Distractibility in Attention Deficit/Hyperactivity Disorder Combined and Predominantly Inattentive Subtypes (JINS2006)

Proposal details

Title: Distractibility in Attention Deficit/Hyperactivity Disorder Combined and Predominantly Inattentive Subtypes (JINS2006)
Research Area(s): ADHD and Allied Conditions
Background: Barkley (1997) states that the deficits in Attention Deficit/Hyperactivity Disorder Combined Subtype (AD/HD-com) are characterized by sustained attention and distractibility. Although much research has been conducted on the former using integrative measures of brain function and performance, there has been little work investigating the latter. It has been reported that distractors (highly deviant stimuli embedded in a task) appear to differentiate hyperactive children and controls using behavioural measures (Leung & Connolly, 1996). The P3a (or P300a) ERP component is thought to reflect detection and evaluation novelty processing, and appears maximally over fronto-central regions (Courchesne, Hillyard & Galamos, 1975). It is thought that P3a abnormalities reflect distractibility, although results are inconsistent with regard to whether children diagnosed with AD/HD-com exhibit P3a abnormalities. Jonkaman (1997) reported no difference between AD/HD-com children and controls, whereas in a recent paper Gumenyuk et al. (2005) detailed smaller P3a amplitudes over left fronto-central regions in 10 children diagnosed with AD/HD-com. Gumenyck (2005, p.212) proposed that ‘deficient control of involuntary attention in AD/HD children… may underlie their [children diagnosed with AD/HD-com] abnormal distractibility’. The Predominantly Inattentive Subtype (AD/HD-in) is characterized by deficits in selective attention and focused attention (Barkley, 1997), and thus it would not be expected that abnormalities in the P3a exist (although it has never been investigated). The current study aims to assess distractibility in the Combined and Predominantly Inattentive Subtypes of AD/HD. It will employ integrative assessment measures including the P3a component during a visuo-verbal paradigm, behavioural measures from the paradigm, as well as neuropsychological measures of distractibility from the Switching of Attention and Word Recall Tasks. Moreover, it will assess relationships between the for-mentioned variabilis with measures of arousal including skin conductance latency (SCL) and skin conductance response (SCR). These relationships will allow for the investigation of the cognitive-energetic model of AD/HD (Sergeant, 2000) that specifies that behavioural and psychophysiological deficits apparent in AD/HD are due to a misallocation or lack of allocation of arousal and activation.
Aims: Children and adolescents diagnosed with AD/HD-com will display abnormalities in the strength and speed of novelty processing (as indicated by the P3a). Children and adolescents diagnosed with AD/HD-in will not display abnormalities in the strength and speed of novelty processing (as indicated by the P3a). Children and adolescents diagnosed with AD/HD-com will display greater deficits than those diagnosed with AD/HD-in on neuropsychological measures of distractibility including the Switching of Attention and Word Recall Tasks; although those diagnosed with AD/HD-in are predicted to display some decrease in performance compared to controls due to deficits in selective and focused attention. The correlations between SCR (as a measure of ‘arousal’) and P3a variables (amplitude and latency) will be significant within the control and AD/HD-in groups, and insignificant within the AD/HD-com group. The correlations between SCL (as a measure of ‘activation’) and behavioural/neuropsychological variables will be significant within the control group, however insignificant within the AD/HD-com and AD/HD-in groups.
Method: Subjects: Males and Females diagnosed with AD/HD-in and AD/HD-com between the ages of 6 and 17 years; and age- and sex- matched controls. Psychophysiological data: amplitude and latencies values of the P3a during the Working Memory paradigm. Behavioural data: reaction time (RT), standard deviation of RT (SDRT), false positives (FP) and false negatives (FN) during the WM paradigm. Psychometrics data: all data from the Switching of Attention and Word Recall tasks.