ebook_ADHD2019

26 Rohde, Buitelaar, Gerlach & Faraone the verbal or phonological domain. 51 Visuo-spatial working memory is subserved predominantly by the inferior and superior parietal areas together with dorsola- teral prefrontal regions. 52-56 There is additional evidence of activation in the cere- bellum during visuo-spatial working memory tasks. 57,58 The available fMRI studies of ADHD reveal a differential activation pattern in the fronto-striatal areas 59 and reduced activation in the dorsolateral prefrontal areas, 60,61 right inferior and supe- rior parietal lobes, 56,62,63 and right caudate nucleus. 63 REWARD SENSITIVITY Reward sensitivity is an evolutionary important construct; because rewards are accompanied by positive feelings, they reinforce reward-linked behaviour. This process of reinforcing behaviour forms the basic principle of learning. 64 Yet, if an individual is highly sensitive to rewards, this can lead to maladaptive behaviour, such as risky behaviour and addictions. Especially during adolescence, reward sensitivity is heightened, which is demonstrated by increased risky behaviour when rewards are at stake. 65 Current theoretical models of ADHD consider alte- red reward sensitivity to be a key cognitive mechanism. 66,67 In general, studies of reward processing show that individuals with ADHD patients make suboptimal and more risky decisions, prefer immediate compared with delayed rewards 66 and overestimate the magnitude of proximal relative to distal rewards. The greater sensitivity to rewards in individuals with ADHD is further demonstrated by faster behavioural responses to trials which lead to rewards than to non-reward trials in the socalled monetary incentive delay task. 67 Alterations in reward sensitivity in ADHD have alo been observed at the neural level, using fMRI paradigms. Various brain regions, including the orbitofrontal cortex, medial prefrontal cortex, and the ventral striatum are activated in healthy subjects when receiving or anticipating rewards. Findings in ADHD are mixed, with increased activations in the anterior cingulate and anterior frontal cortex during reward anticipation, and in the orbitofrontal cortex and nucleus accum- bens during reward receipt 68 and a community study associating increased activa- tion with impulsivity, a related concept. Other studies in adolescents and (young) adults with ADHD however have reported less striatal activation during reward anticipation compared to controls. OTHER COGNITIVE DEFICITS Among other domains that have found to be impaired in ADHD are temporal information processing and timing, 69 speech and language functions, 70 motor con- trol problems, 71 memory span, processing speed, arousal/activation, and reaction