More than a hundred years ago, a theory assumed that memories were physically formed in our brains. The engram has been defined as the substance of our memory. At the time, it was impossible to confirm this hypothesis. Where are we today?
Imagine a scientist analyzing memories under a microscope. The idea that a memory could have a physical existence was raised in 1904 by German researcher Richard Semon. He believed that life experiences left traces in the brain, called engrams. The subsequent stimulation of the engram, if done with the same signals as when it was formed, can lead to memory retrieval. The stronger the connections between the neurons in the engram, the longer the memory lasts. However, at the beginning of the 20th century, no scientific experiment could support this.
Since 2013, engram theory is again at the center of research. In fact, new hypotheses indirectly suggest the presence of these physical traces of memory. Two neuroscientists have analyzed them. Their study is published in the journal Science.
In search of the engram
In every investigation, the experiment was conducted on mice. In the first, scientists noticed a memory loss in those who were deprived of a lateral amygdala neural network. For them, this suggests the likely presence of an engram. In the second, researchers stimulated a series of neurons in the hippocampal gyrus, which is activated when fear is experienced. In fact, mice have experienced fear as a result of this, but without experiencing it. This suggests the presence of a memory that has not been reactivated by an external signal. And therefore, the existence of a potential engram.
The questions remain
The engrams would be composed of neurons. A study published in December 2019 showed that a certain type of synapses can be observed in certain configurations, always in relation to memory and recall. This grouping of synapses would help build memory. We can therefore consider the engram as a basic unit of our memory. However, there are still many questions, especially about how it works.