Poster A79, Saturday, March 25, 5:00 – 7:00 pm, Pacific Concourse
Altered hippocampal-prefrontal oscillatory dynamics coordinating memory binding in two cases of developmental amnesia
Nicholas B. Diamond1,2, Rosanna K. Olsen2, Jennifer D. Ryan1,2; 1University of Toronto, 2Rotman Research Institute, Baycrest Health Sciences
The hippocampus and medial prefrontal cortex (mPFC) are critical for binding information across space and time into memory representations. However, it is unclear how hippocampal and mPFC activity is coordinated during binding. A recent model suggests that theta and beta oscillations are the resonant frequencies along two distinct thalamic pathways – including the anterior and mediodorsal thalamic nuclei, respectively – that connect the hippocampus and surrounding medial temporal lobes with the mPFC (Ketz, Jensen, & O’Reilly, 2014). Yet little is known about how human brain lesions affect local and distributed oscillations in memory. We used magnetoencephalography to investigate how damage along hippocampal-prefrontal pathways perturbs the oscillatory dynamics that organize memory formation. Two developmental amnesic cases (H.C., N.C.) with distinct thalamic lesions and matched control participants performed a task requiring the formation and temporary maintenance of spatiotemporal relations among successively presented objects. Control participants exhibited increasing theta power and decreasing beta power in the hippocampus and mPFC with increasing binding demands, and mPFC power changes predicted subsequent memory. Case H.C. exhibited impaired binding performance and aberrant hippocampal theta and beta dynamics relative to controls, with over-recruitment in medial frontopolar cortex. Case N.C. performed normally despite marked reductions in theta power encompassing the hippocampus and mPFC, exhibiting stronger hippocampal beta desynchronization and recruitment of lateral prefrontal and temporal regions, which may reflect compensatory processes. These findings demonstrate that lesion-induced alterations to oscillatory dynamics are complex and not band-limited and, more broadly, that memory binding depends on distributed frontotemporal interactions across multiple timescales.
Topic Area: LONG-TERM MEMORY: Episodic