2.1.2 Brain chemistry and ADHD
Many neurotransmitters and pathways are thought to be involved in the development of ADHD symptoms. Focusing again on selective attention, acetylcholine is thought to be the most important neurotransmitter for exogenous attention, while dopamine may preferentially contribute to endogenous attention (Mueller et al., 2017). In line with this, changes in acetylcholine (cholinergic) receptor functioning have been found in the few studies that have investigated this in ADHD (Wallis et al., 2009; Johansson et al., 2013). However, research into dopamine functioning in ADHD has been central to most investigations.
Dopamine, along with serotonin and noradrenalin, is one of the monoamine transmitters. These neurotransmitters are produced by neurons making up relatively small areas within the brain, but the axons of these neurons form pathways sending signals to many other brain regions, so the effects of the neurotransmitter can be quite widespread. Certainly, ADHD is not the only condition that dopamine is thought to be involved in. Other mental health conditions in which dopamine may be involved include addiction and psychosis.
In Activity 7 you will explore neurotransmitter pathways and see how these pathways may be involved in ADHD.
Activity 7 Exploring the monoamine neurotransmitters
You should now explore the pathways for the monoamine neurotransmitters dopamine, serotonin, noradrenalin and acetylcholine using the interactive below. Click on each pathway for information about the pathway and structures involved. Make notes about the start and end points of each pathway in order to complete Table 3 that follows.
You should be able to see from Activity 7 that the involvement of various neurotransmitters and brain regions in ADHD is very complex. At present it is not clear what changes, if any, take place in ADHD for all of the different neurotransmitters and brain regions shown in Figure 8. It is likely that, as for other conditions involving brain functioning, altered connectivity between brain networks underlies some of the changes in brain functioning seen in ADHD. Investigating this altered connectivity is extremely complex and is an active area of research into this condition.
As mentioned previously, much research has focused on the involvement of dopamine and the PFC, which will be looked at in more detail in the next section.