Políticas y reformas educativas

Key insights of DCT are that disruptions to the process of cognitive control play a central role in the generation of hypnotic phenomena, and that these disruptions stem from a fundamental shift in the organization of executive functions within the brain. From the perspective of the conflict-monitoring model, it would be expected that such disruptions in cognitive control would result in greater cognitive interference, particularly during tasks eliciting response conflict such as the Stroop paradigm. This greater interference should elicit greater activation from conflict-sensitive monitoring processes in the ACC of highly susceptible individuals in hypnosis. Egner et al. (2005) set out to test this novel prediction of DCT and the conflict-monitoring model. Using an adaptation of the MacDonald et al. (2000) paradigm, they administered an event-related fMRI paradigm consisting of congruent and incongruent Stroop stimuli, requiring either word naming or colour naming responses to individuals of high and low susceptibility in baseline and hypnosis conditions (see also Egner and Raz, Chapter 3). Similarly to MacDonald et al., they were able to identify regions of conflict-related activation within the ACC

by contrasting conditions of high response conflict (colour naming incongruent trials) and medium response conflict (colour naming congruent and word naming incongruent) with the low conflict condition (word naming congruent trials). Regions that were identified in both contrasts were selected as the most conflict-sensitive ACC regions for further analysis of response conflict effects. Prefrontal regions sensitive to differences in task demands for cognitive control were identified by contrasting colour naming (higher control) with word naming (lower control) trials. This contrast identified a control-related region of activation within the left lateral PFC.

In this paradigm, the activation of ACC regions most sensitive to response conflict showed a classic interaction between hypnotic susceptibility and the hypnotic condition.

As predicted by the contemporary interpretation of DCT advanced above, conflict-related ACC activation increased for highly susceptible individuals in hypnosis (but not for those with low susceptibility). There were no behavioural differences between individuals with high and low susceptibility in either baseline or hypnosis conditions due to the very long (12 s) interstimulus interval in this experiment. This is a stringent methodological safeguard adopted (where possible) in imaging studies to rule out differ-ences in task difficulty as an alternative explanation for obtained differdiffer-ences between conditions. Recall that Jamieson and Sheehan (2004) demonstrated a decrease in the efficiency of the cognitive control in the face of sufficiently demanding response conflict, through increased error commission in hypnotized highly susceptible individuals.

Egner et al. (2005) demonstrated a similar decrease in the efficiency of this cognitive control system, through increased activation in the cortical regions maximally sensitive to the level of response conflict. Taken together, these two studies constitute strong evidence in favour of one of the principal predictions of DCT.

In the study by Egner and colleagues (2005), the anterior system of rapid, flexible cognitive control sketched by Norman and Shallice (1986) and carefully fractionated by Cohen and his associates (Cohen et al. 2004) appears to have been disrupted by hypnosis.

However, the individuals with high and low susceptibility continued to perform the task with comparable levels of speed and accuracy even in the hypnotized condition. There were no significant differences between individuals with high and low susceptibility in the activation of left frontal regions identified as corresponding to the demand for cognitive control in either baseline or hypnotized conditions. These results are not consistent with a simple shift from SAS to CS control in the highly susceptible individuals in hypnosis. Rather, components of the SAS (prefrontal representations of task require-ments) appear to continue to be involved in task performance (which still requires response selection in the presence of competing response tendencies), but without flexible regulation to carefully match changing cognitive demands.

The conflict-monitoring function of the ACC component of anterior cognitive control appears to be undiminished in hypnosis, as indicated by the increase in conflict-related activation observed by Egner et al. (2005). This conclusion is also supported by the find-ings of Kaiser et al. (1997). Using a response conflict paradigm, they showed that although error rates increased for individuals with higher susceptibility in hypnosis, there was no change in the error-related negativity (N_E), an event-related potential

component generated by the ACC when a response error occurs. Although there is some controversy about the role of the N_E(Holroyd et al. 2004), the N_Eis plausibly explained as a post-response consequence of conflict between the error response and continued processing of the correct response (Yeung et al. 2004). How, then, is cognitive control impaired if ACC error and conflict monitoring remain intact and PFC representations of task-relevant goals and rules continue to exert an active influence?

The conflict-monitoring model provides a plausible answer to this question. However, it is important to distinguish between two different levels of cognitive control within the model. The first level of SAS control is implemented by active task or rule representa-tions in the PFC, which facilitate non-routine cognitive and motor responses. A second-order level of cognitive control within the SAS is the flexible modulation of the implementation of control in response to changing cognitive requirements. This level of attentional control emerges from the ability to detect interference or conflict (in processes influenced by currently active PFC representations) by the regions within the ACC. This conflict detection, in turn, signals appropriate changes in the activation of concurrent task-relevant goal representations in specific regions of the PFC. For example, working within this paradigm, Kerns et al. (2004) demonstrated that increases in ACC conflict-related activation on a preceding trial led to increases in the activation of PFC task-related representations on subsequent trials, corresponding in turn to improved behavioural performance on those trials. Similarly, Ridderinkoff et al. (2003) demon-strated that, in comparison with correct trials, response errors (failures of control) were preceded by lower levels of ACC activation in the previous (correct) response. If conflict-related ACC activation increases in hypnosis, then cognitive control is being less appro-priately matched with task demands. Because the PFC representations implementing the primary level of attentional control remain active (indeed unchanged), it follows that on the basis of this model, it must be the second level of cognitive control, rather than the first, that is impaired. Therefore, it may be the functional integration of ACC and PFC components that is being disrupted in hypnosis.

This interpretation garnered further support in the EEG results obtained by Egner et al. (2005). These authors also found an interaction in the coherence of the gamma (30–50 Hz) frequency band between left frontal and frontal midline recording sites.

These sites largely reflect electrophysiological activity in left lateral PFC and ACC regions, respectively. This result was observed in the same participants performing the same task and conditions when outside the scanner environment. Coherence is a measure of linear statistical dependence in the amplitude and timing of cortical oscilla-tions at different recording sites in the same time slice (Nunez et al. 1997). It can be considered to represent the functional connectivity (i.e. shared or mutual information) between oscillatory activities in separate cortical regions, in response to functional changes in task demands (see, for example, Edelman and Tononi 2000; Friston 2002).

Synchronization in fast frequency (gamma band) EEG activity has been associated both theoretically and in numerous empirical studies with the binding of activity in separate cortical locations into a single unified perceptual or cognitive representation (see De Pascalis, Chapter 5; see also Kaiser and Lutzenberger 2003; Tallon-Baudry 2004).

Gamma coherence between these regions decreased in hypnosis for highly susceptible individuals, whereas for individuals with low susceptibility it increased. This pattern is clearly consistent with a breakdown in highly susceptible individuals under hypnosis in the integration of processing in ACC and left PFC during ongoing cognitive control.

This modification of DCT maintains the key insights of Woody and Bowers’ original version while specifying precisely those forms of control that are dissociated in hypnosis and those which are not. It also entails an extension of the understanding of forms of control available in hypnosis beyond the strict limitations of CS proposed in the initial formulation. As Brown and Oakley (2004) and Dienes and Perner (Chapter 16) point out, hypnotic suggestions do not appear to call only for routine or overlearned responses, implying at least some degree of SAS involvement. Consistent with recent advances in cognitive neuroscience, the revised DCT model incorporates the further distinction within the SAS between a first-order level of cognitive control and a second-order level of cognitive control based on higher order monitoring. It is the latter rather than the former level of control that appears to be dissociated in hypnosis. This dissociation alters the fundamental functioning of the SAS as a whole. PFC representations of task-related goals and rules are still able to regulate cognitive processes; however, both the flexibility and complexity of the cognitive processes able to be managed in this way remain much more limited than those normally available to the SAS.