Methylphenidate-induced improvements of various measures of attention in adults with attention deficit hyperactivity disorder

Attentional and sensory effects of lowered levels of intrinsic alertness

Low levels of intrinsic alertness are associated with lateralized performance in visual tasks, similar to neglect of the left (ipsilesional) visual hemi-field. However, it is unclear whether reduced alertness produces a specific lateralization of spatial-attentional processes in terms of the prioritization of right- over left-side stimuli, or whether it affects more basic functions of visuo-sensory coding, and/or higher function of the top-down control of selection, of stimuli on the left side. To decide between these alternatives, the present study examined the effects of lowered alertness, induced by a 50-min vigilance task, in a partial-report paradigm of briefly presented letter displays. With only one (unilateral) stimulus in display, no specific hemi-field effects were found under low-alertness conditions, indicating that reduced alertness impairs neither sensory effectiveness nor the top-town control of selection. However, with dual, bilateral stimuli, report accuracy was specifically affected for left-side targets (in subjects who showed comparable performance for both sides under normal-alertness conditions). This pattern can be interpreted in terms of a specific bias in spatial-attentional weighting, where prioritization of stimuli on the right leads to (mild) extinction of targets on the left. Moreover, participants who had a lower general level of alertness also showed a more pronounced re-distribution of weights, evidenced by a more severe imbalance in report accuracy, in a low compared to a normal state of alertness. This suggests that a low general level of intrinsic alertness engenders a specific vulnerability to neglect-like performance with a (mild) left-side extinction.

Vigilance and sustained attention in children and adults with ADHD

OBJECTIVE

The present article tests the hypothesis of a sustained attention deficit in children and adults suffering from ADHD.

METHOD

Vigilance and sustained attention of 52 children with ADHD and 38 adults with ADHD were assessed using a computerized vigilance task. Furthermore, the attentional performance of healthy children (N = 52) and healthy adults (N = 38) was examined.

RESULTS

Children and adults with ADHD performed significantly less well in the vigilance task than healthy participants (main effect for group). Furthermore, children and adults showed a significant decrease of performance over time (time-on-task effects). However, there was no greater decrement of performance with the passage of time in patient groups than in control groups (group-by-time interaction).

CONCLUSION

The present results do not support the hypothesis of a sustained attention deficit in children and adults with ADHD.

Methylphenidate improves performance on the radial arm maze in periadolescent rats

Methylphenidate (Ritalin; MPD) is one of the most commonly prescribed drugs in childhood and adolescence and many clinical studies have documented its efficacy. Due to the limitations of conducting invasive research in humans, animal models can be beneficial for studying drug effects. However, few animal studies have demonstrated the effects of methylphenidate on cognitive processes. The objective of this study was to find a dose of methylphenidate that was effective in improving performance on a spatial working memory cognitive task when administered orally to periadolescent rats. Therefore, we dosed subjects with methylphenidate at 1 or 3 mg/kg/day via gastric intubation from postnatal day 22 to 59 and assessed the effects of the drug on performance on the radial arm maze each day. To enhance performance overall, a second experiment was conducted where the subjects were moderately food restricted (to 90% of the free-feeding weight). Results of Experiment 1 show that during the first week of testing only the 3 mg/kg MPD-treated males showed improved performance (entries prior to repeated entry) when ad lib fed and housed in pairs while the same dose significantly improved performance in both males and females under conditions of food-restriction and individual housing in Experiment 2. MPD also produced a pattern of increased errors and arms entered during the first week, especially in Experiment 2. MPD increased locomotor activity when tested at postnatal day 60 in both experiments. The data suggest that 3 mg/kg oral methylphenidate improves performance on a spatial cognitive task only early in treatment in the rat. While males show improvement under conditions of both high and low motivation, females only show MPD effects when highly motivated. Hypothetically, methylphenidate may improve radial arm maze performance through increased attention and improved spatial working memory and/or alterations in locomotion, reactivity to novelty or anxiety. Regardless, the study supports the utility of the rat as a suitable model to examine the effects of low dose oral MPD.

Effects of methylphenidate in ADHD adults on target evaluation processing reflected by event-related potentials

Attention deficit/hyperactivity disorder (ADHD) is a widely examined disease in childhood. There is evidence that the disease responds well to medication with methylphenidate (MPH). The effect of MPH in adults with ADHD is a question that is often raised, because many adults request such therapy today. As yet, there is a lack of studies on event-related potentials (ERPs) and MPH in ADHD adults. In the present study we examined 10 adults diagnosed with ADHD, with and without MPH medication (30 mg daily), by means of ERP in a visual Go/NoGo experiment to gain information about target evaluation processing in these patients and about the effects on these attentional processes during medication with MPH. Visually, there seem to be differences in the frontal electrodes for the N2 and in the parietal electrodes for the P300. But these differences do not achieve statistical significance. There are also no statistically relevant differences for the N1 or the slow wave. MPH does not seem to have an effect on target evaluation processing, when comparing the ERPs of non-medicated and medicated ADHD adults. Especially the P3 does not appear to be modulated by medication with MPH in these ADHD adults, in contrast to findings in ADHD children.