1 Department of Psychology, University of Toronto, Toronto M5S 3G3, Canada. Electronic address: alana.brown@mail.utoronto.ca.
2 Department of Psychology, University of Toronto, Toronto M5S 3G3, Canada; Groningen Institute for Evolutionary Life Sciences, University of Groningen, Groningen 9712 CP, the Netherlands. Electronic address: n.j.gervais@rug.nl.
3 Department of Psychology, University of Toronto, Toronto M5S 3G3, Canada. Electronic address: laura.gravelsins@mail.utoronto.ca.
4 Psychology Department, University of Montreal, Montreal H3T 1J4, Canada; Department of Health, Kinesiology and Applied Physiology, Concordia University, Montreal H3G 1M8, Canada. Electronic address: jordan.obyrne@umontreal.ca.
5 Department of Psychology, University of Toronto, Toronto M5S 3G3, Canada. Electronic address: noelia.calvo@utoronto.ca.
6 Department of Psychology, University of Toronto, Toronto M5S 3G3, Canada. Electronic address: shreeyaa.ramana@utoronto.ca.
7 Genetics Program, North York General Hospital, Toronto M2K 1E1, Canada; Department of Pediatrics, University of Toronto, Toronto M5G 1X8, Canada. Electronic address: zhuoshawn.shao@nygh.on.ca.
8 Princess Margaret Hospital, Toronto M5G 2C4, Canada. Electronic address: marcus.bernardini@uhn.ca.
9 Princess Margaret Hospital, Toronto M5G 2C4, Canada; Women's College Hospital, Toronto M5S 1B2, Canada. Electronic address: michelle.jacobson@wchospital.ca.
10 Department of Psychology, Toronto Metropolitan University, Toronto M5B 2K3, Canada. Electronic address: natasha.rajah@torontomu.ca.
11 Department of Psychology, University of Toronto, Toronto M5S 3G3, Canada; Baycrest Academy of Research and Education, Baycrest Health Sciences, Toronto M6A 2E1, Canada; Tema Genus, Linköping University, Linköping 581 83, Sweden. Electronic address: gillian.einstein@utoronto.ca.

Bilateral salpingo-oophorectomy (BSO; removal of ovaries and fallopian tubes) prior to age 48 is associated with elevated risk for both Alzheimer's disease (AD) and sleep disorders such as insomnia and sleep apnea. In early midlife, individuals with BSO show reduced hippocampal volume, function, and hippocampal-dependent verbal episodic memory performance associated with changes in sleep. It is unknown whether BSO affects fine-grained sleep measurements (sleep microarchitecture) and how these changes might relate to hippocampal-dependent memory. We recruited thirty-six early midlife participants with BSO. Seventeen of these participants were taking 17ß-estradiol therapy (BSO+ET) and 19 had never taken ET (BSO). Twenty age-matched control participants with intact ovaries (AMC) were also included. Overnight at-home polysomnography recordings were collected, along with subjective sleep quality and hot flash frequency. Multivariate Partial Least Squares (PLS) analysis was used to assess how sleep varied between groups. Compared to AMC, BSO without ET was associated with significantly decreased time spent in non-rapid eye movement (NREM) stage 2 sleep as well as increased NREM stage 2 and 3 beta power, NREM stage 2 delta power, and spindle power and maximum amplitude. Increased spindle maximum amplitude was negatively correlated with verbal episodic memory performance. Decreased sleep latency, increased sleep efficiency, and increased time spent in rapid eye movement sleep were observed for BSO+ET. Findings suggest there is an association between ovarian hormone loss and sleep microarchitecture, which may contribute to poorer cognitive outcomes and be ameliorated by ET.