A study has found that melatonin,' the hormone of darkness,'which is produced by body to regulate patterns of sleeping and awakening in humans, might be responsible for poor learning and memory formation during the night.
In addition to what the body produces naturally, many people take melatonin supplements to fight jet lag, balance out seasonal affect disorder and regulate nighttime dementia.
The study with zebrafish, led by Gregg W. Roman, assistant professor in the department of biology and biochemistry at UH, found that melatonin could hurt memories formed at night.
In the research, zebrafish was used because they are small and breed in large numbers, and they are diurnal, having the same activity rhythms as people.
Zebrafish are most active during the day and less active at night, whereas many other vertebrate model systems, such as rodents, are nocturnal.
Roman said that melatonin directly inhibits memory formation.
'We were interested in the circadian control - the day-night cycle control - of learning and memory formation. We found zebrafish are capable of learning very well during their active phase during the day, but learn very poorly at night during their sleep or quiet phase.' Roman said.
With the study, Roman and his colleagues hypothesized that melatonin might be responsible for poor learning and memory formation during the night.
In order to test whether melatonin was involved in inhibiting nighttime learning and memory formation, they treated the zebrafish during the day with the hormone to see how the fish performed.
The analysis found that melatonin failed to affect learning, but dramatically inhibited the formation of new memories, with the melatonin-treated fish resembling fish trained during the night in a test for 24-hour memory.
'The next step was to inhibit melatonin signalling during the night with a melatonin receptor antagonist and test for effects on memory formation.
'It was tremendous - the results were, excuse the expression, like night and day. We saw dramatic improvements in nighttime memory formation by inhibiting melatonin signalling, indicating that the reason the zebrafish did not form memories at night was because of the melatonin hormone,' Roman said.
Roman considers that a natural role of melatonin might be to facilitate the storage of memories made during the day.
The value of melatonin as a supplement is largely due to its antioxidant properties.
'The use of melatonin receptor antagonists will not affect this attribute, but may alleviate an important side effect on nighttime cognitive function.' Roman said.