C ONCLUSION

One of the core deficits of ADHD is a disturbed response inhibition, manifested in the difficulty in delaying responses, in blurting out answers to questions before they have been completed, in difficulty in awaiting one´s turn in games or in group situations and in interrupting or intruding on others (American Psychiatric Association, 2000). Inhibitory deficits were verified in more than one study with responding to visual stimuli. But the question arises if inhibitory deficits are restricted to the visual modality.

Inhibition of reaction on acoustic cues has a high practical relevance. Thus, a child on a bike, for example, has to pay his or her full attention to the traffic in the moment of crossing a road instead to a person calling his or her name. Or else, children in the classroom having the motivation to listen to the teacher have to inhibit knee-jerk,

focusing on whispering neighbours or siren sounds from outside. Thus, children and, of course, adults need to be able to inhibit reflexive responses to acoustic stimuli.

It has to question if children with ADHD also impaired in this kind of inhibition performance. This question immediately suggest itself due to impairments in range of acoustic tasks (Riccio & Hynd, 1996), the large degree of overlaps between ADHD and APD (although there are some behaviours more often associated with one disorder than the other; Chermak, Tucker, & Seikel, 2002; Ptok, Buller, Schwemmle, Bergmann, &

Luerssen, 2006) and the up to 70% high comorbidity rate of learning disabilities (Mayes, Calhoun, & Crowell, 2000), which enclose deficits in recording, integration, storing and retrieving of visual as well as acoustic information.

In order to answer the core question whether children with ADHD are impaired in their inhibitory control of reflexive reactions to visual as well as to acoustic cues and thereby to promote the needed differential diagnostic, it is important to develop tests with comparable performance measurements in different modalities. Thus, it is possible to gain assumptions in which modality systems deficits are prior-ranking.

To enlarge the already existing multimodal diagnostic approach the idea of the present thesis was to investigate the impulsivity in antisaccade experiments with different modality inputs. Saccades triggered by visual stimuli are well investigated in children with and without ADHD (Rommelse, et al., 2008). Some studies investigated also prosaccades elicited by acoustic stimuli in adults (Fendrich, et al., 1991; Frens & Van Opstal, 1995; Shafiq, et al., 1998; Yao & Peck, 1997; Zambarbieri, 2002; Zambarbieri, et al., 1995; Zambarbieri, et al., 1982; Zambarbieri, et al., 1981). However, to date there are only two studies that investigated antisaccades elicited by acoustic cues in the context of schizophrenia and hemispherectomy, respectively (Reuter-Lorenz, et al., in press;

Schooler, et al., 2008) and none had investigated the antisaccade performance on acoustic stimuli in children.

The aim of Study I was to test the practicability of the designed experiment and to investigate the comparability of pro- and antisaccades elicited by visual and acoustic stimuli in a control group. Based on primary interest in the behavioural performance an eye tracker system was used. Because of the transformation from craniotopic into retinocentric coordinates it was assumed to extend prior results of slower acoustically compared to visually triggered prosaccades (Goldring, et al., 1996; Zambarbieri, et al., 1982; Zambarbieri, et al., 1981) to antisaccades and to children. Additionally, eccentricity effects were investigated during antisaccades and in children in order to compare the results to the described effects in prosaccades (SRTs decreasing of acoustically triggered saccades and SRTs increasing of visually triggered saccades with larger

stimulus eccentricities; Frens & Van Opstal, 1995; Yao & Peck, 1997; Zambarbieri, 2002;

Zambarbieri, et al., 1995). Finally, the gap effect regarding SRTs, which appears less pronounced for acoustically than for visually elicited prosaccades (Fendrich, et al., 1991;

Shafiq, et al., 1998; Taylor, et al., 1999; Zambarbieri, 2002), was investigated also for the first time in acoustically triggered antisaccades.

Constructively based on the results on Study I the same experiment was carried out with children with and without ADHD. One constriction of behavioural tests is that the measurement of the performance is the end product of information processing. EEG permits the measurement of brain activity – induced by task stimuli – before the performance takes place, e.g. an answer will be observable. Therefore, Study II measured along with the behavioural performance the brain activity. Functional brain imaging studies have shown that a distributed fronto-parietal network is more active when subjects perform antisaccades compared with prosaccades (McDowell, et al., 2008). The DLPFC activity seems to provide an inhibitory signal that precedes a correct antisaccade performance (Clementz, McDowell, & Stewart, 2001; Fitzgerald, et al., 2008;

McDowell, et al., 2005). Additionally, the ACC is relevant for the visual antisaccade performance (Brown, Goltz, Vilis, Ford, & Everling, 2006; Ford, et al., 2005; Gaymard, Ploner, et al., 1998; Polli, et al., 2005). Given that children with ADHD showed structural and functional changes in a fronto-subcortical network (Bush, Valera, & Seidman, 2005;

Dickstein, et al., 2006; Seidman, et al., 2005) it was anticipated that children with ADHD will generate more errors and altered brain activities in the antisaccade task compared to control subjects.

Finally, children have difficulties to generate a prosaccade with a preceding antisaccade (Hanisch, et al., 2006) or more generally, they have difficulties when mixed-saccade tasks were applied (O'Driscoll, et al., 2005). In adults a context effect was also detected on the behavioural (Barton, Greenzang, Hefter, Edelman, & Manoach, 2006;

Barton, Raoof, Jameel, & Manoach, 2006; Ethridge, Brahmbhatt, Gao, McDowell, &

Clementz, 2009) as well as on cortical level (Dyckman, et al., 2007). Blocked conditions are easier and do not add a third step to the inhibition of prepotent response and the execution of the appropriate eye movement: interpretation of the cue (Irving, Tajik-Parvinchi, Lillakas, Gonzalez, & Steinbach, 2009). In order to simplify the experiment for Study III a block design of the experiment was developed. It was assumed that through this design it will be possible to differentiate children with and without ADHD on the behavioural as well as on cortical level and, in doing so, to gain a differentiated view on damages of children with ADHD in the different modalities.