Our literature review identified ANS dysfunction in individuals with ADHD , more often in the direction of hypo-arousal than hyper-arousal , particularly at rest and during tasks requiring response regulation and sustained attention .
Stimulant medications  increased ANS activity and , in some studies , reinforcers and rewards produced a similar effect , suggesting that ANS function can be modified in ADHD .
Although arousal mechanisms have frequently been found to be atypical in ADHD , these findings usually emerged from indirect behavioural measures which give only a limited underst and ing of arousal dysregulation in this condition .
Caffeine effects on resting-state arousal
OBJECTIVE This study examined the use of caffeine to manipulate arousal level without the confounds associated with task-related activation . From previous work in our laboratory , an increase in skin conductance level ( SCL ) and EEG alpha frequency , together with a global decrease in alpha power , were used as markers of arousal increase , and we sought to identify these effects with caffeine ingestion . METHODS We examined the effect of a single oral dose of caffeine ( 250 mg ) in a r and omised double-blind placebo-controlled repeated- measures cross-over study . Eighteen healthy university students ( mean age 21 years ; 13/18 females ) participated in two sessions 1 week apart . EEG and autonomic data ( SCL , heart rate , systolic and diastolic blood pressure , and respiration rate ) from a 2 min eyes-closed epoch , commencing approximately 30 min after ingestion of caffeine or placebo , were examined . RESULTS Caffeine was associated with increased SCL , a global reduction in EEG power in the alpha b and , and a global increase in alpha frequency . There were no cardiovascular effects . CONCLUSIONS The positive results are consistent with recent electrodermal and EEG studies of arousal and suggest that caffeine may be utilised as a task-free means of manipulating arousal in future investigations . Further work is necessary to clarify the absence of cardiovascular effects , and to integrate those data with emerging conceptualisations of arousal and activation . SIGNIFICANCE The present data support the use of caffeine as a simple tool to explore the role of arousal in both normal and atypical functioning , and this may be useful in determining the validity and importance of supposed hyper- or hypo-arousal in such syndromes as attention-deficit/hyperactivity disorder ( AD/HD )
Our literature review identified ANS dysfunction in individuals with ADHD , more often in the direction of hypo-arousal than hyper-arousal , particularly at rest and during tasks requiring response regulation and sustained attention .
Stimulant medications  increased ANS activity and , in some studies , reinforcers and rewards produced a similar effect , suggesting that ANS function can be modified in ADHD .
Although arousal mechanisms have frequently been found to be atypical in ADHD , these findings usually emerged from indirect behavioural measures which give only a limited underst and ing of arousal dysregulation in this condition .