Cross-region neuron co-firing mediated by ripple oscillations supports distributed working memory representations

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Systems Neuroscience

Background:

• High-frequency (~90Hz) ripple oscillations are implicated in integrative brain processing.
• Previous research linked ripple co-occurrence to enhanced temporal binding in human cortical neurons up to 12mm apart.
• The extent to which ripple coupling supports cognition and operates over greater distances remained unclear.

Purpose of the Study:

• To investigate if ripple oscillation co-occurrence facilitates neuronal coupling for cognitive processing.
• To determine if this coupling occurs over distances greater than previously observed.
• To examine the role of ripple oscillations in supporting working memory.

Main Methods:

• Analysis of intracranial recordings from human patients undergoing a working memory task.
• Microwire electrodes were implanted bilaterally in the hippocampus, amygdala, ventromedial prefrontal cortex, anterior cingulate cortex, and pre-supplementary motor area.
• Quantification of ripple oscillations and cross-region neuronal firing patterns during different working memory phases.

Main Results:

• Ripple oscillations increased significantly across all recorded brain regions during encoding, maintenance, and retrieval.
• Cross-region ripple co-occurrence increased, accompanied by ~30% increases in cross-region co-firing, without decrement up to 220mm.
• Increased co-rippling and co-firing scaled with memory load and promoted reinstatement of encoding-related neural patterns during retrieval.

Conclusions:

• Ripple oscillations orchestrate long-range neural communication essential for human cognition.
• This long-range communication supports distributed neural representations during working memory.
• Ripple-mediated synchrony facilitates cognitive functions by coordinating activity across widespread brain networks.