Working memory retrieval differences between medial temporal lobe epilepsy patients and controls: A three memory layer approach

Abstract

Multi-store models of working memory (WM) have given way to more dynamic approaches that conceive WM as an activated subset of long-term memory (LTM). The resulting framework considers that memory representations are governed by a hierarchy of accessibility. The activated part of LTM holds representations in a heightened state of activation, some of which can reach a state of immediate accessibility according to task demands. Recent neuroimaging studies have studied the neural basis of retrieval information with different states of accessibility. It was found that the medial temporal lobe (MTL) was involved in retrieving information within immediate access store and outside this privileged zone. In the current study we further explored the contribution of MTL to WM retrieval by analyzing the consequences of MTL damage to this process considering the state of accessibility of memory representations. The performance of a group of epilepsy patients with left hippocampal sclerosis in a 12-item recognition task was compared with that of a healthy control group. We adopted an embedded model of WM that distinguishes three components: the activated LTM, the region of direct access, and a single-item focus of attention. Groups did not differ when retrieving information from single-item focus, but patients were less accurate retrieving information outside focal attention, either items from LTM or items expected to be in the WM range. Analyses focused on items held in the direct access buffer showed that consequences of MTL damage were modulated by the level of accessibility of memory representations, producing a reduced capacity.

Flexibility of representational states in working memory

“…A few studies have demonstrated a role of the hippocampus in maintenance of items outside FOA, with their retrieval accompanied by activation in MTL (Oztekin et al, 2009, 2010; Nee and Jonides, 2011). Consistent with such observations, patients with hippocampal sclerosis have impaired WM performance only for items presented earlier in the sequence, that is items outside the FOA (López-Frutos et al, 2014). Alternatively, it has been suggested that the maintenance of unfocused items is supported either through sustained rapid short-term synaptic plasticity (Mongillo et al, 2008; Buonomano and Maass, 2009; Stokes et al, 2013) or sustained neuronal firing in non-sensory regions (Fuster and Alexander, 1971; Goldman-Rakic, 1995).…”

Visual Working Memory Capacity in Patients with Temporal Lobe Glioma

“…Our present study primarily investigates the influence of WM in a group of homogenous patients with a glioma relatively limited to the temporal lobe. In our study, we enrolled patients for evaluation within 1 week after seizure symptom onset because there is evidence that long-term epilepsy-impaired recognition is a component of the neuropsychological profile that is associated with epilepsy [14, 15].…”

Glioma of The Temporal Lobe That Impair Working Memory

“…Our present study primarily investigates the in uence of WM in a group of homogenous patients with a glioma relatively limited to the temporal cortex. In our study, we enrolled insular patients for evaluation within one week after seizure symptom onset because there is evidence that long-term epilepsy impaired recognition is a component of the neuropsychological pro le that is associated with epilepsy [14,15].…”