Inhibitory control is a way to inhibit attentional or behavioral responses that are prepotent. Barkley (1997a), according to Barkley, inhibitory controls are the foundation of executive function and one of its most important cognitive functions. The brain uses this to correct a behavior. It allows one to refrain from saying something inappropriate when they want to, or to think positively and not negatively. The laboratory has explored inhibitory skills in great detail using experiments including ‘The Marshmallow Experiment. In both situations, you need to resist the urge to eat the marshmallow and read the word. Many psychologists have suggested that the behaviour symptoms of Attention Deficit/Hyperactivity Disorder are caused by a lack of inhibitory control.
This essay seeks to define and explain Attention Deficit/Hyperactivity Disorder before analysing research and examining existing theories for the inhibitory control deficiencies in ADHD. ADHD is an impulsive, hyperactive and inattentive disorder. According to research conducted in westernised cultures, between 3 and 5% of school-aged children exhibit hyperactive and impulsive behaviours that are severe enough to warrant a diagnosis of Attention Deficit Disorder. This is not all. Many children exhibit similar behaviours, but do not meet the criteria for ADHD. These are the most common behavioural issues in children (Barkley 1998). DSM-IV recognizes three types of ADHD: combined, predominantly hyperactive and predominantly inattentive. The combined type requires that a child display six out of nine hyperactivity symptoms and six out of nine inattention symptoms. The child only needs to meet one of the two criteria to be classified as having ADHD. Barkley (1997)a proposed the most comprehensive model. This model focuses on ADHD as a problem with inhibitory control. Barkley also believes that inhibition is the key to all executive functions. He says that one must first inhibit a response to allow for other executive functions to take place. Barkley argues that children with ADHD are more likely to have difficulties with executive functions. He identifies five of these: internalisation of speech, self-regulation, affect, motivation, and arousal. Therefore, he organised his model in a hierarchical way with a reduced inhibitory control at the top, leading to a reduction in other executive functions below it, all leading to an account of the deficits associated with ADHD, as presented in the model as Motor Control/fluency/syntax. Barkley’s Model is by far the best known, however there are many competing theories.
Gray’s Theory of BIS/BAS was presented in 1982. This is an interplay between three systems in neuropsychology: The behavioural activation and inhibition systems (BIS), non-specific arousal, (NAS). The BAS is conditioned to respond to stimuli in order to receive a reward or to relieve punishment. The BIS, on the other hand, responds to stimuli conditioned to experience novelty and punishment. The NAS reacts to punishment and pain without condition, and it is a flight or fight system. Gray (1982), at first, used it to explain anxiety problems that he claimed were due to an overactive BIS. Quay explained the ADHD deficits in 1997 by stating that an underactive BIS was responsible. In 1997, Quay used this theory to explain the deficits in ADHD, suggesting that they are associated with an underactive BIS. 1993). Gray’s explanation of this finding is that BIS is an inhibition system which is tied to punishment and reward. This is a completely different concept to Barkley’s definition of inhibition. Nigg (2000) presents a taxonomy on inhibition that refers to BIS as motivational inhibition, while Barkley’s definition is executive inhibition. It is important to make this distinction, because it means that BIS function can only measured under motivational circumstances.
Rothbarts effortful-control theory is a theory which explains the link between ADHD and a deficit of inhibition. This study evaluates two systems, fear/behavioural inhibiting system and effortful-control. The fear/behavioural system has a modulatory effect via its connections to other systems. This system suppresses reward-oriented behaviours. A system of active control, effortful control regulates itself. It is a way to inhibit a dominant reaction in order to perform a subdominant one. A weakened fear-regulation could lead to impulsive behavior in ADHD. This is because the person cannot control their behaviour by using the system of effortful controls.
Numerous studies have been conducted to support these theories. These studies show that ADHD sufferers are less inhibited. In most cases, the research is based Barkley’s deficit model for ADHD, which shows a lower level of executive inhibition along with a lack of other executive functions. It has been found that ADHD patients have lower levels in impulse control than the control groups, when tested with stop-signal or go/nogo tasks. Dunn, et.al. also conducted two studies. Poor inhibition has been linked to hyperactivity (1998). The interference control was examined – an example of a control which helps to suppress or suppresses irrelevant responses or habits. With external distractions on tasks, ADHDers do not show any difference from control subjects. The performance of those with ADHD is significantly lower than that of those without ADHD when distractions are introduced into the task.
Barkley’s model has many other executive functions that children with ADHD may not be able to perform. Children with AHDH show significant differences when it comes to non-verbal work memory. This was demonstrated through memory tasks for specific locations. Mariani & Barkley (1997) showed that ADHD patients had a problem with verbal working memories by repeating digit spans. Children with severe ADHD have been shown to delay internalisation. Barkley’s model of executive dysfunction is further supported by research that shows significant differences in ADHD and controls when it comes to self-regulation of emotion and verbal proficiency. It is also important to examine the studies in which no significant differences have been found, for example with regards to verbal or working fluency. In addition, it’s important to evaluate Barkley’s theory by considering the studies that did not find significant inhibition group differences.
A number of biological studies have been conducted to support the idea that ADHD is different from the norm. According to the localizationist theory, inhibition is associated with different areas of frontal cortex. This pattern of development is also correlated with the maturational changes of the frontal cortex. Neuroimaging structural and function studies in ADHD subjects show a wide range of abnormalities. Functional imaging studies reveal that ADHD is characterized by a delayed maturation of the cerebral cortex.
I believe that based on the discussion and points that I made, that research in theory, experimentation, and neuroscience generally supports that inhibition is greatly reduced among people with ADHD. There is debate about how this deficit occurs, and further research in this area would be beneficial.
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