The aim of this study was to clarify which cognitive mechanisms underlie Trail Making Test (TMT) direct and derived scores. A comprehensive review of the literature on the topic was carried out to clarify which cognitive factors had been related to TMT performance. Following the review, we explored the relative contribution from working memory, inhibition/interference control, task-switching ability, and visuomotor speed to TMT performance. Forty-one healthy old subjects participated in the study and performed a battery of neuropsychological tests including the TMT, the Digit Symbol subtest [Wechsler Adult Intelligence Scale (Third Version) (WAIS-III)], a Finger Tapping Test, the Digits Forward and Backward subtests (WAIS-III), Stroop Test, and a task-switching paradigm inspired in the Wisconsin Card Sorting Test. Correlation and regression analyses were used in order to clarify the joint and unique contributions from different cognitive factors to the prediction of TMT scores. The results suggest that TMT-A requires mainly visuoperceptual abilities, TMT-B reflects primarily working memory and secondarily task-switching ability, while B-A minimizes visuoperceptual and working memory demands, providing a relatively pure indicator of executive control abilities. (JINS, 2009, 15, 438–450.)

The Trail Making Test (TMT) has been a useful assessment tool to investigate executive function. Several studies have recently improved the existing TMT norms by mean of large samples of healthy individuals stratified by a number of demographic variables from different populations. In contrast, criticisms have been raised about the utility of norms from healthy samples to detect changes across time in clinical samples where TMT performance used to be altered. In addition, few studies have compared groups of patients with deficits in TMT performance, making it difficult to decide whether a single set of norms is sufficient to assess different clinical populations. We provide normative data from three large samples of patients with traumatic brain injury (TBI) (n=90), schizophrenia spectrum disorders (n=127), and healthy Spanish speakers (n=223). Differences between healthy participants and patients in all TMT direct (TMT-A, TMT-B) and derived (B-A, B:A, B-A/A) scores were found. TMT performance was poorer in TBI patients than in schizophrenia patients except for the B:A and B-A/A scores, suggesting a similar underlying executive deficit. Normal ageing impaired both direct and derived TMT indices, as revealed by lower scores in the healthy elderly group (55-80 years old) as compared with young (16-24) and middle-aged (25-54) healthy participants. Three different sets of norms stratified by age, education, or both are presented for clinical use. Recommendations on TMT scores are made for future research.

The abrupt onset of a novel event captures attention away from, and disrupts, ongoing task performance. Less obvious is that intentional task switching compares with novelty-induced behavioral distraction. Here we explore the hypothesis that intentional task switching and attentional capture by a novel distracter both activate a common neural network involved in processing contextual novelty [Barcelo, F., Periáñez, J. A., & Knight, R. T. Think differently: A brain orienting response to task novelty. NeuroReport, 13, 1887–1892, 2002.]. Event-related potentials were recorded in two task-cueing paradigms while 16 subjects sorted cards following either two (color or shape; two-task condition) or three (color, shape, or number; three-task condition) rules of action. Each card was preceded by a familiar tone cueing the subject either to switch or to repeat the previous rule. Novel sound distracters were interspersed in one of two blocks of trials in each condition. Both novel sounds and task-switch cues impaired responses to the following visual target. Novel sounds elicited novelty P3 potentials with their usual peak latency and frontal-central scalp distribution. Familiar tonal switch cues in the three- and two-task conditions elicited brain potentials with a similar latency and morphology as the novelty P3, but with relatively smaller amplitudes over frontal scalp regions. Covariance and principal component analyses revealed a sustained frontal negative potential that was distorting concurrent novelty P3 activity to the tonal switch cues. When this frontal negativity was statistically removed, P3 potentials to novel sounds and task-switch cues showed similar scalp topographies. The degree of activation in the novelty P3 network seemed to be a function of the information (entropy) conveyed by the eliciting stimulus for response selection, over and above its relative novelty, probability of occurrence, task relevance, or feedback value. We conclude that novelty P3 reflects transient activation in a neural network involved in updating task set information for goal-directed action selection and might thus constitute one key element in a central bottleneck for attentional control.