Children with attention deficit hyperactivity disorder or ADHD (formerly known also as ADD) are classically seen as the kids in class who have trouble staying in their seats and paying attention during long lessons. Underlying these problematic behaviors is a confluence of factors, with evidence pointing to genetics, neural function, and environmental factors (including parenting and lead exposure), which all can affect ADHD behavior. Many children diagnosed with ADHD seem to simply “grow out” of their symptoms. They may learn particularly effective strategies for managing inattention and disorganization (I myself am a notorious list maker), or learn to control some of the fidgeting and restlessness or channel that energy into sports or other activities.
Scientists who want to find the source of inattention, hyperactivity, and impulsivity try to use measures that more directly approximate brain activity. Therefore, neurocognitive tests, presumably linked to specific functions in the brain, may help to gain insight into the causes of ADHD. These tests vary widely, and measure things like the response speed, planning, memory capacity, and the extent to which someone chooses a smaller reward now or a larger rewards later.

One recent neurocognitive study asked children with and without ADHD to pay attention to a series of word lists with 12 words each, after which they would have to tell an examiner all of the words they could remember. This type of task requires you to try to hold as many ideas in place at one time, which can be very difficult. Most adults can usually hold between 5 and 9 items in their working memory. This explains why the number of digits in phone numbers around the world tends to be about that length. So asking people how many words they can remember of the 12 words could give a pretty good sense at general short term memory capacity. In every day life, the size of our memory storage may not seem essential. What might matter more is which of the many things you actually do recall. For example, if you were going to the grocery store to get supplies for making cookies, it is probably more important to remember ingredients like flour and sugar than something extraneous, like sprinkles. Of course it would be great to remember everything, but certainly some things have more utility to certain tasks.

The researchers in the study described above (full disclosure, I am a co-author on the study) added a feature to the task. Each word on the wordlist was paired with a point value between 1 and 12. For example, bird is paired with 2 points, shoe is paired with 6 points, and clock is paired with 11. You would do best if you could recall all of the words, because that would result in the greatest number of points. However, if you realize that you may not be able to recall all 12 words, it makes sense to try harder to remember the words worth the highest value. So in this case, you should try the hardest to remember clock, followed by shoe, and then bird. Those individuals who are more selective in the words they recall focus strategically on high-value words. Given a memory that can only store a certain number of words, recalling on words worth more points is the most effective strategy. Given that memory capacity (amount of words remembered) and memory efficiency (value of word remembered) are not the same, perhaps figuring out if some individuals have poorer performance in one area versus another can give insight into the neural factors related to behaviors relevant to daily life.

Children with and without ADHD were able to remember the same number of words from the lists – on average each group recalled just over 3 words per list. However, when it came to the memory efficiency, or choosing to remember high value words over lower value words, there was a difference. Children with the Combined Type of ADHD (those with symptoms above the cutoff for inattention and hyperactivity and impulsivity) had significantly worse selective memory than children without ADHD. Typically developing children were more likely to recall the words paired with 10, 11, and 12 – seeing quickly that these words are very important to remember. However, children showing many ADHD symptoms did not have as strong as a response. For some reason, their “high alert” was not activated for high value words the same way it was for the non-ADHD kids, because they were less likely to recall high value words.

This has interesting implications for thinking about ADHD. We know that these individuals are just as capable in remembering information, but what is selected to be remembered could be an issue. The brain areas associated with planning, memory, and decision-making are also implicated in a number of other psychological disorders. Decisions about risk-taking, substance use, and other problematic behaviors may be impaired in children with ADHD compared to their non-ADHD counterparts. A recent analysis looking at the long term outcomes of children with ADHD found that as adolescents and adults, they are more likely to try smoking and marijuana, and more likely to develop substance abuse or depending on nicotine, marijuana, alcohol, cocaine, and other drugs. That being said, there are certainly many healthy and successful adults who had ADHD as children and still have many symptoms. Yet, this group merits further attention for prevention and intervention efforts in the domain of addiction.

Another analysis is provided here.