The brain is the most extraordinary of our organs, and although we are far from having unraveled all its mysteries, some of them have been exposed in recent years. The tools and approaches that allow us to explore it have made giant strides. Here are some current discoveries that should interest and surprise you!
Water revealing brain connectivity
Since the 1970s, magnetic resonance imaging (MRI) has been the preferred tool for visualizing brain activity, in other words, for observing the “reflecting” brain in real-time. However, it is by using a type of MRI called “diffusion MRI” that Denis Le Bihan developed an image analysis program in the 1990s-2000 to map the brain’s connectivity. This method has the particularly of calculating the micromovements of water molecules present in the nerve fibers of the brain since the diffusion of water is slower when it is done perpendicular to the direction of the nerve fibers. Let us note that these nerve fibers, also called axons, form the white substance of the brain that connects different areas of grey matter and that nearly 80% of the brain is made up of water! Le Bihan’s image analysis program reconstructs the path of axons in three dimensions from the images he makes of them in several directions. At present, it is the only existing means of visualizing the spatial arrangement of brain nerve fibers and all the connections between the different regions of the human brain.
This application of diffusion MRI, which has revolutionized the management of stroke, has also become essential to understand better neurological and psychiatric pathologies that affect white matter: Alzheimer’s disease, multiple sclerosis, epilepsy, schizophrenia, bipolar disorders, depression, etc. Recently, this type of MRI has been used in two studies examining how learning manifests itself in the brain. The first of these two studies, published in 2018, found that, contrary to popular belief, new learning can leave its mark very quickly on the cortex, as little as an hour later. The second study, published in 2019, showed a change in the diffusion of water molecules – and therefore contact (synapses) between neurons – in a specific region of the hippocampus as a result of learning.
Forgetting as you never thought about it
It is often treated as a dysfunction of our memory, and yet forgetting is an essential mechanism for its proper functioning! In a recent article entitled Why forgetting may make your mind more efficient, science blogger Tom Siegfried invites us, by exposing the latest discoveries on the subject, to see forgetting from a new perspective. Pointing out that this could be “the brain’s frontline strategy in processing incomming information,” the blogger explains that, according to some researchers, forgetting would be essential since “the biological goal of the brain’s memory apparatus is not preserving information, but rather helping the bain to make sound decisions.”
Of course, this is not about memory disorders, but about the normal and continuous forgetting that would occur in any healthy brain. This would therefore not be synonymous with failure, nor would it be accidental or the result of a conscious sorting of our memories. There is evidence that this process would be initiated by cellular and molecular mechanisms, and that it would, therefore, be involuntary and daily. Contrary to what has long been believed, “normal” forgetting would not result from a gradual erasure of the data recorded by our brain.
Let us return to this function of memory, which involves helping us to make the best decisions at all times. Since our brain must process a tremendous amount of information every day, it seems logical that it should have a powerful information management system that includes methods to eliminate unused memories (Davis and Zhong, 2017). Imagine, as Siegfried suggests, that you are bitten by a dog in a park. Why would it be better for your brain to retain only the essential elements from such an event rather than the constellation of details it has captured? Because if small details were to take precedence over the “big picture,” you would be less able to apply the lessons learned from this unfortunate event later in a similar – but not identical – situation. In other words, by facing other dogs in another place, you would be less skilled at making good decisions to avoid getting bitten again. From this perspective, forgetting appears to be a vital long-term adaptive advantage: it helps us to exercise good judgment in this ever-changing environment of ours.
This ability to purify our memories could, therefore, be as crucial as the ability to retain important information. Some researchers believe that failures in the mechanisms of this forgetting process could be involved in various disorders such as post-traumatic stress disorder, schizophrenia, or autism. If these hypotheses are confirmed, we could see the development of drugs to improve our ability to retain important information, but also to help eliminate those that are less important!
The intriguing “doorway effect”
Did it happen to you to walk into a room and no longer remember what you wanted to do? You may have already experienced this phenomenon that scientists have called the “doorway effect.” Because, yes, researchers have tried to elucidate these small amnesias, as intriguing as they are widespread, and have found an explanation for them!
First, it should be noted that the contextual nature of the systems involved in memory was already known: when memory “records” new information, it takes into account the context and emotional state in which we find ourselves. The classic example: you probably remember where you were on September 11, 2001. We, therefore, knew that this contextual effect was at play in our memorization process, which makes it difficult to retrieve it by finding oneself in a different context than the one in which an “X” information was recorded.
However, a team from the University of Notre Dame in Indianapolis demonstrated in 2011 that the “doorway effect” goes beyond the contextual effect. As part of an experiment, they subjected their participants to similar exercises in three environments, each with a different degree of immersion: the first two using virtual reality (the first less immersive than the second) and the last taking place in a real context, i.e., totally immersive. Each participant had to choose objects and place them in a box (therefore temporarily out of sight) either in the original room or by changing rooms, but always over the same distance. It turned out that participants were two or three times more likely to forget the contents of the box after moving from one room to another, even when they were back in the original room. What can be deduced from this? That it was the passage into another room, and not the fact of being or not in the original room, that emerged as the element that affected the memory.
This experiment suggests that the brain must memorize much more information when it enters a new environment. Taking into account that some types of memories – particularly our working memory – are made to retain the most relevant information on a short term, and to separate themselves from others, Notre-Dame researchers suggested that entering a new environment would be perceived by the brain as a signal that it is time to discard the memories recorded in the previous room. Seen in this light, the “doorway effect” would represent an adaptive advantage of our working memory. The next time you lose track of your ideas when you change rooms, you can feel reassured!
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