This review discusses whether deficient inhibitory motor control is the core deficit of attention-deficit/hyperactivity disorder (ADHD). Inhibitory motor control is commonly assessed using the stop-signal paradigm. Since the last meta-analysis that was performed, 33 new studies have appeared. The current meta-analysis revealed a significant difference between ADHD patients and matched controls in stop latency (stop-signal reaction time) in both children and adults. Basic reaction time was significantly longer in children with ADHD, but not in adults, and there was a significant interaction between the elongation of the latency to stop and to respond in adults, but not in children. Deficient inhibitory motor control may be less crucial in children than in adults with ADHD.

P50, N100, and P200 auditory sensory gating could reflect mechanisms involved in protecting higher-order cognitive functions, suggesting relationships between sensory gating and cognition. This hypothesis was tested in 56 healthy adults who were administered the paired-click paradigm and two adaptations of the continuous performance test (Immediate/Delayed Memory Task, IMT/DMT). Stronger P50 gating correlated with fewer commission errors and prolonged reaction times on the DMT. Stronger N100 and P200 gating correlated with better discriminability on the DMT. Finally, prolonged P200 latency related to better discriminability on the IMT. These findings suggest that P50, N100, and P200 gating could be involved in protecting cognition by affecting response bias, behavioral inhibition, working memory, or attention.

Introduction-Impulsivity, a component of the initiation of action, may have a central role in the clinical biology of affective disorders. Impulsivity appears clearly to be related to mania. Despite its relationship to suicidal behavior, relationships between impulsivity and depression have been studied less than those with mania. Impulsivity is a complex construct, and it may be related differently to depression and to mania.

Background Impulsivity as a trait characteristic is increased in bipolar disorder and may be a core factor of the illness. We have investigated relationships between trait-like impulsivity, measured by the Barratt Impulsiveness Scale (BIS-11), and demographic and illness-course characteristics of bipolar disorder. Methods We studied 114 subjects with bipolar disorder and 71 healthy comparison subjects. Diagnoses were based on the Structured Clinical Interview for DSM-IV. In addition to impulsivity, we examined age, education, gender, psychiatric symptoms, and characteristics related to course of illness. We used general linear mixed model analysis to evaluate the manner in which the variables contributed to BIS-11 scores. Results All BIS-11 subscale scores were higher in bipolar disorder than in comparison subjects. There were less consistent independent effects of education and age. Elevated BIS-11 scores were associated with early onset, more frequent episodes of illness, and a history of suicide attempts. These relationships persisted when age, gender, and education were taken into account. Discussion These results show that, after accounting for common confounding factors, trait-like impulsivity was substantially higher in subjects with bipolar disorder than in nonbipolar comparison subjects, regardless of symptoms. Within subjects with bipolar disorder, high trait impulsivity was associated with a more severe course of illness.

Background-Pathological impulsivity in bipolar disorder could be related to deficiencies in mechanisms involved in attention or response inhibition. We investigated these mechanisms in subjects with bipolar disorder and examined relationships to severity of course of illness, use of medication, affective state, age, education, and gender. We measured two complementary aspects of response inhibition: attention-based and reward-based.Methods-Subjects with bipolar disorder (n=112) and healthy controls (n=71) were recruited from the community. Diagnoses were rendered using the SCID for DSMIV. Impulsivity-related measures included the Immediate Memory Task (IMT), a form of the Continuous Performance Task, and the Single Key Impulsivity Paradigm (SKIP), an operant procedure measuring ability to delay responding for a reward.Results-Subjects with bipolar disorder had fewer correct detections (Effect Size (ES)=0.5), prolonged reaction times (ES=0.88), and decreased discriminability (ES=0.57) on the IMT compared to controls. History of frequent episodes, substance use disorders, or suicide attempts predicted faster reaction times, especially to a commission error. Subjects with bipolar disorder who also met criteria for an Axis II disorder had fewer correct detections, more commission errors relative to correct detections, and poorer discriminability on the IMT than other subjects with bipolar disorder. Subjects with bipolar disorder made more responses on the SKIP than did controls (ES=0.5), with a shorter maximum delay (ES=0.62), consistent with inability to delay reward. Probit analysis showed that faster reaction time to a commission error on the IMT was associated with history of substance use disorder, suicide attempt, or many previous episodes. Effects of medication or affective state did not account for these differences.Discussion-Bipolar disorder was associated with impairment in attention and response inhibition, encompassing impaired inhibition of rapid responses and an inability to delay reward, and resulting in impulsivity. Response inhibition mechanisms are impaired further in subjects with more severe complications of illness.