The current study would examine whether increases in endogenous dopaminergic activity via tyrosine and the (presumed) excitation of these by anodal tDCS of the dlPFC could causally be related to cognitive flexibility as measured by task switching and reversal learning. Additionally, the study will test whether the Val158Met-polymorphism in the catechol- O-methyltransferase (COMT) gene could also predict the effect of TYR supplementation, as this gene is involved in DA degradation in the prefrontal cortex.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
BASIC_SCIENCE
Masking
DOUBLE
Enrollment
32
tDCS= A DC Stimulator Plus (neuroConn, Germany) with one 5 cm x 7 cm rubber electrode (anode) and a 10 cm x 10 cm (cathode; reference electrode), encased in saline soaked sponges will be used. The anode will be positioned over the left dlPFC, centered on F3 in the 10e20 electroencephalography (EEG) system, while the cathode on the contralateral supraorbital ridge (Fp2).Current will be delivered at 1.5mA for 20 min plus 30 s fade in/fade out periods.For sham stimulation, the current will be faded in over 30 s, at 1.5mA and then will be switched off. Drugs= 2.0 g of L-Tyrosine and 2.0 g of the placebo microcrystalline cellulose will be dissolved in 400ml of orange juice as per previously published protocols.
Psychology labs
Sheffield, South Yorkshire, United Kingdom
RECRUITINGWisconsin Card Sorting Test (WCST) performance
Measuring change in perseverative errors in the WCST
Time frame: Measured twice in each session (4 arms): at time 0 and 80 minutes into testing.
Probabilistic Reversal Learning (PRL) performance
Measuring change in reversal errors in the WCST
Time frame: Measured twice in each session (4 arms): at time 0 and 80 minutes into testing.
Flanker Task performance
Measuring change in conflict cost (defined as the difference in reaction time between congruent and incongruent responses)
Time frame: Measured twice in each session (4 arms): at time 0 and 80 minutes into testing.
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