The researchers at the University of Michigan through an animal study examined how memories related to a specific sensory event are formed and stored in mice during sleep. The study was conducted before the coronavirus pandemic. In this study, the formation of a fearful memory concerning a specific visual stimulus was particularly observed by the researchers. Upon examination, it was found that not only did the neurons get activated by the visual stimulus during subsequent sleep but sleep is the most essential factor to connect the fearful memory to the sensory event.
Previous studies have highlighted the regions of the brain that get highly active during intensive learning that tend to show more activity during subsequent sleep. However, it was unclear whether this “reactivation” of memories during sleep needs to occur in order to fully store the memory of newly learned material.
Focusing on a particular set of neurons in the primary visual cortex, researchers created a visual memory test. They displayed a group of mice to a neutral image and represented genes in the visual cortex neurons activated by the image. To confirm whether these neurons expressed the neutral image, researchers tested whether they could stimulate the memory of the image by selectively activating the neurons without showing them the image. When they initiated the neurons and paired that activation with a mild foot shock, they found that mice would subsequently get afraid of the visual stimuli that looked similar to the image those cells encode.
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Brittany C. Clawson, Emily J. Pickup, Amy Ensing, Laura Geneseo, James Shaver, John Gonzalez-Amoretti, Meiling Zhao, A. Kane York, Femke Roig Kuhn, Kevin Swift, Jessy D. Martinez, Lijing Wang, Sha Jiang, Sara J. Aton. Causal role for sleep-dependent reactivation of learning-activated sensory ensembles for fear memory consolidation. Nature Communications, 2021; 12 (1) DOI: 10.1038/s41467-021-21471-2 1 Clawson, B.C., Pickup, E.J., Ensing, A. et al. Causal role for sleep-dependent reactivation of learning-activated sensory ensembles for fear memory consolidation. Nat Commun 12, 1200 (2021). https://doi.org/10.1038/s41467-021-21471-2
