Pharmacologically perturbing the effect of tDCS on the speed-accuracy tradeoff.
Creators: name: Leow, Li-Ann
Publisher: name: Open Science Framework
Year: 2022
Subjects: subject: Life Sciences

description: We are constantly negotiating between the competing demands of the rapidity with which we make decisions versus the accuracy of these decisions. This phenomenon, known as the speed-accuracy trade-off, has long been recognised (Woodworth, 1899), and is ubiquitous in animals from fire ants (Franks et al., 2003) to human beings (Woodworth, 1899). Yet, despite extensive research, exactly how the brain trades-off speed and accuracy is yet to be definitively determined. Theories of the speed-accuracy trade-off implicate a network encompassing the cortico–basal ganglia circuit (Bogacz et al., 2010). Such theories have their genesis from neuroimaging studies implicating the pre-supplementary motor area (pre-SMA) and the striatum (Forstmann et al., 2008), and the prefrontal cortex (Van Veen et al., 2008) in the speed-accuracy tradeoff. This line of evidence is supported by findings of altered speed-accuracy tradeoff when using non-invasive brain stimulation to perturb the pre-SMA (Georgiev et al., 2016; Berkay et al., 2018; Filmer et al., 2021) and the prefrontal cortex (Georgiev et al., 2016; Filmer et al., 2021). For example, delivering cathodal transcranial direct current stimulation (tDCS) to the area overlying the left prefrontal cortex increases response caution, whilst cathodal tDCS to the area overlying pre-SMA increases response caution (Filmer et al., 2021). Yet we do not fully understand how non-invasive brain stimulation methods such as transcranial direct current stimulation alters the speed-accuracy tradeoff. One possible mechanism of action for tDCS is by modulating dopamine levels in the cortico-basal ganglia pathways. tDCS can alter striatal activity (Chib et al., 2013; Meyer et al., 2019) and midbrain dopamine release (Fonteneau et al., 2018; Fukai et al., 2019). Pharmacological manipulations of dopamine strongly modulates the effects of non-invasive brain stimulation (Nitsche et al., 2006; Kuo et al., 2008; Monte-Silva et al., 2009; Monte-Silva et al., 2010; Fresnoza et al., 2014). For example, Levodopa combined with 2mA motor cortex tDCS resulted in a 20-fold increase in the persistence of tDCS-induced aftereffects (Kuo et al., 2008). Here, we aim to test the proposal that tDCS modulates the speed-accuracy tradeoff by altering dopamine function, using pharmacological manipulations. Specifically, we will increase dopamine availability in neurotypical young adults by asking them to ingest the dopamine precursor Levodopa (Madopar 100mg Levodopa, 25 mg benserazide hydrochloride) prior to undergoing cathodal or sham tDCS over the pre-SMA or left PFC, and examining how this dopamine manipulation alters the effect of tDCS on the speed-accuracy tradeoff. We hypothesize that the pre-SMA and PFC are involved in the speed-accuracy tradeoff. Thus, we predict that in the placebo condition, cathodal tDCS to the area overlying the pre-SMA will decrease response caution, whereas cathodal tDCS to the area overlying the left PFC will increase response caution, consistent with previous findings (Filmer et al., 2021). Further, we hypothesize that the effect of tDCS on the pre-SMA and/or the left-PFC relies on dopamine. Thus, we predict that boosting dopamine availability will modulate the effect of tDCS in either the pre-SMA, left-PFC, or both conditions.