Wouldn’t it be great if playing a videogame in study breaks can help you remember what you studied? Well, a study published in Nature suggests that this is possible. The study investigated how memory retention in humans and animals is enhanced by the occurrence of a novel event before or after memory encoding (Takeuchi et al., 2016). Dr. Robert Greene, a professor of neuroscience, put this simply as “anything that will grab your attention in a persistent kind of way can lead to activation” (Science Daily, 2016). This is called environmental novelty, which is when an unexpected event occurs in an unrelated way to reward persistent behavior (Takeuchi et al., 2016). Environmental novelty can enhance memory retention by affecting a specific neuromodulatory system that has extensive hippocampal connectivity that can lead to an activation of memory processes (Takeuchi et al., 2016; Frey and Morris, 1998).
The study, by Takeuchi et al. (2016), used mice placed in an arena to search for hidden food in sandwells that changed location daily; this search was a model for a “novel experience”. The researchers gave the mice a novel experience of exploring an unknown location, 30 minutes after being trained to remember food locations. They found that the mice found the food better the next day after using the novel experience to enhance their memory. Takeuchi et al. (2016) also injected the mice with a genetically encoded light-sensitive activator to determine which neurons were responsible for the memory enhancement. They used an activator called channelrhodopsin that allowed them to selectively activate dopamine-carrying neurons of the locus coeruleus (LC), a part of the brain that affects memory, that go to the hippocampus. Selectively activating the channelrhodopsin-labeled neurons with blue light (a technique called optogenetics that is outlined in figure 1) was found to substitute the novelty experience in mice and enhance their memory. In addition, they found that this activation can cause a process that can arbitrate learning and memory improvement. The process is simply an enhancement of communication that is relevant to memory that occurs between neurons in the hippocampus at the junctions.
So how does this process occur? Dopamine has always been linked to memory enhancement (Takeuchi et al., 2016). Dr. Greene recently identified that the LC as a source for dopamine in the brain (Smith and Greene, 2012). The neurons that mediate dopamine’s effect on the association for memory with events are tyrosine-hydroxylase-expressing (TH+) neurons (Takeuchi et al., 2016). The source of TH+ neurons was previously thought to be the in the ventral tegmental area (VTA), however the LC was also found to be a source of these neurons (Takeuchi et al., 2016; Smith and Greene, 2012). Furthermore, LC-TH+ neurons have stronger hippocampal connectivity and the LC has more responsive neuronal firing than VTA-TH+ neurons. Therefore, the study concluded that memory enhancement by optogenetic activation is a result of LC-TH+ neurons (Takeuchi et al., 2016).
These findings can be quite impactful in many fields. The use of environmental novelty can enhance memory can expand our knowledge on how humans learn and how to improve learning and teaching techniques. In addition, these findings can enhance our understanding of memory disorders, and can potentially provide new treatment discoveries. So how do we get there? The next steps is a human study that tests the relevancy of the results in human brains more directly.
References
Frey, U. and Morris, R., 1998. Synaptic tagging: implications for late maintenance of hippocampal long-term potentiation. Trends in Neurosciences, 21(5), pp.181-188.
Frostig, R., 2012. What is brain plasticity, and can it help relieve psychiatric or degenerative brain disorders?. [online] Brain Facts. Available at: <http://www.brainfacts.org/about-neuroscience/ask-an-expert/articles/2012/what-is-brain-plasticity> [Accessed 26 Oct. 2016].
Libunao, J., 2015. Optogenetics. [image] Available at: <http://futurism.com/scientists-turn-brain-cells-on-and-off-using-light-receive-high-honors/> [Accessed 27 Oct. 2016].
Science Daily. (2016). Effortless studying? Creating long-lasting memories while having fun. [online] Available at: https://www.sciencedaily.com/releases/2016/09/160907135439.htm [Accessed 5 Oct. 2016].
Smith, C. and Greene, R., 2012. CNS Dopamine Transmission Mediated by Noradrenergic Innervation. Journal of Neuroscience, 32(18), pp.6072-6080.
Takeuchi, T., Duszkiewicz, A., Sonneborn, A., Spooner, P., Yamasaki, M., Watanabe, M., Smith, C., Fernández, G., Deisseroth, K., Greene, R. and Morris, R. (2016). Locus coeruleus and dopaminergic consolidation of everyday memory. Nature, 537(7620), pp.357-362.