Contextual fear learning in virtual reality: The role of the vmPFC and the hippocampus in the contextual modulation of fear expression
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2015-08-13
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en
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Abstract
Correctly using contextual information to modulate our assessment of a situation is crucial for healthy emotion
and cognition, and deficits in this ability to correctly contextualise information may lead to psychopathology such
as post-traumatic stress disorder (PTSD). Using a virtual reality (VR) model for delay differential contextual fear
conditioning combined with functional magnetic resonance imaging (fMRI), we aimed to shed some light on how
the brain enables this contextual modulation of fear. Inside the VR, two different buildings represented a safe
context and a threat context, respectively. Two different cues (CS+ and CS-) were presented in both buildings in
exactly the same way, but the CS+ was consistently (at a reinforcement rate of 100%) paired with a mild electric
shock only in the threat context and never in the safe context, while the CS- was never paired with a shock. In
order to validate the presence of conditioned fear in the threat context, but not the safe context, we used skin
conductance responses (SCR) and pupil dilation, which indeed confirmed that conditioned fear in response to the
CS+ (as compared to the CS-) was present in the threat context, but not the safe context. We observed
significantly greater blood-oxygen-level dependent (BOLD) responses for CS+threat>CS-threat than for CS+safe>CSsafe
in the dorsal anterior cingulate cortex (dACC), anterior insula, amygdala, hippocampus as well as several
other regions, showing that conditioned fear in response to the CS+ was indeed present in the threat context, but
not in the safe context. Furthermore, we found a significant cue by context interaction in the ventromedial
prefrontal cortex (vmPFC), with significantly greater activity in response to the CS+ in the safe context than in the
threat context. This finding is similar to findings of studies on fear extinction, suggesting that change of context
and fear extinction are enabled by similar mechanisms linked to the vmPFC. One possibility for such a
mechanism is that the vmPFC, in interaction with the hippocampus, inhibits fear expression by signalling safety
to other areas implicated in conditioned fear, such as the amygdala and dACC.
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Faculteit der Sociale Wetenschappen