  We observed in a previous study (PLoS ONE 6:e24522) that the self-regulation
of amygdala activity via real-time fMRI neurofeedback (rtfMRI-nf) with positive
emotion induction was associated, in healthy participants, with an enhancement
in the functional connectivity between the left amygdala (LA) and six regions
of the prefrontal cortex. These regions included the left rostral anterior
cingulate cortex (rACC), bilateral dorsomedial prefrontal cortex (DMPFC),
bilateral superior frontal gyrus (SFG), and right medial frontopolar cortex
(MFPC). Together with the LA, these six prefrontal regions thus formed the
functional neuroanatomical network engaged during the rtfMRI-nf procedure. Here
we perform a structural vector autoregression (SVAR) analysis of the effective
connectivity for this network. The SVAR analysis demonstrates that the left
rACC plays an important role during the rtfMRI-nf training, modulating the LA
and the other network regions. According to the analysis, the rtfMRI-nf
training leads to a significant enhancement in the time-lagged effect of the
left rACC on the LA. The training is also accompanied by significant increases
in the instantaneous (contemporaneous) effects of the left rACC on four other
regions - the bilateral DMPFC, the right MFPC, and the left SFG. The
instantaneous effects of the LA on the bilateral DMPFC are also significantly
enhanced. Our results are consistent with a broad literature supporting the
role of the rACC in emotion processing and regulation. Our analysis provides,
for the first time, insights into the causal relationships within the network
of regions engaged during the rtfMRI-nf procedure targeting the amygdala. It
suggests that the rACC may constitute a promising target for rtfMRI-nf training
along with the amygdala in patients with affective disorders, particularly
posttraumatic stress disorder (PTSD).
