Prenatal manganese biomarkers and operant test battery performance in Mexican children: Effect modification by child sex

BACKGROUND

Manganese (Mn) is essential to healthy neurodevelopment, but both Mn deficiency and over-exposure have been linked to prefrontal cortex (PFC) impairments, the brain region that regulates cognitive and neurobehavioral processes responsible for spatial memory, learning, motivation, and time perception. These processes facilitated by attention, inhibitory control, working memory, and cognitive flexibility are often sexually dimorphic and complex, driven by multiple interconnected neurologic and cognitive domains.

OBJECTIVE

We investigated the role of child sex as an effect modifier of the association between prenatal Mn exposure and performance in an operant testing battery (OTB) that assessed multiple cognitive and behavioral functional domains.

METHODS

Children (N = 575) aged 6-8 years completed five OTB tasks. Blood and urinary Mn measurements were collected from mothers in the 2nd and 3rd trimesters. Multiple regression models estimated the association between Mn biomarkers at each trimester with OTB performance while adjusting for socio-demographic covariates. Covariate-adjusted weighted quantile sum (WQS) regression models were used to estimate the association of a Mn multi-media biomarker (MMB) mixture with OTB performance. Interaction terms were used to estimate modification effect by child sex.

RESULTS

Higher blood Mn exposure was associated with better response rates (more motivation) on the progressive ratio task and higher overall accuracy on the delayed matching-to-sample task. In the WQS models, the MMB mixture was associated with better response rates (more motivation) on the progressive ratio task. Additionally, for the linear and WQS models, we observed a modification effect by child sex in the progressive ratio and delayed matching-to-sample tasks. Higher prenatal Mn biomarker levels were associated with improved task performance for girls and reduced performance in boys.

CONCLUSION

Higher prenatal blood Mn concentrations and the MMB mixture predicted improved performance on two of five operant tasks. Higher prenatal Mn concentrations regulated executive functions in children in a sexually dimorphic manner. Higher prenatal Mn exposure is associated with improved performance on spatial memory and motivation tasks in girls, suggesting that Mn's nutritional role is sexually dimorphic, and should be considered when making dietary and/or environmental intervention recommendations.

Prenatal metal mixture concentrations and reward motivation in children

Reward motivation is a complex umbrella term encompassing the cognitions, emotions, and behaviors involved in the activation, execution, and persistence of goal-directed behavior. Altered reward motivation in children is characteristic of many neurodevelopmental and psychiatric disorders. Previously difficult to operationalize, the Progressive Ratio (PR) task has been widely used to assess reward motivation in animal and human studies, including children. Because the neural circuitry supporting reward motivation starts developing during pregnancy, and is sensitive to disruption by environmental toxicants, including metals, the goal of this study was to examine the association between prenatal concentrations of a mixture of neurotoxic metals and reward motivation in children. We measured reward motivation by administering a PR test to 373 children ages 6-8 years enrolled in the Programming Research in Obesity, Growth, Environment and Social Stressors (PROGRESS) Study in Mexico City. Children were asked to press a response lever for a token reward; one press on the response lever was required to earn the first token and each subsequent token required an additional 10 lever presses. Maternal blood concentrations of lead, manganese, zinc, arsenic, cadmium, and selenium were measured using inductively-coupled plasma mass spectrometry during the 2nd and 3rd trimesters of pregnancy. We performed generalized Weighted Quantile Sum (gWQS) regression analyses to examine associations between the prenatal metal mixture and reward motivation; adjusting for child sex, birthweight and age; and maternal IQ, education, and socioeconomic status. The prenatal metal mixture was significantly associated with higher motivation as indicated by more lever presses (ß = 0.02, p < 0.001) and a shorter time between receiving the reinforcer and the first press (ß = 0.23, p = 0.01), and between subsequent presses (ß = 0.07, p = 0.005). Contributions of different metals to this association differed by trimester and child sex. These findings suggest that children with increased exposure to metal during the 2nd and 3rd trimesters of gestation demonstrate increased reward motivation, which may reflect a tendency to perseverate or hypersensitivity to positive reinforcement.

Acetyl-l-carnitine does not prevent neurodegeneration in a rodent model of prolonged neonatal anesthesia

Many studies have shown that prolonged or repeated use of general anesthesia early in life can cause an increase in neurodegeneration and lasting changes in behavior. While short periods of general anesthesia appear to be safe, there is a concern about the neurotoxic potential of prolonged or repeated general anesthesia in young children. Unfortunately, the use of general anesthesia in children cannot be avoided. It would be a great benefit to develop a strategy to reduce or reverse anesthesia mitigated neurotoxicity. The mechanisms behind anesthesia related neurotoxicity are unknown, but evidence suggests that mitochondrial dysfunction and abnormal energy utilization are involved. Recent research suggests that a class of compounds known as carnitines may be effective at preventing anesthesia related neurotoxicity by influencing fatty acid metabolism in the mitochondria. However, it is unknown if carnitines can provide protection against changes in behavior associated with early life exposure to anesthesia. Accordingly, we evaluated the neuroprotective potential of acetyl-l-carnitine in 7-day old rats. Rat pups were exposed to 6 h of general anesthesia with sevoflurane or a control condition, with and without acetyl-l-carnitine. The oxygenation level of animals was continuously monitored during sevoflurane exposure, and any animal showing signs of hypoxia was removed from the study. Animals exposed to sevoflurane showed clear signs of neurodegeneration 2 h after sevoflurane exposure. The hippocampus, cortex, thalamus, and caudate putamen all had elevated levels of Fluoro-Jade C staining. Despite the elevated levels of Fluoro-Jade C, few behavioral changes were observed in an independent cohort of animals treated with sevoflurane. Furthermore, acetyl-l-carnitine had little impact on levels of Fluoro-Jade C staining in animals treated with sevoflurane. These data suggest that acetyl-l-carnitine may offer little protection again anesthesia related neurotoxicity in fully oxygenated animals.

Sevoflurane exposure has minimal effect on cognitive function and does not alter microglial activation in adult monkeys

Postoperative Cognitive Dysfunction (POCD) is a complication that has been observed in a subset of adult and elderly individuals after general anesthesia and surgery. Although the pathogenesis of POCD is largely unknown, a growing body of preclinical research suggests that POCD may be caused by general anesthesia. A significant amount of research has examined the effects of general anesthesia on neurocognitive function in rodents, yet no studies have assessed the adverse effects of general anesthesia on brain function in adult nonhuman primates. Thus, this study sought to determine the effects of an extended exposure to sevoflurane anesthesia on cognitive function and neural inflammation in adult rhesus macaques. Five adult rhesus macaques (16-17 years of age) were exposed to sevoflurane anesthesia for 8 h and, and micro-positron emission tomography (PET)/computed tomography (CT) imaging and a battery of operant tasks were used to assess the effects of anesthesia exposure on ¹⁸F-labeled fluoroethoxybenzyl-N-(4-phenoxypyridin-3-yl) acetamide ([¹⁸F]-FEPPA) uptake, a biomarker of microglia activation, and aspects of complex cognitive function. Exposure to sevoflurane anesthesia for 8 h did not increase [¹⁸F]-FEPPA uptake in the adult monkey brain. Sevoflurane anesthesia significantly decreased accuracy (mean difference = 22.79) on a learning acquisition task 6 days after exposure [t(3) = 6.92, p =  0.006], but this effect did not persist when measured 1 week and 2 weeks after additional exposures. Further, sevoflurane anesthesia had no impact on performance in 4 additional cognitive tasks. These data suggest that exposure to anesthesia alone may not be sufficient to cause persistent POCD in adult populations.

Single and repeated exposures to the volatile anesthetic isoflurane do not impair operant performance in aged rats

Postoperative Cognitive Dysfunction (POCD) is a complication that can occur in the elderly after anesthesia and surgery and is characterized by impairments in information processing, memory, and executive function. Currently, it is unclear whether POCD is due to the effects of surgery, anesthesia, or perhaps some interaction between these or other perioperative variables. Studies in rodents suggest that the development of POCD may be related directly to anesthesia-induced neuroactivity. Volatile anesthetics have been shown to increase cellular inflammation and apoptosis within the hippocampus of aged rodents, while producing corresponding impairments in hippocampal-dependent brain functions. However, it is unclear whether volatile anesthetics can affect additional aspects of cognition that do not primarily depend upon the hippocampus. The purpose of this study was to use established operant tests to examine the effects of isoflurane on aspects of behavioral inhibition, learning, and motivation in aged rats. Twenty-one adult Sprague-Dawley rats (11 male, 10 female) were trained to perform fixed consecutive number (FCN), incremental repeated acquisition (IRA), and progressive ratio (PR) tasks for a minimum of 15 months prior to receiving anesthesia. At 23 months of age, rats were exposed to 1.3% isoflurane or medical grade air for 2h. Initial results revealed that a 2h exposure to isoflurane had no effect on IRA, FCN, or PR performance. Thus, rats received 3 additional exposures to 1.3% isoflurane or medical grade air: 2, 4 and 6h exposures with 2 weeks elapsing before exposure two, 3 weeks elapsing between exposures two and three, and 2 weeks elapsing between exposures three and four. These additional exposures had no observable effects on performance of any operant task. These results suggest that single and repeated exposures to isoflurane do not impair the performance of aged rats in tasks designed to measure behavioral inhibition, learning, and motivation. This lack of significant effect suggests that the impairments associated with isoflurane exposure may not generalize to all aspects of cognition, but may be selective to tasks that primarily measure spatial memory processes.

Neurodevelopment of children exposed to anesthesia: design of the Mayo Anesthesia Safety in Kids (MASK) study

There is increasing evidence that exposure of developing brains in animals, including nonhuman primates, to commonly-utilized anesthetic agents may cause adverse effects on cognition and behavior. In this paper, we summarize our methodology for a population-based, propensity-matched study to evaluate possible anesthesia-related sequelae in preschool children when evaluated in elementary or high school. A cohort of all children born in Olmsted County, Minnesota between the years 1994 and 2007 who are currently local residents has been identified. Existing medical records are being used to identify all episodes of exposure to general anesthesia prior to the age of 3 years (i.e., prior to their 3rd birthday). Children with multiple, single, and no anesthesia exposure are sampled for testing between the ages of 8 and 12 years or 15 and 19 years during the period 2012-2016. To match children in different exposure groups as closely as possible, sampling is guided by propensity-matching for the likelihood of receiving anesthesia. Selected children are invited to participate in a single 4-hour session of neuropsychological testing, including the National Center for Toxicological Research-Operant Test Battery, which has been used to study anesthetic neurotoxicity in nonhuman primates. The results of this testing will be compared among children with different anesthetic exposure histories. The expected products of this research will be a detailed phenotype of possible anesthetic-associated neurotoxicity in humans, utilizing a robust patient database and neuropsychological testing battery, and the first comparison of effects of anesthetic exposure in children and nonhuman primates performing nearly identical behavioral tasks.

Comparison of delayed matching-to-sample performance in monkeys and children

Although research has consistently demonstrated that accuracy on a variety of memory tasks decreases as delay increases, relatively little research has been conducted to quantify this relationship across development in humans or directly compare rates of forgetting between humans and monkeys. This study utilized a delayed matching-to-sample (DMTS) task to compare the relative contributions of proactive interference and attention on the rate of forgetting in monkeys and children. The performance of 1125 children from four to fourteen years of age and 10 adult rhesus monkeys was compared. For this DMTS task, a shape was displayed on the center one of three press-plates. After a delay, the subjects were required to match the original shape with one of three choice shapes to receive a banana-flavored food pellet for monkeys, or a nickel for children. A modified power function provided an excellent fit for the data for monkeys and children. The forgetting rates in children decreased with age, and the forgetting rates for monkeys were most comparable to those of younger children. The data also suggest that proactive interference did not significantly contribute to the forgetting rates for monkeys or younger children. Further, the monkeys appeared to attend to the task at a level similar to that of younger children as evidenced by the similarities in response latencies. The results from this study indicate that the rate of forgetting in monkeys, as well as the mechanisms underlying this rate, appears to share more similarities with that of younger children than of older children.

Assessing motivation in children using a progressive ratio task

The association of age and sex on the performance of a progressive ratio task was studied in 847 children, ages 4-14 years. Variations of this task have been used extensively with animals and to a lesser extent with humans to study factors that affect aspects of motivation. The participants in this study were required to press a response lever for nickel reinforcers during a 10 min period. One response was required to earn the first nickel and each subsequent nickel required an additional 10 more responses. Older children had a significantly higher breakpoint than younger children. This appeared to be mostly the result of older children having significantly shorter inter-response times than younger children. In addition, boys had significantly higher breakpoints than girls, especially at older ages. The results of this study illustrate that both age and sex influence the performance of this task and thus suggest that age and sex influence aspects of motivation in children. Further, characterization of performance of this task by humans facilitates comparisons with animal models and, thus, enhances its translational utility.

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.

The effect of variable delays on self-control

Five pigeons served as subjects in an experiment that examined the effects of variable as opposed to fixed delays on preference in a self-control paradigm (choice between larger, more delayed and smaller, less delayed reinforcers). Nonindependent concurrent variable-interval schedules were used to measure choice. When delays to the larger, more delayed reinforcers were variable as opposed to fixed, the subjects showed an increased preference for that alternative (the self-control alternative). A series of regressions revealed that the hyperbolic decay model and incentive theory provided poor fits to the data, but a modified version of the generalized matching law provided an adequate fit. Together, consistent with a general prediction made by discounting models, the data supported the conclusion that variable delays can increase self-control. However, specific discounting models were not able to explain the present data well.

WITHDRAWN: Use of Interval Schedules to Examine Motivation and Sustained Attention

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WITHDRAWN: Effects of Reinforcer Type on Performance of Psychological Tasks

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Estimates of the Validity and Utility of the Conners’ Continuous Performance Test in the Assessment of Inattentive and/or Hyperactive-Impulsive Behaviors in Children

This study evaluated the validity and classification utility of the Conners' Continuous Performance Test (CCPT) in the assessment of inattentive and hyperactive-impulsive behaviors in children. Significant, positive correlations between the CCPT parameters and behavioral ratings of ADHD behaviors were hypothesized. In addition, it was hypothesized that the CCPT parameters would perform better than a random test (chance) and show fair to moderate utility of classification across the different indices. Participants were 104 children between 6 and 12 years of age who were referred for evaluation of attention problems. The first hypothesis was not supported. There were no significant, positive correlations between the CCPT parameters and parent and teacher ratings of inattentive and hyperactive-impulsive behaviors. The second hypothesis was only partially supported. The CCPT Overall Index and the Omission Errors (84th percentile cutoff) performed better than a random test; however, the utility of the CCPT Overall Index only ranged from poor to slight. Receiver operating characteristic analyses showed the accuracy of the CCPT to be low. The implications and limitations of this study and future research directions are discussed.

The relationship between behavioral inhibition and time perception in children

PURPOSE

To test one component of Barkley's (1997) model of executive functions by examining the relationship between behavioral inhibition and time perception in children.

METHOD

Correlation analysis was used to determine the relationships between measures of behavioral inhibition and time perception for the entire sample, and for boys (n = 34) and girls (n = 26) separately.

FINDINGS

For both parent and child measures, behavioral inhibition and time perception scores were correlated for the total group and for girls. Child measure of behavioral inhibition and time perception were not correlated for boys.

CONCLUSIONS

The findings of this study support Barkley's theory and indicate a relationship between poor behavioral inhibition and poor time perception in children.

Stimulation of the semicircular canals via the rotary chair as a means to test pharmacologic countermeasures for space motion sickness

OBJECTIVE

Space motion sickness is currently treated pharmacologically with the empiric use of the H1 antihistamine promethazine, but use of this intervention is limited by the side effect of significant sedation. This creates a dilemma, as full cognition is particularly important during the same conditions likely to exacerbate the symptoms of space motion sickness. Using overstimulation of the semicircular canals with a rotary chair as a paradigm for space motion sickness, we evaluated four medications, commonly used for the treatment of terrestrial motion sickness and vertigo, for their efficacy in alleviating the simulated symptoms of space motion sickness.

STUDY DESIGN

Randomized, prospective, double-blind study.

SETTING

Tertiary referral center.

PATIENTS

Healthy male and female volunteers, 18 years of age or older, without history of neurologic or psychiatric disorders, and with no known allergies or any previous adverse reactions to the drugs used.

INTERVENTIONS

Lorazepam 1 mg, meclizine 25 mg, promethazine 25 mg, scopolamine 0.4 mg, or placebo.

MAIN OUTCOME MEASURE

The ability of each treatment to control the nausea and vomiting associated with our paradigm for space motion sickness was evaluated by measuring time of rotation pre- and posttreatment and time of symptom onset pre-and posttreatment.

RESULTS

Only scopolamine effected a mean change in duration of rotation that reached statistical significance when compared with placebo (p <0.008), with a greater than 40% increase in rotation time. Results with promethazine were not statistically significant.

CONCLUSION

Results showed a rank order of efficacy of scopolamine > promethazine > placebo > meclizine > lorazepam. Scopolamine significantly increased rotation time, but none of the treatments resulted in a significant delay to onset of symptoms.

Effects of drug countermeasures for space motion sickness on working memory in humans

Space motion sickness (SMS) is a problem during the first 72 h of space flight and during transitions from different gravity environments. There currently are no effective drug countermeasures for SMS that also accommodate the retention of optimal cognitive function. This creates a dilemma for astronauts because cognitive skills are particularly important during gravity transitions (e.g., take-off and landing). To quantify the cognitive side effects of potential drug countermeasures, an automated delayed matching-to-sample (DMTS) procedure was used to assess visual working memory before and after drug countermeasures (meclizine 25 mg, scopolamine 0.4 mg, promethazine 25 mg, or lorazepam 1 mg, given orally approximately 45 min prior to testing) and/or the induction of SMS by vestibular stimulation in a rotary chair (spinning). Sixty-seven normal healthy volunteers (mean age, in years, 26.6+/-4.8 S.D.; 24 females and 43 males) each participated in two test sessions, one 'off' drug and one 'on' drug. Spinning by itself significantly decreased task accuracy (Acc) and choice response speed, especially at longer recall delays. Meclizine alone had no effect on Acc or speed with or without spinning. Scopolamine alone decreased Acc, and with spinning, slowed speed. Promethazine alone had no adverse effect, but combined with spinning, decreased Acc and speed. Lorazepam alone decreased speed, and with spinning, decreased Acc. The data suggest that, at clinically useful doses, the rank order of the drugs with the best cognitive profiles is meclizine>scopolamine>promethazine>lorazepam.

Developmental aspects of timing behavior in children

This research examined the association of age, sex, and intelligence on the performance of a time production (temporal response differentiation, TRD) task. Variations of this task have been used extensively with both animals and humans to study factors that affect aspects of timing ability. The participants in this study (720 children, ages 5 to 13 years) were required to hold down a response lever for at least 10 s, but no more than 14 s, to receive a nickel. Older children made more correct lever holds and exhibited less variability in the duration of their lever holds than did the younger children. Boys and girls performed similarly on this task, whereas children with higher IQs made more correct lever holds. Young children with below average IQs exhibited increased variability in lever hold duration compared with young children with average and above average IQs. The results of this study illustrate that both age and intelligence influence timing ability. The use of this timing task in children, which also has been widely used in animal models, provides unique opportunities for interspecies comparisons.

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.

The effects of prenatal cocaine exposure on reversal learning using a simple visual discrimination task in rhesus monkeys

The purpose of this research was to determine if adult animals that were exposed to cocaine prenatally would be able to adapt to changes in the rules of reinforcement for a simple discrimination task. Treatment groups included 0.0, 1.0, and 3.0 mg cocaine/kg/day and an escalating-dose group that began treatment at 3.0 mg cocaine/kg/day, after which the dose was increased by 0.5 mg cocaine/kg/day every 2 weeks throughout the pregnancy. All animals performed a color and position discrimination task for food reinforcers for approximately 6 years before the present study. For this task, subjects were presented with colored stimuli that determined the correctness of subsequent position choices: left for red or yellow and right for blue or green. At 7 years of age, the rules for obtaining reinforcement were reversed. Animals exposed to all doses of cocaine showed impaired reversal performance. Further, animals exposed to the escalating doses of cocaine continued to show this impairment for over 285 sessions (about 21/2 years). The number of sessions required by subjects to master these contingency changes indicated that, using a task with which they have an extensive history, cocaine-exposed animals have greater difficulty in adapting to important changes in their environment.

Time perception differences in children with and without ADHD

INTRODUCTION

The purpose of this study was to compare time perception in children with and without attention deficit hyperactivity disorder (ADHD) with use of a time reproduction task.

METHODS

The sample consisted of 60 children (30 with ADHD and 30 without ADHD) ranging in age from 9 to 12 years. Children were asked to watch a light, verbally estimate how long the light was illuminated, and hold a lever in a depressed position for the same amount of time they thought the light was on. Each child participated in 16 trials of 3, 6, 12, or 24 seconds for a total of 64 trials.

RESULTS

Children with ADHD had significantly greater absolute discrepancy scores on the time reproduction task (F(1,58) = 10.878; P <.01) than did children in the control group. In addition, children with ADHD had greater increases in absolute discrepancy scores across time intervals (F(3,174) = 82.08; P <.01).

DISCUSSION

Poor time perception affects the performance of social skills and other adaptive behaviors such as health consciousness and concerns for safety. The findings of this study indicate that children with ADHD have impaired time perception compared with children who do not have ADHD.

Developmental aspects of delayed matching-to-sample task performance in children

The influence of age, sex, and intelligence (IQ) on performance of a delayed matching-to-sample (DMTS) task, commonly used with animals and adult human subjects to study aspects of short-term memory, was examined for 674 children, 5 to 13 years old. The data suggest that younger children were less accurate at short delays and displayed a greater decrease in accuracy as recall delay increased than older children. Children with lower IQs demonstrated consistent impairment in recall of information when compared to children with higher IQs. No significant differences in task performance were observed between boys and girls. These normative data provide insights into the developmental time course of behaviors thought to serve as metrics of short-term memory. These data will be critical for ongoing and future studies in determining whether specific clinical diagnoses, drug treatments, or other risk factors (e.g., perinatal drug exposure, pregnancy complications, exposure to toxicants) are associated with differences on specific aspects of task performance. The use of tasks that are also applicable to animal models provides great opportunities for the conduct of important comparative studies.

Attention deficit/hyperactivity disorder: characteristics, interventions and models

An epidemiological study of Attention Deficit/Hyperactivity Disorder (ADHD) suggests that the prevalence may be two to three times higher than the figure of 3-5% often cited. In addition, the data suggest that both underdiagnosis and overdiagnosis occur frequently. Rodent animal models of ADHD, like the Spontaneously Hypertensive Rat (SHR) and other rat models such as those with chemical and radiation-induced brain lesions and cerebellar stunting, and the Coloboma mouse model exhibit clear similarities with several aspects of the human disorder and should prove useful in studying specific traits. Operant behavioral tasks that model learning, short-term memory and simple discriminations are sensitive to ADHD and methylphenidate has been shown to normalize ADHD performance in a short-term memory task. Recent findings challenge not only the current postulate that response inhibition is a unique deficit in ADHD, but also the concepts of ADHD and its treatment, which presume intact perceptual abilities. Time perception deficits may account, in part, for the excessive variability in motor response times on speeded reaction time tasks, motor control problems and motor clumsiness associated with ADHD. The Multimodality Treatment Study of ADHD (MTA) provided data suggesting that pharmacological interventions that included systematic and frequent follow-up with parents and teachers, with or without psychosocial interventions, are superior to psychosocial interventions or standard community care alone. Additionally, the MTA was one of the first studies to demonstrate benefits of multimodal and pharmacological interventions lasting longer than 1 year. Imaging studies have demonstrated differences in brain areas in children with ADHD: anterior corpus callosum, right anterior white matter, and cerebellar volumes are all decreased in children with ADHD and there is less brain asymmetry in ADHD subjects. Additionally, functional imaging studies, coupled with pharmacological manipulations, suggest decreased blood flow and energy utilization in prefrontal cortex and striatum and the dysregulation of catecholamine systems in persons with ADHD.

The use of timing behaviors in animals and humans to detect drug and/or toxicant effects

Behavioral paradigms applicable for use in both human and nonhuman subjects for investigating aspects of timing behavior are presented with a view towards exploring their strengths, weaknesses, and utility in a variety of experimental situations. Tri-peak, peak interval, differential reinforcement of low rate responding, and temporal response differentiation procedures are highlighted. In addition, the application of timing tasks in preclinical and clinical settings is discussed: pharmacological manipulations are providing information on the neurotransmitters involved and species differences; normative data for children are being developed; and noninvasive imaging procedures are being employed in adult human subjects to explore the involvement of specific brain areas.

Operant test battery performance in children: correlation with IQ

The relationship between intelligence and money-(nickel-)reinforced operant behaviors were compared in 115 six year old children. The Operant Test Battery (OTB) consists of tasks thought to engender responses dependent upon specific brain functions that include motivation, color and position discrimination, learning, short-term memory, and time estimation. OTB endpoints were compared with Full Scale, Verbal and Performance IQ scores. Highly significant correlations were noted between several OTB measures (e.g., color and position discrimination accuracy) and IQ scores, but not in others (e.g., motivation task response rate). The results demonstrate the relevance of these measures as metrics of important brain functions. Additionally, since laboratory animals can readily perform these same tasks, these kinds of behaviors in laboratory animals should be useful in studying the effects of neuroactive/neurotoxic compounds on aspects of cognitive function in animals and in predicting adverse effects of such agents on related brain functions in humans.

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

Behavioral paradigms applicable for use in both human and nonhuman subjects for investigating aspects of working/short-term memory are presented with a view towards exploring their strengths, weaknesses, and utility in a variety of experimental situations. Such procedures can be useful in teasing out specific aspects of mnemonic processes including discrimination, encoding, and retention. Delayed matching-to-position, delayed matching-to-sample (DMTS), and titrating matching-to-sample procedures are highlighted. Additionally, the application of DMTS tasks in preclinical and clinical settings is presented: drug effects on memory processes can be explored preclinically in animal models; normative data have been developed in human populations where they have been used in adults to explore the relationships between mnemonic processes and specific clinical entities such as Parkinsonism, senile dementia of the Alzheimer's type, schizophrenia, and depression. Studies in children indicate that encoding and retention processes improve rapidly in the early years, plateauing prior to puberty. Noninvasive imaging techniques such as positron emission tomography (PET) indicate that activity in specific brain areas is associated with DMTS task performance and may serve to confirm roles for such structures in mnemonic processes.

Cocaine decreases self-control in rats: a preliminary report

Cocaine abuse is often associated with behavior that takes into account short-term, but not long-term consequences. However, there has been no empirical research concerning the effects of cocaine on self-control (choice of a larger, more delayed reinforcer over a smaller, less delayed reinforcer). In the present research, when food-deprived rats repeatedly chose between a larger, more delayed food reinforcer and a smaller, less delayed food reinforcer, chronic intraperitoneal injections of 15 mg/kg cocaine (but not 10 mg/kg fluoxetine) decreased the rats' choices of the larger, more delayed reinforcer. Cocaine can decrease rats' self-control.