Neural populations in human posteromedial cortex display opposing responses during memory and numerical processing

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Electrophysiology

Background:

• The human default mode network (DMN) is primarily understood through neuroimaging, with limited knowledge of its electrophysiological underpinnings.
• The posteromedial cortex (PMC) is a key DMN structure, crucial for internally directed thought processes like memory retrieval.

Purpose of the Study:

• To investigate the electrophysiological correlates of the human default mode network, specifically within the posteromedial cortex (PMC).
• To differentiate neural activity during internally directed tasks (autobiographical memory) versus externally directed tasks (arithmetic calculation).

Main Methods:

• Intracranial recordings were performed in the human PMC during tasks involving autobiographical memory retrieval and arithmetic calculation.
• Analysis focused on high gamma-band power (70-180 Hz) as an electrophysiological marker of neural activity.

Main Results:

• Late-onset increases in high gamma-power (>400 ms) were observed in PMC during episodic autobiographical memory retrieval.
• High gamma-power was reduced during self-referential semantic memory retrieval and self-judgment tasks.
• A significant decrease in high gamma-power occurred during arithmetic calculation, correlating with reaction time.
• The degree of PMC activation during memory retrieval predicted the extent of suppression during arithmetic tasks.

Conclusions:

• These findings provide detailed electrophysiological and anatomical insights into PMC engagement during autobiographical memory retrieval.
• The study demonstrates how specific neural populations in the PMC are actively suppressed during externally focused tasks like numerical processing.