Intermittent tACS during a visual task impacts neural oscillations and LZW complexity

Area of Science:

• Neuroscience
• Computational Neuroscience
• Brain-Computer Interfaces

Background:

• Transcranial alternating current stimulation (tACS) is a non-invasive brain stimulation technique, but its precise interactions with endogenous brain activity remain poorly understood.
• Characterizing these interactions is crucial for optimizing tACS protocols for therapeutic and research applications.

Purpose of the Study:

• To investigate the effects of tACS on brain activity and cognitive performance using an intermittent stimulation protocol.
• To explore the utility of Lempel-Ziv-Welch complexity (LZW) alongside traditional metrics for analyzing brain dynamics during tACS.

Main Methods:

• A cross-over study involving 30 participants performing a change-of-speed detection task.
• Multichannel tACS was applied over the visual cortex at 10 Hz, 70 Hz, and a control condition, delivered intermittently.
• EEG was recorded throughout, with analysis including power, phase locking value (PLV), and LZW complexity.

Main Results:

• 10 Hz tACS enhanced theta and gamma power, increased gamma-LZW complexity, and improved theta-PLV, while also increasing reaction time (RT).
• 70 Hz tACS primarily increased RT with minimal effects on other measured metrics.
• Higher gamma power and lower gamma-LZW complexity correlated with shorter RTs.

Conclusions:

• 10 Hz tACS appears to disrupt functionally relevant fast oscillations by increasing gamma-band power, leading to slower behavioral responses and increased gamma oscillation complexity.
• The findings underscore the complex interplay between tACS and endogenous brain dynamics.
• Algorithmic complexity metrics like LZW offer valuable insights into cortical dynamics on a behaviorally relevant timescale.