Neuroimaging studies have variably implicated the ventromedial prefrontal cortex (vmPFC) in emotion regulation, inhibitory control of fear, action control, memory and comparative reward evaluation. Reported reductions or increases in activity have been linked to the aetiology of depression and reversal of this dysregulation can be an effective treatment for refractory depression. However, this is a large, structurally heterogenous region composed of a number of sub-regions including areas 25, 32, 24, 14 and 10. Perhaps surprisingly though, there have been few studies that have attempted to determine the extent to which this structural heterogeneity reflects functional heterogeneity. To address this issue, we have performed a series of investigations in the common marmoset, a new world monkey, combining temporary manipulations of distinct regions within the vmPFC with behavioural and physiological analysis of animal’s reactivity to a wide range of rewarding and threatening contexts. Fluorodeoxyglucose PET imaging has been used in concert with these manipulations to determine circuit-wide changes. Focussing on the effects of inactivation and over-activation of caudal subcallosal region, area 25, results will be presented that highlight the specific role of this region in maintaining a negative affective state that, through apparently distinct downstream circuits, activates cardiovascular, endocrine and behavioural reactivity to threat; whilst blunting anticipatory and motivational appetitive arousal. These findings will be discussed in the context of the markedly different functional profile of neighbouring regions with respect to positive and negative emotion regulation, altogether providing important new insights into the functional heterogeneity within vmPFC.