Portraits and memory: Investigating HF-rTMS effects on episodic recall through a sham-controlled fMRI study

Area of Science:

• Neuroscience
• Cognitive Psychology
• Neuroimaging

Background:

• The dorsolateral prefrontal cortex (DLPFC) is crucial for cognitive control and memory.
• Its precise role in episodic retrieval, particularly for abstract stimuli, requires further investigation.
• Understanding DLPFC's causal influence on memory is key to advancing cognitive neuroscience.

Purpose of the Study:

• To investigate the causal role of the left DLPFC in episodic retrieval of complex abstract stimuli.
• To examine how high-frequency repetitive transcranial magnetic stimulation (HF-rTMS) over the left DLPFC affects memory performance and brain activity.
• To explore the neural mechanisms underlying memory retrieval for abstract visual information.

Main Methods:

• A within-subject, sham-controlled functional magnetic resonance imaging (fMRI) design was employed.
• 20 healthy female participants underwent encoding of abstract portrait images.
• Following active or sham HF-rTMS, participants performed a recognition memory task during fMRI scanning, with behavioral data and brain activation recorded.

Main Results:

• Active HF-rTMS over the left DLPFC led to a speed-accuracy trade-off, reducing accuracy for recognized stimuli.
• fMRI revealed increased blood-oxygen-level-dependent (BOLD) activity in the left hippocampus and right calcarine cortex during recognition of previously seen stimuli.
• No significant effects were observed for unseen stimuli, indicating selective modulation by stimulation.

Conclusions:

• A single session of left DLPFC HF-rTMS selectively modulated neural dynamics of episodic memory retrieval for abstract stimuli.
• Despite no behavioral improvement and reduced accuracy for recognized items, stimulation increased hippocampal and visual cortex activation during recall.
• These findings highlight a dissociation between neural recruitment and memory accuracy, emphasizing the role of DLPFC in modulating hippocampal-visual network engagement.