Human Imaging Studies-- Magnetic Resonance Imaging
August 18, 2015 at 02:02 AM | categories: mri
Contents
1 MRI and fMRI Studies
A single dose of methylphenidate (MPH) in attention-deficit/hyperactivity disorder (ADHD) subjects upregulates and normalizes the underfunctioning of the dorsomedial frontal cortex, left inferior frontal cortex, posterior cingulate, and parietal regions that in concert play an important role in error processing [1]. In a cognitive task, during error trials, ADHD boys treated with placebo compared with healthy control subjects showed significant underactivation in this error processing and performance monitoring network [1]. However, with MPH treatment, brain activation differences between control subjects and ADHD patients were no longer observed [1]. The normalization of ADHD dysfunction in these key regions of performance monitoring reinforce the association between dopaminergic neurotransmission abnormalities, ADHD, and poor performance monitoring and may underlie the behavioral effects of improving attention and school performance in boys with ADHD [1].
Regularly prescribed, clinically effective stimulant medications alter ADHD brain activity during a working memory fMRI task by increasing the magnitude of some frontoparietal networks’ activity and changing regional functional connectivity across the brain [3]. Insofar as increased connectivity reflects enhanced interregional communication, this indicates that the net effect of psychostimulants is to facilitate neurotransmission through long-distance connections between widespread brain regions [3].
For two different cognitive tasks, studying verbal working memory and verbal attention, MPH increased brain activation in ‘dorsal attention network’ areas, and increased deactivation of some ‘default mode network’ areas. Overall, the MPH treated group had increased activation and increased deactivation in brain regions that were moderately activated/deactivated in controls, suggesting that MPH enhanced the BOLD responses similarly for the verbal working memory and verbal attention tasks over control subjects. However, there were no differences in performance accuracy between the control and MPH group [2].
Acronyms
- ADHD
- attention-deficit/hyperactivity disorder
- MPH
- methylphenidate
References
[1] K. Rubia, R. Halari, A.-M. Mohammad, E. Taylor, and M. Brammer. Methylphenidate normalizes frontocingulate underactivation during error processing in attention-deficit/hyperactivity disorder. Biol Psychiatry, 70 (3):255–62, Aug 2011. doi: 10.1016/j.biopsych.2011.04.018.
[2] D. Tomasi and N. D. Volkow. Abnormal functional connectivity in children with attention-deficit/hyperactivity disorder. Biol Psychiatry, 71 (5):443–50, Mar 2012. doi: 10.1016/j.biopsych.2011.11.003.
[3] C. G. Wong and M. C. Stevens. The effects of stimulant medication on working memory functional connectivity in attention-deficit/hyperactivity disorder. Biol Psychiatry, 71(5):458–66, Mar 2012. doi: 10.1016/j.biopsych. 2011.11.011.