Attention modulates hippocampal ripples in humans

Hippocampal ripples are high-frequency events critical for memory consolidation, typically studied during sleep and quiet wakefulness. Emerging evidence suggests that ripples also occur during active behavior, yet their role in awake cognition remains unclear. Here, we demonstrate that changes in sustained attention modulate the occurrence of ripples, their temporal alignment to ongoing hippocampal oscillations, and hippocampal-entorhinal synchronization. Using intracranial electroencephalogram (EEG) recordings from epilepsy patients performing a sustained attention-to-response task (SART), we first identified attentional states based on behavioral variability and subjective reports. Next, we observed that ripples were more frequent during high-attention periods, despite the absence of memory demands. Importantly, ripples occurring during periods of reduced attentional engagement exhibited stronger local phase locking to low-frequency oscillations (theta to lower beta) and enhanced hippocampal-entorhinal synchronization, suggesting increased endogenous coordination of hippocampal activity. These findings demonstrate that ripple dynamics are shaped by attentional state, supporting a broader role for hippocampal ripples in active cognitive processing.