and we realized that this memory function has scarcely been examined. Furthermore, there is also a lack of information regarding white-matter (WM) interhemispheric seizure propagation pathways and commissures. Addressing these weaknesses, we examined patients with mesial TLE (MTLE; unilateral, bilateral or with TLE surgery) in two projects with specific aims: (i) To examine the AM neurofunctional correlates in TLE patients and (ii) to identify the WM microstructural connectivity in TLE and bitemporal HS (TLE+BHS) patients.

First, to study AM-functional related activity in TLE patients we designed a new fMRI AM paradigm. We selected, for the first time to our knowledge, a group of 19 TLE patients with anterior temporal lobe resection (ATLR) or BMTLE, as well as 18 subjects for the control group. We observed that, while the control and right MTLE group showed a left-lateralized AM network, left MTLE and patients with BMTLE also showed strong activation in the right temporal and frontal lobe regions. These results support the idea of the use of alternate brain areas involved in retrieval of specific AM memories and encourage the idea