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Related Experiment Video

Updated: Jul 13, 2026

Optogenetic Entrainment of Hippocampal Theta Oscillations in Behaving Mice

Optogenetic Entrainment of Hippocampal Theta Oscillations in Behaving Mice

Published on: June 29, 2018

Melatonin and the human hippocampus, a time dependent interplay.

Tali Gorfine¹, Nava Zisapel

¹Department of Neurobiochemistry, Tel Aviv University, Tel Aviv, Israel.

Journal of Pineal Research

|July 7, 2007

Summary

Melatonin, a darkness signal, impacts human memory. This study found melatonin alters hippocampal activity during memory tasks, suggesting a role in circadian regulation of cognition.

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Last Updated: Jul 13, 2026

Optogenetic Entrainment of Hippocampal Theta Oscillations in Behaving Mice

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Published on: June 29, 2018

Evaluation of Hemisphere Lateralization with Bilateral Local Field Potential Recording in Secondary Motor Cortex of Mice

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Published on: July 31, 2019

Tuning in the Hippocampal Theta Band In Vitro: Methodologies for Recording from the Isolated Rodent Septohippocampal Circuit

Tuning in the Hippocampal Theta Band In Vitro: Methodologies for Recording from the Isolated Rodent Septohippocampal Circuit

Published on: August 2, 2017

Area of Science:

Neuroscience
Chronobiology
Cognitive Psychology

Background:

Melatonin is a key hormone regulating sleep-wake cycles and signaling darkness.
Animal studies suggest melatonin influences hippocampal synaptic plasticity.
The role of melatonin in human hippocampal function, particularly memory, remains unclear.

Purpose of the Study:

To investigate the effects of melatonin on human hippocampal activity during a memory task.
To examine time-of-day variations in hippocampal activation related to endogenous melatonin levels.
To assess the impact of exogenous melatonin on hippocampal function.

Main Methods:

Functional magnetic resonance imaging (fMRI) was used to measure hippocampal activity.
Participants performed a memory task at 16:00 hr (low melatonin) and 22:00 hr (increasing melatonin).
Exogenous melatonin was administered in a double-blind, placebo-controlled crossover study.

Main Results:

Hippocampal activation during memory tasks was reduced at 22:00 hr compared to 16:00 hr.
Exogenous melatonin further decreased hippocampal activation at 22:00 hr in subjects with rising endogenous melatonin.
Left para-hippocampal activation increased at 22:00 hr, correlating with endogenous melatonin levels.

Conclusions:

Hippocampal and para-hippocampal memory-related activation show differential responses to time of day and melatonin.
Circadian rhythms and melatonin levels appear to modulate human memory processing, especially during nighttime hours.
These findings highlight the intricate relationship between the circadian clock, melatonin, and cognitive functions like memory.