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Neural oscillations

Do different brain rhythms handle seeing versus linking a memory?

Griffiths BJ, Martín-Buro MC, Staresina BP, et al. · NeuroImage · 2021

Open access · cc by · source: Europe PMC

Drops in cortical alpha/beta rhythms predicted later memory while people were taking in information, whereas hippocampal theta-gamma coupling predicted memory only when they were binding the pieces together.

Study at a glance

Design
Human experiment — Within-subject MEG study of an associative memory task: participants saw an object, a pattern and a scene, then had a short window to bind them; brain activity in each phase was related to how many associates were later recalled.
N
N=17 · 28 recruited; participants were excluded for head movement (1), poor data quality (4) or extreme memory performance (6), leaving 17 for analysis.
Population
Healthy young adults (analysed sample aged 20 to 32) at the University of Birmingham
Outcome
Sensor and source-level alpha/beta power and hippocampal theta-gamma phase-amplitude coupling as predictors of the number of associates later recalled

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Key findings

During perception of the sequence, lower alpha/beta power (roughly 8 to 15 Hz) over posterior sensors, localised to early visual cortex, predicted more items recalled, but this was not seen during binding. During the binding window, stronger coupling between hippocampal theta phase and gamma amplitude predicted more items recalled, but this was not seen during perception. A formal interaction test confirmed a double dissociation between the two stages. Memory was better for scenes than for patterns.

Methodology

Seventeen adults in an MEG scanner saw sequences of a line-drawn object, a coloured pattern and a scene, and then had a short window to combine them into one vivid mental image. After a short distractor task, they were shown the object and had to pick its pattern and scene from three options each. The researchers used single-trial regressions to ask how brain rhythms during the perception phase and the binding phase predicted how many associates were later remembered.

Limitations

The analysed sample was small (17 of 28 recruited) after many exclusions, including six for extreme memory performance. Measuring the deep hippocampus with MEG relies on source reconstruction, and the authors caution that apparent left-right differences may be artefacts. Perception and binding cannot be completely separated in time, and the alpha effect could reflect attention rather than information representation. Eye movements were not recorded, so ocular activity could partly mediate the effects.

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