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

Abstract

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.

Figure 1

Response predictability according to side of the screen. Predictability of consecutive responses according to side of the screen (left or right), depicted as mean explained variance (autocorrelations squared), across segments (Seg. 1–5) and lags (1–5 per segment), for ADHD and non-ADHD groups. Abbreviations: Seg.: segment of session. Lag: number of responses that has to be correlated to the present one, i.e., correlations between response n and n+1 is the first lag, between n and n+2 is the second lag, and so on up to correlations between response n and n+5 being the fifth lag.

Figure 2

Response predictability according to distance from the centre of a square. Predictability of consecutive responses according to distance from the centre of a response square, whether correct or not, to where on the screen the responses were placed. Curves show mean explained variance (autocorrelations squared) across segments (Seg. 1–5) and lags (1–5 per segment), for ADHD and non-ADHD groups. Abbreviations: Seg.: segment of session. Lag: number of responses that has to be correlated to the present one, i.e., correlations between response n and n+1 is the first lag, between n and n+2 is the second lag, and so on up to correlations between response n and n+5 being the fifth lag.

Figure 3

Response predictability according to distance from the centre of the correct target. Predictability of consecutive responses according to distance from the centre of the correct target square to where on the screen the responses were placed. Curves show mean explained variance (autocorrelations squared) across segments (Seg. 1–5) and lags (1–5 per segment), for ADHD and non-ADHD groups. Abbreviations: Seg.: segment of session. Lag: number of responses that has to be correlated to the present one, i.e., correlations between response n and n+1 is the first lag, between n and n+2 is the second lag, and so on up to correlations between response n and n+5 being the fifth lag.

Figure 4

Mean percent correct. Mean percent correct choice of response target across consecutive segments (Seg) for ADHD and non-ADHD groups. Abbreviations: ADHD-C: ADHD combined type; ADHD-HI: ADHD hyperactive/impulsive type; ADHD-PI: ADHD predominantly inattentive type.