Analysis of SR-FP data
LABView files of video recording and of optical signal data were used to score social events using an ethogram (Table S2). Per test phase, the number and total duration of social episodes, and from this the mean duration of each social episode, were calculated. The data for the first SR test were used for statistical analysis unless they included substantial artefacts in which case the second test was used (in the case of one mouse). Social events were manually time stamped onto the optical signal data. The time of each social event that resulted in the onset of a social episode, e.g. approach, approach+mount, approach+copulation, was designated as t=0 s. The fibre photometry data were analyzed with custom-written MATLAB programs . Optical signal data were demodulated at 970 Hz, down-sampled to a sampling frequency of 20 Hz, and smoothed using an exponential smoothing function with damping factor 0.5, thereby excluding some of the broad-spectrum signal noise. The social event-specific mean Ca2+ (or EGFP) activity during the 5 s prior to event onset at t=0 s provided the measure of baseline activity. For 10 s after social-event onset, regardless of the duration of the social episode that it initiated, for each 0.05 s time bin (t), the z -scored (normalized) signal intensity (F ) was calculated using the formula (F (t ) -F 0)/SD 0, whereF0 and SD0 denote mean and standard deviation of 5-s baseline activity (mean z-scored Ca2+ baseline signal = 0). After the onset and offset of a social episode, if the onset of the next social episode occurred within 10 s, this latter episode was not analyzed; this was done in order to achieve some separation between baseline signal and social episode-related signal. For each mouse and each phase (distal SR, proximal SR), the mean peri-event/episode histogram was calculated, and these mouse-specific histograms were used to calculate the overall mean histograms per phase.