Episodic memory is a type of memory that collects and stores personal experiences that individuals encounter during specific time periods. It is typically located in the temporal cortex. Injuries to the temporal cortex or the aging process can lead to a decline in this type of memory. Synapses in the brain are structures that enable nerve cells to connect with other neurons or cells such as glands, with most synapses functioning through dendritic spines. Dendritic spines play a critical role in the establishment of synaptic connections, and the loss of these spines occurs naturally during the aging process. This situation contributes to a weakening of synaptic communication and, consequently, adversely affects memory processes.
The study conducted by Walker and colleagues investigates the impact of dendritic spine diameters on episodic memory performance. In this study, tissue samples from the premotor cortex (BA6) and temporal cortex (BA37) were obtained from 128 individuals participating in the ROSMAP study. The average age of these participants was 90, and variations in their cognitive performance and Alzheimer’s disease-related pathologies were observed. The collected samples were examined under a microscope at 60x magnification and were reconstructed in three dimensions using Neurolucida 360 software.
Dendritic spine data were analyzed using learning algorithms to determine which features best predict episodic memory performance. Other factors, including neuropathologies associated with Alzheimer’s disease, were also considered in this analysis. Dendritic spine characteristics affecting episodic memory performance were identified using the LASSO regression method.
According to the findings of the study, dendritic spine density and morphology in two distinct brain regions, particularly the frontal and temporal cortices, have been associated with episodic memory. Frozen tissue samples of suitable sizes from the BA6 and BA37 regions, obtained from ROSMAP participants, facilitated the execution of experiments in this study. fMRI studies indicate activity in the BA37 and BA6 regions during episodic memory tasks. While BA37 is associated with face recognition and episodic memory, the BA6 region is involved in memory encoding and recognition processes. Based on the preliminary analysis findings, the hypothesis is proposed that the morphology of spines in these regions is reshaped by different mechanisms to preserve types of memory throughout the aging process.
Previous studies have shown that older adults with larger spine head diameters in the BA37 region exhibit better episodic memory performance. Significant inverse correlations have been found between spine head diameter in BA37 and Aβ pathology. Experimental models suggest that Aβ leads to spine loss in neurons, resulting in cognitive decline. In contrast, tau pathology is thought not to affect spine density but rather to impair synaptic function. These findings indicate that spine head diameter plays a critical role in preserving synaptic strength during aging and may serve as a potential biomarker that could be targeted in future therapies.
In conclusion, based on these findings, it has been observed that older individuals with larger dendritic spine head diameters in the temporal cortex exhibit better episodic memory performance, even when spine density is unaffected. These results suggest that, rather than focusing on the creation of new synapses, strategies aimed at preserving the strength of existing synapses may enhance treatment efficacy in the early stages of Alzheimer’s disease. Future research is anticipated to contribute to the development of new therapeutic approaches that improve episodic memory performance by testing the validity of these findings across broader age groups and various neuropathological conditions.
Author: Selin Beyazkılınç
Editor: Elif Duymaz
Reference: Walker, C. K., Liu, E., Greathouse, K. M., Adamson, A. B., Wilson, J. P., Poovey, E. H., Curtis, K. A., Muhammad, H. M., Weber, A. J., Bennett, D. A., Seyfried, N. T., Gaiteri, C., & Herskowitz, J. H. (2024). Dendritic spine head diameter predicts episodic memory performance in older adults. Science Advances, 10(32). https://doi.org/10.1126/sciadv.adn5181
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