Out of Sight, Out of Mind

It has been a common supposition that suppressing conscious recall of unpleasant or traumatic memories doesn't prevent their stealthly emotionally damaging unconscious effects. Assuming this, various talk therapies attempt to elicit recall, "working through", and desensitization to, the trauma. Gagnepain at al. use now provide direct evidence that a frontal, top-down, inhibition suppresses both explicit and implicit visual cortex activities that correlate with the memories. They found that suppressing visual memories made it harder for people to later see the suppressed object compared to other recently seen objects. (Brain activity was recorded using functional magnetic resonance imaging (fMRI) while participants either thought of the object image when given its reminder word, or instead tried to stop the memory of the picture from entering their mind.) Here is their abstract:

Suppressing retrieval of unwanted memories reduces their later conscious recall. It is widely believed, however, that suppressed memories can continue to exert strong unconscious effects that may compromise mental health. Here we show that excluding memories from awareness not only modulates medial temporal lobe regions involved in explicit retention, but also neocortical areas underlying unconscious expressions of memory. Using repetition priming in visual perception as a model task, we found that excluding memories of visual objects from consciousness reduced their later indirect influence on perception, literally making the content of suppressed memories harder for participants to see. Critically, effective connectivity and pattern similarity analysis revealed that suppression mechanisms mediated by the right middle frontal gyrus reduced activity in neocortical areas involved in perceiving objects and targeted the neural populations most activated by reminders. The degree of inhibitory modulation of the visual cortex while people were suppressing visual memories predicted, in a later perception test, the disruption in the neural markers of sensory memory. These findings suggest a neurobiological model of how motivated forgetting affects the unconscious expression of memory that may be generalized to other types of memory content. More generally, they suggest that the century-old assumption that suppression leaves unconscious memories intact should be reconsidered.