Frequency-specific neuromodulation of local and distant connectivity in aging and episodic memory function

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Brain Imaging

Background:

• The aging brain recruits distant neural communities to compensate for local decline.
• Bilateral prefrontal cortex (PFC) is recruited for cognitive function maintenance in aging.
• The impact of local neural activity changes on this adaptive mechanism is not well understood.

Purpose of the Study:

• To investigate how aged brains flexibly adapt to local changes in cortical activity.
• To determine the causal relationship between local cortical activity and network recruitment for memory encoding.
• To test if structural connectivity influences adaptive network responses.

Main Methods:

• Functional MRI (fMRI) with graph theoretical measures.
• Diffusion weighted imaging (DWI) for structural connectivity.
• Repetitive transcranial magnetic stimulation (rTMS) to modulate local PFC activity (5 Hz and 1 Hz).

Main Results:

• 5 Hz rTMS to left dorsolateral PFC (DLPFC) increased local activity and PFC connectivity.
• 1 Hz rTMS to left DLPFC decreased local activity and induced more distributed bilateral PFC connectivity.
• Increased between-module degree (BMD) in PFC correlated positively with structural connectivity.

Conclusions:

• Local stimulation-induced changes in PFC activity causally affect network interactions during memory encoding.
• The aging brain flexibly adapts by altering long-range PFC connectivity to compensate for local activity modulation.
• Structural connectivity plays a role in mediating these adaptive network responses in older adults.