Processing Speed Delays Contribute to Executive Function Deficits in Individuals with Agenesis of the Corpus Callosum

University of California, San Francisco, San Francisco, California, United States
Journal of the International Neuropsychological Society (Impact Factor: 2.96). 03/2012; 18(3):521-9. DOI: 10.1017/S1355617712000045
Source: PubMed


Corpus callosum malformation and dysfunction are increasingly recognized causes of cognitive and behavioral disability. Individuals with agenesis of the corpus callosum (AgCC) offer unique insights regarding the cognitive skills that depend specifically upon callosal connectivity. We examined the impact of AgCC on cognitive inhibition, flexibility, and processing speed using the Color-Word Interference Test (CWIT) and Trail Making Test (TMT) from the Delis-Kaplan Executive Function System. We compared 36 individuals with AgCC and IQs within the normal range to 56 matched controls. The AgCC cohort was impaired on timed measures of inhibition and flexibility; however, group differences on CWIT Inhibition, CWIT Inhibition/Switching and TMT Number-Letter Switching appear to be largely explained by slow performance in basic operations such as color naming and letter sequencing. On CWIT Inhibition/Switching, the AgCC group was found to commit significantly more errors which suggests that slow performance is not secondary to a cautious strategy. Therefore, while individuals with agenesis of the corpus callosum show real deficits on tasks of executive function, this impairment appears to be primarily a consequence of slow cognitive processing. Additional studies are needed to investigate the impact of AgCC on other aspects of higher order cortical function.

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    • "On cognitive tasks, their performance is characterized by slow reaction times and processing speed, particularly when processing complex information (Brown et al., 1999; Brown, Thrasher, & Paul, 2001; Hines, Paul & Brown, 2002; Marco et al., 2012). On Wechsler IQ measures, surveys of "
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    ABSTRACT: The role of interhemispheric interactions in the encoding, retention, and retrieval of verbal memory can be clarified by assessing individuals with complete or partial agenesis of the corpus callosum (AgCC), but who have normal intelligence. This study assessed verbal learning and memory in AgCC using the California Verbal Learning Test-Second Edition (CVLT-II). Twenty-six individuals with AgCC were compared to 24 matched controls on CVLT-II measures, as well as Donders' four CVLT-II factors (i.e., Attention Span, Learning Efficiency, Delayed Memory, and Inaccurate Memory). Individuals with AgCC performed significantly below healthy controls on the Delayed Memory factor, confirmed by significant deficits in short and long delayed free recall and cued recall. They also performed less well in original learning. Deficient performance by individuals with AgCC during learning trials, as well as deficits in all forms of delayed memory, suggest that the corpus callosum facilitates interhemispheric elaboration and encoding of verbal information.
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    • "These communicative deficits seem to arise from difficulties in over-riding literal interpretation together with difficulties in using context to infer meaning (Sanders, 1989; Banich and Brown, 2000; Paul et al., 2003; Brown et al., 2005; Huber-Okrainec et al., 2005). Additional deficits in AgCC include impairments in social problem solving (Symington et al., 2010), abstract reasoning (Brown and Paul, 2000), generalization (Solursh et al., 1965) and processing speed (Marco et al., 2012). Overall, AgCC often involves pronounced real-world social impairments similar to those seen in high-functioning people with autism, encompassing diminished social self-awareness (Brown and Paul, 2000), difficulty imagining the social perspective of others (Symington et al., 2010; Turk et al., 2010), poor conversation skills (O'Brien, 1994) and restricted verbal expression of emotional experience (similar to alexithymia; Buchanan et al., 1980; O'Brien, 1994). "
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    ABSTRACT: The corpus callosum, with its ∼200 million axons, remains enigmatic in its contribution to cognition and behaviour. Agenesis of the corpus callosum is a congenital condition in which the corpus callosum fails to develop; such individuals exhibit localized deficits in non-literal language comprehension, humour, theory of mind and social reasoning. These findings together with parent reports suggest that behavioural and cognitive impairments in subjects with callosal agenesis may overlap with the profile of autism spectrum disorders, particularly with respect to impairments in social interaction and communication. To provide a comprehensive test of this hypothesis, we directly compared a group of 26 adults with callosal agenesis to a group of 28 adults with a diagnosis of autism spectrum disorder but no neurological abnormality. All participants had full-scale intelligence quotient scores >78 and groups were matched on age, handedness, and gender ratio. Using the Autism Diagnostic Observation Schedule together with current clinical presentation to assess autistic symptomatology, we found that 8/26 (about a third) of agenesis subjects presented with autism. However, more formal diagnosis additionally involving recollective parent-report measures regarding childhood behaviour showed that only 3/22 met complete formal criteria for an autism spectrum disorder (parent reports were unavailable for four subjects). We found no relationship between intelligence quotient and autism symptomatology in callosal agenesis, nor evidence that the presence of any residual corpus callosum differentiated those who exhibited current autism spectrum symptoms from those who did not. Relative to the autism spectrum comparison group, parent ratings of childhood behaviour indicated children with agenesis were less likely to meet diagnostic criteria for autism, even for those who met autism spectrum criteria as adults, and even though there was no group difference in parent report of current behaviours. The findings suggest two broad conclusions. First, they support the hypothesis that congenital disruption of the corpus callosum constitutes a major risk factor for developing autism. Second, they quantify specific features that distinguish autistic behaviour associated with callosal agenesis from autism more generally. Taken together, these two findings also leverage specific questions for future investigation: what are the distal causes (genetic and environmental) determining both callosal agenesis and its autistic features, and what are the proximal mechanisms by which absence of the callosum might generate autistic symptomatology?
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    • "Il est e ´galement e ´vident que l'ACC peut aller de pair avec un retard mental, ainsi que différents symptômes neurologiques ou psychologiques avec ou sans désordres hyperactifs [46]. Certaines patientes ont présenté des déficiences en matière d'intelligence, de traitement cognitif et sensorimoteur, de facultés attentionnelles, de prise de décision et des fonctions exécutives [23] [18] [19] [27] [35] [6]. L'association entre AVC et ACC manque de clarté. "
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