Distinct neurophysiological features and memory representations along the long axis of the developing medial temporal lobe

The medial temporal lobe (MTL) is crucial for episodic memory, whereby posterior MTL preferentially represents visuospatial information, and anterior MTL is involved in the representation of semantic or conceptual information. The neurophysiological underpinnings of content-preferential organization in the developing MTL are largely unknown. Here we utilized rare electrocorticography (ECoG) recordings from 23 pediatric epilepsy patients who completed a visual scene recognition memory task to systematically examine the neurophysiological underpinnings of memory formation along the MTL long axis. The timing of high-frequency activity (HFA, ~70-150 Hz) differed between the posterior and anterior MTL, peaking after scene onset in the posterior MTL and around scene category response (indoor/outdoor scene categorization) in the anterior MTL. Further, in the posterior MTL, HFA was predictive of successful memory formation and positively linked to memory performance, highlighting the importance of posterior MTL HFA to memory formation. In contrast, theta frequency in the anterior MTL was linked to memory performance, and theta-HFA phase-amplitude coupling before scene category responses was predictive of successful memory formation, highlighting the importance of anterior MTL theta oscillations to memory formation. Our findings establish distinct neurophysiological features along the posterior-to-anterior axis of the developing MTL that differentially support the representation of perceptual and conceptual information during memory formation.