BEHAVIORAL FUNCTIONS OF ADULT NEUROGENESIS: BEYOND LEARNING AND MEMORY

Dentate gyrus granule cells are generated throughout life and integrate into hippocampal circuits, but it is not clear how this affects cognition and behavior. We have been using pharmacogenetic (GFAP-TK) mouse and rat models to specifically inhibit neurogenesis during adulthood in order to identify the structural and behavioral impacts of chronic neurogenesis suppression that might be seen with stress, depression, or aging. Well-established roles for the hippocampus in learning and memory suggest that suppression adult neurogenesis should affect these functions. However, learning and memory appear largely intact in animals lacking adult neurogenesis. Instead, we find effects on shifting of attention, motivation to work for unpredictable rewards, and decisions involving conflicts between competing goals or stimuli. Rats and mice with suppressed adult neurogenesis show robust differences from control in an approach-approach gambling task, an approach-avoidance platform-mediated avoidance task, and tests of social aggression – all situations with inherently conflicting behavioral options. We also find that adult neurogenesis is required for growth of ventral CA1 volume and increased novelty approach behavior following rewarded learning or during recovery from stress. Decreased investigation of novel objects is often interpreted as impaired memory, but we have found evidence that it often reflects a shift toward preference for familiarity instead, particularly after a stress. Taken together, our work suggests that adult neurogenesis may direct attention toward lower salience stimuli and alternate strategies, driving focus toward the most important goals in threatening environments and increasing curiosity and exploration in safer environments.