EEG-TMS and Auditory Working Memory
Working memory allows us to hold on to information for a few seconds—like remembering a phone number or a melody. While scientists have long known the prefrontal cortex helps store this information through continuous neural firing, a newer theory suggests something more intriguing: our brains might also keep memories in a quiet, “activity-silent” state.
In this silent mode, information is stored through short-term changes in synaptic strength rather than ongoing electrical activity. The latest study from researchers at Massachusetts General Hospital and Harvard Medical School used transcranial magnetic stimulation (TMS) and electroencephalography (EEG) to directly test this idea in the auditory domain.
Probing Hidden Memory States with TMS
The research team applied single-pulse TMS (spTMS) to a specific brain area called the posterior superior temporal cortex—a region involved in processing complex sounds. Participants were asked to remember ripple-like tones while their brain activity was recorded using EEG.
During the maintenance phase—when participants were silently holding a sound in memory—the researchers delivered a quick magnetic pulse. This “impulse” temporarily perturbed the targeted brain area. Using multivariate pattern analysis (MVPA), they found that EEG signals following the pulse carried more decodable information about the remembered sound.
In other words, the TMS pulse briefly reactivated a hidden memory trace, allowing the EEG to “read out” what the brain was holding in silence.
Decoding the Silent Brain
Previous studies mostly focused on visual working memory, often showing that sensory regions can retain information without continuous firing. But auditory working memory—critical for speech, language, and music—has remained less explored.
This new TMS-EEG experiment provides the first causal evidence that auditory information can also be maintained in activity-silent states. The ability to decode these hidden patterns supports the idea that memory is distributed and dynamic, not tied to constant neural activity.
According to the researchers, these silent states rely on short-term synaptic plasticity, where temporary chemical changes strengthen connections between neurons. Even without ongoing electrical firing, these modified connections can preserve memory traces for seconds at a time—until a perturbation like TMS brings them back online.
Implications for Future Brain Stimulation Research
This finding has major implications for the future of interventional psychiatry. TMS is already used clinically to treat depression, but combining it with EEG and advanced decoding methods could help scientists understand how stimulation interacts with hidden brain networks.
Targeting these “activity-silent” mechanisms may one day lead to more precise neuromodulation therapies for cognitive deficits, such as those seen in schizophrenia, ADHD, or traumatic brain injury. The combination of EEG-TMS allows researchers to map how memory and attention circuits operate at millisecond resolution—something traditional brain imaging methods cannot achieve.
By showing that TMS can uncover the neural code of auditory working memory, this study opens the door to future protocols that monitor and even strengthen silent brain states underlying perception, learning, and emotion.
References
- Iuluc, C. M. et al. (2025). Decoding activity-silent auditory working memory states using single-pulse TMS and EEG. Brain Stimulation, 18(3), 649–658. https://doi.org/10.1016/j.brs.2025.02.020
- Stokes, M. G. (2015). ‘Activity-silent’ working memory in prefrontal cortex: A dynamic coding framework. Trends in Cognitive Sciences, 19(7), 394–405. https://doi.org/10.1016/j.tics.2015.05.004