Processing time affects sequential memory performance beginning at the level of visual encoding

Abstract

Electrophysiological studies have demonstrated that theta-band activity is useful for investigating neural mechanisms of memory. However, mechanisms specifically driving memory performance remain poorly understood. In sequential memory, performance can be artificially attenuated by shortening the inter-stimulus interval (ISI) between memory item presentations. Therefore, we sought to clarify the mechanisms of sequential memory performance by analyzing theta-band (4–8 Hz) activity recorded via magnetoencephalogram in 33 participants during performance of a sequential memory task where memory items were presented at either slow or fast rates in accordance with longer or shorter ISIs, respectively. Particularly in the slow task, theta activity clearly modulated in accordance with the presentation of memory items. Common cortical target regions in the occipital and frontal cortex were identified in both tasks and related to visual encoding and memory maintenance, respectively. Compared to the slow task, occipital-theta activity was significantly lower in the fast task from the midterm until the ending of encoding, in correspondence with significantly lower recall for memory items in this same period. Meanwhile, despite a loss of clarity in responsiveness to individual memory items in the fast task, frontal-theta activity was not different between tasks and exhibited particularly strong responses in both tasks during the holding period prior to recall. Our results indicate that shorter processing time erodes sequential memory performance beginning at the level of visual encoding.

Differential working memory function between phonological and visuospatial strategies: a magnetoencephalography study using a same visual task

“…The authors concluded that alpha activity in sensory areas reflects storage buffers ( Kawasaki et al, 2010 ). In recent studies, during encoding, increases in theta activity in occipito-parietal regions have been commonly observed, and have been shown to reflect sensory processing of visual information and attention to visual stimuli ( Dugué et al, 2015 ; Pisella, 2017 ; Takase et al, 2022 ).…”

“…In each recording, the helmet-shaped sensor-array was tilted forward 10°. Three head position indicator coils were attached at subjects’ left and right pre-auricular points and nasion, and the head points were obtained using a digitizer according to standard MEG operating procedure ( Takase et al, 2022 ). Each subject was seated in the MEG measurement chair, onto which a table was attached.…”

Broad Alpha-rhythm Enhancement and Its Convergence during Sequential Memory Task

“…The MEG recording procedure was approved by the Faculty of Health Sciences, Hokkaido University (Approval No. [21][22][23][24][25][26][27][28][29][30][31][32][33][34]. Written informed consent was obtained from all participants prior to the experiments.…”

“…We have previously investigated amplitude modulation of alpha- [15,16] and theta- [30] rhythms during the performance of similar or identical sequential memory tasks. One of our previous works [16], in which 20 healthy older persons participated, revealed relationships between alpha-rhythm amplitude, memory performance, and scores indicative of possible mild cognitive impairment (MCI).…”