Do our memories define who we are? Does memory contain all our experiences, and if not, why do some memories get encoded and others don’t? Once forming a memory, can we erase it? These are all questions we must ask when examining our brain attempts to encode all the bits and pieces from our daily lives. Whilst most of it will stay with us in the long run, we may easily lose some of our precious experiences.
Memories start taking shape in the region of the brain called the hippocampus. Like a clay sculpture, they take time to solidify. In most cases, 4 to 6 hours are sufficient to allow them to fully consolidate at the cellular level. During this time, neurons in this region are repeatedly stimulated together, growing stronger connections between each other.
Not unsurprising, they are not entirely safe in the hippocampus. The hippocampus has limited resources. Each time we encode another memory, we take the risk of losing recent memories. Proteins in the hippocampus get used towards storing a new memory, at the expense of consolidating the previous one.
Yet there is a bright side to it. Certain brain states facilitate memory consolidation, sleep being among them. First demonstration dates back to 1924 – Jenkins and Dallenbach found that memories encoded just before sleep were remembered better than those encoded prior to other activities. That is partly because it is impossible to form new memories during sleep, meaning that the consolidation process can proceed uninterrupted.
Drinking to remember or drinking to forget?
We see a similar effect with alcohol. In a study by Dr Bruce and Dr Pihl (1997), participants who formed memories before consuming an alcoholic beverage forgot the newly acquired knowledge to a lesser degree than those who had placebo. The rationale is that alcohol induces a state of temporary amnesia. This state reduces the competition between the memories to be consolidated and those which are being consolidated. At this point, some may think this could be a handy revision tip. However, it is worth bearing in mind that the undesirable side effects of alcohol are rarely disputed.
After memories consolidate at the cellular level, they are ready to be transferred to the long term store in the neocortex. The neocortex is the part of the brain that covers the two cerebral hemispheres. Each memory decomposes into pieces, each piece going to its designated area. Visual memories are transferred to the visual cortex, auditory memories move to the auditory cortex and so on. This back-up process, too, occurs during states of reduced interference such as sleep. If at any point you thought that the brain is resting during sleep, you were wrong.
Being stored in the hippocampus is not the end in a memory’s life, although this is what most researchers in the field believed until 15 years ago. A group of neuroscientists at New York University made an intriguing discovery that changed the way memories were seen. Dr Nader and his colleagues showed that every time a memory is remembered, it needs proteins to reconstruct itself from its pieces. It becomes plastic, meaning that it offers opportunity to be updated, or even erased. Rats permanently lost the memory of a maze if – after navigation – were given propranolol, a substance that inhibits protein synthesis.
This intriguing memory process has also been demonstrated in humans. In one experiment, researchers conditioned participants to learn a mild fear reaction. Sat at a computer, they learned that a green square was followed by an electric shock to the hand. Participants came back to the lab the second day to practise this association. At that, time the green square still triggered a fear response. Researchers then gave people propranolol. When tested the following day, participants no longer feared the green square.
‘Scientists believe that the role of this reconstructing process is to update memories to our current beliefs’
Scientists believe that the role of this reconstructing process is to update memories to our current beliefs. This also means that our memory is prone to contamination by subsequent experiences. Knowing that memory can play tricks on us can be a bit worrying, especially in settings such as eyewitness identification. Nonetheless, this dark side of memory can also be manipulated to our advantage. For instance, those suffering from phobias and post-traumatic stress disorder can particularly benefit from this knowledge, since these disorders depend largely on associations between strong emotional memories and anxiety reactions.
Put simply, memory is a complex process. Whilst research has been able to reveal its basic mechanisms, there is much to be discovered. The ethics of manipulating memories are still being debated. Yet in the meantime, research reaches new avenues. Before long, we may be able to live our own Eternal Sunshine of The Spotless Mind.