Executive dysfunction

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ADHD's executive dysfunction is milder, generally. ADHD most consistently affects inhibition and sustained attention, while other executive functions are inconsistently affected. ASD, in contrast, affects all executive functions fairly severely.

Attention Deficit Hyperactivity Disorder (ADHD)

Children with ADHD have serious difficulties with EF in so many areas that some psychiatrists and psychologists have proposed renaming this disorder as EF disorder (Parker, 2011) or EF deficit disorder (Barkley, 2012). Many of the executive dysfunctions described earlier are found in children with ADHD including difficulties with priority and time management, planning and organization, initiating and completing tasks in a timely manner, difficulty shifting cognitive set, a high level of procrastination, forgetfulness and poor working memory.

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Autism Spectrum Disorders (ASD)

One of the most consistently replicated cognitive deficits in individuals diagnosed with autism is executive dysfunction. Recent structural and functional imaging work as well as neuropathology and neuropsychology studies provide strong empirical support for the involvement of the frontal cortex in autism (Ozonoff et al., 2004). Several studies comparing children with ASD (autism and Asperger syndrome) with age and IQ matched control groups have demonstrated EF deficits (Happe, Booth, Charlton, & Hughes, 2006). Behavioral similarities between patients with frontal lobe lesions and individuals with ASD led to the notion that some of the everyday social and non-social behaviors seen in individuals with ASD may reflect specific executive dysfunction (Robinson et al., 2009). A review of studies that had explicitly assessed EF skills such as planning ability, mental flexibility, inhibition, generativity and self-monitoring in people with ASD, as compared to a well matched controlled group or standardized test data, reported deficits in each of these domains (Hill, 2004).

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3413474/

The overarching goal of this investigation was to profile EF deficits for two major childhood disorders, ASD and ADHD, compared to children with typical development while not controlling for ADHD symptoms. The initial aim was accomplished by assessing performance using a comprehensive neuropsychological battery of EF measures across six domains (response inhibition, vigilance, working memory, flexibility/shifting, planning and fluency). We confirmed our hypothesis that children with ASD demonstrate pervasive impairment across a broad range of EF tasks. Specifically, children with ASD showed poor performance relative to the typical group in inhibition, working memory, flexibility/shifting and vigilance. The ASD performed more poorly than the ADHD group in regards to inhibition, working memory, and flexibility. There were no significant differences observed on measures of planning and fluency across the groups. As can be seen in Table 3, the ASD group consistently showed more impairment than the control or ADHD group on all of the aforementioned EF measures. Thus, the current investigation supports previous findings that children with ASD demonstrate generalized and profound impairment in EF skills (Geurts et al., 2004; Goldberg et al., 2005). It is also consistent with recent studies in autism reporting working memory deficits (Goldberg et al., 2005; Landa & Goldberg, 2005; Pennington & Ozonoff, 1996; Verte et al., 2006), as well as set-shifting deficits (Hughes, 1994; Ozonoff et al., 2004; Ozonoff & Strayer, 1997; Sergeant et al., 2002). The finding that children with ASD performed more poorly than children with ADHD on measures of flexibility has also been previously reported (Geurts et al., 2004). Conversely, it has been shown that some ASD subjects have less severe and persistent EF deficits than ADHD children (Happe et al., 2006). It appears, however, that the majority of the ASD subjects had Asperger syndrome (81%) compared to the current study in which the majority had autism and few ASD participants had Asperger syndrome (17%). Thus, developmental and diagnostic issues likely serve as important distinctions in EF within ASD.

The ADHD group exhibited deficits in vigilance and response inhibition when compared to the TYP group corroborating our previous findings (Corbett & Constantine, 2006) and consistent with a meta-analytic review showing these as the most consistently reported domains of executive dysfunction in ADHD (Willcutt et al., 2005). Other comparative investigations report similar and specific deficits in inhibition (Geurts et al., 2004; Happe et al., 2006; Pennington & Ozonoff, 1996; Verte et al., 2006). Our ADHD group also showed some impairment in working memory, however, they did not show statistically significant deficits in the remaining areas of EF. The current findings are in contrast to previous studies, which found impairments in working memory, planning, and attentional set-shifting (Kempton et al., 1999; Rhodes et al., 2005, 2006; Vance et al., 2003). Although the sensitivity of some of the measures may be called into question (Goldberg et al., 2005), the results in the current investigation are consistent with the notion that children with ADHD demonstrate variable deficits on neuropsychological measures of EF (Doyle et al., 2000; Pennington & Ozonoff, 1996; Rhodes et al., 2005, 2006; Vance et al., 2003; Willcutt et al., 2005). Further, it was shown that such variability, as in our own investigation, is not attributed to medication (Doyle et al., 2000).

While EF deficits are associated with ADHD, they appear to be merely part of the etiology contributing to the complex cognitive and behavioral profile (Willcutt et al., 2005). In consideration of the heterogeneity, more recent neuropsychological models are emerging suggesting that there may be additive or interactive effects arising from multiple neural networks contributing to the complexity of the symptom profile of ADHD (e.g., (Nigg et al., 2005; Sergeant et al., 2003; Sonuga-Barke, 2005)). Further, it has been suggested that studies of both ADHD and autism need to take into account the overlapping symptoms of these neurodevelopmental disorders (Verte et al., 2006); thus, a more dimensional (symptom profile) rather than a categorical approach (diagnostic grouping) may be warranted (Frazier et al., 2007).

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2683039/

What's the difference between executive dysfunction caused by ASD and executive dysfunction caused by ADHD?