Stimulant
medication, such as methylphenidate and dexamphetamine, is commonly prescribed
to children, adolescents and adults with attention-deficit/hyperactivity
disorder (ADHD).
While stimulant medication is generally effective in reducing overall severity
of ADHD symptoms, its effects on the developing brain and on behavioural
outcomes remain incompletely understood.
Adolescence is a crucial and sensitive developmental period, and previous
findings suggest that stimulant treatment during adolescence may have
short-term age-dependent effects on brain development. However, it remains
unclear whether these effects are long-lasting. Moreover, it is not
well-understood how stimulant medication effects on the brain’s dopamine and
noradrenaline systems lead to changes in brain function and clinical and
cognitive improvements.
The overall aim of
this thesis was to investigate the influence of stimulant medication on the
brain and behaviour in individuals with ADHD. We employed various study designs
and analytical approaches, to obtain a multidimensional perspective and provide more nuanced
insights into the effects of stimulant medication. In part I,
we take a developmental perspective, evaluating the relation between long-term
stimulant medication use and regional brain development as measured with
structural and functional MRI. In part II, we take a network
perspective, assessing how stimulant medication influences the complex
interactions between brain regions and between individual ADHD symptoms. In
addition, we characterised essential methodological choices in network analysis
and discussed their implications in the context of fMRI-based network
neuroscience.
