ANALISIS 5: PERFIL DE DISOLUCION EN APARATO IV USP

psychopathology

The present thesis aimed at investigating influences of emotion on executive attention. It is therefore informative to review research on other factors that influence executive attention in order to see how these modulations are reflected in electrophysiology and imaging. This possibly helps to formulate concrete and directional hypotheses about what an influence of emotion on conflict processing might look like.

Development. Rueda, Rothbart, McCandliss, Saccomanno, and Posner (2005) presented a version of the arrow flanker task to 4 and 6 year old children. These age groups were selected because executive attention as measured by conflict tasks strongly develops during this period (Rueda, Posner, & Rothbart, 2005). In comparison to younger children, older children showed a reduced flanker interference that was accompanied by the presence of a frontal negativity in the ERP for incongruent compared to congruent trials. However, after a training period of 5 days, the 4 year olds also showed this frontal conflict negativity. This study provides strong evidence that a conflict negativity in the ERP emerges as executive attention (i.e., the ability to efficiently process conflict) emerges in childhood development. Two studies in adolescence show that the conflict N200 is still subject to change later in development. Ladouceur, Dahl, and Carter (2004) also used an arrow flanker task in 9 to 17 year olds who they split into a younger (mean age =

12.2) and an older group (mean age = 15.8). They only observed a conflict N200 in the older group. The lack of an N200 conflict effect in the younger group contrasts the findings of Rueda, Rothbart, et al. (2005); they may however be due to the small sample size (n = 5 in the younger and n = 6 in the older group) and consequently reduced power. Nevertheless, in a more recent study (Ladouceur, Dahl, & Carter, 2007) the authors examined a larger population including also adults (young adolescents: n = 15, mean age = 12.4; older adolescents: n = 15, mean age = 16.5; adults: n = 16, mean age = 28.7). Even though there was a small negativity for incongruent trials at frontal electrode sites in the young adolescents, it did not reach significance. The two older groups did show reliable N200 conflict effects. If statistical power is not the problem, the lack of an effect in the younger adolescence may be due to differences in the experimental procedures. Rueda, Rothbart, et al. (2005) used a version of the flanker task that was especially designed for children using animals instead of simple arrows (Rueda, Posner, & Rothbart, 2004) whereas Ladouceur et al. applied the standard version of the arrow flanker task which may be more difficult for the younger adolescents. In conclusion, the conflict N200 seems to emerge as executive attention develops. The studies in adolescence hint at the possibility that the amplitude of the conflict N200 still increases when conflict processing becomes more efficient in later development.

Aging. Evidence for altered conflict processing in older adults comes from a study on a version of the Stroop task in which participants were in some blocks told to name the ink color, in others to read the word (West, 2004). Critically, there were also mixed blocks in which a cue told the participant before each trial what the task for the present trial was (color/word). In the standard Stroop task (naming the ink color) the older group (mean age = 72.2) showed a larger conflict effect than the younger adults (mean age = 21.4). When reading the word, Stroop interference of the same magnitude was observed in both age groups. The authors also observed a conflict negativity (N450) that was reliably present in the younger group. In the older adults the conflict negativity was only present in the mixed blocks and ceased to be significant when the task was constant throughout a block. The results are less clear than those for the development of executive attention, but point in a similar direction. Efficient conflict processing seems to be related to the presence of a conflict negativity and to its amplitude.

Psychopathology. The current paragraph reviews studies of executive attention in patients with a focus on attention deficit hyperactivity disorder (ADHD), and side notes on Schizophrenia, and Huntington’s disease. ADHD is the classical case of lack of self control, characterized by pervasive behavioral symptoms of hyperactivity, impulsivity and inattention, mainly beginning in childhood (for a review see Castellanos, Sonuga-Barke, Milham, & Tannock, 2006).

Pliszka, Liotti, and Woldorff (2000) had 11 year old boys with and without ADHD perform a stop signal task in which a stop signal followed with variable onset on a go signal eliciting conflict between the already activated response and its inhibition (see Section 2.3.2). Healthy boys succeeded more often in inhibiting a response to the stop signal than ADHD boys. Interestingly, healthy boys also showed a much larger N200 response in stop trials compared to the ADHD children. A very recent study provided similar results in a flanker task (Albrecht et al., 2008). They investigated three groups of 8 to 15 year old children (1) with ADHD, (2) their unaffected siblings, and (3) unrelated unaffected controls. There was a linear trend between RTs and “genetic concordance with ADHD”, i.e., RTs were longest in ADHD children, intermediate in their siblings, and shortest in controls. The ERP results parallel the behavioral results with a reduced conflict N200 in ADHD children, an intermediate N200 in the sibling group, and largest N200 amplitudes in the control children. These data from children with ADHD corroborate the conclusion drawn from the developmental and aging studies that more efficient conflict processing is reflected in an enlarged conflict N200 amplitude.

For ADHD there are also two fMRI studies investigating ACC activation to conflict. Bush et al. (1999) applied a counting Stroop task (Bush et al., 1998) in which varying numbers of number words were presented on the screen. The participants’ task was to indicate how many number words were presented, i.e., “three three” yielded an incongruent trial. Neutral trials consisted of none-number words, e.g., “cat cat”. The authors only reported statistical tests for the two experimental groups separately, but described increased RTs and a larger conflict interference in adults with ADHD (age range 22 - 47) compared to healthy controls. In addition, only the healthy controls showed activation in the ACC to incongruent compared to neutral trials. The ADHD group did not activate the ACC. Results from an intervention study also point in the direction that recruitment of the ACC is necessary for efficient conflict processing. Lévesque, Beauregard, and Mensour (2006) had 10 year old ADHD children randomly assigned to a control and an experimental group that received neurofeedback training (for details see

Fuchs, Birbaumer, Lutzenberger, Gruzelier, & Kaiser, 2003). The children in the experimental group showed improvement in accuracy in the counting Stroop task from a pre- to a post-test, whereas the control group did not change. In the pre-test neither group showed ACC activation, in the post-test however, the training group, not so the control group, showed ACC activation for incongruent over neutral trials. As for the N200, ACC activation for conflict seems to be stronger in participants capable of efficient conflict processing.

In line with the results is also a study in schizophrenics revealing larger Stroop interference for the patient group, but an attenuated conflict N450 amplitude (McNeely, West, Christensen, & Alain, 2003). One study observed prolonged RTs in patients with Huntington’s disease (Beste, Saft, Andrich, Gold, & Falkenstein, 2008) who are known for ACC dysfunction (Reading et al., 2004; Beste et al., 2007). In a flanker task these patients exhibited an attenuated conflict N200 as well.