Disentangling deficits in adults with attention-deficit/hyperactivity disorder.

Contains fulltext : 48988.pdf (publisher's version ) (Open Access)CONTEXT: A lack of inhibitory control has been suggested to be the core deficit in attention-deficit/hyperactivity disorder (ADHD), especially in adults. This means that a primary deficit in inhibition mediates a cascade of secondary deficits in other executive functions, such as attention. Impaired stopping has been claimed to support the inhibition hypothesis. However, executive functions such as inhibition and attention are hard to disentangle. OBJECTIVE: To use event-related potentials in adult patients with ADHD to show that impaired stopping is associated with abnormalities of attention. DESIGN: The stop signal task was presented to 24 adults with ADHD combined subtype and 24 controls. Stop event-related potentials are distorted by overlap from event-related potentials to other stimuli in close temporal proximity, but we applied a method (Adjar level 2) to effectively remove this overlap. RESULTS: In line with an inhibitory control deficit, the stop signal reaction time was longer in adults with ADHD (F(1,46) = 7.12, P<.01) whereas there was no significant difference for go stimulus reaction time. Overlap-free stop event-related potentials revealed smaller stop P3s in adults with ADHD (F(1,44) = 4.20, P<.05). In children with ADHD, this has been interpreted to reflect deficient inhibitory control. However, controls were also found to have larger early responses in the auditory cortex (N1) when stop signals resulted in successful stops, relative to failed stops, signifying increased attention (F(1,23) = 11.88, P<.01). This difference was completely absent in adults with ADHD. CONCLUSIONS: Disturbed attentional processing of the stop signal contributed to impaired stopping in adults with ADHD. This finding may have implications for treatment

Stopping and changing in adults with ADHD.

Contains fulltext : 48141.pdf (publisher's version ) (Open Access)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

Methylphenidate restores link between stop-signal sensory impact and successful stopping in adults with attention-deficit/hyperactivity disorder.

Contains fulltext : 79579.pdf (publisher's version ) (Closed access)BACKGROUND: The ability to revise one's action plans, as reflected in so-called stopping performance, is of fundamental importance to adaptive behavior. Previous studies in children and adults with attention-deficit/hyperactivity disorder (ADHD) have revealed impaired stopping, which improved after the administration of methylphenidate (MPH). Event-related brain potentials revealed that one crucial mechanism in adequate stopping is the link between the cortical areas that process the signal to stop and the motor system (stop N1). This stop N1 was severely compromised in adults with ADHD. The present study investigates whether methylphenidate can restore the stop N1, in addition to improving stopping performance. The acute effect of a serotonergic reuptake inhibition on these parameters was also assessed. METHODS: Twelve adult combined-type ADHD patients received either placebo, MPH .4 mg/kg or .6 mg/kg, or 20 mg paroxetine in a double-blind, randomized, within-subjects design. RESULTS: The .6 mg/kg dose of methylphenidate improved stopping performance, whereas it did not affect go reaction time (RT). It also restored the stop N1 that was absent under placebo. Methylphenidate reduced a later stop-related potential, the stop P3, which may reflect monitoring of failed stops. Paroxetine had no effect on stopping performance or on stop N1, but it reduced stop P3. CONCLUSIONS: A .6 mg/kg dose of methylphenidate improves stopping performance and directly targets a stop-related brain mechanism that has been reported before to be compromised in a group of ADHD patients. This mechanism was not influenced by acute serotonergic reuptake inhibition

Inhibition in children with attention-deficit/hyperactivity disorder: a psychophysiological study of the stop task.

Item does not contain fulltextBACKGROUND: The purpose of the study was to investigate and identify abnormal brain activity, as revealed by event-related potentials (ERPs) concurring with deficient inhibitory control in children with attention-deficit/hyperactivity disorder (ADHD). METHODS: Performance and ERPs from 16 children with ADHD and 16 control subjects were compared in the stop-signal paradigm. RESULTS: The ADHD children showed a lower inhibition percentage and their (estimated) response time to the stop signal was disproportionally longer compared to the slowing of reaction times to primary-task stimuli. In normal control subjects, fronto-central positivity (100-400 msec) after the onset of the stop-signal was larger in case of successful inhibition, relative to failed inhibition; this was less so in ADHD children. A late positive wave (500-700 msec), maximal at Oz on failed inhibition trials, and possibly related to error-detection, was smaller in ADHD children. CONCLUSIONS: These results point to abnormalities in brain processes involved in motor inhibition and error-detection in ADHD children

Effects of methylphenidate, desipramine, and L-dopa on attention and inhibition in children with Attention Deficit Hyperactivity Disorder.

Contains fulltext : 119536.pdf (publisher's version ) (Closed access)The objective of this study was to investigate the effects of methylphenidate (MPH) on attention and inhibition in children with Attention Deficit Hyperactivity Disorder (ADHD) and to establish what the relative contributions of the noradrenergic and dopaminergic systems to this effect were. In addition to MPH, two other drugs were administered in order to affect both transmitter systems more selectively, L-dopa (dopamine (DA) agonist) and desipramine (DMI) (noradrenaline (NA) re-uptake inhibitor). Sixteen children with ADHD performed a stop-task, a laboratory task that measures the ability to inhibit an ongoing action, in a double-blind randomized within-subjects design. Each child received an acute clinical dose of MPH, DMI, L-dopa, and placebo; measures of performance and plasma were determined. The results indicated that inhibition performance was improved under DMI but not under MPH or L-dopa. The response-time to the stop-signal was marginally shortened after intake of DMI. MPH decreased omission and choice-errors and caused faster reaction times to the trials without the stop-tone. No effects of L-dopa whatsoever were noted. Prolactin levels were increased and 5-HIAA levels were lowered under DMI relative to placebo. It is suggested that the effects of MPH on attention are due to a combination of noradrenergic and dopaminergic mechanisms. The improved inhibition under DMI could be serotonergically mediated