Northwest Labs 243
Social memory engram in the hippocampus
Teruhiro Okuyama
Institute for Quantitative Biosciences (IQB), University of Tokyo
For social animals, it is crucial to remember and recognize different conspecifics (i.e., having “social memory”) and exhibit appropriate social behaviors (approach or avoidance behavior) toward different individuals. In humans, lesion in the hippocampus leads to multiple memory deficits including social memory impairment, suggesting that the hippocampus, at least for a certain period, stores memory information of individuals as well as other components of episodic memory such as spatial or temporal memory.
Since mice naturally tend to spend longer time interacting with novel mice compare to familiar mice (social discrimination behavior), we can quantify the existence of social memory by calculating the total duration spent with novel versus familiar individuals. Using the social discrimination behavioral assay, we demonstrated that vCA1 pyramidal neurons in the hippocampus store social memory (social memory engram was formed). Even when the memory seemed to lost after long separation period, optogenetic activation of the engram can fully restore that social memory. Additionally, an artificial association between the social engrams encoded for specific individuals with fear or reward events can elicit avoidance or preference to that individual, respectively.
Additionally, one tiny dissonance in social memory can easily disrupt the appropriate social behavior, even for humans. Social impairments caused by a genetic mutation, especially those related to the familiarization with other individuals, are commonly exhibited by patients diagnosed with autism spectrum disorder (ASD). Patients with ASD have difficulty either with social memory itself or showing normal social communication driven by social memory. We will show our recent findings regarding neural mechanisms underlying social familiarization impairments observed in ASD.
References
Tao K, Chung M, Watarai A, Huang Z, Wang M, Okuyama T. (2022). Disrupted social memory ensembles in the ventral hippocampus underlie social amnesia in autism-associated Shank3 mutant mice. Molecular psychiatry 27(4) 2095-2105.