Biomedical subjects

C C Overtoom

Publications and source records attributed to C C Overtoom.

5 recordsLinked to original sources

PubMed2005

Stopping and changing in adults with ADHD.

BACKGROUND: A lack of inhibitory control has been suggested to be the core deficit in children with attention deficit hyperactivity disorder (ADHD). This means that a primary deficit in behavioral inhibition mediates a cascade of secondary deficits in other executive functions, such as arousal regulation. Clinical observations have revealed that with increasing age symptoms of hyperactivity and impulsivity decline at a higher rate than those of inattention. This might imply that a deficit in attention rather than a lack of inhibitory control is the major feature in adult ADHD. METHOD: To study whether an attentional or inhibitory deficit predominates, the stop-signal task and the stop-change task were presented to 24 adults with ADHD combined subtype and 24 controls. RESULTS: Relative to controls, the stop-signal reaction time (SSRT) was significantly more prolonged than the go-stimulus reaction time (RT) in patients with ADHD. This disproportionate elongation of the SSRT was comparable across tasks, even though the stop-change task exerted more complex (or at least different) demands on the inhibitory system than the stop-signal task. ADHD patients had a higher proportion of choice errors, possibly reflecting more premature responses. Specifically in the stop-change task, patients had more variable choice responses and made more inappropriate change responses, which may also reflect enhanced impulsivity. CONCLUSIONS: The results support a core deficit in behavioral inhibition in adults with ADHD. We further suggest that there is more evidence for a critical role of deficient inhibitory control in adults than in children with ADHD.

Adolescent↗

PubMed2000

The ability to activate and inhibit speeded responses: separate developmental trends.

When children grow older they respond faster and are less susceptible to interference caused by task-irrelevant information. These observations suggested the hypothesis that a global mechanism may account for developmental change in the speed of responding and that inhibitory function may underlie the ability to activate speeded responses. The current study examined these issues by comparing the performance of 4 age groups (5-, 8-, and 11-year-olds and young adults) on a battery of 6 speeded performance tasks, 4 of which required the inhibition of response activation. An analysis of reaction and inhibition times supported a hypothesis of generalized developmental changes in response activation, but revealed a less pronounced development of inhibition. A nonselective mechanism of response inhibition seems to be fully developed during early childhood.

Adult↗

PubMed1998

The continuous performance test revisited with neuroelectric mapping: impaired orienting in children with attention deficits.

A total of 11 children with attention deficit disorder (ADD) and nine control children performed a continuous performance test (CPT) of the A-X type with concurrent neuroelectric brain mapping to assess preparatory processing, purportedly mediated by the frontal lobes. This cued CPT task proved to be a highly specific task. The groups could be clearly differentiated both at the behavioral and electrophysiological level. ADD children detected fewer signals and made more false alarms. There were no major group differences in topographical distribution of the event-related potential microstates, but ADD children displayed reduced global field power (GFP) in an early CNV/P3 microstate to cues. This indicated that impaired orienting to cues, rather than impaired executive target processing, determines the initial processing stages in ADD. In comparison with data from the same task run in Utrecht, the same orienting deficit in clinically diagnosed ADHD children was demonstrated. Low resolution electromagnetic tomography (LORETA) estimated posterior sources underlying these orienting processes and the orienting deficit. This argued against frontal lobe involvement at this stage and suggested involvement of a posterior attention system.

Arousal↗

PubMed1998

Associations between event-related potentials and measures of attention and inhibition in the Continuous Performance Task in children with ADHD and normal controls.

OBJECTIVES: First, to differentiate between inattention and impulsivity based on type of errors made in the AX version of the Continuous Performance Task (CPT), and second, to investigate whether differences in performance between children with attention-deficit hyperactivity disorder (ADHD) and normal controls also occur in specific forms of brain activity, namely event-related potentials (ERPs), presumably related to inattention and impulsivity or inhibition. METHOD: Sixteen ADHD and 16 normal control children performed the CPT-AX. ERPs were recorded at occipital (Oz), parietal (Pz), central (Cz), and frontal (Fz) leads. RESULTS: The ADHD children had a higher CPT-Inattention score and showed smaller parietal positive waves at a latency of approximately 300 msec in reaction to target stimuli, target P3s, likewise indicating less attention. In contrast, they showed neither higher CPT-Impulsivity nor a smaller frontocentral negative wave at about 200 msec (N2); the N2 is generally seen as reflecting inhibition. A subgroup of children with ADHD and oppositional defiant disorder (n = 6) had smaller N2 waves than controls, however. CONCLUSIONS: The ADHD group studied showed deficits in attention but not in impulsivity (or inhibition).

Adolescent↗

PubMed1994

Methylphenidate influences on both early and late ERP waves of ADHD children in a continuous performance test.

Although it has frequently been reported that hyperactive children have abnormally small P3 amplitudes of the event-related potential (ERP), which are normalized by the stimulant drug methylphenidate (MPH), the literature is inconsistent concerning earlier ERP waves. The aim of the present study was to investigate whether the normalizing effect of a 10-mg dose of MPH was also apparent on earlier waves, such as the N1, the P2, and the N2, besides the P3. Twelve attention deficit with hyperactivity disorder (ADHD) children performed a Continuous Performance Test involving a button-press response to the letter X (CPT-X) under the influence of MPH in a double-blind placebo controlled acute dosage design. ERPs were recorded at Oz, Pz, Cz, and Fz. The expected increase of the parietal P3, both to targets and nontargets, was apparent, as well as a significant increase in percentage of hits. There also was a significant increase of an earlier, negative going, wave, the N2, with a frontal maximum, under the influence of MPH. This wave was probably a manifestation of an increase in processing negativity for target stimuli only, after the intake of the stimulant drug. No effect of MPH was found on the N1 or the P2.

Adolescent↗