Organizational problems are an essential part of executive functions.
For a description of executive functions, see ⇒ Organizational difficulties / executive problems In the article ⇒ Overall list of ADHD symptoms by manifestation in the chapter ⇒ Symptoms.
Executive functions are primarily controlled by working memory.
1. The working memory¶
Working memory consists of three memory units that are coordinated by a central entity:
- Processing processor unit (“central executive”)
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DlPFC
- Processes information held in the two memory stores
- Visuo-spatial memory
- Right posterior parietal lobe
- Acoustic-linguistic (“phonological”) memory
- Short-term memory
- Episodic buffer for visuospatial and auditory-linguistic information for processing by the central executive. Storage capacity on average 7 (+/-2) units (Miller’s number)
Transferred to a PC, the central executive could be described as the main processor, the short-term memory as the random access memory (RAM), and the memory stores as different segments of the hard disk.
Working memory in the dlPFC is primarily controlled by dopaminergic and noradrenergic processes. Thereby, predominantly phasic and less tonic dopamine seems to control the processes of working memory.
For example, DA neurons respond phasically to stimuli to be remembered and show no tonic activity during the retention interval, the time during which the information is kept active.
ADHD is characterized by 3 pathways (according to Sonuga-Barke) that neurophysiologically cause symptoms:
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Dopamine deficiency (among others) in dlPFC (working memory)
- Disorganized
- Forgetfulness
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Dopamine deficiency (among others) in the striatum (reinforcement center)
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Motivation problems
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Impulsivity
- Hyperactivity
- Changes in the cerebellum
Whereas in ADHD norepinephrine, like dopamine, is decreased in the PFC, in PTSD norepinephrine is increased in the PFC, which (above a certain level) deactivates the PFC and activates the amygdala, which is why PTSD is typically treated with alpha-1 or beta adrenoreceptor antagonists, which counteract the shutdown of the PFC by too much norepinephrine.
D1 agonists improve, D1 antagonists impair, working memory function. Excessive D1 stimulation, as in acute stress, leads to working memory deficits as does inadequate stimulation.
D2 receptor agonists improve, D2 antagonists impair spatial (not nonspatial) working memory and thereby executive functions in healthy adults.
CRH in general, as well as in PFC in particular, dose-dependently impairs visuospatial working memory, which is particularly impaired in ADHD. Nonspecific CRH receptor antagonists such as selective CRH-1 receptor antagonists remediated the impairment of working memory and were therefore considered by the authors as possible treatment targets in ADHD.
2. Working memory problems in ADHD¶
ADHD correlates with working memory problems, unlike tic disorders.
One study reported that the various components of working memory were impaired with varying frequency (and varying greatly among individuals) in AD()H)S. Around 70% of those affected showed impairment in one of the 3 areas:
- Reordering of the working memory (very often)
- Retaining and rearranging information
- Updating working memory (frequent)
- Active monitoring of incoming information and replacing outdated information with relevant information
- 8% of those affected showed particular strength in this area
- Dual processing (rare)
- Maintaining information during the execution of a secondary task
- 20% of those affected showed particular strength in this area
In the dlPFC, sustained attention is mapped to problem solving. The ADHD symptoms caused by impaired sustained attention therefore correlate with a dysfunction of the dlPFC. Selective attention (distractibility), on the other hand, is located in the dorsal nucleus accumbens.
One long-term study found that working memory problems in ADHD do not diminish in adulthood. In some cases, a worsening of distractibility was noted.
Another study surprisingly found that language acquisition and arithmetic-math skills, which require working memory, were not significantly worse in children with ADHD. However, performance plummeted significantly when those affected believed they were less gifted.
In addition to executive problems, one study also found problems with the Theory of Mind (ToM) in children with ADHD (in contrast to other studies). However, these did not correlate with executive problems, so working memory involvement seemed unlikely. Another study found lowered Theory of Mind abilities in adults with ADHD that correlated with executive problems.
One study found a correlation between working memory impairment and eye movement abnormalities in reading in children with ADHD. Visual scanning of words in reading was discontinuous, uncoordinated, and chaotic. ADHD groups showed higher entropy index among the four categories of saccades than non-affected.
In ADHD, it takes 250 ms for an error in sentence structure to be detected. For non-affected persons, it takes only 100 ms.
Organizational difficulties (disorganization) are further supposed to be frequently related to time perception problems. However, this is not consistent with the neurophysiological correlates of organization problems/executive problems described here (deficits in working memory located in the dlPFC), which differ from the neurophysiological correlates of time (perception) problems, which are primarily located in the cerebellum.
One study found evidence that the cognitive deficits of patients with ADHD measurable with the N-back task are not due to a deficit in working memory but to a disturbance in cognitive state (memory load, task duration, and novel stimuli). ADHD sufferers and controls showed no significant differences in reaction time and accuracy.
- Spatially, adult ADHD patients in the left orbitofrontal area and left frontopolar area (channels 4 and 11) had significantly higher activation levels of oxyHb in the 2-back task and lower activation levels of deoxyHb in the 3-back task than healthy controls (corrected p < 0.05).
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Temporally, adults with ADHD peaked in ROIs earlier than healthy controls.
3. Measurement of working memory problems¶
The problem-solving skills and sustained attention items associated with working memory can be measured with tests.
3.1. Measuring working memory problems with the N-back test¶
Working memory and sustained attention can be tested with the N-back test.
More on this at ⇒ N-back test In the subsection ⇒ Attention and reaction tests in the section ⇒ Tests in the ⇒ article ADHD - diagnostic methods in the section ⇒ Diagnostics.
4. Other executive functions¶
Inhibition (control of the inhibition of reaction)
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PFC right inferior
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Basal Ganglia
Fault detection
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PFC medial
- ACC rostral and the temporoparietal junction
Control of interference (a component of response inhibition)
- ACC
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PFC lateral
-
Cortex parietal
Planning and solving problems
-
DlPFC
- ACC
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OFC
- Motor/premotor areas
correct execution of working memory tasks
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DlPFC
- VlPFC
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Rostral PFC
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Parietal cortex (bilateral and medial-posterior)
Word fluency:
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Phonemic word fluency
Number of words with a given initial letter that a proband can form:
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Frontal regions
- Left motor/premotor regions
- Left or bilateral opercular regions
- Left lateral orbitofrontal regions
- Right dorsolateral regions
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Semantic / categorical word fluency
Number of words a respondent can form from a given semantic category (e.g., animals), regardless of the initial letter
cognitive flexibility
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Cortex inferior parietal
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Superior colliculus
- Thalamus posterior lateral
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Medial frontal regions
- Pre-supplementary motor area
5. Cerebellum damage as a cause of executive problems¶
Children with tumor-related damage to the cerebellum showed significantly more executive problems and social-emotional problems.
