Monday, February 16, 2009

Nicotine Withdrawal Effects Differ in ADHD Individuals

There is a relatively strong connection between ADHD and drug abuse, with nicotine being one of the most common types of "self-medication". It is believed that ADHD and nicotine addiction share similar neural pathways, although there still remains a fair amount of debate as to the exact underlying mechanisms at work between the two conditions.

One topic of equal intrigue may be the relative effects of withdrawal from nicotine in ADHD vs. non-ADHD individuals. If smoking and ADHD do share overlapping neural pathways, then we might expect that cessation of smoking may have different effects between people with and without ADHD. According to a recent study by Kollins and coworkers on ADHD and smoking abstinence, individuals with ADHD have a much wider array of behaviors with regards to reaction times to specific stimuli and cognitive processing. In other words, smokers with ADHD who temporarily give up nicotine have a greater variety (and hence less predictability) with regards to concentration-related tasks than do non-ADHD smokers. A more detailed explanation of this study follows:
  • Giving up cigarettes and other forms of nicotine has a wide range of negative effects such as working memory, attention, and the ability to control or inhibit ones' responses. However, these effect typically subside when one resumes original smoking behaviors. As a result, based on the negative side effects due to decreased cognitive function, quitting smoking can result in a number of disadvantages with regards to brain function.

  • Many previous studies have shown that individuals with ADHD are more prone to some of these disadvantages, especially with regards to slower reaction times to external stimuli when abstaining from smoking. This may be one of many reasons why smoking is more popular among individuals with ADHD than within the general population.

  • For example, using a special computerized test called Conners Continuous Performance Test, to test for reaction time, comparison studies were done between ADHD and non-ADHD smokers under conditions where they were allowed to smoke and conditions where they were required to abstain from smoking (typically starting the previous night before the morning Continuous Performance Test. Briefly, the test consists of pressing a specific key on a computer keyboard when any letter (except for "X") flashes on the computer screen continuously for a period of approximately 15 minutes. If the letter "X" were to appear on the screen, the test subjects were instructed not to press any keys on the keyboard. Reaction times and accuracies were based on these behaviors.

  • However, based on the study by Kollins and coworkers on smoking abstinence and ADHD, there is a relatively significant amount of evidence that the above point may not entirely be true. Based on the results of their study, Kollins and coworkers suggest that the average impairment with regards to reaction times during smoking cessation may actually be less for most ADHD smokers when compared to non-ADHD smokers. For example, when deprived of smoking, the reaction time of highest frequency for ADHD smokers was somewhere around 0.3 seconds, while the non-ADHD group was slightly slower (but still significant and measurable), hovering around 0.35 seconds. However, the ADHD group is also more likely to have a few individuals who are prone to lengthy delays in reaction times (as in multiple seconds). Kollins instead attributes this to attention lapses in which the individuals concentration was broken. In other words, it appears that while the majority of individuals with ADHD smokers may actually have faster reaction times than non-ADHD smokers, ADHD smokers have more extreme cases of reaction time delays due to attentional lapses, especially when deprived of nicotine. Therefore, by separating out the "common" cases from the more "extreme" cases in their study, Kollins and coworkers may have uncovered this underlying trend.

  • There are several possible causes for these potential attentional lapses due to smoking withdrawal. One may stem from a brain region called the cingulate gyrus, whose approximate location is shown below (region #7, for orignal file source, click here) on the diagram.

The actual area is a specific subsection of this region, but we will not go into the detail here. This region, the cingulate gyrus (#7), is in some ways analogous to a gear shifter in a car. If this brain region is underactive (think of a loose gear shifter), then an individual often bounces around from one thought, idea or focus to the next, which is a common characteristic of ADHD. Lapses in attention have been attributed to subsections of this cingulate region. On the other hand, generalized overactivity in this brain region often leads to excessive fixation on a particular topic, idea or behavior (think of it as pushing too hard on a gear shift and getting stuck in a gear). This latter condition is often seen in dysfunctions such as obsessive compulsive disorder (OCD). With regards to our topic of discussion, Kollins suggests that this brain region may be the culprit for increased attentional lapses in ADHD smokers.

  • Kollins and coworkers also found that when the smokers are "satiated" (i.e. allowed to smoke their desired amounts leading up to the reaction-time test), the ADHD smoking group also had relatively faster reaction times when compared to the non-ADHD smoking group. The ADHD smoking group also had a greater variability in reaction times (i.e. more "extreme cases" or extra-long response times) during satiated conditions, but the differences in variation between these "extreme" cases of ADHD and non-ADHD groups' reaction times were less pronounced than during the nicotine abstinence trials.

  • Finally, it may seem strange that the majority of ADHD smokers appeared to have faster reaction times both with and without smoking. What is even more interesting is that in the nicotine-deprived state, most of the ADHD smokers actually showed a slightly faster reaction time than in the nicotine-satiated state (although the extreme cases of multi-second attention lapses were also greater). One potential explanation of this may be due to the increase in impulsive behaviors, where the individuals attempted to "guess" or predict when the designated letter flashed on the screen (see the previous point about the nature of the Conners Continuous Performance Test). This would be in agreement with fact that nicotine, which is a stimulant and a common form of "self-medication", may help curb impulsive behaviors in ADHD individuals.

  • A final take-home message from this study is that it highlights a relatively common and important trend which we must often consider when dealing with ADHD: studies of ADHD groups which deal with response or reaction times have shown data which is more skewed with a higher variability (and hence a lower predictability) than comparative non-ADHD groups. If study sample numbers are small, these highly variable measurements can sometimes throw off the data and lead researchers to the wrong conclusions. In other words, when doing comparative studies between ADHD and non-ADHD individuals, we must be careful to consider these higher degrees of variability and unpredictability in the ADHD groups and factor these in to our calculations and conclusions accordingly. I will be touching on other cases where we see this significantly greater levels of variability and unpredictability in ADHD in future posts.