Temporal lobe interictal spikes disrupt encoding and retrieval of verbal memory: A subregion analysis

Area of Science:

• Neuroscience
• Epilepsy Research
• Cognitive Science

Background:

• The medial temporal lobe (MTL) is crucial for memory encoding and recall.
• Medial temporal lobe epilepsy (MTLE) frequently exhibits interictal spikes (IS) within the MTL.
• The precise impact of IS on memory function remains incompletely understood.

Purpose of the Study:

• To investigate the effect of interictal spikes (IS) in MTL subregions and the lateral temporal cortex on episodic memory encoding and recall.
• To determine if IS transiently impair memory performance in patients with focal epilepsy.

Main Methods:

• Seventy-eight epilepsy patients with depth electrodes underwent a verbal free recall task.
• Interictal spikes (IS) were manually annotated during pre-encoding, encoding, and recall phases.
• Mixed-effects logistic regression analyzed the association between IS and word recall.

Main Results:

• IS during left hippocampal encoding (specifically CA1 and dentate gyrus) and left middle temporal gyrus significantly reduced subsequent recall.
• IS during retrieval in the right hippocampus and parahippocampal regions decreased word recall probability.
• IS in other temporal regions or during the pre-encoding phase did not significantly impact memory performance.

Conclusions:

• Interictal spikes (IS) in medial and lateral temporal cortex regions contribute to transient memory deficits in patients with focal epilepsy.
• These findings underscore the direct link between specific epileptic activity and episodic memory impairment.
• Targeting IS in these critical memory regions may offer therapeutic potential for memory recovery.