The human brain is incredibly complex and still not well understood; as such models for studying brain function often involve more simple organisms, like the honeybee. Such animals often have more going on in their heads than you might think. A new report published in the journal Frontiers in Molecular Neuroscience used the honeybee to delve deeper into how long-term memories are formed.
"Honeybees have an amazing capacity to learn and remember," said Dr Stephanie Biergans, first author of the study and researcher at the University of Queensland, Australia. "They can count up to four, and orientate themselves by learning patterns and landmarks. They are also social insects that interact, teach and learn, making them successful foragers. Bees remember how to find a food source, how good the source was, and how to return to the hive."
Honeybees form memories in a way that seems to be similar to that of humans; because they are bees though, they have a smaller genome and a much more fundamental brain.
When memories are created, scientists know that changes occur in the brain on a physical level. Neural connections are made or altered, and neuronal activity undergoes molecular changes. All of those changes work together to embody our long-term memory. Some of those molecular changes occur at the level of genes. Alterations to those genes, epigenetic modifications, can affect gene expression – whether or not a gene is made into a protein, and how much of it is made. This work studied how those epigenetic modifications function in memory.
"We show that DNA methylation is one molecular mechanism that regulates memory specificity and re-learning, and through which experiences of the organism could be accumulated and integrated over their lifetime," said Biergans.
"We knew that DNA methylation is an epigenetic process that occurs in the brain and is related to memory formation. When we block this process in honeybees it affects how they remember,” Biergans explained.
The researchers used two different groups of honeybees that had been taught to expect sugar when exposed to a particular scent; one group learned over time, and was exposed to the smell and the sugar many different times while the other was exposed only once. The scientists utilized a compound that would stop DNA methylation, one type of epigenetic modification, in some bees of both groups. The memory formation of all of the groups was then compared.
"When the bees were presented with sugar and a smell many times together, the presence of DNA methylation increased memory specificity - they were less responsive to a novel odor. On the other hand, when only introduced to the combination once, DNA methylation decreased specificity," Biergans reported.
Their result makes sense for a foraging honeybee, that would not need to remember how a flower smells if that flower it the sole source of food. But if other flowers with different smells are present, then it’s better to see which might be the best source, and to then remember which it is.
The same kind of epigenetic change happens in the human brain as well. These findings could be very helpful to the study of memory problems in people.
"By understanding how changes to the epigenome accumulate, manifest and influence brain function, we may, in the future, be able to develop treatments for brain diseases that also develop over a lifetime. There is thought to be a genetic predisposition for some conditions, such as Alzheimer's and dementia, but in many cases environmental factors determine whether the disease will manifest," Biergans concluded.