Abstract
Working memory (WM) tasks may involve brain activation actually implicated in long-term memory (LTM). In order to disentangle these two memory systems, we employed a combined WM/LTM task, using a spatial relational (object-location) memory paradigm and analyzed which brain areas were associated with successful performance for either task using fMRI. Critically, we corrected for the performance on the respective memory task when analyzing subsequent memory effects. The WM task consisted of a delayed-match-to-sample task assessed in an MRI scanner. Each trial consisted of an indoor or outdoor scene in which the exact configuration of four objects had to be remembered. After a short delay (7–13 s), the scene was presented from a different angle and spatial recognition for two objects was tested. After scanning, participants received an unexpected subsequent recognition memory (LTM) task, where the two previously unprobed objects were tested. Brain activity during encoding, delay phase and probe phase was analyzed based on WM and LTM performance. Results showed that successful WM performance, when corrected for LTM performance, was associated with greater activation in the inferior frontal gyrus and left fusiform gyrus during the early stage of the maintenance phase. A correct decision during the WM probe was accompanied by greater activation in a wide network, including bilateral hippocampus, right superior parietal gyrus and bilateral insula. No voxels exhibited supra-threshold activity during the encoding phase, and we did not find any differential activity for correct versus incorrect trials in the WM task when comparing LTM correct versus LTM incorrect trials.
Highlights
The underlying neural substrate of working memory (WM) is still under debate. ‘‘Classical’’ dual-process theories implied frontal as well as parietal regions as being critical for the processing and maintenance of a limited amount of information across a short interval
In order to identify the brain areas supporting the successful execution of associative Working memory (WM) tasks, we developed a paradigm consisting of a delayed-match-to-sample (WM) task, assessed in a event-related functional MRI study and an unexpected delayed recognition memory (LTM) task outside the scanner, testing the same stimuli as during the WM task
For the long-term memory (LTM) task, we investigated which brain regions predicted successful LTM when pairs had already been correctly classified in the WM task
Summary
The underlying neural substrate of working memory (WM) is still under debate. ‘‘Classical’’ dual-process theories implied frontal as well as parietal regions as being critical for the processing and maintenance of a limited amount of information (supposed to be within WM capacity) across a short interval. More recent accounts suggested to distinguish memory systems based on the underlying processing operations required to successfully complete the task at hand, rather than on the interval between study and test (Jonides et al 2008; Konkel and Cohen 2009; Ranganath and Blumenfeld 2005) In this view, the exact task characteristics as well as how the task is typically executed should be concisely defined and analyzed a priori. Cogn Process (2016) 17:377–387 working memory function (Jeneson and Squire 2012)— irrespective of the length between study and test and whether the stimuli had been processed consciously or not in the first place (Henke 2010) This is most likely due to the anatomical characteristics and extensive reciprocal connectivity of the hippocampus with polymodal neocortical association areas (Suzuki and Amaral 1994), serving as a hub of brain network communication for memory (Battaglia et al 2011). WM tasks may recruit brain regions that are more typically associated with LTM (cf. Baddeley 2012)
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