RESULTS The fMRI analysis showed that methylpheni date significantly enhanced activation in bilateral inferior frontal cortex (IFC)/insula during inhibition and time discrimination but had no effect on working memory networks .
The meta- analysis , including 14 fMRI data sets and 212 children with ADHD , showed that stimulants most consistently enhanced right IFC/insula activation , which also remained for a subgroup analysis of methylpheni date effects alone .
A more lenient threshold also revealed increased putamen activation .
CONCLUSIONS Psychostimulants most consistently increase right IFC/insula activation , which are key areas of cognitive control and also the most replicated neurocognitive dysfunction in ADHD .
These neurocognitive effects may underlie their positive clinical effects
BACKGROUND Psychostimulant medication , most commonly the catecholamine agonist methylpheni date , is the most effective treatment for attention-deficit/hyperactivity disorder ( ADHD ) .
However , relatively little is known on the mechanisms of action .
Acute effects on brain function can eluci date underlying neurocognitive effects .
We tested methylpheni date effects relative to placebo in functional magnetic resonance imaging ( fMRI ) during three disorder-relevant tasks in medication-naïve ADHD adolescents .
In addition , we conducted a systematic review and meta- analysis of the fMRI findings of acute stimulant effects on ADHD brain function .
Colored noise and computational inference in neurophysiological (fMRI) time series analysis: resampling methods in time and wavelet domains.
Even in the absence of an experimental effect , functional magnetic resonance imaging ( fMRI ) time series generally demonstrate serial dependence . This colored noise or endogenous autocorrelation typically has disproportionate spectral power at low frequencies , i.e. , its spectrum is (1/f)-like . Various pre-whitening and pre-coloring strategies have been proposed to make valid inference on st and ardised test statistics estimated by time series regression in this context of residually autocorrelated errors . Here we introduce a new method based on r and om permutation after orthogonal transformation of the observed time series to the wavelet domain . This scheme exploits the general whitening or decorrelating property of the discrete wavelet transform and is implemented using a Daubechies wavelet with four vanishing moments to ensure exchangeability of wavelet coefficients within each scale of decomposition . For (1/f)-like or fractal noises , e.g. , realisations of fractional Brownian motion ( fBm ) parameterised by Hurst exponent 0 < H < 1 , this resampling algorithm exactly preserves wavelet-based estimates of the second order stochastic properties of the ( possibly nonstationary ) time series . Performance of the method is assessed empirically using (1/f)-like noise simulated by multiple physical relaxation processes , and experimental fMRI data . Nominal type 1 error control in brain activation mapping is demonstrated by analysis of 13 images acquired under null or resting conditions . Compared to autoregressive pre-whitening methods for computational inference , a key advantage of wavelet resampling seems to be its robustness in activation mapping of experimental fMRI data acquired at 3 Tesla field strength . We conclude that wavelet resampling may be a generally useful method for inference on naturally complex time series
RESULTS The fMRI analysis showed that methylpheni date significantly enhanced activation in bilateral inferior frontal cortex (IFC)/insula during inhibition and time discrimination but had no effect on working memory networks .
The meta- analysis , including 14 fMRI data sets and 212 children with ADHD , showed that stimulants most consistently enhanced right IFC/insula activation , which also remained for a subgroup analysis of methylpheni date effects alone .
A more lenient threshold also revealed increased putamen activation .
CONCLUSIONS Psychostimulants most consistently increase right IFC/insula activation , which are key areas of cognitive control and also the most replicated neurocognitive dysfunction in ADHD .
These neurocognitive effects may underlie their positive clinical effects
BACKGROUND Psychostimulant medication , most commonly the catecholamine agonist methylpheni date , is the most effective treatment for attention-deficit/hyperactivity disorder ( ADHD ) .
However , relatively little is known on the mechanisms of action .
Acute effects on brain function can eluci date underlying neurocognitive effects .
We tested methylpheni date effects relative to placebo in functional magnetic resonance imaging ( fMRI ) during three disorder-relevant tasks in medication-naïve ADHD adolescents .
In addition , we conducted a systematic review and meta- analysis of the fMRI findings of acute stimulant effects on ADHD brain function .