Fig. 1

a Left: MAP-mapping²² of 2-hr isolated fish vs fish in groups. Green voxels indicate significantly higher activity. Map combines data from 5 experiments in which isolated fish are compared with groups of 3 (2 experiments), 5 (1 experiment), or 10 (2 experiments). Yellow = outline of preoptic (PO) and posterior (PT) OXT populations used to quantify activity in Right. Tel = telencephalon, cH caudal hypothalamus, LC locus coeruleus, AP area postrema, HB hindbrain. A anterior, L left, V ventral. Scale bar = 100 µm. Right: Social isolation significantly activates PO and PT regions. Data for other stimuli were also included in Wee et al. (2019)⁶. Adjusted p-values for social isolation: ***p = 0.00084 (PO), *p = 0.03 (PT), p = 0.42 (whole brain), two-sided Wilcoxon signed-rank test relative to a median of 1, Bonferroni correction. b Maximum-intensity projection images showing pERK expression (magenta) in Tg(oxt:GFP)-positive (green) and surrounding neurons, from a representative dissected brain of an isolated fish (bottom) and a fish kept in groups of 3 (top). White arrows indicate examples of OXT neurons with high pERK intensities. Scale bar = 20 µm. This experiment was repeated more than 5 times with similar results. c Fish were either kept in groups of 3 (gray, n = 835 OXT_PO/158 OXT_PT neurons from 12 fish), isolated (pink, n = 803 OXT_PO/128 OXT_PT neurons from 11 fish), isolated but exposed to visual cues of conspecifics (red, n = 796 OXT_PO/106 OXT_PT neurons from 12 fish), or isolated but exposed to non-kin-conditioned water (blue, n = 751 OXT_PO/115 OXT_PT neurons from 11 fish) or kin-conditioned water (orange, n = 722 OXT_PO/134 OXT_PT neurons from 11 fish). Boxplot shows the median (center), interquartile range (IQR; box), 1.5 IQRs of the lower and upper quartile (whiskers), and outliers beyond this range (diamonds); Half-violin plot shows kernel-density estimate of normalized pERK values. OXT_PO neurons: adjusted p = 0*** (group vs isolated)/0*** (group vs visual)/1.7×10⁻⁴*** (group vs non-kin water)/1 (group vs kin water)/0.023* (isolated vs visual)/3.4×10⁻¹⁸*** (isolated vs non-kin water)/0*** (isolated vs kin water)/4.8×10⁻⁸*** (visual vs non-kin water)/4.2×10⁻²²***(visual vs kin water)/0.0014** (kin vs non-kin water). Kruskal–Wallis Test with Tukey–Kramer correction for multiple comparisons. OXT_PT neurons: adjusted p = 7.9×10⁻⁶*** (group vs isolated)/0.0071** (group vs visual)/4.3×10⁻⁶*** (group vs non-kin water)/0.20 (group vs kin water)/1.1×10⁻¹³*** (isolated vs visual)/6.8×10⁻²¹*** (isolated vs non-kin water)/1.0×10⁻¹⁰*** (isolated vs kin water)/0.58 (visual vs non-kin water)/0.69 (visual vs kin water)/0.032* (kin vs non-kin water). Kruskal–Wallis test with Tukey–Kramer correction for multiple comparisons. d Spatial distribution of OXT neurons from each category, color coded according to normalized pERK intensity (most active = yellow, least active = deep blue, colorbar shows normalized pERK value). See Methods. e Anterior–posterior (AP) localization of “active cells” sampled from each category. See Methods. Source data are provided as a Source Data file.