Like us, birds also have periods of deep, slow-wave sleep in direct proportion to how long they’ve been awake. Moreover, in both birds and humans, the brain regions used more extensively in waking hours sleep more deeply during subsequent sleep—another similarity born of convergent evolution. A team of international researchers headed by Niels Rattenborg at the Max Planck Institute for Ornithology recently discovered this convergence in a clever study that made use of birds’ ability to do something we can’t do: modulate their deep sleep by opening one eye, limiting the slow-wave sleep to only
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