Stimulant medication improves recognition memory in children diagnosed with attention-deficit/hyperactivity disorder.

The effect of stimulant medication on recognition memory was examined in 18 children with attention-deficit/hyperactivity disorder (ADHD). Recognition memory was assessed using a delayed matching-to-sample task at 6 delays ranging from 1 to 32 s. Each child was tested on 2 separate occasions, once 60 to 90 min after taking stimulant medication and the other at least 18 hr after taking medication. Children performed significantly better on medication than off. Stimulant administration significantly increased accuracy and the number of nickel reinforcers earned. Decreases in observing response latency and correct choice response latency occurred after taking stimulant medication. The results indicate that stimulant medication improved recognition memory for children with ADHD. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Symposium overview: the use of delayed matching-to-sample procedures in studies of short-term memory in animals and humans

The authors examined the hypothesized association between the body burden of polychlorinated biphenyls (PCB) in women and the risk of low birth weight for their infants. In Sweden, a main exposure route for PCBs and other persistent organochlorine compounds is through the consumption of fatty fish from the Baltic Sea (on the Swedish east coast). A previous comparison between a cohort of consumers of large quantities of fish from the Swedish east coast and a reference population, together with a following analysis based on questionnaire data from a case-control study within the east coast cohort, supported the hypothesized association. In 1995, blood samples were collected from the wives and ex-wives of fishermen from the Swedish east coast (n = 192) who had given birth during the period 1973-1991. Cases (n = 57), i.e., infants with low birth weight (1,500-2,750 g), were matched with controls (n = 135; birth weight, 3,250-4,500 g) on gender, parity, and calendar year of birth. The concentration of 2,2',4,4',5,5'-hexachlorobiphenyl (CB-153) in plasma was analyzed; it has been suggested that CB-153 is a relevant biomarker of exposure to PCBs. The concentration of CB-153 in the plasma of mothers during the year of childbirth was "estimated" using some alternative plausible kinetic models. For two alternative estimated exposure datasets, which were focused on separately, an increase in the risk of a low birth weight was observed at a CB-153 concentration of 300 and 400 ng/g lipid weight, respectively (adjusted odds ratios of 2.1 (95% confidence interval (CI) 1.0-4.7) and 2.3 (95% CI 0.9-5.9)). The present results strengthen the findings reported previously for this study population.     

Effect of methylphenidate on motivation in children with attention-deficit/hyperactivity disorder.

The effects of methylphenidate (MPH) on motivation were examined using a progressive ratio (PR) task in children who were prescribed MPH for the treatment of ADHD. Twenty-one children, 7 to 12 years of age, completed two test sessions, one under the effects of medication and one not. During each session, children pressed a lever to earn nickel reinforcers, where the first press resulted in a reinforcer and 10 additional presses were required for each subsequent reinforcer. Children on MPH had a significantly higher breakpoint than when off medication. This MPH-associated increase in the breakpoint manifested as a significant decrease in the interresponse times (IRT). Further, MPH administration resulted in a significant decrease in IRT variability. In contrast, MPH administration had no significant effects on the means and variability of postreinforcement pause duration. These results suggest that MPH increased motivation in children being treated for ADHD. Further, the inability of MPH to significantly reduce postreinforcement pause duration while simultaneously decreasing IRTs suggests that while MPH may increase motivation to perform an ongoing task, it may have little effect on the initiation of that task. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Effect of Methylphenidate on Time Perception in Children With Attention-Deficit/Hyperactivity Disorder.

The effects of methylphenidate (MPH) on performance of a time-production task were studied in 17 children with attention-deficit/hyperactivity disorder who participated in 1 test session on and 1 off MPH. Participants held a response lever down for at least 10 but no longer than 14 s. Administration of MPH had no effect on the number of correct responses or on the mean duration of lever holds. MPH administration significantly decreased timing response variability, increased holds of 10- to 11-s duration, and decreased lever holds of extremely short durations. These results indicate that administration of MPH resulted in more precise timing performance without changing the mean duration of lever holds, suggesting an enhancement in working memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)