Biomedical subjects

Heidi Aase

Publications and source records attributed to Heidi Aase.

7 recordsLinked to original sources

PubMed2006

Moment-to-moment dynamics of ADHD behaviour in South African children.

BACKGROUND: The behaviour of children with Attention-Deficit/Hyperactivity Disorder is characterized by low predictability of responding. Low behavioural predictability is one way of operationalizing intra-individual ADHD-related variability. ADHD-related variability may be caused by inefficient behavioural selection mechanisms linked to reinforcement and extinction, as suggested by the recently published dynamic developmental theory (DDT) of ADHD. DDT argues that ADHD is a basic neurobehavioural disorder, caused by dysfunctioning dopamine systems. For establishing ADHD as a neurobehavioural disorder, findings from studies conducted in Western countries should be replicated in other cultural populations. The present study replicated the study conducted in Norway, with children from the Limpopo province in the Republic of South Africa. METHODS: Boys and girls, aged 6-9 yr, from seven ethnic groups participated. Scores by teachers on the Disruptive Behavior Disorders rating scale defined participation in either ADHD-hyperactive/impulsive (-HI), ADHD-predominantly inattentive (-PI), or ADHD-combined (-C) groups. Children below the 86th percentile were matched on gender and age and comprised the non-ADHD group. The children completed a computerized game-like task where mouse clicks on one of two squares on the screen resulted in delivery of a reinforcer according to a variable interval schedule of reinforcement. Reinforcers were cartoon pictures presented on the screen together with a sound. Predictability of response location and timing were measured in terms of explained variance. RESULTS: Overall, the results replicated findings from Norway. Specifically, the ADHD-C group showed significantly lower predictability of responding than the non-ADHD group, while the ADHD-HI and the ADHD-PI groups were in-between. In accordance with the previous study, response location, but not response timing, was a sensitive behavioural measure. There were no significant gender differences. Cartoon pictures were effective reinforcers as the non-ADHD group showed learning of the task. There was no relation between behavioural predictability and motor functions. CONCLUSION: The present study makes a strong case for ADHD as a basic, neurobehavioural disorder, not a cultural phenomenon, by replicating findings from a wealthy Western country in a poor province of a developing country. The results were, generally, in line with predictions from the dynamic developmental theory of ADHD by indicating that reinforcers were less efficient in the ADHD group than in the non-ADHD group. Finally, the results substantiated ADHD-related variability as an etiologically important characteristic of ADHD behaviour.

Journal Article↗

PubMed2006

Infrequent, but not frequent, reinforcers produce more variable responding and deficient sustained attention in young children with attention-deficit/hyperactivity disorder (ADHD).

BACKGROUND: The underlying behavioral/psychological processes of attention-deficit/hyperactivity disorder are unclear. Motivational factors, related to dopamine dysfunction, may play an important role in the development of the behavioral symptoms. Particularly, infrequent, but not frequent, reinforcers have been suggested to be associated with altered responding and deviant behavior in children with ADHD. The present study was designed to analyze the influence of reinforcement frequency on operationalized measures of hyperactivity, impulsiveness, sustained attention, and response variability. METHODS: Fifty-six boys, half of whom were diagnosed with ADHD, completed a computerized task presented as a game with two squares on the screen. One square was associated with reinforcement. The task required responses by the computer mouse under contingencies alternating between variable interval schedules of short (mean 2 s) and long (mean 20 s) durations. Reinforcers were cartoon pictures and small trinkets. RESULTS: Overall, there was no difference between children with ADHD and comparison children when reinforcers were given frequently. Statistically significant differences on measures of sustained attention and variability, but not hyperactivity and impulsiveness, were found during infrequent reinforcement only. Age effects interacted with group effects on sustained attention, showing that group differences were found in the young children only. Surprisingly, older comparison children showed increased response variability and no learning. CONCLUSIONS: When reinforcers are infrequent, children with ADHD show deficient sustained attention and increased variability in responding. Computer experience may have interfered with measures of hyperactivity and impulsiveness. The unexpectedly poor performance of the older comparison children may have been due to inefficient reinforcers or to verbally governed behavior overruling reinforcer effects. Reinforcer characteristics and experimental procedures are important factors influencing findings in studies investigating motivational factors. The study provides some support for the dynamic developmental theory of ADHD predicting relationships between neurobiological deficits, altered reinforcement mechanisms, and treatment recommendations.

Age Factors↗

PubMed2005

Moment-to-moment dynamics of ADHD behaviour.

BACKGROUND: The behaviour of children with Attention-Deficit/Hyperactivity Disorder is often described as highly variable, in addition to being hyperactive, impulsive and inattentive. One reason might be that they do not acquire complete and functional sequences of behaviour. The dynamic developmental theory of ADHD proposes that reinforcement and extinction processes are inefficient because of hypofunctioning dopamine systems, resulting in a narrower time window for associating antecedent stimuli and behaviour with its consequences. One effect of this may be that the learning of behavioural sequences is delayed, and that only short behavioural sequences are acquired in ADHD. The present study investigated acquisition of response sequences in the behaviour of children with ADHD. METHODS: Fifteen boys with ADHD and thirteen boys without, all aged between 6-9 yr, completed a computerized task presented as a game with two squares on the screen. One square was associated with reinforcement. The task required responses by the computer mouse under reinforcement contingencies of variable interval schedules. Reinforcers were cartoon pictures and small trinkets. Measures related to response location (spatial dimension) and to response timing (temporal dimension) were analyzed by autocorrelations of consecutive responses across five lags. Acquired response sequences were defined as predictable responding shown by high explained variance. RESULTS: Children with ADHD acquired shorter response sequences than comparison children on the measures related to response location. None of the groups showed any predictability in response timing. Response sequencing on the measure related to the discriminative stimulus was highly related to parent scores on a rating scale for ADHD symptoms. CONCLUSION: The findings suggest that children with ADHD have problems with learning long sequences of behaviour, particularly related to response location. Problems with learning long behavioural sequences may ultimately lead to deficient development of verbally governed behaviour and self control. The study represents a new approach to analyzing the moment-to-moment dynamics of behaviour, and provides support for the theory that reinforcement processes are altered in ADHD.

Journal Article↗

PubMed2005

Rodent models of attention-deficit/hyperactivity disorder.

An ideal animal model should be similar to the disorder it models in terms of etiology, biochemistry, symptomatology, and treatment. Animal models provide several advantages over clinical research: simpler nervous systems, easily interpreted behaviors, genetic homogeneity, easily controlled environment, and a greater variety of interventions. Attention-deficit/hyperactivity disorder (ADHD) is a neurobehavioral disorder of childhood onset that is characterized by inattentiveness, hyperactivity, and impulsiveness. Its diagnosis is behaviorally based; therefore, the validation of an ADHD model must be based in behavior. An ADHD model must mimic the fundamental behavioral characteristics of ADHD (face validity), conform to a theoretical rationale for ADHD (construct validity), and predict aspects of ADHD behavior, genetics, and neurobiology previously uncharted in clinical settings (predictive validity). Spontaneously hypertensive rats (SHR) fulfill many of the validation criteria and compare well with clinical cases of ADHD. Poor performers in the five-choice serial reaction time task and Naples high-excitability rats (NHE) are useful models for attention-deficit disorder. Other animal models either focus on the less important symptom of hyperactivity and might be of limited value in ADHD research or are produced in ways that would not lead to a clinical diagnosis of ADHD in humans, even if ADHD-like behavior is displayed.

Animals↗

PubMed2005

A dynamic developmental theory of attention-deficit/hyperactivity disorder (ADHD) predominantly hyperactive/impulsive and combined subtypes.

Attention-deficit/hyperactivity disorder (ADHD) is currently defined as a cognitive/behavioral developmental disorder where all clinical criteria are behavioral. Inattentiveness, overactivity, and impulsiveness are presently regarded as the main clinical symptoms. The dynamic developmental behavioral theory is based on the hypothesis that altered dopaminergic function plays a pivotal role by failing to modulate nondopaminergic (primarily glutamate and GABA) signal transmission appropriately. A hypofunctioning mesolimbic dopamine branch produces altered reinforcement of behavior and deficient extinction of previously reinforced behavior. This gives rise to delay aversion, development of hyperactivity in novel situations, impulsiveness, deficient sustained attention, increased behavioral variability, and failure to "inhibit" responses ("disinhibition"). A hypofunctioning mesocortical dopamine branch will cause attention response deficiencies (deficient orienting responses, impaired saccadic eye movements, and poorer attention responses toward a target) and poor behavioral planning (poor executive functions). A hypofunctioning nigrostriatal dopamine branch will cause impaired modulation of motor functions and deficient nondeclarative habit learning and memory. These impairments will give rise to apparent developmental delay, clumsiness, neurological "soft signs," and a "failure to inhibit" responses when quick reactions are required. Hypofunctioning dopamine branches represent the main individual predispositions in the present theory. The theory predicts that behavior and symptoms in ADHD result from the interplay between individual predispositions and the surroundings. The exact ADHD symptoms at a particular time in life will vary and be influenced by factors having positive or negative effects on symptom development. Altered or deficient learning and motor functions will produce special needs for optimal parenting and societal styles. Medication will to some degree normalize the underlying dopamine dysfunction and reduce the special needs of these children. The theory describes how individual predispositions interact with these conditions to produce behavioral, emotional, and cognitive effects that can turn into relatively stable behavioral patterns.

Adolescent↗

PubMed2005

The control of responsiveness in ADHD by catecholamines: evidence for dopaminergic, noradrenergic and interactive roles.

We explore the neurobiological bases of attention deficit hyperactivity disorder (ADHD) from the viewpoint of the neurochemistry and psychopharmacology of the catecholamine-based behavioural systems. The contributions of dopamine (DA) and noradrenaline (NA) neurotransmission to the motor and cognitive symptoms of ADHD (e.g. hyperactivity, variable and impulsive responses) are studied in rodent and primate models. These models represent elements of the behavioural units observed in subjects with ADHD clinically, or in laboratory settings (e.g. locomotion, changed sensitivity/responsivity to novelty/reinforcement and measures of executive processing). In particular, the models selected emphasize traits that are strongly influenced by mesocorticolimbic DA in the spontaneously hypertensive (SHR) and the Naples high excitability (NHE) rat lines. In this context, the mode of action of methylphenidate treatment is discussed. We also describe current views on the altered control by mesolimbic catecholamines of appropriate and inappropriate goal-directed behaviour, and the tolerance or intolerance of delayed reinforcement in ADHD children and animal models. Recent insights into the previously underestimated role of the NA system in the control of mesocortical DA function, and the frontal role in processing information are elaborated.

Animals↗

PubMed2002

Attention-deficit/hyperactivity disorder (ADHD) behaviour explained by dysfunctioning reinforcement and extinction processes.

Inattentiveness, overactivity and impulsiveness are presently regarded as the main clinical symptoms of attention-deficit/hyperactivity disorder (ADHD). Inattention is, however, a characteristic of most psychiatric disorders. It is argued that the ADHD Inattentive subtype may have heterogeneous origins and be qualitatively different from the ADHD Hyperactive/Impulsive subtype. At the neurobiological level, ADHD symptoms may to a large extent be caused by a dysfunctioning dopamine system: A dysfunctioning meso-limbo-cortical dopamine branch will produce altered reinforcement and extinction processes, on a behavioural level giving rise to deficient sustained attention, hyperactivity, motor and cognitive impulsiveness. A dysfunctioning nigro-striatal dopamine branch will cause 'extrapyramidal' symptoms. Our model disentangles the behaviours usually explained by 'executive functions' into cognitive impulsiveness, motor impulsiveness and deficient motor control. The various dopaminergic branches may not be equally dysfunctional in all individuals with ADHD. Etiologically, dopamine dysfunctioning will probably mainly be genetically determined while sometimes be induced by environmental factors like drugs of abuse or pollutants, which may explain geographical differences in prevalence rates.

Animals↗