Measuring inhibitory control in children.

The Stop Signal Task is a measure of inhibitory control in which subjects must press a button in response to a stimulus. On certain trials, the subject receives a second stimulus (the Stop Signal) after the primary stimulus and must withhold his/her response during those trials. The onset of the Stop Signal is varied, sometimes coming immediately after the primary stimulus (inhibition is easy); at other times, the Stop Signal arrives quite late, making inhibition difficult. Results from the Stop Signal Task were obtained from children with attention-deficit/hyperactivity disorder (ADHD) and from controls; children with ADHD had significantly more difficulty inhibiting their responses than did controls. In a second study, results from the Stop Signal Task were obtained from a large sample of both behaviorally disturbed and community children; variables from the Stop Signal Task correlated well with both laboratory observations and teacher ratings of inattention and hyperactivity.

Classical conditioning in children with attention deficit hyperactivity disorder (ADHD) and anxiety disorders: a test of Quay's model.

Quay (1988) put forward a model of childhood mental disorders based on Gray's (1982) theory that there exists within the brain a behavioral inhibition system (BIS), which processes signals related to aversive or punishing stimuli. According to this model, children with attention deficit hyperactivity disorder (ADHD) show lower than optimal levels of activity in this system, which leads to less responsiveness at a physiological level to signals related to punishment. Children with ADHD and controls were compared on a classical conditioning paradigm. Skin conductance and cardiac responses were measured in response to a conditioned stimulus that had been paired with an aversive unconditioned stimulus. There were no differences between the groups, suggesting that, in terms of classical conditioning, ADHD children are equally responsive to signals related to punishment as controls.

Effect of experimental stress on masseter and temporalis muscle activity in human subjects with temporomandibular disorders.

Temporomandibular (TM) disorders have an uncertain aetiology. The purpose of this study was to replicate and extend the work of Yemm (1969) (Archs oral Biol. 14, 873-878, 1437-1439; Br. dent. J. 127, 508-510), who reported a lack of habituation to experimentally induced stress in subjects with TM disorders. In this study, 20 TM disorder patients and 20 controls, matched for age and sex, performed a timed psychomotor task while bilateral masseter and anterior temporalis electromyographic (EMG) activity, finger temperature and skin admittance were monitored. These data were sampled, stored every 4s and averaged by an Apple II Plus/ISAAC interface. A significant trials effect for finger temperature (F[4/152] = 34.99, p less than 0.001) and skin admittance (F[4/152] = 41.90, p less than 0.001) was found, suggesting that the independent variable (stress) had been successfully manipulated. A significant trials by groups effect was found for right temporalis EMG activity (F[3/144] = 3.94, p less than 0.05); the left temporalis showed a similar, but not significant, trend. The masseter muscles did not show differences or trends between groups. No significant differences were found in resting EMG levels or in the initial magnitude of EMG responses during baseline. These results provide support for the hypothesis that TM disorder and control groups respond differently to stress in terms of habituation to stressful stimuli.