In This Issue Brain Waves and Recall PAGE 845 Yamamoto et al. report a strong temporal association between a particular neural activity-a transient burst of high gamma synchrony-and correct execution of a working memory behavior in mice. Optogenetic inhibition of the relevant neuronal circuit reduced both the synchrony and the correct behavior, suggesting a role for this neural oscillation in spatial working memory. Polar Bear Genome PAGE 785 Liu et al. present polar bear reference genome and

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... e population genomic modeling to estimate a divergence time between brown bears and polar bears of only c. 400,000 years. The authors find strong selection in genes related to fatty acid metabolism, pigmentation, and cardiovascular function, reflecting the unique adaptations in response to Arctic climates and a hyperlipid diet of marine mammals.