Exploring memory-based attention in Temporal Lobe Epilepsy patients

Visuospatial attention has thoroughly been studied to understand the main sources of its guidance. Top-down mechanisms based on long-term memory (LTM) are deepened on this occasion, given the increasingly recognised relevance of derivation of expectations based on the past, to guide future adaptive behaviour. The process, called memory-based attention (or premembering), arises from a widened definition of memory, has been recognized to rely behaviourally on both explicit and implicit forms of memory, and has been observed to rely functionally on the hippocampus. However, the lack of consistent findings regarding the neural networks involved in the process led to exploit dysfunctions of hippocampal activity in patients with refractory Temporal Lobe Epilepsy (rTLE) and left Hippocampal Sclerosis (HS) to fill the gap. The current thesis aims to compare patients to healthy subjects, to understand the impact of hippocampal deficits on memory-based attention. Surprisingly, no significant difference in the ability to use contextual memories to guide attention has been observed between the two groups. Visuospatial abilities have resulted to be fundamental for premembering in both groups, while explicit LTM has supported the process in healthy subjects but not in left HS patients. Probably, a selective impairment in explicit but not implicit memory has caused deficits in encoding information, resulting in poor performance in explicit retrieval but not in the orienting task. Priming or other implicit forms of memory might be at the basis of memory-based attention in left HS patients. These results provide a starting point to implement a multilayered approach to evaluate structural, functional, and microstructural brain tissue alterations in these patients and to understand whether brain reorganization has eventually occurred.