CONTEXTUAL INFLUENCE ON FEAR-RELATED NEURONAL ACTIVITY AND BEHAVIOUR IN THE VENTRAL HIPPOCAMPUS

The ventral hippocampus is a cortical brain region involved in imbuing contexts with emotional and motivational salience. In this study, we investigated the role of contextual information on the gating of stimulus-related neuronal and behavioural responses. We used a novel fear conditioning paradigm in head-fixed mice during virtual reality navigation to investigate the impact of safe, ambiguous and frightening environments to neutral (CS-) and fear-associated (CS+) cue responses. To investigate the neuronal correlates involved in this process, we recorded ventral hippocampal neurons using silicon probes and juxtacellular recording and labelling technique during trace fear conditioning and a subsequent context-dependent cue memory test. Simultaneously, we quantified fear-related behaviours using locomotion and pupil dilatation. During conditioning, behavioural responses and neuronal activity recorded from pyramidal neurons and interneurons in ventral hippocampus suggest that animals successfully differentiated between CS- and CS+, reflecting the conditioning process. In the context-dependent memory test, the behavioural responses and neuronal activity patterns of neuronal correlates in ventral hippocampus, further demonstrated that animals encoded aversive stimuli in a context-dependent manner and exhibited a generalisation of both stimulus- and fear-related responses in the ambiguous context. By optogenetically manipulating parvalbumin interneurons, we altered fear generalisation in ambiguous context, suggesting that parvalbumin interneurons have a role in context-dependent fear responses. Collectively, these data suggest that the ventral hippocampus gates stimulus and behavioural responses in a context-specific manner.