Journal of the International Neuropsychological Society

Research Articles

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

Elysa J. Marcoa1a2a3, Kathryn M. Harrella4, Warren S. Browna4, Susanna S. Hilla1, Rita J. Jeremya4, Joel H. Kramera1a2, Elliott H. Sherra1a3 and Lynn K. Paula4a6 c1

a1 Department of Neurology, University of California, San Francisco, San Francisco, California

a2 Department of Psychiatry, University of California, San Francisco, San Francisco, California

a3 Department of Pediatrics, University of California, San Francisco, San Francisco, California

a4 Fuller Graduate School of Psychology, Travis Research Institute; Pasadena, California

a5 Clinical & Translational Science Institute-Pediatric Clinical Research Center, University of California, San Francisco, San Francisco, California

a6 Division of Humanities and Social Sciences, California Institute of Technology, Pasadena, California


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. (JINS, 2012, 18, 521–529)

(Received September 15 2011)

(Revised January 06 2012)

(Accepted January 06 2012)


c1 Correspondence and reprint requests to: Lynn K. Paul, 1200 E. California Blvd., Caltech, HSS 228-77, Pasadena, CA 91125. E-mail:


Elysa J. Marco and Kathryn M. Harrell contributed equally to this manuscript; Elliott H. Sherr and Lynn K. Paul contributed equally as well.