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Using fiber photometry in monogamous prairie voles, we track prefrontal cortex synchrony across pair bond formation. Bonded voles show stronger synchrony with partners than strangers, mirroring human findings. A linear mixed model reveals that synchrony is jointly shaped by bond strength, inter-animal distance, and time since interaction onset, with relationship type modulating how each factor contributes. Using a machine-learning behavioral classification pipeline we developed for freely interacting voles, we demonstrate that the coupling between specific behaviors and synchrony depends on the nature of the dyadic relationship. These findings establish that neural synchrony is not a simple function of proximity or interaction time but is fundamentally shaped by relationship history\u2014a conclusion with direct implications for understanding the synchrony in human social attachment.<\/jats:p>","DOI":"10.64898\/2026.04.15.718291","type":"posted-content","created":{"date-parts":[[2026,4,16]],"date-time":"2026-04-16T15:20:15Z","timestamp":1776352815000},"source":"Crossref","is-referenced-by-count":0,"title":["Social attachment shapes interbrain synchrony"],"prefix":"10.64898","author":[{"given":"Kathleen","family":"Murphy","sequence":"first","affiliation":[{"name":"Department of Psychology & Neuroscience, University of Colorado Boulder, Boulder, CO 80309"},{"name":"IQ Biology Program, BioFrontiers Institute, University of Colorado Boulder, Boulder, CO 80309"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Liza E.","family":"Brusman","sequence":"additional","affiliation":[{"name":"Department of Molecular, Cellular & Developmental Biology, University of Colorado Boulder, Boulder, CO 80309"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yevgenia","family":"Kozorovitskiy","sequence":"additional","affiliation":[{"name":"Department of Neurobiology, Northwestern University, Evanston, IL 60208"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6699-7905","authenticated-orcid":false,"given":"Zoe R.","family":"Donaldson","sequence":"additional","affiliation":[{"name":"Department of Psychology & Neuroscience, University of Colorado Boulder, Boulder, CO 80309"},{"name":"Department of Molecular, Cellular & Developmental Biology, University of Colorado Boulder, Boulder, CO 80309"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"54368","reference":[{"key":"2026042001450600000_2026.04.15.718291v1.1","doi-asserted-by":"publisher","DOI":"10.1006\/nimg.2002.1150"},{"key":"2026042001450600000_2026.04.15.718291v1.2","doi-asserted-by":"crossref","unstructured":"Czeszumski, A. et al. 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