This Mammal Shrinks, Regrows Its Brain

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Common shrews are mammals known to flexibly shrink and regrow their brains.

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This rare seasonal cycle, known as Dehnel's phenomenon, has puzzled scientists for decades.

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This phenomenon has been named after the Polish scientist August Dehnel, who first described the seasonal changes in shrews in 1949.

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When undergoing Dehnel's, shrews' brains become smaller from summer to late winter, then regrow in spring.

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Scientists call this reversible resizing "brain plasticity," and it is thought to help shrews conserve energy when food is scarce.

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They have a high metabolic rate and do not hibernate, meaning they need high-energy food sources to sustain them whatever the season.

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Shrinking themselves also shrinks their food demands in winter, when resources are scarce.

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Their brain cells lose water but they do not die, meaning they retain their brain function.

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