Attention Deficit

I’ve briefly mentioned research studies in the past that find ADHD children have decreased brain volumes (essentially smaller brains) than their peers. Recently, another of these studies was published in the American Journal of Psychiatry (April 2007). Using MRI, the study followed 36 children over two years. How research like this gets published is beyond speculation, but in the publish or perish world of academia, it’s fairly standard trash.

The journal reports that the researchers (a group of MDs and PhDs) “…compared the volumes of each lobe of the cerebellar hemispheres and vermis in children with ADHD and comparison subjects and used a new regional cerebellar volume measurement to characterize the developmental trajectory of these differences.”

Just an anatomical note, the cerebellar vermis is a part of the structure of animal brains. It’s a thin wormlike structure between the hemispheres of the cerebellum. It would take far too long to fully detail the brain structures the researchers have noted as being reduced in volume, but the anatomy is easily available for review on the web.

According to the researchers, the “36 children with ADHD were divided into a group of 18 with better outcomes and a group of 18 with worse outcomes and were compared with 36 matched healthy comparison subjects. The volumes of six cerebellar hemispheric lobes, the central white matter, and three vermal subdivisions were determined from MR images acquired at baseline and two or more follow-up scans conducted at 2-year intervals.”

I’m not bothered by the low number of children in the study. However, we cannot forget that ADHD is a subjective diagnosis. This study, like many others before it, seeks to find some biological marker that might reveal the nature of ADHD. Unfortunately, we have several problems: one, go to any search engine you wish, type in ADHD and then any structure in the brain that you wish, e.g. cerebellum, frontal cortex, basal ganglia, putamen, etc. You’ll find a controlled study indicating that that structure of the brain is diminished in volume, not functioning normally, etc. Apparently, if one takes these studies seriously, the brains of ADHD persons are extraordinarily damaged. Not likely.

The Holy Grail of ADHD is to find a correlation between brain structure and specific dysfunction which would cause ADHD. This is a foolhardy endeavor. Since ADHD is diagnosed through a checklist of symptoms presented over time, it is very likely it is caused by a variety of factors including environment, heredity, etc.

Furthermore, brain structures that are smaller in volume (if this rot could be proven), or function differently, may be related to the manner in which they ADHD person engages with his environment, i.e. the different structures may not have been congenital, but are the direct effect the person’s interaction with their environment. This is a problem of antecedence (chicken and egg). Secondly, until we study several million brains to find out what the ‘normal’ brain looks like among the full spectrum of human traits and personality characteristics, studies of the sort mentioned are simply a house of cards ready to fall.