Span, M. M. | Search bioRxiv

bioRxiv2026

Phase of transcranial alternating current stimulation modulates working memory processing speed

BackgroundTheta-frequency transcranial alternating current stimulation (tACS) over prefrontal cortex has been proposed to modulate working memory (WM), yet behavioral effects are often inconsistent. One potential source of variability is the tACS phase during stimulus presentation. ObjectiveWe tested whether behavioral performance during WM depends on the phase of prefrontal theta-tACS. MethodsTwenty participants completed two sessions of prefrontal 4 Hz tACS in a within-subject design, receiving active and sham stimulation in separate sessions. Participants performed a visuospatial change detection task (CDT) and a verbal N-back task. Stimulation effects on overall accuracy and reaction time were analyzed. Subsequently, phase-specific analyses related stimulation phase at task-relevant stimulus presentation to behavioral performance using circular regression models. Preferred phases across participants were tested using Rayleigh tests. ResultsNo significant overall effects of active compared with sham tACS on accuracy or reaction time were observed in either task. However, phase-specific analyses revealed stronger phase-dependent modulation of reaction time during active tACS compared with sham. In the CDT, this effect was present across difficulty levels, whereas in the N-back task it was observed only in the 3-back condition. No reliable phase-dependent effects were observed for accuracy. Preferred phases varied across participants and did not cluster around a common phase. ConclusionsPrefrontal theta-tACS can modulate WM performance in a phase-dependent manner even in the absence of average behavioral effects. The observation of phase-dependent reaction-time modulation across visuospatial and verbal WM tasks suggests that stimulation phase may be a relevant source of variability across cognitive domains.

neuroscience↗

bioRxiv2025

Rapid Invisible Frequency Tagging (RIFT) with a consumer monitor: A proof-of-concept

Rapid Invisible Frequency Tagging (RIFT) enables neural frequency tagging at rates above the flicker fusion threshold, eliciting steady-state responses to flicker that is almost imperceptible. While RIFT has proven valuable for studying visuospatial attention, it has so far relied on costly projector systems, typically in combination with magnetoencephalography (MEG). The recent emergence of high-speed organic light-emitting diode (OLED) monitors for consumers suggests that RIFT may also be feasible with much more accessible hardware. Here, we provide a proof-of-concept demonstrating successful RIFT using a consumer-grade 480 Hz OLED monitor in combination with electroencephalography (EEG). We also share practical recommendations for achieving precise stimulus timing at 480 Hz with minimal frame drops. In a central fixation task, participants viewed a tapered disc stimulus flickering either centrally or peripherally. Luminance was modulated sinusoidally at 60 Hz or 64 Hz, frequencies at which the flicker was barely visible. Photodiode recordings confirmed that the monitor delivered accurate frame timing with few dropped frames. Cross-coherence analysis between occipital EEG channels and a photodiode revealed robust, frequency-specific neural tagging responses for central stimuli at both frequencies. In comparison, weaker coherence was observed for 60 Hz peripheral flicker. Our findings demonstrate that RIFT can be reliably implemented using affordable stimulation hardware, a low-density EEG montage, and a minimal processing pipeline. We hope that this lowers barriers to entry, facilitating broader use of RIFT in basic research and in applied settings where cost and portability matter.

neuroscience↗