By L. Jansons
ADHD is a condition that is diagnosed using behavioral observation. A trained clinician observes a number of hallmark behaviors and arrives at a diagnosis. The clinician often uses a number of subjective opinions to help the diagnostic process since the individual is not always displaying the symptoms in the clinician’s office. Much like how your car doesn’t always make that noise once you bring it into the mechanic. Clinicians will rely on behavior checklists from a teacher, parent, or grandmother who has regular contact with the individual. There are 18 symptoms that can be endorsed to arrive at diagnosis. This is according to our current diagnostic manual, the DSM-IV. What is interesting or actually unfortunate about this process is there is nothing objective going on when we are making this diagnosis.
In fact, Neuropsychology at this time does not offer much by way of helping the clincian arrive at a diagnosis. If anyone has contemplated this, they have realized that the DSM-IV does not mention word-one about objective testing or on neuroanatomical findings. That is, the DSM-IV is not organized by objective test results based on actual brain-behavior relationships. The authors of the DSM-IV have not consulted with the field of neuropsychology. Our current understanding about ADHD is based on a disease-model understanding that implicates the frontal lobes in ADHD. However, what we know now through fMRI studies, there are a number of brain networks involving a number of brain regions, particularly subcortical regions that are conspicuously absent from being mentioned in either the DSM-IV and the newly published DSM-V.
Furthermore, we as clinicians should be thinking about brain architecture in terms of loops of connections rather than landmarks. For example implicated in ADHD, there are cerebro-cortical, cortical-basal ganglia, cerebo-cerebellar and basal ganglia-cerebellar loops. The exact function of each region may be beyond the scope of this writing, however it is important to know the various brain regions are communicating with each other and by far the connections are more than merely cortical.
Also, Yeo and colleagues in 2011 identified seven brain networks. Many of them are dysfunctioning in individuals with ADHD. Networks are seen as distinct, independent and efficient paths of communication among diverse brain regions.
Stevens and colleagues, 2007 and 2009, provided the first description of how multiple neural network dynamics are associated with response inhibition in normal control adolescent and adult subjects in the performance of a “Go-No-Go” task. The Go-No-Go task can be thought of what’s being measured if we were to jump “off sides” at a distracting stimuli. We commit an error. Again, what we are learning, there is not one region in the brain responsible for inhibiting response. When you jump into a conversation and it’s not your turn to speak this would be considered a commission error. There are “loops” of neural communication that lead to disinhibition, in fact there are at least three loops. It’s important to think there is a lot going on when you are inhibiting a response. Using an analogy of a car waiting at a stop light, when the light is red, the car is not “off”, we are always “idling” and anticipating going. The Go-No-Go task measures our ability to select stopping when stopping is required, starting when we need to start and not jumping when we see the turn arrow and we are not turning. These three neural loops are both interdependent and hierarchical. Researchers are discovering there are causal relationships among ensembles of different brain regions and they are temporally independent, that is there is time separating the activation of each network. This may help us understand that there is no one linear cause for disinhibition, alterations in specific connections or brain region could impact psychopathological conditions. That is, disinhibition can be linked to a number of brain regions anywhere along the circuitry.
The three loops involved in response inhibition are: Fronto-striatal-thalamic indirect pathway engagement consistent with modulation of motor function, precentral gyri deactivation concurrent with prefrontal and inferotemporal activation and the frontoparietal circuit activity consistent with higher-order presentations. Essentially, what’s going on: “pay attention there’s something unique going on here, what do I do?”. One must transform senses into actions which involve areas of the brain responsible for object recognition, and selection based on salience and reward value. Executive control and working memory are then engaged and are responsible to execute the proper response which is “do nothing” or “do something”.
Previous studies suggest that the anterior cingulate and other prefrontal brain regions might form a functionally-integrated error detection network in the human brain. In research studies, there are Go-No-Go measures in which correct responses engaged a network comprising left lateral prefrontal cortex, left postcentral gyrus/inferior parietal lobule, striatum, and left cerebellum. So we have definitive brain activation in the networks responsible for a correct response; that is, going when it’s time to go. In contrast, a similar network was uniquely engaged during errors, but this network was not integrated with activity in regions believed to be engaged for higher-order cognitive control over behavior. Then there was a second network identified when “going” was not the correct response. Interestingly, this network was found to be outside of cortical control, that is under the error condition there is evidence that thoughts essentially disconnect or “decouple” from the motor response. We can perhaps relate to this in situations where we tell ourselves, okay I’m going to enter the drive through and order a salad and the next thing we hear ourselves saying, “I’ll have the cheeseburger” as if our higher functioning was temporarily disconnected. There is a third circuit comprised of the anterior temporal lobe, limbic, and pregenual cingulate cortices, possibly representing an affective response to errors. Meaning there is an internal sub-vocal “groan” or “oops” network that activates when we commit an error.
Another finding of the Stevens work is that there were developmental differences in error-processing activity within many of these neural circuits, typically reflecting greater hemodynamic activation in adults. These findings characterize the spatial structure of neural networks underlying error commission and identify neurobiological differences between adolescents and adults.
While this discussion was limited to the understanding of neural network dynamics and ADHD this is only one condition of the many we see in our practices. We at Advanced Neuropsychological Systems have found it astonishing that the Go-No-Go tests are available for research but not available to the clinician. Advanced Neuropsychological Systems is excited to announce that this is another application in the works, quick easy to use software for measuring this “go-no-go” brain circuitry. The software will be available to clinicians from a variety of disciplines including physicians, psychologists, school psychologists, nurses, teachers and those in the legal systems.
Research articles available upon request.