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Social memory is a fundamental cognitive process that helps animals recognize and remember their peers, an ability that is impairedin neurological disorders.
Neurons in the CA2 region of the hippocampus respond to external social novelty stimuli and encode social memory signals
.
Activation of the supracapamic papillary nucleus (SuM) to the glutamatergic neural circuit in the CA2 region affects the encoding of social novelty information, but inhibition of this circuit does not
.
Both phases of sleep, non-rapid eye movement (NREM) and rapid eye movement sleep (REM)), play an important role
in memory consolidation.
It is generally believed that during the sharp ripples of NREM sleep, reactivating neurons and neural circuits that are active in the learning process will further consolidate learning memory
.
More specifically, social memory is promoted during sharp ripples in the hippocampal CA2 region during the NREM phase and spatial memory
during spikes in the CA3 region.
On October 21, 2022, the research team of Chen Xiaowei of the Third Military Medical University published an article in the journal Neuron revealing that the SuM-CA2 neural circuit regulates social memory
during the REM period.
1
The REM phase activates the SuM-CA2 neural circuit
Although SuM can be projected to the hippocampal DG region and CA2 region, the two projected neurons in retrograde virus tracing experiments do not overlap to a large extent and are independent neural circuits.
Fiber calcium imaging records found that the calcium ion activity of the SuM-CA2 neural circuit was enhanced during the NREM and REM periods, and more
enhanced during the REM period.
In vivo electrophysiology experiments also showed that the firing frequency of SuM-CA2 neural circuits increased during the transition from NREM to REM, and decreased in the frequency of neuronal firing from REM to awakening
.
Figure 1: Neural circuits projected by SuM parallel to CA2 and DG
2
The SuM-CA2 neural circuit regulates social memory
.
Familiar companion mice and strange companion mice were placed on each side of the test stage, and the experimental mice preferred to stay on the side of the strange mouse, showing social novelty
.
However, after photoinhibition of the SuM-CA2 neural circuit during the REM phase, mice could not distinguish between familiar companions and unfamiliar companions, so they did not show novelty
to social interaction.
In another direct social behavior, the experimental mice were directly socialized with the companion mice in a box, and the familiar mice and unfamiliar companion mice were put into the test stage, and the social time between the experimental mice and the familiar mice increased after photoinhibition of the SuM-CA2 neural circuit during the REM period
.
Figure 2: Inhibition of the SuM-CA2 neural circuit impairs social memory
3
The SuM-DG neural circuit regulates spatial memory
In spatial learning and memory experiments, photoinhibition of SuM-CA2 neural circuits during REM does not affect the spatial memory ability ofmice.
However, inhibition of the SuM-DG neural circuit during this period did not affect the social memory of mice, but impaired the spatial memory ability
of mice.
Electrophysiological recordings showed that photoinhibition of SuM-CA2 neural circuits during REM did not affect the δ, θ, α and β rhythms and neuronal firing activities of local field potentials in the CA1 region of the hippocampus, but the inhibition of SuM-DG neural circuits during this period significantly reduced the θ, α and β rhythm activities
of local field potentials in the CA1 region.
Figure 3: Inhibition of the SuM-DG neural circuit impairs spatial memory
summary
This paper found that the loop of parallel projection of the supramaslavamic nucleus into the CA2 and DG regions of the hippocampus regulates different memories: the former regulates social memory, and the latter regulates spatial memory
.
【References】
1.
Qin et al.
, REM sleep-active hypothalamic neurons may contribute to hippocampal social-memory consolidation,Neuron (2022),
https://doi.
org/10.
1016/j.
neuron.
2022.
09.
004
The images in the article are from references
