Abstract
How “intelligent” is the unconscious fast feedforward sweep? To test this issue, we used functional magnetic resonance imaging to investigate the potential depth of processing of unconscious information in the human brain. We devised a new version of the Go/No-Go task that included conscious (weakly masked) No-Go trials, unconscious (strongly masked) No-Go trials as well as Go trials. Replicating typical neuroimaging findings, we observed that response inhibition on conscious No-Go trials was associated with a (mostly right-lateralized) “inhibition network”, including the pre-supplementary motor area (pre-SMA), the anterior cingulated cortex, middle, superior and inferior frontal cortices as well as parietal cortex. Here we demonstrate, however, that also an unconscious No-Go stimulus can travel all the way up to the prefrontal cortex, most prominently the inferior frontal cortex and the pre-SMA. Interestingly, if it does so, it brings about a substantial slow-down in the speed of responding; as if participants tried to cancel their response but just failed to do so completely. The strength of activation in the “unconscious inhibition network” correlated with the extent of unconsciously triggered RT slowing, which suggests that the observed prefrontal activations are truly “functional”. These results expand our understanding of the limits and depths of the unconscious fast feedforward sweep of information processing in the human brain.