Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain
the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in
Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles
and JavaScript.
A new paper reports that dopaminergic neurons initially responded optimistically in rats given free choice between two rewards, as though the animal had chosen the better reward, even on trials when it failed to do so. These findings suggest that current computational theories of dopaminergic function may need to be revised.
Brain microglia increase their numbers in response to threats. Some of these cells were thought to enter the CNS from the blood, but two new studies suggest that experimental confounds could in part account for such results.