The relationship between conscious experience of perception and neural events is a key issue in modern neuroscience (Crick & Koch,
2003). Although we lack a complete knowledge of the function of consciousness to help us in understanding its relationship to brain function, there is good reason to believe that consciousness is involved in the higher order gating of sensory inputs. Dopaminergic neurons to the striatum have been proposed to play a determining role in gating of sensory inputs (Horvitz,
2002), and enhanced sensory experience during Yoga Nidra meditation is linked to dopamine release in nucleus accumbens of the ventral striatum (Kjaer et al.,
2002), suggesting that dopamine may be active in regulating conscious experience. One way to understand this idea is to approach conscious experience as a form of higher order signal detection. On this approach, conscious experience is determined by the setting of a criterion for when the sensory signal-to-noise ratio warrants confidence that the stimulus represents something real (Lau,
2007). Consistent with this approach, work on schizophrenia shows not only that patients with auditory hallucinations have enhanced sensitivity to speech stimuli, but they also set more liberal criteria for deciding that a perceived event is an actual stimulus. Psychotic symptoms may, accordingly, be explained at least partly as a result of setting too liberal a signal-to-noise criterion leading to confusion between perception and imagination (Moritz & Larøi,
2008; Vercammen, de Haan, & Aleman,
2008; Winterer et al.,
2000). Abnormally up-regulated dopaminergic neurotransmission (Gjedde & Wong,
2001; Kroener, Chandler, Phillips, & Seamans,
2009) may be one of the mechanisms responsible for this difference, with an effect of dopamine on the cellular level being to influence the signal-to-noise ratio (Kiyatkin & Rebec,
1996,
1999; Williams & Goldman-Rakic,
1995; Winterer et al.,
2000). Functional brain imaging has established that abnormal conscious experiences, like hallucinations, are associated with abnormal dopaminergic neurotransmission. For instance, striatal dopamine transporter availability is inversely correlated with hallucinations (Schmitt et al.,
2006). Accordingly, acute psychosis is generally considered a consequence of a hyperdopaminergic state (Howes & Kapur,
2009; Laruelle & Abi-Dargham,
1999).