memory-drugCredit: Yuji Ikegaya and Hiroshi Nomura CC-BY


During recent studies by researchers in Japan, histamine improved people's long-term memory test scores depending on the strength of the original memory and could temporarily extend mice memories by as much as 25 days longer than normal. Clarifying the role of histamine in memory may help alleviate symptoms of memory disorders, such as Alzheimer's disease and other forms of dementia.

Professor Yuji Ikegaya and lecturer Hiroshi Nomura, PhD, of the University of Tokyo led a research team that included collaborators at Hokkaido University and Kyoto University in Japan.

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"In real life, we cannot know what we forgot. This is why we do human memory tests with pictures on a computer screen," said Ikegaya.

Seven or nine days later, participants were given either a placebo (a "sugar pill," or fake medicine) or a large dose of a medication that increases the amount of histamine in the brain. The unusually large dose ensured the medication crossed the blood-brain barrier, the body's natural defense that makes it difficult for medication to reach the brain. The same medication is normally prescribed at lower doses to treat dizziness.




"Increased histamine helped research participants remember an image they knew once but couldn't remember during a long-term memory word-association test," said Ikegaya.


Histamine threshold

Ikegaya suggests memory is a combination of a gradient system and a yes:no or 1:0 digital system. Information might be stored in the brain as a gradient, but nerves do not fire until they are above a particular threshold. Below this threshold is "no" or 0, and we cannot remember. Above this threshold is "yes" or 1, and we can remember.

"You still have the memory, but you can't access it unless it is above a particular threshold," said Ikegaya.


Histamine had no effect on participants' scores on tests unrelated to long-term memory.

Mice memories




Bad memories




Future memories

Researchers are currently planning future studies to test how histamine levels might affect memory test results in older adults. Other studies will also examine how histamine might be involved in prospective memory, the "don't forget" type of memories for the future, such as things we might write on reminder sticky notes to our future selves.