Fig. 1

Cooperative behavior and related brain activity trace. A Schematic diagram of the experimental box for cooperation training and testing. B Cooperation requirement in the behavioral paradigm: the two mice need to press levers synchronously to obtain subsequent rewards. C Training schedule; reward value and time window of joint pressing for reward were changed according to criteria in Additional file 1: Fig. S1A. D Gradual increase of the cooperation index (CI) with training. The CI in the cooperative group (n = 20) was significantly greater than that in the non-cooperative group (n = 16) on the last day of training. ***p < 0.001; Mann–Whitney test. E Schematic diagram of social contact. F Social contact number of the coop group (mean of each pair of coop group during training days 17, 19 and 21, n = 10 pairs) was higher than that of the non-coop group (mean of each pair of non-coop group during training days 17, 19 and 21, n = 8 pairs). One-way ANOVA test. G Social contact number was positively correlated with CI. Dots with different shapes indicate the data of ten training pairs on various training days. The heat level indicates the number of training days. H Schematic diagram of waiting behavior. I Wait number of the coop group (mean of each mouse of the coop group during training days 17, 19 and 21, n = 20) was higher than that of the non-coop group (mean of each mouse of the non-coop group during training days 17, 19 and 21, n = 16). Mann–Whitney test. J Waiting number was positively correlated with CI. Dots with different shapes indicate the data of ten training pairs (mean waiting number of two mice) on various training days. The heat level indicates the number of training days. K Schematic diagram of the blocking social contact test. The partition wall was windowed, and the illumination was on under normal condition (left). The partition wall was unwindowed, and the illumination was off under the block condition (right). L Blocking social contact impaired cooperative behavior. Paired t test (normal vs block of coop group, n = 8) or Mann–Whitney test (normal of coop group vs normal of non-coop group, n = 8). M, O c-Fos expression of the coop and non-coop groups in different coronal sections (50 μm thick) of Bregma 2.96 mm (M) and 1.42 mm (O). Scale bar = 500 μm. N, P Enlarged details of the rectangular area in M (N) and O (P). Scale bar = 200 μm. Q Brain-wide neuronal activity trace during cooperation. Top: c-Fos density for each brain region of each mouse, normalized across all mice using the z-score (color-coded). Bottom: mean c-Fos density of the coop and control groups. Linear regression models (Y = βX + α) were established to compare the difference in c-Fos density between the coop (n = 12) and control groups (n = 6). Shading or error bars indicate the SEM. *p < 0.05, **p < 0.01, ***p < 0.001