Why is Memory so Important?

Ali Piracha

Blog 2

Understanding the mechanisms behind memory formation is essential to our progress as human beings. With increasing reliance on technology to help remember facts, we often take the concept of memory for granted. Being able to form memories is an integral part of the human experience. Strong neural connections of a given memory can induce physiological  changes in the body, whether those changes are positive or negative. We often hear about memory in terms of PTSD, which is becoming more prevalent in the United States. Thus, by understanding the roles of the different parts of the brain and the different receptors involved in the formation of memories, we may be able to select which memories to keep and which to suppress one day.

Dr. Voss and colleagues sought to strengthen cortical-hippocampal brain networks to see if it would strengthen associative memory. Instead of doing ablation studies, Dr. Voss focused on noninvasive electromagnetic methods of modulating the strength between the hippocampus and surrounding cortical areas to simulate a “strong” versus a “weak” connection in healthy adults. He focused on the parietal cortex of a specific cortical-hippocampal network. He used rTMS to make the connection stronger and to ensure there was a stronger connection by using an fMRI. Face cued-word recall was used to test stronger associative memories. Results showed that compared to the sham (control) condition, people in the stimulation condition showed a significant gain in associative memory.

In a study lead by Kazu Nakazawa and colleagues, they sought to understand the requirement of the CA3 NMDA receptor in associative memory recall. This study is similar to Dr. Voss’ study in that it also seeks to understand how one can strengthen or weaken associative recall. However, this study used bacterial recombination techniques to see how the presence of a specific receptor can decrease or increase the ability to form associative memories. Both studies complement one another in that the strengthening of the connections between the cortical-hippocampal network may be the result of an upregulation of the CA3 NMDA receptor.

Associative networks have the ability to retrieve whole memories given only a piece of it through pattern recognition. For example, one may have associated a picture of a banana with the word beach. Thus, when one sees the word banana, they think about a beach.

In the study, mice were put in a morris water maze in which there is a hidden platform which allows them to get out. The platform was placed near a light which the the mice begin to associate with the location of the platform. This was done several times until the mice could effectively find the location of the platform. Next, the CA3 NMDA receptor was knocked out in the mice using bacterial recombination of a gene silencer. These mutant mice were then put in the morris water maze again to see how long it took them to find the platform. Average speed, swimming ability, and wall hugging was also measured to control for other differences. Results showed that the mice took a much longer time to form an association of the light with the platform compared to their control times. There was no change in the average speed, swimming ability or the amount of wall hugging. This suggests that CA3 NMDA receptor is important in forming associative memories.

The problem with this study is that it does not account for any upregulation or downregulation of associated receptors. In other words, it does not check whether it is indeed CA3 NMDA receptor which is essential in associative memory formation or did the knockdown result in a downregulation of another associated receptor which is directly the cause of this decrease in ability to form associative memories. To further improve this study, one may consider also monitoring the expression level of associated receptors after the knockdown of the CA3 NMDA receptor. To connect the two studies, one may consider looking at the differences in the level of expression of the CA3 NMDA receptor in adults before and after rTMS.

Indeed, studying memory is essential to our survival, as it is something we need daily. We form associations everyday, whether it is a specific word which reminds us of something we have to do, or using a landmark to remember how to get somewhere. Memory is complex topic and it is imperative that we consider each receptor and protein involved because one day we may be able to develop a way to suppress associations to treat PTSD and alleviate other problems associated with memory.