The Turner lab is using optogenetic mouse lines to examine the function of genetically defined neurons in the habenulopeduncular pathway linking the limbic system to the midbrain. Our emphasis is on the function of the medial habenula, about which very little is known. Recent evidence indicates that this pathway may mediate behavioral reponses to nicotine. Other lines of evidence suggest a role in motivated behavior, and in sleep. We will use mice expressing optogenetic channels to explore these functions in brain slice preparations and in behaving animals.