A university-based randomized, placebo controlled research study of Concerta (methylphenidate), examines the effects of methylphenidate in regulating attention lapses.
Research studies on the neurocognitive profiles (memory, attention, executive functioning, etc) of kids with attention-deficit-hyperactivity disorder have one common denominator: there is no unified or common neuropsychological profile that characterizes ADHD. That is, there is no specific pattern of memory, language, attention, etc., deficits that are universally common in kids of ADHD. Such diverse neuropsychological profile reflects the heterogeneity and diversity of ADHD itself. However, there is one finding that is consistently observed in most studies. When compared to non-affected kids, those with ADHD have significantly variable or uneven performance across most tasks. This is noticeable on cognitive tasks that require sustained periods of attention. On these tasks, children with ADHD show marked within-task variability, oscillating between normative and impaired performance. Thus, instead of consistent impaired attention, most kids with ADHD show variable attention, or rapid “lapses” in attention.
Yet, despite the popularity of stimulant medications in the treatment of ADHD, there has been no single randomized, placebo-controlled study on the effects of methylphenidate on lapses of attention. The last issue of the Journal of Abnormal Child Psychology published a very sound study on the effects of methylphenidate on attention problems.
The study was conducted at the University at Buffalo (SUNY) and included 49 children with a diagnosis of ADHD. The sample included 39 boys and 10 girls, age 9 to 12, of average IQ, and average academic achievement. Twenty nine were diagnosed with ADHD-combined type, 8 were diagnosed with ADHD-inattentive type, and 2 were diagnosed with ADHD-hyperactive/impulsive type. All kids were not taking medication at the start of the trials. Specifically, those kids who were taking stimulant medication were asked to stop at least 24 hours prior to the first day, and those who were taking Strattera were asked to stop the medication at least 7 days before the first day (because Strattera takes longer to clear from the body). These kids were randomly assigned to a medication or a placebo condition. The medication consisted of long active Concerta provided at dosages ranging from .3 to .6 mg/kg.
During the testing, the children completed a simple computerized test of attention called the X and O Discrimination Task, which is very sensitive to lapses in attention. Specifically, the kids were presented with either the letter X or the letter O, and they had to respond by pressing two different corresponding keys as fast as possible. The task included 10 practice trials and 100 task trials.
To measure variability the authors focused on the right tail of reaction time distribution. When a child is presented with the X or O the computer records how long it takes the child to respond (in milliseconds). Since ADHD is characterized by variability in attention, the interest in the responses to the X or O task was not really on how how fast the child responded, but instead on how variable the child responded. For example, a child with little variability in responses would look like this:
Note that on the horizontal axis you can see the milliseconds and on the vertical axis you can see the number of times the child responded at each speed. In this example, the child responded 50 times at 500ms, 40 times at 600ms, and 10 times at 700ms. This could be considered a highly stable pattern of performance in that most of the responses were between 500 and 700ms. Now compare that performance to a performance like this:
In this case the responses are still highly stable (all responses within 300ms of each other) but the responses were slower. So this is what you would see if the child was simply slow in responding. Now, compare the two previous graphs to the pattern of responses below:
In this final case, the child was not necessarily slow, but the responses were more variable in that in some trials the child was very fast (in 5 of the trials the child responded within 400ms) while in some trials the child was very slow. Since this type of variability (rather than simple slowness) is commonly observed in ADHD, the authors examined whether Concerta affected the variability in responses during the task.
1. The authors found a significant effect of the medication on speed, and this effect was dose-dependent. That is, those taking the placebo were significantly slower responding to the task than kids taking a low dose of methylphenidate. Furthermore, kids that were taking a low dose of methylphenidate were significantly slower than those taking a high dose of the medication. Therefore, the results show a strong effect of the medication in increasing speed of responding.
2. The authors also found that the medication resulted in a significant reduction in variability (deviation from the mode), however this was not dependent upon dosage. That is, kids who took the medication showed significantly more consistent/stable responses than kids who took the placebo, but there was no difference in response variability between those taking a low vs. a high dosis of methylphenidate.
3. The increase in speed was not at the cost of accuracy. On the contrary, Kids taking the medication were not only faster and less variable than those taking the placebo, but they were also more accurate.
This study thus provides strong empirical support for the effectiveness of Concerta in facilitating attentional processes. Specifically, methylphenidate seems to 1) improve speed of responding (likely by facilitating sensory-motor processing) and 2) reduce variability in performance (likely by reducing lapses in attention).
Now some final thoughts about this study. This study was conducted by an academic team (university-based) and was financed by the National Institutes of Health (NIH)– NOT by the makers of the drug.
Reference: Spencer, S., Hawk, L., Richards, J., Shiels, K., Pelham, W., & Waxmonsky, J. (2009). Stimulant Treatment Reduces Lapses in Attention among Children with ADHD: The Effects of Methylphenidate on Intra-Individual Response Time Distributions Journal of Abnormal Child Psychology DOI: 10.1007/s10802-009-9316-2
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