Response Inhibition in Attention Deficit/Hyperactivity Disorder: Relation of Subtype

Proposal details

Title: Response Inhibition in Attention Deficit/Hyperactivity Disorder: Relation of Subtype
Research Area(s): ADHD and Allied Conditions
Background: Impairments in Response Inhibition (RI) have previously been found in a sample of non-medicated children diagnosed with ADHD without an additional comorbid diagnosis (Houghton et al, 1999). The study found a significantly greater deficit in RI in children diagnosed with the combined subtype compared to a sample of normal controls. The same result was not found however, between controls and ADHD-in. Unfortunately, children diagnosed as ADHD-hyp/imp were not included in the study. These findings were supported by Nigg, Blaskey, Huang-Pollock and Rappley, (2002), who also found the combined subtype to possess significantly greater deficits in inhibitory processing, than ADHD-in. Again however, ADHD-hyp/imp were not represented in this study. Previous research has hypothesised that ADHD-in possess deficits that are less severe than those found in either ADHD-hyp/imp or ADHD-com (Barkley, 1997; Houghton et al, 1999; Nigg et al 2002; Nigg, 2001; Quay, 1997). A prominent theory of ADHD proposed by Barkley (1997), isolates RI as a core deficit of ADHD yet emphasises that this theory is not applicable to ADHD-in; a position that has since gained some empirical support (Houghton et al, 1999; Nigg et al 2002; Quay, 1997). It has been suggested that the inattentive subtype may in fact be a qualitatively different disorder in comparison to the hyperactive/impulsive and combined subtypes; the inattentive subtype being more related to deficits in attention (e.g. sustained, focused attention, etc), while the hyperactive/impulsive and combined subtypes being more related to deficits in RI (Houghton et al, 1999). In an attempt to identify whether or not a deficit in RI exists in the inattentive subtype that is comparable to the hyperactive/impulsive and/or combined subtypes, the aim of this study is to further investigate RI in the three subtypes of ADHD via both electrophysiological and neuropsychological cognitive testing.
Aims: The aim of this study is to assess RI in the three subtypes of ADHD (inattentive, hyperactive/impulsive, and combined), using both electrophysiological and neuropsychological cognitive testing. The question of whether each subtype possesses comparable deficits in RI will be addressed.
Method: Participants will be both male and female aged 6-17 years. All three subtypes of ADHD will be equally represented, along with an age- and sex-matched control group. Paradigms utilised in this study will be: the go/nogo, auditory oddball, verbal interference, choice reaction time, digit span, spot the real word, and switching of attention tasks.