Dissociated Control as a Paradigm for Cognitive-Neuroscience Research and Theorising in Hypnosis

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Chapter 7
Dissociated Control as a Paradigm for Cognitive-Neuroscience Research and
Theorising in Hypnosis
Graham A Jamieson
University of New England
Erik Woody
University of Waterloo
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7.1. Introduction
For much of its history, hypnosis has tended to be somewhat of a rogue topic,
difficult to connect with the main body of psychological understanding. Hilgard’s
(1977) neodissociation theory of hypnosis represented an attempt to integrate a
scientific understanding of hypnosis into the broader landscape of psychology. He
commented, “Any satisfactory theory of hypnosis should also be a theory bearing on
psychology at large” (Hilgard 1991, p. 101).
Accordingly, he attempted to explain hypnotic phenomena in terms of
underlying cognitive control mechanisms and the alteration of their function in
hypnosis (Hilgard 1991, 1992). He posited a system of multiple cognitive control
subsystems that can operate somewhat autonomously, but which are ordinarily
subordinate to a higher-order executive system that monitors and coordinates the
interaction among them. He hypothesized that hypnosis somehow alters the executive
functions and their hierarchical relationship to the subsystems of control. For
example, he indicated that the hypnotist may take over some of the executive control
functions that would otherwise be managed autonomously by the subject.
Hilgard’s attempts to develop and clarify these ideas took two rather distinct
directions, relying on different conceptions of dissociation, the idea at the center of
his theory. On one hand, the term “dissociation” can be taken to mean a
“disassociation” or “disaggregation” of mental processes, whereby processes that are
normally closely related become functionally more separate. Along these lines,
Hilgard remarked, “If dissociation is conceived broadly to imply an interference with
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or loss of familiar associative processes, most phenomena of hypnosis can be
conceived as dissociative” (Hilgard 1991, p. 84). One of Hilgard’s most important
speculations about such disassociation of processes concerned the possible loss of
integration of the monitoring and control functions of the executive system. For
example, in hypnotic age regression, when the hypnotic subject experiences himself
or herself as a child, “all available information is not used by the activated subsystem,
and the monitor does not offer a correction; hence imagination may be confused with
external reality” (Hilgard 1992, p. 97).
On the other hand, a contrasting conception of dissociation is one that stems
more directly from Janet (1901, 1907/1965) and his emphasis on conscious versus
unconscious processes. Specifically, the term “dissociation” can be taken to mean
“the splitting off of certain mental processes from the main body of consciousness
with various degrees of autonomy” (Hilgard 1992, p. 69). This is the conception of
dissociation that Hilgard pursued more vigorously, partly because of the great
importance he attached to the discovery of the “hidden observer” (Hilgard 1977). The
finding that a “hidden observer” could report the presence of pain in an otherwise
hypnotically analgesic subject implied to Hilgard that there is a split in consciousness,
in which two parallel streams of consciousness coexist. He hypothesized that the split
in consciousness is effected by an amnesia-like barrier, which divides perceptions into
separate, coexisting channels. This conception of dissociation, instead of focusing on
the relationship of monitoring to control, focused on division within the monitoring
function: “some fraction of it exists behind an amnesia-like barrier” (Hilgard 1992, p.
99).
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In hindsight, so closely yoking neodissociation theory to the hidden-observer
phenomenon may have been a mistake. Not only is the empirical basis of the hidden
observer open to telling lines of criticism (Bayne this volume; Spanos and Hewitt
1980), but so is the amnesic-barrier conception of dissociation in hypnosis (e.g.,
Kirsch and Lynn 1998). Indeed, the postulation of multiple coexisting channels of
consciousness in order to explain the partial reversal of analgesia with the suggestion
of a hidden observer has struck many commentators as gratuitous and unconvincing
(e.g., Kallio and Revonsuo 2003).
Perhaps the most generative line of criticism of Hilgard’s theory came from
Bowers (1990, 1992). He pointed out that amnesic barriers were not a plausible
mechanism for most hypnotic effects. Spontaneous amnesias (ones not directly
unsuggested) are very rare in hypnosis; hence, the amnesic-barrier concept was
perversely attempting to explain relatively common hypnotic effects in terms of a
very rare one. In addition, the theory required these barriers to be implausibly and
arbitrarily selective: “The pain and cognitive effort to reduce it is hidden behind an
amnesic barrier, but not the original suggestions for analgesia, nor the goal-directed
fantasies that typically accompany the reductions in pain” (Bowers 1992, pp. 261-
262). Furthermore, Bowers pointed out that the concept of amnesic barriers implied,
in contradiction to the rest of Hilgard’s theory, that in hypnosis there need not be any
change in the cognitive control of behaviour, but only a distortion in its self-
perception. Specifically, the amnesic-barrier concept implied that the hypnotic subject
would simply enact suggestions voluntarily and effortfully in the usual fashion, but
this fact would be occluded from his or her awareness by an amnesic barrier. Hence,
the subject’s perception of his or her hypnotic behaviour as involuntary and effortless
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would be an illusion, rather than a reflection of a true underlying alteration in the
control of behaviour (see also Kihlstrom 1992; Shor 1979).
To salvage what Bowers (1990, 1992) perceived to be the viable aspects of
neodissociation theory, he jettisoned the amnesic-barrier concept of dissociation,
which he termed a theory of “dissociated experience,” and refocussed attention on the
concept of hypnotically altered control of behaviour, which he termed a theory of
“dissociated control.” He argued that “dissociation is not intrinsically a matter of
keeping things out of consciousness—whether by amnesia, or any other means”
(Bowers 1992, p. 267). Instead, he argued that “dissociation is primarily concerned
with the fact that subsystems of control can be directly and automatically activated,
instead of being governed by high level executive control” (Bowers 1992, p. 267).
That is, the dissociation at work in hypnosis was between subsystems of control and
the higher, executive level of control. This revised statement of Hilgard’s
neodissociation theory then served as the beginning proposition of dissociated control
theory, which we review in the next section.
To set the stage for the rest of this chapter, we wish to draw out two major
themes from the foregoing discussion of neodissociation theory. First, Hilgard’s
attempts to devise a cognitive-control model of hypnosis remained frustratingly
incomplete and vague. Indeed, he was eventually quite apologetic for its promissory
nature: “I regret to leave the theory in this incomplete form, so that it is more of a
promise than a finished theory” (Hilgard 1991, p. 98). Even Bowers’ reformulation
mainly trimmed away some of what he perceived to be the theory’s excesses. A major
problem is that the implied model was always, to use a technical term,
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“underidentified”—within the theory, it was not straightforward to disambiguate what
its multiple hypothetical entities (subsystems of control, monitors, and so forth) really
referred to and how to measure them. Dixon and Laurence (1992) made a closely
related comment: “As elegant as Hilgard’s rendition of Janet’s dissociation theory
may be, it is and will remain an exercise in metaphors” (p. 42).
The problem with the theory has always been, in a sense, how to get beyond
the level of metaphor. What was needed for this purpose, in our view, is an additional
level of analysis, which is provided by cognitive neuroscience. Woody and
McConkey (2003) described such a combination of levels as follows:
The exciting prospect of a bridge to the underlying biology of
hypnosis encourages us to reformulate some basic themes in hypnosis
research, so as to ask more sophisticated and differentiated questions
…. In addition, … the challenge of connecting our psychological
understanding to underlying biology can reveal important gaps in our
psychological understanding, which serve a vital role in stimulating
future research. (p. 332)
We believe the work to be reviewed in this chapter demonstrates the creative interplay
between two levels of analysis—the careful functional analysis of behaviour, on one
hand, and the detailed mapping of neural underpinnings, on the other. In this
interplay, we see the application of powerful new tools which are quite different from
anything that was available to Hilgard, just a few years ago.
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Second, the strong distinction between dissociated experience and dissociated
control, proposed by Bowers, was important rhetorically for re-emphasizing that
hypnosis may alter the control of behaviour, rather than simply its self-perception.
However, as Woody and Sadler (1998) pointed out, the concepts of dissociated
experience and dissociated control are not at all incompatible, and the sharp
distinction between them may have been somewhat premature. As mentioned
previously, before Hilgard’s thinking became dominated by the hidden observer, his
focus was on changes in the relationship between the monitoring and control
functions of the executive system. As we will detail shortly, recent work breathes rich
new life into this old idea.
7.2. Dissociated Control Theory
Woody and Bowers’ (1994) formulation of dissociated control theory (DCT)
may be considered the first of a new generation of hypnosis theories based within the
emerging perspective of cognitive neuroscience. Of course, other, alternative
approaches may also be taken within a cognitive-neuroscience framework; the further
development and testing of these competing accounts is a task for the readers of this
volume. DCT in its initial formulation is a theory which integrates findings across 3
domains of data and explanation: phenomenological, functional (behavioural), and
neurophysiological. DCT theory applies an early and influential cognitive
neuroscience account of cognitive control systems in the human brain to one of the
principal phenomenological characteristics of hypnosis—the sense of involuntariness
in response to hypnotic suggestions (Weitzenhoffer 1953).
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Norman and Shallice (1986) sought to account for the pattern of functional
deficits observed in neuropsychological testing with frontal lesion patients. They
proposed 2 distinct but interacting systems of cognitive control, which they labelled
Contention Scheduling (CS) and the Supervisory Attentional System (SAS). For well-
learned habitual tasks, unconscious, automatic, modular neural processing structures
(schemata) control the required actions. CS controls the selection of specific schemata
through a decentralised process of competitive and co-operative activation of
schemata by sensory input and the input of other active schemata. When a specific
schema reaches its required activation threshold, the corresponding action or
cognitive operation is performed. However, when the task is novel or complex or
requires a strong habitual response to be overcome, a higher level control system, the
SAS, is engaged to assist CS.
The SAS incorporates representations of goals and intentions and monitors
contention scheduling. The SAS does not implement actions directly, but instead
biases the selection of particular schemata by CS through modulating their activation
levels. As elaborated by Shallice (1988), SAS modulation of the selection of schemata
corresponds to the phenomenal experience of will. In contrast, when the SAS is
neither monitoring nor modulating contention-scheduling, action is experienced as
automatic. The SAS is mediated by frontal cortical structures, and the classic
functional impairments associated with frontal lesions may be understood as a
consequence of the disruptions of SAS regulation of the largely posterior cortically
mediated process of CS.
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Woody and Bowers (1994) applied the Norman and Shallice model to explain
the range of dissociations observed in hypnosis. In response to the suggestions of the
hypnotist, motor and cognitive processes normally experienced as under willed,
volitional control seem to occur independently of the conscious will of the hypnotized
person. According to DCT, hypnosis, in susceptible individuals, produces a temporary
functional dissociation of CS from SAS control, similar in some respects to the effect
of frontal lesions. For high susceptible individuals, hypnosis partly disables the
higher-level control system associated with the experience of will, resulting in a lack
of spontaneous self-generated action. This leaves the hypnotised person especially
dependent on CS-like, automatic control processes.
In the non-hypnotic condition, SAS control allows for a greater degree of
autonomy from contextual influences and prior expectations. When frontally mediated
executive control is diminished in the hypnosis condition, subjects' expectancies and
interpretations exert influence via the intrinsic linkages of activated representations
rather than the monitored execution of plans and strategies. Contextual cues and the
communications of the hypnotist then become the major factors structuring the
content of cognitive processes and phenomenal experience, as they emerge in
hypnosis (“hyper-suggestibility”). An additional consequence of the release of some
cognitive processes from the constraints of SAS control may be the wider activation
of loose associations idiosyncratic to that individual. More generally, the framework
of cognitive control which regulates the influence of information from contextual
sources and prior expectations on hypnotic responses—what Orne (1959) labelled the
“demand characteristics” of the hypnotic situation—is different from that which
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normally regulates the non-hypnosis condition. Consequently these processes are
even more salient for hypnotized, as compared to non-hypnotized, responses.
7.3. Testing Dissociated Control
DCT predicts a disruption of frontally mediated cognitive processes requiring
executive (supervisory) attentional control in highly susceptible individuals during
hypnosis. Alternatively, it might be expected that individual differences in hypnotic
susceptibility would be positively correlated with disruptions in executive cognitive
control even in non-hypnotic contexts. Several attempts have been made recently to
explicitly test these predictions with a range of behavioural neuropsychological
measures. Kallio et al. (2001) administered a battery of neuropsychological frontal
lobe measures to 8 high and 9 low susceptible individuals both at baseline and during
hypnosis. Letter fluency, a test highly sensitive to Broca’s area (left frontal) lesions,
was found to decline in hypnosis for high but not low susceptible individuals, a result
reported previously by Gruzelier and Warren (1993). Aikens and Ray (2001), using a
different battery, found that a group of 9 high susceptible individuals performed
significantly better than a group of 7 low susceptible individuals on the Wisconsin
Card Sorting Task, a finding contrary to DCT.
These studies utilized relatively small samples and lack of statistical power
may therefore have been a factor. Farvolden and Woody (2004) administered a
battery of memory tasks sensitive to frontal-lobe functioning to 30 high and 30 low
susceptible individuals both at baseline and in hypnosis. High susceptible individuals
generally had more difficulty with frontally mediated memory tasks (but not with
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non-frontal control tasks) than lows in both hypnotized and non hypnotized
conditions, thus supporting the prediction of greater vulnerability to disruptions in
frontal control amongst high hypnotically susceptible individuals. However, no
differences were observed between hypnotized and non hypnotized conditions in the
high susceptible individuals, inconsistent with the state predictions of DCT.
Jamieson and Sheehan (2004) sought to directly contrast the prediction of
DCT that SAS control is compromised in hypnosis versus the alternative prediction
that hypnosis is a state of enhanced SAS control (e.g., Horton and Crawford 2004).
Following Sheehan et al. (1988), they adopted a version of the classic Stroop task,
which required participants to name either the colour or the colour-word of a stimulus
which comprises a colour-word presented in a colour which is incongruent to the
colour named. Successful colour naming requires overcoming the strong conflicting
response tendency produced by the colour-word. The conscious selection of correct
responses against competition from stronger automatic response tendencies is one of
the most fundamental functions of the SAS or indeed any account of anterior-
mediated cognitive control. If SAS control is enhanced in hypnosis, then Stroop
performance should be enhanced in hypnotized high susceptible individuals. However
if DCT is correct, Stroop performance should be impaired in hypnotized high
susceptible individuals.
As predicted by DCT, Stroop task errors increased significantly for high
susceptible individuals in hypnosis, but not for low susceptible individuals. This study
had high power, with 66 high and 66 low susceptible participants. It also utilized a
particularly difficult version of the Stroop task with fast-paced incongruent stimuli
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and rapid changes between colour-naming and word naming requirements. Thus, the
considerable demands of the task required high levels of SAS control; in contrast, less
rigorous paradigms may not result in overt behavioural differences. However 2
previous studies have reported similar results using response-conflict paradigms in
hypnosis or hypnosis-like conditions (Kaiser et al. 1997; Nordby et al. 1999). In
addition to power, both the precise nature of the task demands and the appropriate
setting of task parameters governing difficulty level may be important in obtaining
positive results in these investigations.
The wider body of neuropsychological studies of hypnosis in relation to
frontal functioning are mixed. Some results seem to suggest enhanced attentional
control in high susceptible individuals (Horton and Crawford 2004), whilst others
suggest just the opposite (Gruzelier 1998). Methodological issues, sample size, and
lack of replication make firm conclusions from much of this literature difficult to
reach (there is a great need for some of these intriguing findings to be revisited by
current investigators). In summary, carefully designed studies with appropriate power
do provide support for disruptions in specific aspects of frontally mediated cognitive
control in relation to both hypnotic susceptibility and the hypnotic condition.
However, it is fair to say that current neuropsychological data do not support a simple
global shutdown of frontal functioning during hypnosis.
7.4. Conceptual Problems for Dissociated Control
Brown and Oakley (2004) and Dienes and Perner (this volume) make the
important criticism that DCT leaves cognitive control in hypnosis entirely dependent
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on CS, which normally controls only routine over-learned behaviours. This, they
argue, cannot account for either the novel responses required by some hypnotic
suggestions or the apparent requirement for classic (frontal) executive control in
producing some hypnotic responses. Dienes and Perner (this volume) point out that
response to the hypnotic suggestion “forget the number four” and then to count the
fingers on one’s hand requires both active monitoring for the occurrence of “the
number 4” and the inhibition of the over-learned response to count in sequence
1,2,3,4. Both are classic examples of SAS controlled functions.
DCT does not offer a detailed account of the mechanisms producing the
explicit content of (negative or positive) hypnotic hallucinations. Nor does it give an
obvious account for other arguably core features of hypnotic experience such as
tolerance for logical incongruity (Orne 1959, 1979) or loss of generalized reality
orientation (Shor 1959, 1962, 1979). Sophisticated phenomenological analysis of
hypnotic experience demonstrates that while some participants experience suggestions
in a passive, involuntary way (the classic suggestion effect), some highly responsive
participants experience a complex and fluidly shifting mix of reality and hallucination
(McConkey and Barnier 2004; Sheehan and McConkey 1982). McConkey (1991)
highlighted the active (rather than passive) nature of the cognitive processes needed to
resolve the conflicting demands of reality and suggestion. A full account of the
phenomenological aspects of hypnosis must be able to explain these diverse features.
It could be argued that DCT is a successful account of hypnotic involuntariness and
many of the dissociations which occur in hypnotic consciousness without being a
complete theory of hypnosis. However, successful extension of DCT will ultimately
need to address these additional features of hypnotic consciousness.
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7.5. Lessons from the Neuroscience of Voluntary Motor Control
A detailed account of the discrimination of self- and non-self generated
movement—which is closely related to the experience of movement as volitional or
non- volitional—has emerged from the neuroscience of motor control. This work
highlights the role of the cerebellum and inferior parietal operculum, as well as frontal
cortical regions, in this process (Miall and Wolpert 1996; Weiller et al. 1996). It also
emphasises the role of an “efference copy,” a neural representation of motor
commands produced by or in conjunction with the “motor intentions” that trigger the
commands (Blakemore et al. 1999). The efference copy is the basis for generating a
predictive model of the immediate sensory consequences of those motor commands,
which is then matched against the actual sensory feedback from the movement.
Forward-output model generation and comparison with sensory input is believed to be
mediated by the cerebellum (Wolpert et al. 1998). A match (indicating self-produced
movement) leads to an inhibition of these sensory representations in the parietal
cortex (Blakemore et al. 1999). Thus, these parietal representations are more active in
the case of involuntary than voluntary movements.
According to this account, activity in the cerebellum and parietal cortex plays
an essential role in producing the feeling that a movement is occurring involuntarily.
This hypothesis was tested in relation to hypnotic involuntariness in a recent PET
study by Blakemore et al. (2003). During hypnosis, 6 high susceptible individuals
were scanned whilst voluntarily raising their left hand and forearm, performing
hypnotic arm levitation of the left hand and forearm, having their left hand and
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forearm raised by a mechanical device, and at rest. As predicted, hypnotic arm
levitation (which was perceived as involuntary) was associated both with greater
bilateral cerebellar activation and with greater bilateral parietal operculum and left
inferior parietal cortex than voluntary arm movement (Blakemore et al. 2003).
Blakemore and colleagues propose that when hypnotic subjects responded to the arm
levitation suggestion, motor intentions were unavailable to inform the generation of
an accurate forward-output model, leading to a mismatch between predicted and
actual sensory feedback (corresponding to increased cerebellar activation). This
mismatch resulted in a lack of inhibition of the sensory feedback (corresponding to
greater parietal activation), which formed the basis of the experience of the movement
as not generated by the self.
The model put forward by Blakemore and colleagues is an important advance
in our understanding of some aspects of hypnotic behaviour. However, it leaves
unaddressed why an efference copy either does not result from the motor preparation
for hypnotic arm levitation (an activity orchestrated by the frontal pre-motor cortex in
conjunction with other frontal regions) or is not available to the cerebellum. This itself
points to a fundamental difference in core aspects of frontal-cortical involvement in
the control of voluntary arm raising versus that of hypnotic arm levitation. Neither
does their model obviously generalize to account for the non-volitional quality of
cognitive, rather than motor, responses to hypnotic suggestion (e.g., hypnotic
amnesia). Nonetheless, this important application of a contemporary neuroscience
paradigm to the experience of non-volition in hypnosis has clear implications for the
extension of DCT.
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Higher-order cognitive controls involve wide networks of functional
interactions between specialized frontal, posterior and subcortical regions (see e.g.,
Egner and Hirsch 2005; Friston 2002; Makeig et al. 2004). Frontal regions play
distinctive roles within such processes, but those roles can best be understood by
examining these regions within their wider context of functional interactions. This
broader framework was implicit but undeveloped in the Norman and Shallice SAS
model. The availability of modern imaging technologies and consequent rapid
development of cognitive neuroscience makes possible the detailed analysis of such
relationships. The challenge for DCT is to locate its account of frontal cortical regions
and higher-order cognitive control within a broader understanding of functional
relationships between various brain regions. This new level of detail should permit
the formulation of specific predictions about the changes in cognitive control that
underlie hypnosis, predictions which will be testable with the newly available
technologies.
7.6. The Role of the Anterior Cortex in Cognitive Control
According to the SAS model and many subsequent accounts, cognitive control
is implemented by top-down biasing of task-relevant processes (Miller and Cohen
2000). Specific task or goal representations, which are the source of these biasing
influences, are localized within various regions of the prefrontal cortex (PFC).
However, Cohen et al. (2004), in their conflict-monitoring model, argued that flexible
cognitive control, sensitive to changes in task demands, requires an additional element
to monitor the effectiveness of existing control and to provide feedback for
appropriate control adjustments. They proposed that a specific region of the frontal
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cortex, the anterior cingulate cortex (ACC), performs the function of monitoring for
processing conflicts between operations under the active control of PFC task
representations (Botvinick et al. 2001). Conflict-related activation in the ACC then
signals the need for greater activation in PFC representations to further strengthen the
bias toward task-relevant processing pathways in frontal motor areas, posterior cortex
and related subcortical structures. Thus, monitoring and control, both core elements of
the original SAS formulation, are functionally and anatomically fractionated in this
conflict-monitoring model of cognitive control.
In one earlier event-related fMRI study of this model, MacDonald et al. (2000)
utilized a version of the Stroop task to produce a dissociation between demands for
cognitive-control task preparation and levels of response conflict during stimulus
response. For each Stroop stimulus, the colour and word were either congruent (low
conflict) or incongruent (high conflict). Before each trial, participants received an
instruction to either name the word (low demand for cognitive control) or name the
colour (high demand for cognitive control) of the stimulus. Consistent with the
predictions of the model, the contrast between high and low demands for control in
the preparation period showed activation in the left dorsolateral prefrontal cortex
(lDLPFC) corresponding to the recruitment of control resources. However the
contrast between high and low response-conflict stimuli in the stimulus-response
period showed activation in the ACC corresponding to the detection of increased
response conflict. Predictions from this model have since received further empirical
support by results from a wide range of behavioural, EEG, and imaging studies
(Botvinick et al. 2004).
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7.8. DCT and the Cognitive Neuroscience of Cognitive Control
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 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 high and low susceptible individuals in baseline and hypnosis conditions
(see also Egner and Raz, this volume). 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.
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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 high (but not low) susceptible
individuals in hypnosis. There were no behavioural differences between high and low
susceptible individuals in either baseline or hypnosis conditions due to the very long
(12 second) inter-stimulus interval in this experiment. This is a stringent
methodological safeguard adopted (where possible) in imaging studies to rule out
differences in task difficulty as an alternative explanation for obtained differences
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 high
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 high and low susceptible individuals continued
to perform the task with comparable levels of speed and accuracy even in the
hypnotized condition. There were no significant differences between high and low
susceptible individuals in the activation of left frontal regions identified as
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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 high susceptible individuals in hypnosis. Rather, components of the
SAS (prefrontal representations of task requirements) 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 findings of Kaiser et al. (1997). Using a response-conflict paradigm,
they showed that although error rates increased for higher susceptible individuals in
hypnosis, there was no change in the error-related negativity (Ne), an event-related-
potential component generated by the ACC when a response error occurs. Although
there is some controversy about the role of the Ne (Holroyd et al. 2004), the Ne is
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
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or rule representations 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) demonstrated that, in
comparison to 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
appropriately 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 (30-50Hz) frequency band between left frontal and frontal midline recording
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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 oscillations 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 e.g., 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 this volume; also Kaiser and Lutzenberger 2003;
Tallon-Baudry 2004). Gamma coherence between these regions decreased in hypnosis
for high susceptible individuals, whereas for low susceptible individuals it increased.
This pattern is clearly consistent with a breakdown in high 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 (this
volume) point out, hypnotic suggestions do not appear to call only for routine or over-
learned responses, implying at least some degree of SAS involvement. Consistent
223

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 then 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.
7.9. Signalling the Adjustment of Cognitive Control
The revisions of DCT proposed so far, in addition to offering specific details
on many aspects of the neural implementation of functional aspects of the model,
raise further specific questions that address not only unresolved aspects of the model
but also fundamental issues in the cognitive neuroscience of cognitive control. In
particular, how does ACC conflict monitoring signal appropriate adjustments in
cognitive control, and how does this signalling process break down in hypnosis?
Aston-Jones and Cohen (2005) proposed that ACC projections trigger phasic changes
in the neuromodulatory noradrenergic activity of the locus coeruleus, which brings
about an adjustment in activity of current prefrontal task representations.
Nieuwenhuis et al. (2005) further proposed that this neuromodulatory response is the
cause of the time-locked increase in frontal and posterior EEG activity in response to
motivationally salient sensory stimuli observed in the P3 component of averaged
waveforms. If these proposals are correct, one testable implication for the revised
224

model of DCT advanced here would be a general weakening of the P3 responses (or
similar novelty- or error-detection responses) in hypnotized high susceptible
individuals.
Though there is considerable evidence for attenuation of P3 responses in the
context of specific hypnotic suggestions—for example, analgesia (DePascalis et al.
1999) and obstructive hallucination (Spiegel et al. 1985)—these are not necessarily
equivalent to the broader effects of the hypnotized condition. Interestingly, in the
study by Kaiser et al. (1997), although error-related negativity (Ne) was unaffected by
hypnosis, the later error-related positivity (Pe) was diminished by hypnosis in the
more highly susceptible participants. Even though much more work is needed to
clearly identify the distinct functional role of the Pe, there is evidence for a distinct
role for the Pe in affective evaluation, behavioural adaptation, and error awareness
processes (Falkenstein 2004). In a recent review of experimental literature contrasting
the Pe with the Ne, Overbeek et al. (2005) concluded that different responses to a
range of experimental manipulations demonstrate that the Pe and Ne must correspond
to distinct aspects of the error-response process. They argued that in view of its
latency, topography, and context, the most promising interpretation of the Pe was that
of a P3 to an emotionally salient error response (an interpretation not inconsistent
with any of those listed by Falkenstein). A replication and further investigation of the
Kaiser et al. findings, correcting the methodological limitations of that study, may
open an important avenue for the investigation of the neural processes underlying the
dissociation of conflict monitoring from adaptive change in cognitive control
observed in hypnosis.
225

7.10. Differing Roles of Rostral versus Dorsal ACC in Hypnotic Experience
Increases in the activation of various regions within the ACC have been a
common denominator in almost all imaging studies of the effects of hypnosis or
various specific hypnotic suggestions. One possible interpretation is that this simply
reflects ACC response to increased response conflict as a general feature of the
hypnotic condition. However, the ACC is a functionally heterogeneous region with
roles extending well beyond conflict monitoring. Single-cell recording studies in
monkeys have identified different cells within the ACC that fire differentially in
response to distinct events, such as a reduction in anticipated rewards, the occurrence
of response errors, and the adjustment of behaviour following feedback (Ridderinkhof
et al. 2004). Bush et al. (2000) conducted a meta-analysis of human imaging studies
of cognitive and emotional tasks which supported a division between sensitivity to
affective versus cognitive task demands along the rostral to caudal axis of the ACC.
Ridderinkhof et al. (2004) also conducted a meta-analysis of feedback, error and
conflict related fMRI studies and concluded that despite considerable overlap, ACC
foci activated by response conflict tend to cluster more dorsally than those activated
by error or response feedback (i.e., response evaluation). Yeung (2004) has proposed
that ACC conflict monitoring (as evident in the Ne) forms the bases of cognitive input
into further ACC evaluative, affective processing, which then recruits adjustments in
cognitive control.
PET studies of hypnotic hallucinations have identified changes in activation
common to both hallucinated and real sensory stimuli (but not to imagined stimuli) in
both more rostral (Szechtman et al. 1998; utilizing auditory experience) and
226

caudal/dorsal (Derbyshire et al. 2004; utilizing pain experience) regions of the ACC.
Rainville et al. (2002) carried out a PET study that contrasted activation before and
after hypnotic induction. In addition to other regions, results identified multiple
regions of the ACC along the caudal–rostral axis from mid-cingulate ACC to rostral
ACC, and, further along this axis, to perigenual ACC. Rainville et al. (2002) then
carried out a regression analysis of changes in regional cerebral blood flow on self
ratings of mental relaxation and absorption taken after each scan. Relaxation during
hypnosis was associated with activation in mid-cingulate and perigenual ACC,
whereas ratings of absorption in hypnosis were associated with activations in rostral
ACC (a relationship further accentuated by removal of relaxation-related variance
from absorption scores). In another PET study, Faymonville et al. (2000) found the
analgesic effects of pleasant hypnotic suggestions were related to changes in activity
in the mid-cingulate region of the ACC. Faymonville et al. (2003; see also Boly et al.
this volume) then conducted a psychophysiological interaction analysis to determine
which brain regions were modulated by mid-cingulate activity in their response to
noxious stimuli during the pleasant hypnotic suggestions. Amongst the network of
regions identified was the perigenual ACC. In summary, these studies highlight
multiple regions of ACC involvement in hypnosis as part of wider cortical and
subcortical networks regulating conscious experience.
In addition to regions of the ACC selectively sensitive to response conflict,
other regions engaged by hypnotic suggestions include both more rostral and,
arguably, higher-order evaluative regions of the ACC. For example, ACC activations
corresponding to experiences of pain and “reality” in the studies above may also be
considered to reflect evaluations of the corresponding sensory representations. In
227

these experiments, different ACC regions appear to be playing distinct but connected
roles in the generation of hypnotic experiences. We interpret these findings by first
elaborating on the proposal by Yeung (2004) for unifying conflict monitoring and
motivational accounts of the Ne. We suggest that the activity of specialized conflict-
sensitive regions within dorsal and mid-cingulate ACC (which in the case of errors
generates the Ne) is subsequently monitored and evaluated in relation to affectively
and motivationally relevant performance outcomes in more rostral regions of the
ACC. This process (which may include interactions with other cortical and subcortical
regions) occurs later than the initial conflict-monitoring response and requires strong
functional connectivity between dorsal and rostral regions of the ACC. It is the
outcome of this evaluative monitoring process which then either directly or indirectly
(through the modulation of phasic locus coeruleus activity) triggers adaptive changes
in cognitive control. In the case of error responses, it is this system that triggers the
conscious correction processes associated with the Pe.
7.11. Further Development of DCT
In an important sense, the revised DCT turns out to be a theory about the
control of control. We suggest that the crucial breakdown in the flexible (and, in
particular, the conscious intentional) adjustment of cognitive control occurs as a result
of the disruption, not of the unconscious detection of conflict, but rather of the further
evaluative monitoring of that conflict detection. This evaluative process likely
engages more rostral regions of the ACC and is subsequently responsible for signals
triggering adaptive change. In the results obtained by Egner et al. (2005), conflict-
related activations to colour-naming incongruent stimuli were more extensive than to,
228

for example, colour-naming congruent stimuli. This greater activation occurred
particularly in more rostral regions of the ACC. We suggest that this was due not only
to ACC detection of greater levels of response conflict, but also to the engagement of
processes that evaluate and signal the greater demands for cognitive control
engendered by this conflict. Due to their specificity, these further proposals for the
neural implementation of dissociated control are readily testable in a variety of
available behavioural, EEG, and imaging paradigms.
We conclude by summarizing the two related proposals we have advanced for
the extension of DCT. The first is based upon the cognitive neuropsychological model
of cognitive control developed and tested by Cohen and associates, and applied in
studies such as Jamieson and Sheehan (2004) and Egner et al. (2005) to examine the
effects of hypnosis and hypnotic susceptibility on the resolution of Stroop interference
conflict. This proposal incorporates, as did Hilgard’s earlier formulations of
dissociation in hypnosis (e.g., Hilgard 1977), the critical distinction between
monitoring and the implementation of control in the flexible regulation of cognitive
systems. On this account, top-down biasing by prefrontal representations is able to
play an important role in facilitating responses in hypnosis that would not be possible
by CS alone. However, although information from conflict monitoring, mediated by
regions within the ACC, continues to be processed during hypnosis, it is (to varying
degrees) unavailable to guide the adjustment of active control of PFC representations.
The second proposed extension of DCT is more speculative. It seeks to more
closely specify how the neural implementation of higher-order control breaks down in
hypnosis by drawing on recent attempts to integrate the affective and evaluative
229

functions of the ACC with its conflict-monitoring functions. In so doing, it also seeks
to explain the varied findings with respect to activation of differing regions within the
ACC in a number of diverse imaging studies of hypnotic consciousness.
Both proposals are sufficiently clear to yield results that will show where and
how they fail to fit the phenomena and in what way they will need to be modified and
developed to achieve a more adequate theory. We hope they offer fruitful bases for
the development of our understanding of the altered relationship between
consciousness and control that DCT sees at the heart of hypnosis. In addition, this
work should contribute to a wider understanding of the nature of consciousness and
control and the variety of possible relationships between them, which lie at the core of
human experience.
230

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