L.M.J. de Sonneville

Information processing characteristics in subtypes of multiple sclerosis

The purpose of this study was to evaluate information processing characteristics in patients with multiple sclerosis (MS). We selected 53 patients with MS and 58 matched healthy controls. Using computerized tests, we investigated focused, divided, sustained attention, and executive function, and attempted to pinpoint deficits in attentional control to peripheral or central processing stages. The results substantiate the hypothesis that the slowing of attention-demanding (controlled) information processing underlying more complex cognitive skills is general, i.e. irrespective of type of controlled processing, with MS patients being 40% slower than controls. MS patients may suffer from focused, and divided and sustained attention deficits, as well as from compromised central processing stages, with secondary progressive (SP) patients showing the most extensive range of deficits, closely followed by primary progressive (PP) patients, while relapsing-remitting (RR) patients appear to be much less affected. General slowing appears to be highest in PP and SP type MS patients (50% slower) versus relapsing-remitting MS (24% slower). In contrast to most previous results, (complex) processing speed appeared to be robustly correlated with severity of MS as measured by the expanded disability status scale and with disease duration. Patients did much less differ in accuracy of processing from controls, suggesting the importance of using time strategies in planning everyday life and job activities to compensate for or alleviate MS-related speed handicaps.

Sustained attention and inhibition of cognitive interference in treated phenylketonuria: associations with concurrent and lifetime phenylalanine concentrations

Fifty-seven 7-14-year-old early- and continuously treated phenylketonuria (PKU) patients and 65 matched controls performed a sustained attention task. PKU patients with plasma phenylalanine (phe) levels higher than 360 micromol/l at the time of testing exhibited, compared to controls, lower speed of information processing, a lower ability to inhibit task-induced cognitive interference, less consistent performance, and a stronger decrease of performance level over time. Patients with concurrent phe levels lower than 360 micromol/l did not differ from controls and were significantly better than patients with levels higher than 360 micromol/l. Strong relationships were found with task performance for phe levels during the pre-school years and between ages 5 and 7. These correlations were stronger than those between concurrent phe level and task performance. Significant multiple regression models were found with age accounting for the largest proportion of variance of tempo and tempo fluctuation, and lifetime phe levels (particularly phe level between ages 5 and 7) accounting for the largest proportion of variance of the relative number of inhibition errors and its increase over time. Phe level between ages 5 and 7 also contributed significantly to the variance of tempo and tempo fluctuation. Neuropsychological outcome was independent of IQ. The results indicate that strict dietary adherence during these periods is beneficial to attentional control later in life. We suggest that phe levels should be maintained under 360 micromol/l until approximately age 12, when development of attentional control approaches an adult level.

Motor function under lower and higher controlled processing demands in early and continuously treated phenylketonuria

This study examined motor control in 61 early and continuously treated patients with phenylketonuria (PKU) and 69 control participants, aged 7 to 14 years. The pursuit task demanded concurrent planning and execution of unpredictable movements, whereas the tracking task required a highly automated circular movement that could be planned in advance. PKU patients showed significantly poorer motor control in both tasks compared with control participants. Deficits were particularly observed for younger patients (age < 11 years). Differences between control participants and PKU patients were significantly greater in the pursuit task compared with the tracking task, indicating more serious deficits when a higher level of controlled processing is required. Correlations with historical phenylalanine levels indicated a later maturation of the level of control required by the pursuit task compared with the tracking task.

Face Recognition in Children with a Pervasive Developmental Disorder Not Otherwise Specified

This study investigates the accuracy and speed of face recognition in children with a Pervasive Developmental Disorder Not Otherwise Specified (PDDNOS; DSM-IV, American – Psychiatric Association [APA], 1994). The study includes a clinical group of 26 nonretarded 7- to 10-year-old children with PDDNOS and a control group of 65 normally developing children of the same age. Two computerized reaction time tasks were administered: a face recognition task and a control task designed to measure the recognition of abstract visuospatial patterns. The latter were either easy or difficult to distinguish from a set of alternative patterns. The normally developing children recognized the faces much faster than the hardly distinguishable abstract patterns. The children in the PDDNOS group needed an amount of time to recognize the faces that almost equalled the time they needed to recognize the abstract patterns that were difficult to distinguish. The results suggest that, when processing faces, children with PDDNOS use a strategy that is more attention-demanding and, hence, less automatic or “Gestalt-like” than the one used by the control children. The results are discussed in the light of a theory that explains the development of coherent mental representations.

Short-term dietary interventions in children and adolescents with treated phenylketonuria: Effects on neuropsychological outcome of a well-controlled population

This study addressed two questions: is there an effect of dietary interventions that induce relatively small changes in phenylalanine (Phe) concentration on neuropsychological outcome of early- and continuously treated phenylketonuria (PKU) patients, and are there differences in effects for PKU children and adolescents? To answer the first question, the effect of a short-term dietary intervention (1–2 weeks) was compared for patients whose Phe concentrations increased vs those whose Phe concentrations decreased. Controls were tested twice to control for learning effects. To answer the second question, the effect of dietary interventions was examined in younger patients (aged 7–10 years) and older patients (aged 11–14 years). The effect of dietary interventions was determined with three neuropsychological tasks: one requiring sustained attention; a second demanding maintenance in working memory; and a third in which complex operations were performed in working memory. Relatively small fluctuations in Phe concentration were found to influence neuropsychological task performance of PKU patients. Patients whose Phe concentrations decreased at the second assessment showed generally more improvement than controls. Patients whose Phe concentrations had increased showed minimal improvement or deterioration of task performance. The strongest effects were observed when sustained attention and manipulation of working memory content were required. There were some indications of a greater sensitivity of younger patients to fluctuations in Phe concentration.