In the experiment, 30 days after a social interaction, the 'observer rat' has the choice between two cups of food. It expresses a memory by eating cumin-flavoured food because it was present in the 'demonstrator rat’s' breath and therefore safe to eat.
Credit: Bruno Bontempi/Bordeaux Neurosciences Institute
The interaction phase during which a 'demonstrator rat' fed with cumin flavoured food interacts with an 'observer rat' through a grid. During this 30 min interaction, the observer rat forms an association between the cumin odour and some constituents of the demonstrator’s breath.
Credit: Bruno Bontempi/Bordeaux Neurosciences Institute
SYDNEY: Neuroscientists have looked to rats to help solve the mystery of how memories are stored in the brain, finding that certain cortical neurons - nerve cells that make up the cortex of the brain - must be ‘tagged’ and set aside at the exact time a memory is formed.
The results of the study, which involved observing how rats communicate food safety messages to each other, signify an important step toward understanding how memories are formed, stored and ultimately lost. These findings could lay the groundwork for future medical developments in the fight against diseases such as Alzheimer’s.
“If we could identify the tags, we could find a connection between the impairment of these tags and memory loss – or the inability to effectively store remote memories,” said co-author and CNRS researcher Bruno Bontempi of the Institute of Neurodegenerative Diseases in Bordeaux, France. “It’s a long way away, but this research is paving the way for the potential development of treatments.”
From formation to storage
The formation of short-term memories occurs in a region of the brain called the hippocampus, however, the long-term storage of these memories – so that they can be retrieved months and even years later – happens in a region of the brain called the cortex.
Prior to this study, it was known that the consolidation of remote memories required some kind of interaction between these systems, but scientists were unsure as to when in the communication process this tagging took place.
“In order for remote associative memories to be stored there needs to be an active dialogue between the hippocampus and the cortex,” Bontempi explained. “The hippocampus is a fast learner, which is constantly processing information, but is unable to store that information. The cortex meanwhile is a slow learner, but has the ability to store memories.”
The Ratatouille study
During the study, which was published in Science, the research team investigated the way rats passed information about food safety amongst each other by exploiting a special inherent behavior called ‘social transmission of food preference’ (STFP).
STFP in rats became well documented with the early development of rat poisons. Chemicals that carried a distinct smell or taste and rapidly lethal effects became ineffective because the rats would carry this smell back to their colonies.
Upon dying, the rats would socially transmit to the others that the poison was unsafe to eat, causing researchers to develop a more effective tasteless, odourless and slow-acting poison.
With this fact in mind, the research team fed a demonstrator rat cumin powder and put it in a cage with an observer rat for 30 minutes. Through this single interaction, the observer rat learned that cumin was a safe food by smelling the odour on the breath of the demonstrator rat – thus forming a memory about this smell.
