Dynamics of brain responses to phobic-related stimulation in specific phobia subtypes.

Very few studies have investigated to what extent different subtypes of specific phobia share the same underlying functional neuroanatomy. This study aims to investigate the potential differences in the anatomy and dynamics of the blood oxygen level-dependent (BOLD) responses associated with spider and blood-injection-injury phobias. We used an event-related paradigm in 14 untreated spider phobics, 15 untreated blood-injection-injury phobics and 17 controls. Phobic images successfully induced distress only in phobic participants. Both phobic groups showed a similar pattern of heart rate increase following the presentation of phobic stimuli, this being different from controls. The presentation of phobic images induced activity within the same brain network in all participants, although the intensity of brain responses was significantly higher in phobics. Only blood-injection-injury phobics showed greater activity in the ventral prefrontal cortex compared with controls. This phobia group also presented a lower activity peak in the left amygdala compared with spider phobics. Importantly, looking at the dynamics of BOLD responses, both phobia groups showed a quicker time-to-peak in the right amygdala than controls, but only spider phobics also differed from controls in this parameter within the left amygdala. Considering these and previous findings, both phobia subtypes show very similar responses regarding their immediate reaction to phobia-related images, but critical differences in their sustained responses to these stimuli. These results highlight the importance of considering complex mental processes potentially associated with coping and emotion regulation processes, rather than exclusively focusing on primary neural responses to threat, when investigating fear and phobias.