The dorsal and ventral hippocampus exert cognition and emotion-related functions, respectively. Since both regions display rhythmical activity, specific neural oscillatory pacemakers could underlie their functional dichotomy. Type 1 theta oscillations are strongly observed in the dorsal hippocampus during movement and exploration and are independent of cholinergic transmission. In contrast, type 2 theta depends on acetylcholine and appears when animals are exposed to emotionally laden contexts (e.g. predator odor tests). However, despite its involvement in emotions, the source of type 2 theta has never been attributed to the ventral hippocampus. Here we show that optogenetic activation of oriens-lacunosum moleculare (OLM) interneurons in the ventral hippocampus drives type 2 theta oscillation. We also show that OLM-driven type 2 theta oscillations can coexist with type 1 theta oscillation. Moreover, we found that type 2 theta generation is associated with increased risk-taking behavior in response to predator odor. These results demonstrate that two theta oscillation subtypes predominate in different hippocampal regions that underlie distinct cognitive functions.


Dr Sanja Mikulovic, Institutionen för neurovetenskap, Uppsala universitet
E-post: sanja.mikulovic@neuro.uu.se


Dr Kalicharan Patra, Institutionen för neurokemi