Enhancing prefrontal modulation by phase-locking intermittent theta burst stimulation to a concurrent transcranial...

Area of Science:

• Neuroscience
• Neurostimulation
• Brain Imaging

Background:

• Theta burst stimulation (TBS) modulates cortical excitability but shows high individual variability.
• Transcranial alternating current stimulation (tACS) can influence cortical excitability in a phase-dependent manner.
• Phase-locking TBS to tACS crests may amplify neuronal responses and enhance long-term potentiation (LTP).

Purpose of the Study:

• To investigate if phase-locking intermittent TBS (iTBS) to 5Hz tACS crests enhances prefrontal cortex excitability.
• To evaluate the effects of concurrent tACS-iTBS on TMS-induced activity and EEG resting-state Microstates.
• To determine if baseline oscillatory activity predicts changes in TMS-induced activity.

Main Methods:

• A randomized sham-controlled, cross-over study with 27 healthy participants.
• Participants received iTBS paired with active tACS and sham-tACS.
• Cortical excitability assessed via TMS-induced activity and EEG Microstates before and after stimulation.

Main Results:

• Significant effects of iTBS on channel-wise, global, and oscillatory TMS-induced activity, and changes in Microstates.
• Concurrent phase-locked tACS-iTBS decreased the N100 amplitude of the Global Mean Field Power.
• Baseline TMS-induced oscillatory activity predicted post-stimulation changes, with strengthened gamma oscillations by tACS-iTBS.

Conclusions:

• Phase-locked tACS shows potential to enhance the effects of iTBS on prefrontal cortical excitability.
• The combined tACS-iTBS protocol modulated brain activity and Microstates.
• Baseline oscillatory activity is a crucial factor influencing stimulation outcomes.