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01-11-2009 | Uitgave 8/2009 Open Access

Inhibition, Reinforcement Sensitivity and Temporal Information Processing in ADHD and ADHD+ODD: Evidence of a Separate Entity?

Tijdschrift:
Journal of Abnormal Child Psychology > Uitgave 8/2009
Auteurs:
Marjolein Luman, Steffen J. P. van Noesel, Alky Papanikolau, Janneke Van Oostenbruggen-Scheffer, Diane Veugelers, Joseph A. Sergeant, Jaap Oosterlaan

Introduction

Attention-deficit/ hyperactivity disorder (ADHD) in children is a chronic childhood developmental disorder expressed in symptoms of inattention, hyperactivity, and impulsivity (APA 2000). There is large phenomenological overlap between ADHD and oppositional defiant disorder (ODD) with comorbidity rates of 30–90% (Angold et al. 1999; Pliszka 2000). ODD is expressed as refusing to comply with rules, deliberately annoying others, and a frequent loss of temper. Several researchers have suggested common etiological factors that add to the development of ADHD and ODD. In particular, neurocognitive impairments may be a key route for the development of both disorders through the expression of genetic, perinatal and psychosocial influences (Barkley 1997; Castellanos and Tannock 2002; Loeber et al. 2000). Although many studies have investigated neurocognitive functions in ADHD and ODD (see meta-analyses Willcutt et al. 2008), studies into neurocognitive impairments in children with comorbid ADHD and ODD are scarce. Thus, it remains controversial whether the co-occurrence of ADHD and ODD represents a combination of both disorders, or a separate entity with a distinct neurocognitive functioning profile. Knowledge on comorbid ADHD and ODD has important clinical implications, since this comorbidity is associated with increased morbidity and disability in terms of psychiatric, family and social functioning as compared to ADHD alone, even in the absence of conduct problems (Biederman et al. 1996).
In addition to EF, researchers have related ADHD and ODD to a motivational deficit (Newman and Wallace 1993; Quay 1997; Raine 1993; Sergeant et al. 1999; Sonuga-Barke 2002). An unusual sensitivity to motivational incentives is suggested to result in excessive reward-seeking behavior and impulsive tendencies in the presence of reward, as well as a decreased sensitivity to penalty. In ADHD there are reports of a strong preference for immediate over delayed reward, even when the delayed reward is larger (see for review Luman et al. 2005). This is explained by an aversion for waiting and a decreased sensitivity to cues that predict rewards (Sagvolden et al. 2005; Sonuga-Barke 2002; Tripp and Wickens 2008). Aggressive and delinquent youngsters are found to search for reward, irrespective of decreased total gain and increasing penalty (Daugherty and Quay 1991; Fonseca and Yule 1995; Matthys et al. 1998; O’Brien and Frick 1996). This is explained by a decreased emotional reactivity to the negative consequences of reward-searching behavior (Raine 1993), and researchers argue that, due to comorbid ODD, similar processes explain reward-searching behavior in ADHD (e.g., Daugherty and Quay 1991). Indeed, there is some evidence of decreased sensitivity to aversive stimuli in ADHD+ODD (Herpertz et al. 2001); a reward-immediacy effect in ODD is not supported so far (Van Goozen et al. 2004).
A third potentially underlying neurocognitive deficit in ADHD and ODD is a deficit in temporal information processing (Castellanos and Tannock 2002; Dougherty et al. 2007). Temporal information processing is the ability to order sequential events in time and the ability to create rhythms; skills that depend on intact time perception, time discrimination and time (re)production (Ivry 1996). There is evidence of temporal information processing impairments in children with ADHD and adolescents with anti-social behavior in terms of an internal clock that runs too fast (Barratt and Patton 1983; Dougherty et al. 2007; Toplak et al. 2006), and a decreased stability of time estimation output (Dougherty et al. 2007; Luman et al. 2008). Thus, in these groups time seems to elapse too quickly and too variably, which may explain their problems with waiting and planning (APA 2000). Whether problems with temporal information processing are more related to ADHD or ODD is unclear, since studies comparing children with (ADHD+) ODD and ADHD-only are absent so far.

Methods Experiment 1

Participants and Selection Procedure

Thirty-eight children with ADHD (69% boys) with either only a diagnosis of ADHD ( n = 20) or ADHD and comorbid ODD ( n = 18) were compared to 50 typically developing (TD) children (56% boys) aged 7 to 12. Inclusion criteria were: (a) estimated IQ score >75, (b) absence of a diagnosis of internalizing problems, history of child abuse, or psychiatric disorder other than ADHD or ODD, (c) absence of any neurological disorders, learning disabilities (such as dyslexia), sensory or motor impairment as reported by parents, (d) no medication other than methylphenidate. Group characteristics are reported in Table  1.
Table 1
Group Characteristics Experiment 1

TD
Group comparison a
( n = 20)
( n = 18)
( n = 50)
Measure
M
SD
M
SD
M
SD
Age in months
106
17
118
18
114
15
IQ
99.9
10.7
94.1
14.4
110.2
13.6
DBD Parent b
Inattention
15.7
4.4
16.9
4.5
1.9
2.1
Hyper/Impulsivity
13.1
5.3
16.7
5.0
2.2
1.9
ODD
3.6
2.7
13.1
4.1
1.5
2.0
CD
0.6
0.8
3.5
2.6
0.1
0.4
DBD Teacher b
Inattention
17.3
4.3
13.9
5.2
1.6
2.5
Hyper/Impulsivity
13.2
7.1
14.0
5.4
0.7
1.8
ODD
3.9
5.1
12.1
5.3
0.9
1.9
CD
0.6
1.1
2.2
2.1
<0.1
0.2
DISC b
Inattention
13.4
4.2
14.1
3.3
-
-
ns
Hyper/ Impulsivity
9.8
5.0
13.0
4.5
-
-
ODD
0.6
0.8
5.0
2.0
-
-
CD
0.0
0.0
0.2
0.5
-
-
ns
ADHD Attention-deficit/hyperactivity disorder; CD Conduct disorder; DBD Disruptive behaviour disorder rating scale; DISC Diagnostic interview scale for children; TD Typical development.
aGroups were compared using ANOVA; Tukey’s procedure was used for pair-wise group comparisons.
bRaw scores are tabulated.
* =  p < 0.05, ** =  p < 0.01, *** =  p < 0.001.
All children who were on methylphenidate discontinued use at least 24 h before testing, to achieve complete washout (Pelham et al. 1999). An estimation of the IQ score of each child was obtained by four subtests (Picture Arrangement, Arithmetic, Block Design, and Vocabulary) of the Wechsler Intelligence Scale for Children (WISC-III). These four subtests have been demonstrated to correlate between 0.93 and 0.95 with full scale IQ (Groth-Marnat 1997).

A tracking version of the Stop Task was used (Logan et al. 1997) consisting of go-trials (75%) and stop-trials (25%). On go-trials, children saw a fixation point presented for 500 ms. The fixation point was followed by a go-stimulus, a picture of an airplane, that was displayed for 1,000 ms and presented in the center of the screen. In response to the go-stimulus, children were required to press a response button that corresponded to the direction the plane was flying in (left or right). The inter-stimulus interval was 1,500 ms; the inter-trial interval was 3,000 ms. On stop-trials, a white cross was superimposed on the go-stimulus and acted as stop-signal. Children were instructed not to press any button, when a trial contained a stop-signal. The Stop Task started with a practice block containing only go trials (64 trials), followed by a practice block also containing stop trials (64 trials). After the practice blocks 248 trials were presented in four blocks of 64 trials lasting approximately 5 min per block. Trials were presented in a semi-random fixed order.
The longer the delay between go- and stop-signal (the stop-signal-delay, SSD), the more difficult it is to inhibit the response. To ensure that the percentage of inhibited responses was 50% for each individual child, SSD was systematically varied. If children inhibited correctly, SSD lengthened by 50 ms; if children failed to inhibit their response, SSD shortened by 50 ms. Thus, most often the stop-signal was presented shortly after the airplane was displayed, but the stop-signal could also be presented concurrently or shortly before the airplane, depending on the performance of the child. The ‘horse race’ model of the Stop Task (Logan et al. 1984), which assumes a race between the reaction to the go-stimulus and the reaction to the stop-signal, allows estimating the ‘virtual’ reaction time to the stop-signal (SSRT), as a measure for response inhibition performance. When both the go and stop process have an equal probability of winning the race (by varying the SSD within each child, the percentage of inhibited responses is 50%), SSRT should be approximately equal to the response to the go-stimulus minus SSD. Therefore, for each individual child, SSRT was obtained by calculating the difference between mean RT on go-trials and the mean SSD. For further details on the stop task and calculation of SSRT, please see Logan et al. ( 1984).
Mean RT and SD of RT on go-trials as well as percentage of errors were obtained as additional measures of response execution.

Procedure

Parents completed a written informed consent prior to the study that was approved by the local ethics committee. Travel costs were funded. Both experiments were part of a larger study on cognitive control problems in children with disruptive behavior problems. During the experiment, children viewed a computer screen positioned 60 cm in front of them. Standardized instructions were used. At the end of the session, children received a small gift worth approximately €3. Parents received a report detailing the findings of the study.

Statistical Analyses

Data of the dependent variables were compared between groups (ADHD-only, ADHD+ODD and TD) using ANOVA. If the group effect was significant, post-hoc analyses (Tukey procedure) were used to perform group-wise comparisons. Since children in the ADHD-only group were younger than the ADHD+ODD and TD group, and since the clinical groups had a lower estimated IQ score than controls, age and IQ were inserted as covariates in the ANOVA. Results showed that the covariates did not significantly change the F-values of the dependent variables, and therefore ANOVA results are presented in the Results section without the covariates. Effect sizes (partial eta squared) are reported to indicate the size of the effect being either small (0.01), medium (0.06), or large (0.14) (Cohen 1988).

Results Experiment 1

As hypothesized, both clinical groups group obtained higher scores on the ADHD and ODD scales of the parent and teacher DBD than controls (see Table  1), supporting phenomenological distinctiveness. In addition, children with ADHD+ODD obtained higher scores than children with ADHD-only on the ODD and CD scale of the parent and teacher DBD, as well as higher ODD ratings on the DISC. The ADHD and ADHD+ODD group differed in ADHD ratings: the ADHD-only group showed higher ratings of inattention on the parent DBD and lower hyperactivity/impulsivity ratings on the teacher DBD and DISC.
Group comparisons indicated that children with ADHD-only were slower and more variable on go-trials, and importantly, showed a slower SSRT than the TD group (see Table  2). Children with ADHD+ODD were also slower and more variable on go-trials than controls, and made more errors (combination of omissions and commissions) than both controls and children with ADHD-only. Despite the slow, variable and incorrect responses, children with ADHD+ODD were not slower in terms of SSRT. SSRT of the ADHD+ODD group lay in between that of the ADHD-only and the TD group, as both group comparisons with the ADHD+ODD group were non-significant. Finally, children with ADHD-only and children with ADHD+ODD did not differ in speed and variability of responses on go-trials.
Table 2
Variable
TD
Group comparison
( n = 20)
( n = 18)
( n = 50)
M
SD
M
SD
M
SD
F (2,85)
η p 2
Post-hoc (Tukey)
SSRT (ms)
315
77
275
90
247
56
6.4**
0.13
MRT (ms)
651
109
657
105
547
97
12.2***
0.22
SD of RT (ms)
153
34
169
37
111
26
31.3***
0.42
Errors (%)
3.4
2.5
6.7
7.1
1.7
1.5
12.9***
0.23
ADHD Attention-deficit/hyperactivity disorder; MRT Mean response time; ODD Oppositional Defiant Disorder; SSRT Stop signal response time; TD Typical development.
* p < 0.05, ** p < 0.01, *** p < 0.001.

Discussion Experiment 1

The results demonstrated inhibition problems (slower SSRT) in ADHD-only, but not in ADHD+ODD. Impaired inhibition performance in the ADHD-only group replicates earlier findings (Oosterlaan et al. 1998; Willcutt et al. 2008), and confirms inhibition problems as an important neurocognitive disability in ADHD. This difficulty with inhibiting an initiated motor response, may partly explain the behavioral symptoms of impulse control (APA 2000). Imaging data of the Stop Task in children with ADHD (Rubia et al. 2008) suggest that children with ADHD-only show underactivation of the dorsolateral prefrontal cortex during inhibition, a brain area that is found to play a major role in explaining impulsive and hyperactive behavior in ADHD (Bush et al. 2005; Seidman et al. 2005). The difficulties with inhibiting a motor response in the ADHD-only group may have been caused by ‘poor motor control’, since their responses to go trials were slower and more variable than those in the TD group. However, also children with ADHD+ODD showed poor motor control, while showing intact SSRT.
Reports on a lack of differentiation on stop task performance between ADHD and ADHD+ODD (see Scheres et al. 2001), could be related to differences in the Stop Task used. In the study by Scheres et al. ( 2001) the event rate manipulations may have ‘activated children to perform well’, which resulted in a lack of performance differences between the ADHD groups and the TD group.

Methods Experiment 2

Participants and Selection Procedure

Fifteen children with ADHD+ODD and 22 TD children also participated in Experiment 1. Part of the data of the other children (18 children with ADHD-only, 7 children with ADHD+ODD, and 30 TD children) have been reported in an earlier paper of our group (Luman et al. 2008). Specifically, that paper reported on the data of 25 children with ADHD and 30 typically developing children who performed the Timing Task in both a reward and penalty condition. In that study, no differentiation was made between ADHD-only and ADHD+ODD. Selection criteria of all children were identical to those employed in Experiment 1. Group characteristics are reported in Table  3.
Table 3
Group Characteristics Experiment 2
Measure
TD
Group comparison a
( n = 18)
( n = 22)
( n = 52)
M
SD
M
SD
M
SD
Age in months
123
19
120
16
120
15
ns
IQ
99.1
10.9
96.2
14.7
108.6
16.3
Rating scale parent b
Inattention
18.4
4.1
14.2
5.3
2.6
2.7
Hyper/Impulsivity
15.8
7.2
13.9
5.1
2.1
2.0
ODD
6.3
4.6
10.8
5.5
1.7
1.9
CD
1.2
2.1
2.3
2.2
0.2
0.5
DBD rating scale teacher b
Inattention
16.2
4.8
16.5
4.8
2.1
2.7
Hyper/Impulsivity
12.9
7.4
15.8
4.6
1.7
2.1
ODD
4.9
4.0
11.7
4.9
0.4
1.2
CD
0.6
1.1
2.9
2.6
0.1
0.3
DISC b
Inattention
14.6
2.2
13.6
3.9
-
-
ns
Hyper/ Impulsivity
10.8
5.7
12.7
4.2
-
-
ns
ODD
1.8
1.1
5.0
4.7
-
-
CD
0.1
0.1
0.2
0.6
-
-
ns
ADHD Attention-deficit/ hyperactivity disorder; CD Conduct disorder; DBD Disruptive behaviour disorder rating scale; DISC Diagnostic interview scale for children; TD Typical development.
aGroups were compared using an ANOVA, Tukey’s procedure was used for pair-wise comparisons.
bRaw scores are tabulated.
* =  p < 0.05, ** =  p < 0.01, *** =  p < 0.001.

A self-paced Time Production Task was employed. In this task, children had to produce a time interval of 1,000 ms (see Fig.  1). Processing of intervals up to 1,000 ms is found to depend on activity in the cerebellum, while larger intervals depend more on activity in the prefrontal cortex (Ivry 1996) and choosing a 1-second interval minimizes the influence of working memory and sustained attention functions that are known to be impaired in children with ADHD. The trial started with a colored screen (500 ms) that indicated the reinforcement condition. A green screen signaled that the reward condition was applicable; a red screen signaled the penalty condition; a blue screen the feedback-only condition. Reinforcement information in the reward and penalty condition was presented in the centre of the colored screen (being either +3, −3, +15, −15). Children heard a brief tone (50 ms, 80 db) through headphones. Following the tone, they pressed a response button that could be moved freely on the table, when they thought a 1,000 ms interval had elapsed. One thousand millisecond after the button press, textual accuracy information appeared on the screen for 500 ms that informed the subject whether the estimation was ‘too short’, ‘too long’ (both incorrect) or ‘correct’. Accuracy information was provided on every trial. A staircase algorithm determined the time window in which a response was considered correct. The boundaries of the initial window were 500 and 1,500 ms and narrowed by 100 ms, when a response was correct, while it widened by 100 ms when a response was incorrect (see Miltner et al. 1997). Consequently, this procedure ensured a similar amount of positive and negative feedback (and reward and penalty) for each participant. Depending on the reinforcement condition, coins indicating gain or loss appeared on the screen. In the reward condition, feedback was accompanied by a 3 or 15 cents gain when responses were correct, and children received only feedback in case of an incorrect response. In the penalty condition, feedback was accompanied by a 3 or 15 cents loss when responses were incorrect, and children received only feedback following a correct response. The inter-trial interval was 3,000 ms. Trials from the 5 reinforcement conditions (60 trials per condition) were presented in a random order.
At the beginning of the task, children received 200 eurocents, which was placed in their view. They were instructed to gain as much and lose as little as possible. Participants were informed that their earnings would be calculated at the end of the task. In order to familiarize children with the 1,000 ms interval, children saw a cartoon character that appeared 10 times on the screen for 1,000 ms. Thereafter, a practice session started in which children practiced the feedback-only trials (6 trials), followed by the reward trials (12 trials) and the penalty trials (12 trials). Finally, children practiced the randomized trials (12 trials). The task was presented in five blocks lasting approximately 6 min per block. At the end of the task, children were told that their net score was 245 eurocents, which was an (arbitrary) 45 cents gain. All children exchanged their 245 cents for a gift.
According to the Wing and Kristofferson model ( 1973) time productions consist of two independent aspects: internal clock functioning (a measure of central time keeping) and random variability due to execution of the motor response. Internal clock functioning was indexed by the median time production (investigating either over- or underproduction of time). Motor execution was indexed by the intra-subject variability (ISV), a measure of the trial-to-trial variability in performance that controls for the mean response (Russell et al. 2006). $${\text{ISV}} = \surd \left( {{{\sum {\left( {{\text{RT}}_{\text{i}} - {\text{RT}}_{{{\text{i}} - 1}} } \right)}^2 } \mathord{\left/ {\vphantom {{\sum {\left( {{\text{RT}}_{\text{i}} - {\text{RT}}_{{{\text{i}} - 1}} } \right)}^2 } {\left( {{\text{n}} - 1} \right)}}} \right. } {\left( {{\text{n}} - 1} \right)}}} \right)$$, where i = trial number, n = number of trials, and RT = response time. Time productions longer than four standard deviations of a participant’s mean were considered as outliers and excluded (see Leth-Steensen et al. 2000). In the ADHD-only group this was 0.7% of the data points, in the ADHD+ODD group 0.8%, and in the TD group 0.1%. Procedures were identical to Experiment 1.

Statistical Analyses

Data of the two timing variables were compared between groups (ADHD-only, ADHD+ODD and TD) using ANOVA. To investigate reinforcement sensitivity, performance of the groups was compared between the feedback-only, reward condition (averaged over the 3 and 15 cent gain trials) and penalty condition (averaged over the 3 and 15 cent loss trials) using repeated measure ANOVA. If group effects were significant, post-hoc analyses (Tukey Procedure) were used for pair-wise group comparisons. Three planned contrasts were tested: (a) reward versus feedback-only to test the impact of reward, (b) penalty versus feedback-only to test the impact of penalty, and (c) reward versus penalty to test the impact of the valence of reinforcement. The planned contrasts were orthogonal (uncorrelated with) every other contrast (Kirk 1968). Since children in the ADHD+ODD group had lower IQs than the TD group, IQ was entered as covariate in the ANOVAs. Results showed that the covariate did not significantly change the F-values of the dependent variables, and therefore ANOVA results are presented in the Results section without IQ as covariate.

Results Experiment 2

As hypothesized, both clinical groups group obtained higher scores on the ADHD and ODD scales of the parent and teacher DBD than controls (see Table  3), supporting phenomenological distinctiveness. In addition, children with ADHD+ODD obtained higher scores than children with ADHD-only on the ODD and CD scale of the parent and teacher DBD, as well as a higher ODD ratings on the DISC.

Timing Performance

Group comparisons (see Table  4) indicated that both clinical groups underestimated the time interval compared to controls (lower median time production), although the difference between the ADHD+ODD and TD group was only of marginal significance. The difference in time underestimation between the ADHD-only and ADHD+ODD group was not significant. Time productions were more variable (larger timing ISV) for the ADHD+ODD group than for both the ADHD-only and the TD group. Time production variability of children with ADHD-only did not differ significantly from that of the TD group.
Table 4
Timing Performance Experiment 2
Variable
TD
Group comparison
( n = 18)
( n = 22)
( n = 52)
M
SD
M
SD
M
SD
F (2,89)
η p 2
Post-hoc (Tukey)
Median (ms) a
904
114
916
133
971
89
3.6*
0.08
ISV (ms)
325
133
648
507
280
108
15.2***
0.25
ADHD Attention-deficit/ hyperactivity disorder; ISV Intra-subject variability; ODD Oppositional Defiant Disorder; TD Typical development.
aThe optimal response was 1,000 ms.
bThe difference between ADHD+ODD and TD was marginally significant.
* p < 0.05, ** p < 0.01, *** p < 0.001.

Reinforcement Sensitivity

Response to reward
Overall, median time productions were closer to optimal (1,000 ms) in the face of reward compared to feedback-only, as indicated by a significant condition effect for the reward contrast, $$F_{1,89} = 23,p < 0.001,\eta_p^2 = 0.20$$ (not in Table  5). This effect differed between groups as children with ADHD+ODD profited more from reward in terms of decreasing their tendency to underestimate time than children with ADHD-only or controls (see Table  5). In contrast, children with ADHD-only performed worse in the face of reward than controls, as their tendency to underestimate time became larger in the reward trials compared to the feedback-only trials. For time production ISV, there was no significant difference between the reward and feedback-only condition ( p = 0.72) and no significant interaction between the reward contrast and group.
Table 5
Timing Task Performance Experiment 2: Effects of Feedback-only, Reward and Penalty
Variable
TD
Group comparison b
( n = 18)
( n = 22)
( n = 52)
M diff
M diff
M diff
F (2,89)
η p 2
Post-hoc (Tukey)
Median (ms) a
Reward-FB
872−936 = −64
915−879 = 36
961−952 = 9
10.8***
0.19
(SD = 80)
(SD = 122)
(SD = 62)

ODD
Penalty-FB
920−936 = −16
935−879 = 56
989−952 = 37

0.10
(SD = 49)
(SD = 108)
(SD = 64)
4.8**

Rew-Penalty
872−920 = −48
915−935 = −20
961−989 = −28

0.04
-
(SD = 52)
(SD = 100)
(SD = 64)
1.7

ISV (ms)
Reward-FB
309−411 = −102
598−732 = −134
269−301 = −32
1.3
0.03
-
(SD = 231)
(SD = 446)
(SD = 147)

Penalty-FB
298−411 = −113
655−732 = −77
280−301 = −21
0.9
0.02
-
(SD = 226)
(SD = 409)
(SD = 168)

Rew-Penalty
309−298 = 11
598−655 = −57
269−280 = −11
2.6
0.06
-
(SD = 101)
(SD = 297)
(SD = 101)

ADHD Attention-deficit/hyperactivity disorder; ISV Intra-subject variability; ODD Oppositional defiant disorder; TD Typical development.
aThe optimal response was 1,000 ms.
bThe interaction between groups and condition was calculated using a repeated measure ANOVA.
* p < 0.05, ** p < 0.01, *** p < 0.001.
Response to penalty
Median time productions were closer to optimal (1,000 ms) in the face of penalty compared to feedback-only, as indicated by a significant condition effect for the penalty contrast, $$F_{1,89} = 35,p < 0.001,\eta_p^2 = 0.29$$ (not in Table  5). This effect differed between groups as children with ADHD-only profited less from penalty, in terms of decreasing their tendency to underestimate time, than children with ADHD+ODD or controls (see Table  5). There was no difference in penalty sensitivity between children with ADHD+ODD and controls. For time production ISV, there was no significant difference between the penalty and feedback-only condition ( p = 0.91) and no significant interaction between the penalty contrast and group.
Reward versus Penalty
Median time productions were closer to optimal (1,000 ms) in the face of penalty compared to reward, although this condition effect just escaped conventional levels of significance, $$F_{1,89} = 3.1,p = 0.08,\eta_p^2 = 0.03$$ (not in Table  5). Groups did not differ in their sensitivity to reward versus penalty. For time production ISV, there was no significant difference between the reward and the penalty conditions ( p = 0.93) and there was no significant interaction between the valence contrast and group.

Discussion Experiment 2

Taken together, children with ADHD-only seem distracted by reward and penalty, while children with ADHD+ODD seem to profit from reinforcement. Again, these findings argue against the idea that ADHD+ODD can be considered a more severe form of ADHD.

General Discussion

Clinical implications

Although confirmation of our findings is necessary in a community sample of children with ADHD (not only including children with ADHD symptoms above a certain cutt-off), the findings suggest that ADHD+ODD is not a more severe form of ADHD in terms of impairments in neurocognitive functioning. Since neurocognitive functions are of great importance for daily life functioning, affecting academic (e.g., Geary 1993), and social performance (Lezak 2004), assessing comorbid ODD in ADHD seems highly significant. Therefore, interventions that focus on training these neurocognitive abilities (e.g., Klingberg et al. 2005) seem particularly relevant for children with ADHD-only. Otherwise, the observation that children with ADHD+ODD profit more from reward and penalty than children with ADHD-only suggest that behavioral interventions that make use of rewards and penalties to shape behavior (mediation therapy) may be especially effective in the comorbid group. Rewards may have a distracting impact on performance of children with ADHD, especially when they try to work ‘as quickly as possible’ to obtain a reward.

Open Access

Open AccessThis is an open access article distributed under the terms of the Creative Commons Attribution Noncommercial License ( https://​creativecommons.​org/​licenses/​by-nc/​2.​0), which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.

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