Poster No:
994
Submission Type:
Abstract Submission
Authors:
Sang-Eon Park1, Sang Ah Lee2
Institutions:
1Seoul National University, Seoul, Korea, Republic of, 2Seoul National University, Gwanak-gu, Seoul
First Author:
Sang-Eon Park
Seoul National University
Seoul, Korea, Republic of
Co-Author:
Introduction:
Underlying mechanisms of navigation-based hippocampal enhancement have been elusive due to the co-occurrence of other improvements in general cognitive functions. In addition, although hippocampal size has been correlated with spatial memory performance [4], previous studies using functional MRI presented confounding results of increased/decreased hippocampal activation as a result of spatial training [2, 3]. Given the well-described function of hippocampal theta oscillations in spatial memory, measuring hippocampal intracranial EEG (iEEG) across repeated experience in a navigational task may reveal specific changes in hippocampal function associated with cognitive improvement. In this study, we investigated the possibility that hippocampal theta power may change over the course of multiple trials and sessions of a spatial navigation task with feedback on every trial. We also compared older and younger adults, in order to gain insight into age-related markers of memory improvement.
Methods:
We used iEEG recordings across the whole hippocampus in 67 presurgical epilepsy patients (19 to 61 years of age) while they performed a computer-based spatial navigation task over 1 or 2 sessions (48 trials per session). One trial of the task included two encoding periods, during which participants were asked to memorize the location of the target object while they were passively driven to the target, and a retrieval phase requiring participants to find the hidden object by freely navigating the arena. Specifically, we isolated periodic narrowband power from the aperiodic component (1/f spectral slope) by applying the FOOOF (fitting oscillations & one-over f) algorithm [1]. A change in neural activity over the progress of repeated trials was measured by calculating the slope from a linear fitting between trial number and spectral features.
Results:
We found a subset of participants whose performance gradually improved (slope>0) over the progress of the spatial navigation task (N=35 out of 67). The improvement was observed not only in the first session (48 trials, 12.5% increase) but also in the second session despite a smaller amount (6.5%). To look for the neural correlate of individual differences in performance changes (i.e. decline or improvement), we compared hippocampal aperiodic and periodic features (theta, alpha, beta, and gamma power) over trials. First, we found that all spectral features were engaged during spatial memory encoding, as their amplitude was time-locked to the navigation episode. Among these features, theta power was the only neural correlate of individual performance, as indicated by a marginally significant positive correlation across individuals (r=0.297, p=0.059). More importantly, theta power was a significant marker of individual memory improvement over the course of repeated trials (r=0.377, p=0.026), suggesting that enhanced theta power mediated the improvement in spatial memory.
In addition, we found that a different pattern of spatial memory improvement was observed for the older and younger groups. In the match-view condition in which encoding and retrieval paths were oriented in the same direction, the older group (age>42) showed a significant improvement (t(7)=3.019, p=0.019). However, the young group showed an improvement in the view-independent condition in which the retrieval direction was opposite from the encoding (t(9)=3.461, p=0.007). A comparison of theta power change suggested that increased theta power during the retrieval may have played a crucial role in the old participants for improved view-based spatial memory (e.g. distal landmarks) (r=0.656, p=0.055).
Conclusions:
Using hippocampal iEEG, we demonstrated that improvement in cognitive performance in a spatial navigation task was accompanied by an increase in theta power, the most well-known marker in the medial temporal lobe. These results show promise for a mechanistic explanation of the effectiveness of spatial navigation training for enhancing hippocampal functions.
Higher Cognitive Functions:
Space, Time and Number Coding 1
Learning and Memory:
Neural Plasticity and Recovery of Function 2
Keywords:
Aging
Cognition
ELECTROCORTICOGRAPHY
Electroencephaolography (EEG)
ELECTROPHYSIOLOGY
Memory
Plasticity
Other - cognitive training
1|2Indicates the priority used for review
Provide references using author date format
[1] Donoghue, T. (2020). Parameterizing neural power spectra into periodic and aperiodic components. Nature neuroscience, 23(12), 1655-1665.
[2] Hötting, K. (2013). Effects of a cognitive training on spatial learning and associated functional brain activations. BMC neuroscience, 14, 1-16.
[3] Sacco, K. (2022). A virtual navigation training promotes the remapping of space in allocentric coordinates: evidence from behavioral and neuroimaging data. Frontiers in Human Neuroscience, 16, 693968.
[4] Wenger, E. (2012). Cortical thickness changes following spatial navigation training in adulthood and aging. Neuroimage, 59(4), 3389-3397.