Definition

The State Regulation hypothesis states that a non-optimal energetic state could explain performance deficits in children with ADHD. This hypothesis is based on research using the Cognitive Energetic model of Sanders [45, 46]. In this model, the efficiency with which a task is performed is considered to be a product of elementary cognitive stages and their energy distribution. The elementary stages are stimulus encoding, memory search, binary decision and motor preparation [47] and may be seen as structural computational information processes. The availability of these processes is related to the arousal and activation levels of the subject. Arousal is defined as a time-locked phasic physiological response to input, whereas activation refers to a long-lasting voluntary readiness for action [48, 49]. Effort is necessary to meet task demands and to compensate for a sub-optimal state of arousal and/or activation by either activating or inhibiting the arousal and activation levels. The effort system is under control of an evaluation mechanism, which scans the momentary state of the arousal and activation levels. The state regulation theory states that children with ADHD have difficulty in keeping an optimal activation state, possibly due to inefficient extra effort allocation. Using Sternberg's additive factor method (1969), Sergeant and van der Meere (for reviews, see [50–53]) found the encoding, memory search, and decision stages to be intact. However, deficient response organization was noted, especially when stimuli were presented slowly. Later studies also noted that children with ADHD tend to perform more poorly in conditions of relatively slow, compared with fast and moderate event rates. The typically slow and variable response style in ADHD, when stimuli are presented slowly, is a consistent finding in these studies, whereas with respect to errors of commission, findings are mixed [54–57]. The robustness of the response time (RT) event rate effect also remains under sustained attention conditions of more than 30 minutes. Children with ADHD were found to have a rapid decline in task efficiency over time with a slow presentation rate, but not with a fast presentation rate (for a review, see [52]). According to the Cognitive Energetic model, event rate influences the motor activation level. Activation levels increase with an increase in event rate, whereas slow event rates may induce under-activation. To compensate for a sub-optimal activation state, extra effort allocation is necessary. Consequently, the event rate RT findings may suggest that children with ADHD are easily under-activated and have difficulty in adjusting their under-activated state because of insufficient extra effort allocation. Effort allocation has its physiological costs; hence further testing of the state regulation hypothesis may be critically dependent on the development of direct measures of the energetic pools [50]. In this vein, psychophysiological studies have been recently carried out. Children with ADHD showed higher heart rate variability (HRV) in the slow condition only, suggesting less effort allocation [58]. Using the event-related potential (ERP) methodology, Wiersema and colleagues showed that the poor performance of children with ADHD in the slow condition was related to a missing increase of the parietal P3 amplitude [59], which may be an indicator of effort allocation [60, 61]. The same results were found for male adults with ADHD, indicating that problems in state regulation may persist in adult ADHD [62]. In conclusion, several studies indicate that event rate, which has been argued to have its locus in the activation pool, plays an important role in task performance in ADHD. Recent psychophysiological studies underscore the hypothesis of a state regulation deficit in ADHD and highlight the disturbed involvement of the effort pool in ADHD, especially in relation to an under-activated state. Another factor argued to influence energetic state and to optimise performance of children with ADHD is motivation. As Luman et al. (2005) have noted [63], there is clear evidence that motivational factors such as reward and response cost have a positive effect on performance of both typically developing children and children with ADHD. In some studies, however, reward was more beneficial for children with ADHD than for controls [64, 65]. In a recent study, both factors (event rate and incentive) were combined and ADHD was associated with greater improvement in RT variability from baseline to fast-incentive condition [66]. According to the Cognitive Energetic model, effort allocation and motivation are strongly related. Hence, the sensitivity for reinforcement contingencies in children with ADHD would be interpreted, in state regulation terms, as evidence for a lack of effort allocation in ADHD.

Several issues regarding the State Regulation hypothesis remain. Direct supportive evidence for disturbances in the activation pool in ADHD is limited. Only a few studies have tried to directly measure the motor activation pool. Besides the cardiac response studies of Börger and colleagues [58, 67], most of the evidence for disturbed motor activation comes from studies reporting Contingent Negative Variation (CNV) differences [68–70]. Effects in the first CNV (orienting) wave, however, have been reported more often than in the late CNV (motor readiness) and these studies did not include an event rate manipulation. Moreover, as the state regulation model is based on research using the cognitive-energetic model, a distinction is made between arousal and activation. Yet psychophysiological evidence for this distinction is limited and more research is warranted. The higher theta/beta ratio in the EEG signal, often found in ADHD populations (see for review [71]), has been argued by most investigators to be an indication of cortical under-arousal.

Although most evidence suggest that the state regulation problems in children with ADHD are related to under-activation problems, originally it was suggested that activation and performance take an inverted 'U' function where either increases or decreases in activation from an optimal energetic state lead to performance decrements [72]. In order to test whether ADHD is also related to over-activation, more than two conditions of presentation rate should be used: not many studies have done this. Nevertheless, there is some data supporting the inverted 'U' predictions. Children with ADHD were found to have problems with response inhibition in a fast and slow condition, but performed equally well as controls in a medium condition [72]. Sonuga-Barke (2002) [73] found children with ADHD to experience the largest problems with time use on trials with a short and long duration, while they performed equally well in trials with a medium duration. Finally, it is not clear which exact brain areas underlie the state regulation problems in ADHD. Although several brain structures and neurotransmitters have been argued to be associated with the different energetic mechanisms [48, 49] few attempts have been made to investigate this directly.

Does the theory explain all of the symptoms of ADHD?

The state regulation account argues that ADHD symptoms may increase or decrease depending on the child with ADHD's state. For example, symptoms of inattention may appear when tasks are slow or boring. Children may become impulsive or hyperactive in an attempt to increase stimulation (self-stimulation). This may explain findings such as longer RTs, higher intra-subject variability of responding and increased error rates in children with ADHD.

With respect to the specificity of a state regulation deficit in ADHD, the following findings should be emphasised. Performance in adults with High Functioning Autism (HFA) was disproportionally impaired by a fast event rate condition, whereas no difference between groups was noted in a slow condition [74]. Poor RT performance occurred independently of event rate in children with ADHD and comorbid Tic Disorder [72], in children with early- and continuously treated phenylketonuria (PKU) [75, 76], in learning disabled children without ADHD [57], and in children with Mild Mental Retardation plus Conduct Disorder [77].

Is the theory testable?

Crucially, the state regulation account suggests that differences between children with ADHD and typically developing children will be minimal when children with ADHD are in an optimal state. Unfortunately, it is difficult in practice to specify the optimal state as this may be task/context dependent and will also differ between children.

Has a falsifiable hypothesis been stated?

Falsifiable hypotheses have been stated. The specificity of these hypotheses, however, is not always clear. Most evidence suggests that the state regulation problems in children with ADHD are related to under-activation problems, however originally it was suggested that either increases or decreases in activation from an optimal energetic state lead to performance decrements in ADHD [72]. One way to improve the testability of this hypothesised inverted U function, is to incorporate more than two event rates, including an individually-based optimal event rate.