Summary: Slow repetitive transcranial magnetic stimulation (rTMS) applied to the left prefrontal cortex improves episodic memory by reducing low-frequency brain-wave power during memory encoding.
Source: PLOS
Memories of past events shape our identity, yet the ability to form new episodic memories often weakens with age, neurological disease, or brain injury.
A new study published in the open access journal PLOS Biology by Mircea van der Plas, Simon Hanslmayr, and colleagues from the University of Glasgow demonstrates that low-frequency rTMS over the left dorsolateral prefrontal cortex (DLPFC) can enhance verbal memory formation. The researchers show that 1 Hz rTMS applied during encoding reduces low-frequency (beta) power in posterior brain regions, and this change is associated with improved memory performance.
Based on prior knowledge of rTMS effects and frontal–posterior interactions during memory encoding, the team hypothesized that stimulating the left prefrontal cortex might alter network activity in a way that benefits episodic memory. To test this, they analyzed two experimental datasets: a between-subjects dataset from 40 participants and a within-subjects replication with 24 participants.
In the first experiment, 40 healthy adults learned lists of words while receiving 1 Hz rTMS either to the left DLPFC (n = 20) or to the vertex as a control site (n = 20). Participants who received left DLPFC stimulation remembered more words than those in the control group. Because this effect emerged from a study originally designed for a different question, the authors ran a second, within-subjects experiment to confirm the finding.
In the replication study, 24 participants completed the same list-learning task under both stimulation conditions (left DLPFC and vertex). Consistent with the initial observation, word recall improved when the left DLPFC was stimulated. Importantly, simultaneous EEG recordings during both experiments provided neurophysiological evidence linking stimulation to memory enhancement.
EEG analyses revealed that 1 Hz rTMS to the left DLPFC led to reductions in low-frequency power—particularly in the beta range—over posterior (parietal) regions during encoding. These parietal areas are critical for attention and perception and play a known role in memory formation. The authors propose that because slow rTMS typically suppresses local cortical excitability and the prefrontal cortex exerts inhibitory control over posterior regions, inhibiting frontal activity can disinhibit parietal activity. This disinhibition appears to promote a neural state more favorable for encoding verbal material, resulting in better subsequent recall.
Further spectral analysis suggested that the observed beta changes were not purely oscillatory but reflected a spectral tilt—an overall shift in power distribution—consistent with modulation of underlying neural excitability. In short, DLPFC stimulation produced measurable shifts in network dynamics that aligned with improved memory performance.
van der Plas commented, “Our electrophysiological results indicate that frontal stimulation affects a broader memory network and can enhance encoding by altering activity in parietal regions. These are complex effects that warrant additional studies to map their precise neural mechanisms.” Hanslmayr added, “We were surprised by the initial finding and therefore prioritized replication. The consistent results across experiments strengthen the case that left DLPFC slow rTMS can boost verbal memory formation.”
Funding: S.H. received support from the European Research Council (Nr. 647954) and the Economic and Social Research Council (ES/R010072/1). Funders did not influence study design, data collection and analysis, decision to publish, or manuscript preparation.
About this rTMS and memory research news
Author: Claire Turner
Source: PLOS
Contact: Claire Turner – PLOS
Image: The image is in the public domain
Original Research: Open access. “Stimulation of the left dorsolateral prefrontal cortex with slow rTMS enhances verbal memory formation” by van der Plas M, Braun V, Stauch BJ, Hanslmayr S. PLOS Biology
Abstract
Stimulation of the left dorsolateral prefrontal cortex with slow rTMS enhances verbal memory formation
Encoding episodic memories requires stimulus-specific processing and relies on interactions between frontal and posterior brain regions. Here we report an incidental electrophysiological finding and its replication: 1 Hz rTMS applied to the left DLPFC enhances subsequent word memory.
In the first experiment (between-subjects, N = 40), participants received 1 Hz rTMS to either left DLPFC (n = 20) or vertex (n = 20) while performing a list-learning task. Left DLPFC stimulation produced superior memory performance compared to vertex stimulation. A second, within-subjects experiment (N = 24) replicated this behavioral effect.
Concurrent EEG showed that 1 Hz DLPFC stimulation induced stronger modulation of beta-range power in posterior regions—an electrophysiological pattern associated with effective memory encoding. Additional analysis indicated that these beta changes reflected a spectral tilt rather than a pure oscillatory phenomenon, consistent with inhibition or disinhibition of parietal cortical regions.
These findings demonstrate that slow rTMS to the left DLPFC can improve verbal episodic memory by modulating neural activity in parietal networks, suggesting potential targets for future memory-enhancement interventions and further mechanistic research.