Circadian Rhythm refers to the internal neuronal mechanism which regulates an individual's sleep-wake cycle throughout a twenty-four hour period. Across early adolescent years, circadian rhythm fails to follow a distinct pattern, meaning short-term memory consolidation development must occur on a more consistent basis. However, recent research suggests that as this internal clock shifts to reflect a more dispersed light-darkness cycle, the transition into circadian control then establishes an ability in maintaining the long-term potentiation (LTP) of memory. The practice of Daylight Savings - setting clocks ahead one hour as warm weather approaches and back one hour as it becomes colder - delays this natural cycle and contributes to circadian misalignment. This then begs the question of whether the practice could negatively impact not only the development of long-term memory, but if it could continue to inhibit its efficacy in older individuals during distinct parts of the calendar year.
Dr. Cavanaugh and his colleagues tested this developmental impact of circadian rhythm on memory through Drosophila experimentation. The lab studied the behavior of L2 and early-stage L3 larvae, finding that L2 larvae did not exercise circadian sleep cycles, but rather dispersed them in short bursts across 24 hours, whereas the L3 larvae established sleeping patterns coinciding with a standard circadian rhythm. Similar to human children, these divergences could correlate to feeding times and a need for substantial nutritional intake in infants. Congruent with their sleep cycle patterns, L2 Drosophila displayed an inability to consolidate long-term memory, while L3 larvae achieved this level of consolidation seamlessly. This difference emerges from varying levels of Ca2+ in Dh44 neurons. When attempting to stimulate these neurons with altered Ca2+ levels via CCHal, a method which chemically displays the capability for LTP, only the Dh44 in L3 larvae displayed signs of adeptness proficient enough to accept these signals. L2 larvae lacked this capability to provide sufficient communication between DN1a and Dh44 neurons, effectively contributing to their inability to regulate a circadian sleep cycle.
Daylight Savings creates a similar disconnect in memory consolidation; however, rather than diverging on the basis of developmental neurological capability, it disrupts the circadian cycle already established within individuals. A study has shown that, on average, individuals experience 40 minutes of less sleep the night after setting their clocks ahead in March compared to other nights, as well as greater risks of mood disturbances, suicide and decreased mental acuity following the transition back to Standard Time in November. As a result, these disruptions in environmental routine pose the risk of facilitating insomnia symptoms and sleep debt - in which the effects of regularly receiving inadequate amounts of sleep become chronic - worsening the ability for individuals to processes long-term memories under times of physiological stress due to circadian rhythm upset.
Although these two factors can seem rather disconnected in their details, it remains entirely possible that they can affect long-term potentiation in similar fashions. Dr. Cavanaugh's study on developmental discrepancies proves the importance of an established circadian cycle in the consolidation of LTP, and evidence presented by Dr. Rehman and Danielle Pacheco on Daylight Savings' disruption of circadian rhythm highlights how memory can be impaired at any age by both internal and external factors. In comparing these two scenarios, it displays the complexity of neurological function and memory, opening the door for future research on both biological and environmental components which deter long-term potentiation processes.
References
Pacheco, D. (2020, October 27). Daylight Saving Time - How Time Change Affects Sleep. Sleep Foundation. https://www.sleepfoundation.org/circadian-rhythm/daylight-saving-time
Poe, A. R., Zhu, L., Milán Szuperák, McClanahan, P. D., Anafi, R. C., Scholl, B., Thum, A. S., Cavanaugh, D. J., & Kayser, M. S. (2023). Developmental emergence of sleep rhythms enables long-term memory in Drosophila. Science Advances, 9(36). https://doi.org/10.1126/sciadv.adh2301
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