Neuronal firing in the medial temporal lobe reflects human working memory workload, performance and capacity

Abstract

Significance 15Humans are highly limited in processing multiple objects over a short period of time. 16The capacity to retain multiple objects in working memory is typically associated with 17 frontal and parietal lobe functioning, even though medial temporal lobe (MTL) neural 18 architecture seems capable to process such information. However, there are 19 conflicting findings from patient, electrophysiological and neuroimaging studies. Here 20 we show for the first time that correct performance, workload and individual 21 performance differences are reflected in separate mechanisms of neural activity 22 within the MTL during maintenance of visual information in working memory. The 23 data suggest that low capacity subjects use the MTL to process the overload of 24 information. 25 Abstract 26The involvement of the medial temporal lobe (MTL) in working memory is 27 controversially discussed. Critically, it is unclear whether and how the MTL supports 28 performance of working memory. We recorded single neuron firing in 13 epilepsy 29 patients while they performed a visual working memory task. The number of colored 30

Epileptic High-Frequency Oscillations in Intracranial EEG Are Not Confounded by Cognitive Tasks

“…We have reported earlier (Boran et al, 2020b ) that for the same task in the same subjects, we found neurons in the MTL that fired persistently and increased their firing rate for trials with a high workload during the maintenance period. Neuronal population firing in the MTL during maintenance distinguished workload and we could decode workload of single trials.…”

“…For the selection of data, we build on earlier studies where we asked patients to perform cognitive tasks while we recorded iEEG. In these earlier studies, we recorded and associated the firing of single neurons with task performance, thereby confirming that the tasks were indeed activating regions of the MTL in the patients of this study (Boran et al, 2019a , 2020b ). The datasets are published for re-analysis (Boran et al, 2019b , 2020a ; Dimakopoulos et al, 2020 ; Fedele et al, 2020a , 2021 ).…”

“…In parallel to the iEEG data presented here, we used microelectrodes and high-resolution equipment to record neuronal firing, which has been reported previously (Fedele et al, 2017a ; Boran et al, 2019a , 2020b ).…”

“…Our selection of iEEG data was guided by whether we had found neuronal firing in the same subjects that were associated with task performance (Boran et al, 2019a , 2020b ; Fedele et al, 2020b ). Our previous analysis of neuronal firing in the MTL served to characterize task demand and to predict subject behavior, thus demonstrating the involvement of MTL in cognitive task performance.…”

“…To activate visual working memory, we used a change detection task where the subject had to memorize an array of colored squares ( Figure 2B ; Boran et al, 2020b ). The number of squares determined the working memory load (low workload: one or two squares; high workload: four or six squares; 192 trials per session).…”