Extended Data Fig. 11: Fibre photometry measures of CA2 pyramidal neuron GCaMP6f signals during social interactions.

a, GCaMP6f fluorescence signal as a function of mouse velocity. Pearson test of correlation (r) performed on n = 5,332 1-s time bins. Note the lack of correlation (P = 0.7). Lack of correlation was observed in all mice. b, GCaMP6f responses with fibre over CA2 pyramidal neuron soma during indicated social behaviour (calculated from the mean signal during each episode). Each point represents an episode (49, 31 and 20 episodes from left to right collected from 5 mice). Two-sided one-sample t-tests; ****P < 0.001, ***P = 0.0001. c, As in b with fibre over CA2 pyramidal neuron terminals in LS (34, 27 and 23 episodes collected from 6 mice). Bars show mean ± s.e.m. Two-sided one-sample t-test; ****P < 0.001. d–j, GCaMP6f responses from CA2 somata during various social and non-social behaviours. GCaMP6f recording from CA2 pyramidal neurons in hippocampus during: exploration of a novel environment (d), exploration of a novel object (e), feeding (f), exploration of a female (g), and predator–prey aggression (h). Bar graphs of the GCaMP6f responses during each type of social interaction (calculated from the maximum (i) or the mean (j) signal during each episode). Each point represents an episode except for the novel environment, where episodes were defined as 10-s bins (60, 27, 17, 27, 34, 21, 43, 19 episodes from left to right collected from 6 mice). Bars show mean ± s.e.m. Two-sided one-sample t-tests for i; *P = 0.03, *P = 0.02, *P = 0.047 and ****P < 0.0001 from left to right. Two-sided one-sample t-tests for j; **P = 0.003, ****P < 0.0001, **P = 0.002 and ****P < 0.0001 from left to right. k–m, Behaviour and GCaMP6f responses from dCA2 pyramidal neuron somata during multiple presentations of an ovariectomized female. k, Time (mean ± s.e.m.) spent in social exploration of the same novel female presented in trials 1–4 and a second novel female in trial 5 (4 mice). Resident males normally engaged in non-aggressive social exploration of the female during each exposure, with exploration time showing a trend to decrease during successive trials as a result of increased familiarity. Introduction of a novel female in trial 5 resulted in enhanced social exploration, indicating that the decrease in exploration of the same female represents social memory formation, and not fatigue or disinterest. We previously found that this behaviour required dCA2¹³. Two-sided t-test, **P = 0.005. l, m, Peak (l) and mean (m) GCaMP6f responses recorded from CA2 pyramidal neurons in hippocampus during each period of social exploration in each trial (10, 12, 20, 23 and 26 episodes collected from 4 mice; mean ± s.e.m.). Fibre photometry recordings show that dCA2 responds during social exploration of the female in the familiarization trials, with a trend for activity to decrease with increased familiarization. Introduction of the novel female produced a statistically significant increase in the dCA2 GCaMP6f signal (trial 5). Two-sided t-tests: *P = 0.048 (l) and *P = 0.039 (m).