Maier, P. M. | bioRxiv Science

bioRxiv2025

Long-term memory reorganization of navigational episodes

During navigation, the brain builds representations of self-motion and of environmental information for future action. The classic view suggests that these representations consolidate and eventually stabilize. However, there is no data on their fate at extended memory delays. Here, we investigated memory of navigational episodes from a real-world setting across memory delays of up to three decades. We show that memory of navigational episodes does not achieve a stable state, but rather continues to transform for many years. Our data suggest that at any given point in time, memory of navigational episodes is a changing combination of episode-independent schematic information with several interacting spatial representations that directly relate to a navigational episode and that show distinct decay rates. Consistent with recent accounts of memory reorganization, we further show that neither current theories of systems consolidation nor classic models of forgetting fully explain spatial memory performance at extended memory delays.

neuroscience↗

bioRxiv2021

Post-encoding modulation of spatial memory by a GABAA-agonist

We investigated the role of the post-encoding period for consolidation of self-centered (egocentric) and world-centered (allocentric) spatial memory in neurologically normal human subjects. We used the GABAA-ergic anesthetic propofol to transiently modulate neural activity during the early stage of spatial memory consolidation. A total of 52 patients undergoing minor surgery learned to navigate to a target in a five-armed maze derived from animal experiments immediately prior to injection of propofol (early group) or more than 60 minutes before injection (late group). Two hundred and forty minutes after anesthesia, subjects were tested for memory-guided navigation. Our results show a selective impairment of memory-guided navigation in the early group and near-normal performance in the late group. Both egocentric and allocentric navigation were affected, albeit with distinct error patterns. In the egocentric condition, early group patients navigated significantly more often to a wrong alley of the maze but showed normal navigation times, thus suggesting a deficit mainly for memory of sequences of path segments. By contrast, in the allocentric condition, early group patients mostly navigated to the correct alley of the maze but showed a significant increase in detours and prolonged navigation times, thus suggesting a weakened representation of the relationship between landmarks. We conclude that presumably hippocampus-dependent networks contribute to early consolidation of representations underlying both egocentric and allocentric memory-guided navigation. Distinct aspects of these representations are susceptible to GABAA-ergic modulation within a post-encoding time-window of less than 60 minutes, indicating a redistribution and reconfiguration of spatial memory networks early during consolidation. Significance statementO_LIPropofol modulates consolidation of spatial representations underlying human spatial navigation. C_LIO_LIFollowing administration of propofol, memory-guided navigation using self-centered (egocentric) and world-centered (allocentric) spatial information is impaired. C_LIO_LIError patterns after administration of propofol suggest modulation of a post-encoding integration process relevant for ego- and allocentric memory representations. C_LIO_LIThe transient susceptibility of this process to GABAA-ergic modulation is consistent with rapid reconfiguration of networks for spatial memory shortly after learning. C_LIO_LIPropofol provides a pharmacological tool to investigate spatial memory consolidation in humans. C_LI

neuroscience↗

bioRxiv2019

Age Differences in Hemispheric Lateralization in Spatial and Verbal Visual Working Memory

Due to hemispheric specialization of the human brain, neural signatures of visual working memory (WM) performance are expected to differ between tasks involving verbal versus spatial memoranda. Theories of cognitive aging suggest a reduction of hemispheric specialization in older adults. Using behavioral and neural WM capacity markers, we assessed hemispheric lateralization in younger and older adults performing a spatial or verbal visual WM task. Participants encoded information presented in the left or right hemifield. We observed behavioral advantages for spatial stimuli processed in the right hemisphere and for verbal stimuli processed in the left hemisphere. While younger adults showed lateralization in both tasks, older adults showed lateralization only in the verbal task. Lateralization was assessed by the contralateral delay activity (CDA) on the neural level. CDA amplitudes displayed hemispheric lateralization for verbal versus spatial material, but this effect was age-invariant. While our findings support right-hemispheric specialization for spatial information maintenance, and left-hemispheric specialization for verbal information maintenance, we could not confirm a generalized reduction in hemispheric lateralization at older ages.

neuroscience↗