Working memory impairments in traumatic brain injury: evidence from a dual-task paradigm

Although many individuals with traumatic brain injury (TBI) perform well on standard neuropsychological tests, they often exhibit marked functional difficulties. The functions which are impaired seem to be analogous to the role of the central executive system (CES) in Baddeley's [Working Memory, 1986, Oxford University Press, New York] widely accepted model of working memory. The purpose of this study was to investigate CES function in individuals with TBI with a dual-task paradigm. We studied 25 non-demented persons who were at various stages in their recovery from severe TBI and compared their performance on a dual-task paradigm to a group of age-matched controls. Our dual-task paradigm measured performance on a simple visual reaction time task both alone (baseline) and during concurrent tasks of articulation or digit span. Subjects were also assessed with other neuropsychological tests of executive function. TBI patients had slower reaction times on the primary task when performed alone (P < 0.05) and greater decrements in performance during dual-task conditions (P < 0.01). They also exhibited significantly greater deficits than control subjects on other measures of executive function. Although correlations between dual-task performance and other executive measures were quite low, principle components analysis suggested that a common factor does exist between these measures. These findings support the conclusion that TBI patients have a working memory impairment that is due to dysfunction of the CES and which may be related to executive function deficits as measured by standard neuropsychological testing.