Retrosplenial and hippocampal synchrony during retrieval of old memories in macaques

To understand the neural activity behind recollections of the distant past, we recorded from the hippocampus and retrosplenial cortex of macaques as they retrieved year-old and newly-acquired object-scene associations. Year-old memoranda preferentially evoked retrosplenial sigma oscillations (10-15 Hz), and phase-locking between RSC and eye movements during retrieval. In contrast, gamma-band retrosplenial-hippocampal synchrony was stronger during retrieval of new items. Primate retrosplenial oscillations may therefore guide retrieval of visuospatial events long past.