Here, we investigated the impact of well-known polymorphisms of the dopamine transporter gene (SLC6A3, DAT) and the catechol- O-methyl-transferase gene (COMT) as well as the serotonin transporter gene (SLC6A4, 5- HTT) on these specific working memory subcomponents in a mixed sample of patients and healthy individuals.
Moreover, few studies have examined whether subcomponents of working memory such as encoding and maintenance of information are differentially affected by these deficits.
There is preliminary evidence from pharmacological studies that the verbal and visuospatial subcomponents of working memory are subject to differential neurotransmitter modulation.
In this way, we assessed the functional integrity (in terms of behavioural outcome) of the brain circuits that underlie these different subcomponents of working memory.
In a large series of studies investigating healthy controls [ 9, 10, 13, 15, 16, 25], psychiatric patients [ 14, 20– 22] and patients with focal brain lesions [ 11], clear brain behaviour relationships could be established between specific brain circuits and subcomponents of working memory in humans.
Consistent with previous work showing 2 distinct P3b subcomponents (Bledowski et al. 2006; Morgan et al. 2008), the P3b at retrieval was divided into 2 peaks at 357 and 555 ms. Analysis of ERP latencies revealed no significant task differences.
This is consistent with recent work showing that in complex tasks, the P3b may consist of 2 subcomponents, thought to reflect stimulus evaluation in posterior brain regions followed by executive processes in prefrontal and parietal areas (Bledowski et al. 2006; Morgan et al. 2008).
The results also point to the multimodal nature of working memory and show how experience can shape the development of its subcomponents.
Work from our group found that the size of the pulvinar, a subcomponent of the thalamus that projects to temporal association and sensory cortices, was reduced in individuals with SPD, as well as schizophrenia patients, while the volume of the mediodorsal nucleus of the thalamus, associated with the prefrontal cortex, was decreased only in the schizophrenia patients [ 23].
Inhibition (interference control), working memory and cognitive flexibility (switching attention) have been proposed as essential subcomponents of EF. 13 The Behaviour Rating Inventory of Executive Function (BRIEF), which was designed to improve the ecological validity of EF assessment, 14 to our knowledge has not been used in studies of cognition in adolescent chronic fatigue.
