Why do we forget things?
The question seems trivial, but the answer is not. Forgetting is often perceived as a counterpart to memory and malfunction of the brain, but in fact it is an elementary brain function. In order to adapt to changing environmental conditions, we must learn new things, but also forget or relearn old things. Through the mechanism of forgetting, we learn to separate the unimportant from the important.
By the way, we not only forget declarative facts and episodic contents of our memory – such as knowledge from school or memories of our first birthday – especially when it comes to sensory perception, the deletion of impressions is important in order to ensure a functioning perception in the presence.There would be small benefit to save an old sensory impression in our sensory system forever – rather, the storage takes only about 0.25 seconds until the information reaches the brain, then the old sensory impression must be overwritten by a new one in order to ensure timely perception of the environment and possible dangers.
Forgetting as spam filter
Forgetting is an active process that - like a spam filter - scrolls over our perceptions and helps us to perceive the impression or to call up the memory we need. Forgetting suppresses the “spam” in the respective situation, i.e. related impressions or irrelevant knowledge. But we also forget things that are important, such as the dentist appointment. That’s because in the process of forgetting, as well as in learning (keyword – maladaptive behavior, addiction), our spam filter may be mistaken and important information is not properly classified – perhaps because while we made the dentist appointment, at the same time another important sensory impression (door bells) disturbed our system and thus upset the storage and separation of important and unimportant.
Synaptogenesis in teenage years
There is also a clear correlation for the importance of forgetting: The so-called synaptogenesis during puberty: An adult has significantly fewer synapses – neuronal connections between nerve cells – than a child. The brain ‘forgets’ things - or in this case eliminates synapses- through its development in order to make processing more efficient. What should not be neglected: The human brain and its executive functions are not infinite, but limited in capacity – so the existing structures and storage capacities must be used in the most efficient way to learn, repeat and remind those things which are adaptive to the prevailing environmental conditions.
However, researchers still discuss whether by forgetting we really lose memory content or it simply becomes more difficult to access these content.. It is also exciting that we can change memories on every retrieval – and that there are memories where this is not possible. Patients suffering from post-traumatic stress disorder, for example, cannot change the traumatic memory stored in their memory.Even the spam filter can not surpress those kind of memories - a trigger or an association can lead to flashbacks. This is also because the memory of the trauma – not least because of the involvement of Amygdala– is saved very deeply in the brain. The amygdala also reacts to stimuli that are just somehow associated with the traumatic situation. So how well you remember depends on how well you forget.
Neurofeedback and memory - theta activity can be trained individually
A team of Experimental Neuropsychologists from the University of Saarland investigated in a study with 17 subjects how memory could be improved by a specific neurofeedback training. Using a specially developed neurofeedback protocol, the subjects trained to increase Theta waves (4-8 Hz) in brain activity. Those are known to be associated with relaxed waking states or flow experiences through previous research. If the subjects showed high theta activity, took the speed of a roller coaster that they saw on the screen in front of them; A small proportion of Theta Waves caused the roller coaster to stand still. Subjects trained with neurofeedback in a total of seven sessions for 30 min within almost two weeks. 18 subjects in the control group received sham feedback and were presented randomly selected frequencies of their EEG during the same amount of sessions.
While the training group showed significantly more theta activity from the third session onwards (theta increase of 10-15 % per subject), there was no increase in the theta activity in the control group. The authors concluded that subjects could learn to upregulate the theta waves.Thus, theta activity can be trained individually through neurofeedback training.
Increased theta activity shows improvement in memory performance
The researchers then examined the impact of increased theta activity on long-term memory. Subjects from both groups solved a memory task on three different dates – one day after the first NFB training, one day after the last NFB session and 13 days after the last session. In the task, memory capacity and memory context were considered. The participants were presented with 200 words (for each of the 3 test times new words were chosen here). They should indicate whether these words describe living objects or if they seem pleasant to them. In a subsequent memory test, the previously learned words were presented together with some new words. If the subjects assessed a word as seen before, they were asked in which context (i.e. with the question of alive or pleasant) it had been presented before.
Subjects who previously received neurofeedback training and thus increased their theta waves, showed a clear improvement in their memory performance. After neurofeedback training, they were able to recognise more words and assign them to the right context. This improvement was not only of a short-term nature: Even if the test was repeated 13 days after the last neurofeedback session, a long-term improvement in memory and memory context could be registered. The individual improvement in the memory test was related to the individual increase of the theta activity in neurofeedback training.
At both test times after neurofeedback training, but especially during testing 13 days after the last session, subjects in the training group achieved absolutely better results than subjects in the control group, while the results in the pretest were comparable.
This research was carried out with young and healthy subjects, but forms the basis for investigating the improvement of memory through neurofeedback in the future – possibly using other protocols then theta frequency training – with patients suffering from pathological memory problems. In any case, the results suggest to further investigate the possibilities of neurofeedback training to improve memory. Even in current treatments – with corresponding symptoms – the improvement of memory can be considered as a treatment goal.
Study: Eschmann, K. C., Bader, R., & Mecklinger, A. (2020). Improving episodic memory: Frontal-midline theta neurofeedback training increases source memory performance. NeuroImage, 222, 117219.
