IQ-matched Control Subjects Research Articles

Dissociating executive mechanisms of task control following frontal lobe damage and Parkinson's disease.

Twelve patients with focal damage of the frontal cortex and 12 patients with mild, medicated, early stage Parkinson's disease switched between letter- and digit=naming tasks on every second trial of a task-switching paradigm. Compared with age- and IQ-matched control performance, patients with left-sided, but not right-sided, frontal damage exhibited markedly increased time costs associated with these predictable switches only when there was a general incidence of interference or 'crosstalk' between the tasks, and particularly so when the available task cues were relatively weak and arbitrary. The same patients also showed evidence of an increased sensitivity to the facilitatory and inhibitory effects of previous processing, when required to switch between tasks. Both groups of patients (with left- or right-sided frontal damage) exhibited slow, disorganized performance early in practice. In contrast to these frontal effects, the Parkinson's disease patients showed little indication of larger time costs of task switches but they did show progressive increases in the error costs, while age- and IQ-matched control subjects showed reductions. We propose that while both left and right frontal cortical areas are involved in the organization of cognitive and motor processes in situations involving novel task demands, only the left frontal cortex is involved in the dynamic reconfiguring between already-established task-sets, and specifically, that it is the site of an executive mechanism responsible for the modulation of exogenous task-set activity. Finally, dopaminergic transmission, along the nigrostriatal pathway, may be implicated in sustaining various cognitive and motor processes over prolonged periods, including the operation of those executive control mechanisms that accomplish reconfiguring between task-sets.

Neuroanatomy of fragile X syndrome: the temporal lobe.

Fragile X syndrome, an X-linked genetic disorder caused by a mutation in the FMR-1 gene, is associated with a particular profile of abnormalities of behavior, learning, language, and memory, suggesting temporal lobe dysfunction. We undertook a quantitative neuroimaging study investigating the neuroanatomy of the temporal lobe in individuals with the fragile X mutation. The temporal lobe neuroanatomy of 15 young fragile X subjects was quantified and compared with that of 26 age- and IQ-matched control subjects. Analyses showed the right and left hippocampal volumes to be significantly larger in the fragile X group compared with the control group. Subjects with the fragile X mutation showed an age-related increase in volume of the hippocampus an age-related decrease in volume of the superior temporal gyrus. Along with the findings of previous imaging studies of fragile X subjects, the results of the present investigation are consistent with studies showing a nonrandom distribution of expression of the FMR-1 gene in the developing brain, with increased expression in the cerebellum, hippocampus, and specific cortical regions. The results also suggest involvement of temporal lobe regions in the behavioral and cognitive abnormalities associated with fragile X syndrome.

New-Association Priming of Word Identification in Normal and Amnesic Subjects

Subjects took an implicit memory test in which pairs of unrelated words were flashed briefly and the ability to identify the second word of each pair was measured as a function of prior study. In young subjects, identification was better when the second word had been studied compared to when it had not been studied (word-specific priming). Identification was also better when the two words had been paired at study compared to when they had been studied separately (association-specific priming). In amnesic patients, word-specific priming was normal compared to that in age- and IQ-matched control subjects. Association-specific priming was observed, but it was below normal levels. This outcome suggests that the amnesic dysfunction can encompass priming of new verbal associations but spare priming of existing verbal information.

Impaired extra-dimensional shift performance in medicated and unmedicated Parkinson's disease: Evidence for a specific attentional dysfunction

Groups of patients with Parkinson's disease, either medicated, or unmedicated and early in the course, together with age- and IQ-matched control subjects were tested in two paradigms measuring different aspects of selective attention. The first set of tests compared visual discrimination learning following intra- and extra-dimensional shifts, using a “total change” design in which each shift was made in the presence of novel exemplars of the compound stimuli used as discriminanda. The second test consisted of a visual search task in which the number of alternatives was varied. The results of the first experiment showed a selective deficit in both groups of Parkinsonian subjects in their ability to perform an extra-dimensional shift. In the visual search task, the patients were less accurate, but responded with equivalent choice reaction times to those of controls. The results are discussed in terms of the nature of the attentional dysfunction that occurs in Parkinson's disease.