Shaken, Not Stirred: Emergence of Neural Selectivity in a ''Cocktail Party''

decreased neurogenesis has been implicated in the development of mood disorders (Kheirbek et al., 2012). Newborn neurons integrating into the adult hippocampal circuitry transiently exhibit enhanced excitability that enables contributions to circuit function and behavior. This raises the possibility that young GCs in the dorsal and ventral hippocampus may have distinct functions related to learning or emotional behavior. For the moment, further experiments will be necessary to determine if the effect of optical stimulation on learning or anxiety behavior in the current study reflects the differential stimulation of young granule cells across the dorsal and ventral axis. The results of this study may have important implications for clinical illnesses, notably posttraumatic stress disorder (PTSD). For some returning combat veterans, the sound of a passing helicopter even in a nonthreatening environment can evoke the experience of combat that took place months or years earlier. Theinability toproperly‘‘contextualize’’ traumatic events is considered one of the primary problems of PTSD. The current finding that inhibition of dorsal DG activity blocks the encoding of contextual information offersan important neurobiological framework for understanding how memory of a trauma can generalize to stimuli that resemble cues associated with the traumatic event. In addition, the observation that activation of ventral DG can suppress innate anxiety without adversely affecting learning or memory encoding provides new fundamental information. Targeting these mechanisms may serve as unique strategies to restrain the overgeneralization observed in PTSD and anxiety disorders. In conclusion, the elegant work of Kheirbek and colleagues (Kheirbek et al., 2013) helps to pave the way toward a better understanding of the functional contributions of the dorsal and ventral DG to behavior and represents a prime example of how the combination of optics and genetics can assist in deciphering the inner workings of the brain.