Abstract
RationaleConscious perception is thought to depend on global amplification of sensory input. In recent years, striatal dopamine has been proposed to be involved in gating information and conscious access, due to its modulatory influence on thalamocortical connectivity.ObjectivesSince much of the evidence that implicates striatal dopamine is correlational, we conducted a double-blind crossover pharmacological study in which we administered cabergoline—a dopamine D2 agonist—and placebo to 30 healthy participants. Under both conditions, we subjected participants to several well-established experimental conscious-perception paradigms, such as backward masking and the attentional blink task.ResultsWe found no evidence in support of an effect of cabergoline on conscious perception: key behavioral and event-related potential (ERP) findings associated with each of these tasks were unaffected by cabergoline.ConclusionsOur results cast doubt on a causal role for dopamine in visual perception. It remains an open possibility that dopamine has causal effects in other tasks, perhaps where perceptual uncertainty is more prominent.
Highlights
The relationship between consciousness and the brain is often lauded as one of the big mysteries in contemporary science
Our sample size is on the upper end of sample sizes employed by previous research in which cognitive and neural effects of cabergoline were reported with 12–30 participants (Cavanagh et al 2014; Cohen et al 2007; Frank & O’Reilly, 2006; Nandam et al 2013; Norbury et al 2013; Yousif et al, 2016; Fallon et al 2017; Broadway et al 2018), and in which the behavioral and event-related potential (ERP) effects were reported which we aimed to manipulate with cabergoline (12– 15 subjects; Del Cul et al 2007; van Opstal et al 2014; Slagter et al 2012)
Heart rate decreased over time in both placebo and cabergoline conditions (F(2, 48) = 11.8, p < .001, η2 = .06, BFincl > 100) and was overall higher in the cabergoline condition (F(1, 24) = 9, p = .006, η2 = .03, BFincl = 57.3), but there was no interaction between time and drug (F(2, 48) < 1, p = .63, BFincl = .14; see Fig. 4a)
Summary
The relationship between consciousness and the brain is often lauded as one of the big mysteries in contemporary science. Several influential theories propose that consciousness is related to the “broadcasting” of sensory information to the whole brain and that thalamocortical circuits serve as an important mediator of such broadcasting (Crick & Koch, 2003; Dehaene & Changeux, 2011; Edelman, 2003). The broadcasting of sensory information necessitates the occurrence of selection or filtering, because not everything which takes place in the brain reaches conscious awareness. The basal ganglia are connected through parallel loops via the thalamus to the motor cortex, but to many parts of frontal cortex as well (Alexander et al 1986). It is capable of modulating a wide range of cognitive operations. The basal ganglia have been implicated in working memory updating (Frank & O’Reilly, 2006), attention shifting (Cools, 2011), and visual categorization (Seger, 2008): cognitive acts that support suggestions concerning the common principle underlying the basal ganglia’s operations; namely, selection (Frank et al 2001; Redgrave et al 1999)
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