Dopamine biomarkers

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Two of my PhD students examine the role of dopamine in various cognitive processes. Anke Linssen studies the effects of dopamine enhancement. She treats healthy volunteers with methylphenidate (MPH) or levodopa, two dopaminergic substances that increase dopamine in the brain, and assesses whether this improves memory performance as well as motor preparation. Motor preparation is measured in a test in which a warning stimulus predicts the occurrence of an imperative stimulus exactly 4s later (see figure below, with courtesy of Anke Linssen). Her first studies have shown that the contingent negative variation, a negative deflection in the EEG that is related to response preparation, is increased in a dose-related fashion after treatment with methylphenidate. Also memory was improved. We are now in the process of checking whether these effects of MPH are solely due to dopamine enhancement, or whether this is a combined action of dopamine and norepinephrine. Namely, MPH affects both neurotransmitter systems.



Joep Wolters recently started his PhD project on the role of dopamine in cognitive symptoms related to attention deficit hyperactivity disorder (ADHD). We will first examine which cognitive deficits are most pronounced in patients with ADHD and in healthy volunteers showing quite some ADHD symptoms. For this purpose, various cognitive tests will be run in combination with an EEG recording. The second goal will be to determine to what extent changes in dopamine levels affect performance in these tests. We will use a dopamine depletion method called tyrosine-phenylalanine depletion in this study. Please come back to my website to hear about our first results.