Trail making test errors and executive function in schizophrenia and depression

The Trail Making Test (TMT) frequently is used as a measure of executive cognitive function. However, traditional use of test completion time as the primary outcome score does not give the more detailed information on cognitive processes that analysis of test-taking errors may provide. The present study compared TMT performance of three groups: patients with schizophrenia, patients with major depression, and healthy control participants (n = 30 for each group). Three operationally defined error types were examined: (a) tracking, (b) perseverative, and (c) proximity. Although both patient groups were slower than the healthy control group, only the schizophrenia group made significantly more errors, particularly tracking errors, suggesting a greater degree of cognitive disorganization. Within-group analysis of a larger group of schizophrenia patients (n = 84) revealed that TMT time was most strongly associated with the Withdrawal-Retardation factor of the Brief Psychiatric Rating scale. In contrast, TMT errors were most strongly associated with the Conceptual Disorganization factor. Comparisons of TMT scores and other cognitive tests showed moderate to high associations with tests of working memory, psychomotor speed, and executive function. Stepwise regression analysis revealed an independent association between Digit Cancellation and Part B Time, indicating a unique contribution of visuomotor scanning to performance. In contrast, Part B errors were uniquely associated with the Verbal Series Attention Test and the Token Test, tests of mental tracking and executive-mediated working memory, respectively. These findings demonstrate the utility of TMT error analysis in revealing cognitive deficits not traditionally captured using completion time as the sole outcome variable.