Fear conditioning is a fundamentally important and preserved process across species. In humans it is linked to fear-related disorders such as phobias and post-traumatic stress disorder (PTSD). Fear memories can be reduced by counter-conditioning, in which fear conditioned stimuli (CS+s) are repeatedly reinforced with reward or with novel non-threatening stimuli. However, this procedure involves explicit presentations of CS+s, which is itself aversive before fear is successfully reduced. This aversiveness may be a problem when trying to translate such experimental paradigms into clinical settings. It also raises the fundamental question as to whether explicit presentations of feared objects is necessary for fear reduction. Although learning without explicit stimulus presentation has been previously demonstrated, whether fear can be reduced while avoiding explicit exposure to CS+s remains largely unknown. One recently developed approach employs an implicit method to induce learning by reinforcing stimulus-specific neural representations using real-time decoding of multivariate functional magnetic resonance imaging (fMRI) signals in the absence of stimulus presentation; that is, pairing rewards with the occurrences of multi-voxel brain activity patterns matching a specific stimulus (decoded fMRI neurofeedback (DecNef)). It has been shown that participants exhibit perceptual learning for a specific visual stimulus feature through DecNef, without being given any strategy for the induction of specific neural representations, and without awareness of the content of reinforced neural representations. Here we examined whether a similar approach could be applied to counter-conditioning of fear. We show that we can reduce fear towards CS+s by pairing rewards with the activation patterns in visual cortex representing a CS+, while participants remain unaware of the content and purpose of the procedure. This procedure may be an initial step towards novel treatments for fear-related disorders such as phobia and PTSD, via unconscious processing.
Thursday, February 16, 2017
Hacking the brain to overcome fear
Schiller does a brief review of work by Koizumi et al., which points to a method for reducing defensive responses without consciously confronting the threatening cues, paving the way for fear-reducing therapies via unconscious processing. The fMRI signals associated with fear conditioned stimuli trained on the first day of the experiment are determined . Then, in the absence of the threatening cues, appearance and growth of the activation pattern representing the conditioned stimulus is paired with a monetary reward in sessions over the next three days. On the fifth day, the defensive response of participants to the threatening cues is significantly reduced, as is amygdala activity. The open source articles give a more complete account. Here is the Koizumi et al. abstract: