Not a HOT Dream
Miguel Ángel Sebastián
UNAM/LOGOS
msebastian@gmail.com
Abstract
Higher-Order Thought (HOT) theories of consciousness maintain that the kind of awareness
necessary for phenomenal consciousness depends on the cognitive accessibility that underlies
reporting.
There is empirical evidence strongly suggesting that the cognitive accessibility that underlies the
ability to report visual experiences depends on the activity of the dorsolateral prefrontal cortex
(dlPFC). This area, however, is highly deactivated during the conscious experiences we have
during sleep: dreams. HOT theories are jeopardized, as I will argue.
I will briefly present HOT theories in the first section. Section 2 offers empirical evidence to the
effect that the cognitive accessibility that underlies the ability to report depends on the
dorsolateral prefrontal cortex: dlPFC is the neural correlate of HOTs. Section 3 shows the
evidence we have of the deactivation of this brain area during dreams and, in section 4, I
present my argument. Finally, I consider and rejoin two possible replies that my opponent can
offer: the possibility of an alternative neural correlate of HOTs during dreams and the denial that
we have phenomenally conscious experiences during sleep.
Keywords: Phenomenal Consciousness,
Dorsolateral Prefrontal Cortex.
Higher-Order
Thought
Theories,
Dreams,
1 Introduction
In 'On a confusion about the function of consciousness', Ned Block (1995-2002)
famously maintained that our folk psychological term 'consciousness'
equivocates between two concepts: 'access-consciousness' and 'phenomenal
consciousness'. The first one has to do with the processing of information.
When I look at the cup of coffee in front of me I take in plenty of information: the
cup is located in front of me, to the left of my computer, it has cylindrical shape
and red color and it is filled with a black liquid. When I consciously see the cup,
my brain processes all this information and this information is typically available
for further reasoning (deciding to drink the coffee), motor control (moving my
hand toward the cup), etc. Understanding the mechanisms that underlie these
processes constitutes what Chalmers (1996) calls 'the easy problem of
consciousness'. It is, no doubt, a very complicated issue given the complexity of
our brains, but the research in neurosciences has made huge amounts of
progress in recent years and it is, from a philosophical perspective, relatively
unproblematic.
Nevertheless, there is more to consciousness than this information processing.
When I see my cup, there is something it is like for me to see it; a reddish way,
among others, it is like for me to have this experience. This is phenomenal
consciousness and explaining it is what constitutes the hard problem of
consciousness (Chalmers (1996)).
The relation between access and phenomenal consciousness is an important
issue that cannot be settled without a further clarification of the notions involved.
Even so, some form of access seems to be essential to phenomenal
consciousness, for it is platitudinous that when one has a phenomenally
conscious experience, one is in some way aware of it. Let me call this kind of
access 'Awareness' following Block (2007).
Higher-Order Representational (HOR) theories of consciousness maintain that
Awareness is a form of representation. That is to say, phenomenally conscious
states are states that are the object of some sort of higher-order representation.
The kind of representation that is required by the theory makes a basic
difference among HOR theorists.1 Nonetheless, I want to draw an orthogonal
distinction to make the target of the argument I am about to present clear. My
target in this paper will be theories that maintain that Awareness is a form of
cognitive access, the same cognitive access that underlies the ability to report
−more precisely, higher-order theories that maintain that the cognitive ability
that makes it possible to report the content of a mental state is essential to
phenomenally conscious mental states. My opponent holds a higher-order
cognitive position characterized by the following three claims:
1 The main concern is whether higher-order states are belief-like or perception-like. The former
are called Higher-Order Thought (HOT) theories (Gennaro (1996); Rosenthal (1997, 2005)) and
the latter Higher-Order Perception (HOP) or 'inner-sense' theories (Amstrong (1968); Carruthers
(2000); Lycan (1996)). According to the former theories, when I have a phenomenally conscious
experience as of red I am in a mental state with certain content, call this content RED . For this
mental state to be phenomenally conscious, there has to be, additionally, a higher-order thought
targeting it, whose content is something like I am seeing RED . On the other hand, HOP
theories maintain that what is required is a (quasi-) perceptual state directed on to the first-order
one. A second point of disagreement is whether a given state is conscious in virtue of its
disposition to raise a higher-order representation (Carruthers (2000)) or by being actually the
target of a higher-order representation (Rosenthal (1997, 2005)); this is the difference between
dispositional and actualist HOR theories. According to dispositional HOR theories, the higherorder representation that renders the Awareness of the first-order one doesn't have to be actual;
i.e., there is no need for the higher-order representation to happen actually, what is needed for a
mental state to be conscious is a disposition to be the object of such a higher-order
representation.
Higher-Order Cognitive
1. Consciousness requires Awareness.
2. Awareness requires the right kind of Higher-Order Representation.
3. The right kind of Higher-Order Representation depends on the cognitive
accessibility that underlies reporting.2
This position has been paradigmatically held by Higher-Order Thought (HOT)
theorists.3 According to HOT theories, a mental state M is conscious if and only
if there is another belief-like mental state (a Higher-Order Thought) to the effect
that one is in M. Being conscious requires being Aware of oneself as being in a
certain mental state and this Awareness is explained as being the target of the
appropriate HOT (e.g. a HOT that is non-inferentially caused). The greatest
exponent of this theory, David Rosenthal, explicitly endorses the
correspondence between HOTs, and hence conscious mental states, and the
ability to report being in a particular mental state. In 'Thinking that one thinks'
Rosenthal (Rosenthal (2005, chapter 2)) writes:
[G]iven that a creature has suitable communicative ability, it will
be able to report being in a particular mental state just in case
that state is, intuitively, a conscious mental state. If the state is
not a conscious state, it will be unavailable to one as the topic
of a sincere report about the current content of one's mind. And
if the mental state is conscious one will be aware of it and
hence able to report that one is in it. The ability to report being
in a particular mental state therefore corresponds to what we
2
Note that organisms lacking our ability to report being in a particular mental state might
still have the same kind of cognitive accessibility that we have. Hence, lacking the ability to
report does not prevent that one can have higher-order representations.
3
Not all Higher-Order theories are committed to these three claims. Consider, for
instance, Carruthers (2000)'s dispositionalist view. According to Carruthers, phenomenally
conscious states are, roughly speaking, states that are recognized as representations by a
Theory of Mind. Each experience would, at the same time, be a representation of some feature
of the world (for example, a representation of red) and a representation of the fact that we are
undergoing such an experience (a representation of seems red), through the consumer system
that is the Theory of Mind.
If these mindreading capacities do not depend on the cognitive accessibility that
underlies reporting, as it plausibly doesn't, then Carruther's theory illustrates an example of a
Higher-Order theory that is not jeopardized by the success of my argument.
In section 4 I will present a hypothetical cognitive HOR theory that might be immune to
my argument.
intuitively think of as that state's being in our stream of
consciousness. (Op. cit., p.55, my emphasis)
I will focus on Rosenthal's HOT theory in my criticism for I consider it to be the
quintessence of theories that hold a higher-order cognitive position. The position
that I will be defending, call it non-cognitive position, maintains that Awareness
does not depend on the cognitive accessibility that underlies reporting.
Therefore, it maintains, pace HOT theories, that there can be cases of
phenomenal consciousness on which subjects might not be able to report due
to a failure in the cognitive access.
In the next section, I will provide empirical evidence in favor of the premises of
my argument. Section 3 presents my argument against HOT theories and in
section 4 I consider some possible objections and offer a rejoinder.
2 The Neural Correlate
Experiences: dlPFC
of
Cognitive
Accessibility
for
Visual
The evidence for the neural correlate of the cognitive accessibility, in the case of
visual experiences, is provided by an experiment performed by Lau and
Passingham (2006). This experiment suggests that such cognitive accessibility
depends on the dorsolateral prefrontal cortex (dlPFC).
The experiment is based on a visual discrimination task with metacontrast
masking. Metacontrast masking takes place when a target stimulus is followed,
after a short period of time called Stimulus Onset Asynchrony (SOA), by a mask
that shares a contour with it, leading to a reduction in perceived brightness and
to degraded perception of the spatial shape of the target (Haynes and Rees
(2003)).
Subjects in the experiment are asked to fixate their gaze and they are presented
with one of two possible stimuli, either a square or a diamond on a black
background. After a short variable period of time, the SOA, a mask is presented.
The mask overlaps with part of the contour of both possible stimuli but it does
not overlap with any of them spatially (See Figure 1).
Fig. 1: Lau & Passingham's Experimental Set up.4
Subjects in the experiment have to perform two tasks after the presentation of
the target and the mask:
1. Decide whether the target stimulus was a diamond or a square.
2. Indicate whether they actually saw the target or were simply guessing in
the previous task.
The first question is intended to measure the objective performance capacity of
the subjects: how good they are at identifying the target stimulus. The second
question is intended to measure the perceptual certainty of the subjects: how
confident they are on having seen the stimulus. This subjective report,
according to the authors and to HOT theories, is an indication of phenomenal
consciousness.
Figure 2 shows the result as a function of the SOA, the interval between the
presentation of the target stimulus and the mask. The presence of the mask has
nearly no influence on the performance capacity (represented by a continuous
line) nor on the perceptual certainty (represented by the dotted line) when
presented before or close to the stimulus. As the SOA increases, the mask
interferes with the perception of the target stimulus and both, the performance
capacity and the perceptual certainty decrease until a certain point where the
influence of the mask starts to diminish, having no effect at all when it is
presented much later than the stimulus. The resulting curves have a U-shape,
where two points, corresponding to different SOAs, with the same performance
capacity and two points, also corresponding to different SOAs, with the same
4
Lau and Passingham (2006). Copyright (2006) National Academy of Sciences, U.S.A.
perceptual certainty can be identified.
Fig. 2: Performance Capacity (% correct) vs. Perceptual Certainty (% seen)5
The interesting finding is that we can detect two conditions under which the
performance capacity of the subjects is the same but such that they differ in
their perceptual certainty. Whereas in one (short SOA), subjects tend to report
having guessed when they were asked about the identity of the stimulus; in the
other (long SOA), subjects are fairly confident of having seen it. For HOT
theories, the subject is phenomenally conscious only in the second case where
she reports having seen the stimulus.
Lau and Passingham performed an fMRI study on the subjects of the
experiment. Their study revealed that the long SOA condition was associated
with a significant increase in activity in the left mid-dorsolateral prefrontal cortex
(mid-dlPFC, Brodmann's area 46).
My opponent maintains that Awareness depends on the cognitive accessibility
that underlies reporting. In the Lau and Passingham experiment, subjects report
having seen the stimulus in the long SOA condition but not in the short one.
Hence, we may assume that they are phenomenally conscious of the stimulus
only in the long SOA condition. Since HOTs are associated with reporting
abilities, Lau and Passingham have found the neural residence of HOTs, at
least for visual higher-order thoughts (thoughts of the form 'I see a square').6
Rosenthal explicitly accepts the evidence from this experiment as showing that
5
Lau and Passingham (2006). Copyright (2006) National Academy of Sciences, U.S.A.
6
Lau and Passingham maintain that consciousness should be associated with
perceptual certainty. Lau (2008) explicitly endorses this view. He maintains that consciousness
depends on Bayesian decisions on the presence of the stimuli relying upon a learning process
and on the firing pattern of the first-order representations. Lau named his view Higher-Order
Bayesian Decision Theory. It is unclear to me why a proposal along these lines should be
considered a Higher-Order Representationalist one. See fn. 12.
the neural correlate of HOTs is in the dlPFC:
There is, however, some evidence that states are conscious
when, and only when, a distinct neural state occurs in middorsolateral prefrontal cortex (area 46) (Lau & Passingham,
2006), and it is reasonable to explore identifying these neural
occurrences with the posited HOTs. Rosenthal (2008, p. 835).
On the other hand, the defender of the non-cognitive position would maintain
that the curve corresponding to phenomenology could be somewhere in
between the two curves in figure 2 (% correct and % seeing) and is not
impressed by the fMRI data. The reason is that she would have predicted
exactly this result: the judgment of having seeing the stimulus, which
corresponds to a HOT, is reflected in the prefrontal cortex.7
So, does the Lau and Passingham's experiment bring some light to the debate
between higher-order cognitive and non-cognitive approaches? I think it does,
but precisely in the opposite direction from which the authors intended. If HOTs
live (or at least a significant part of their neural correlate is) in the dlPFC, as the
experiment suggests, and there were a case of phenomenology without
activation of dlPFC, HOT theories would be in trouble. It's time for dreaming.
3 Dreams and dlPFC
Revonsuo (2000) defines dreams as a subjective experience during sleep,
consisting of complex and organized images that show temporal progression .
Dreams are phenomenally conscious experiences, experiences that are similar
in many respects to the ones we have during wakefulness. Our dreams are
highly visual, with rich colors, shapes and movements, and include sounds,
smells, tastes, tactile sensations, and emotions, as well as pain and pleasure
(Hobson et al (2000)).
Dreams can be so similar to our waking experiences that the dreamer may be
uncertain whether he is awake or asleep. This platitude has been taken for
granted by most philosophers. It has, for instance, led philosophers to wonder
whether we can distinguish the two states or even whether one could actually
be dreaming constantly. This has been considered by Plato, Aristotle and most
famously in Descartes’ skeptical argument in the First Meditation. The view that
dreams are conscious experiences has been explicitly endorsed, in the
7 This possibility has been suggested by Ned Block in the Second Consciousness Online
Conference (http://consciousnessonline.wordpress.com)
philosophical field, by, among others, Kant, Russell, Moore, and Freud (Malcolm
(1959, p.4)). Most contemporary philosophers working on dreams also hold this
view (see for instance Ichikawa (2009); Ichikawa and Sosa (2009); Metzinger
(2003, 2009); Revonsuo (2006); Sosa (2005)).
I do not intend to argue that dream experiences are exactly like waking
experiences. According to Tononi (2009, p.100), dreaming experiences in
comparison to waking experiences are characterized by disconnection from the
environment, internal generation of a world-analogue, reduction of voluntary
control and reflective thought, amnesia and a high emotional involvement.
Furthermore, dream reports may include phenomena that resemble
neuropsychiatric conditions such as distortion of time perception, perceived
distortion of body parts, bizarre illogical situations, prominence of negative
emotions, anxiety and fear, and misidentification syndromes like erroneously
recognizing a familiar person despite the lack of any obvious physical
resemblance (Karim (2010)). The only point that is relevant for the purpose of
this paper is that we have dreams and that dreams include phenomenally
conscious visual experiences.8
Sleep is traditionally divided into two phases: non-rapid eye movement (NREM)
sleep and rapid eye movement (REM) sleep.9 The succession of this two
phases is called a sleep cycle, and, in humans, it lasts for approximately 90-110
minutes. There are 4-5 cycles per night. It has been established that dreams
occur during (though probably not exclusively) REM phase of sleep.
Although there is some controversy as to whether or not there are dreams that
occur during NREM, there is no doubt that we dream during REM phase. If
subjects were awakened from that stage of sleep and asked whether they had
dreamed, they would say yes at least 80% of the time. What happens in the
brain during this period?
3.1 Neurophysiology of Sleep
During sleep there is a global reduction in metabolic activity and blood flow in
the brain. Compared to resting wakefulness, the decrease during NREM phase
can reach a 40% as shown by positron emission tomography (PET) studies
(Braun et al (1997)). At the cortical level, activation is reduced in the
orbitofrontal and anterior cingulate and dorsolateral prefrontal cortex
8 Some philosophers have tried to resist this claim. I will present their views and offer a
rejoinder in subsection 5.2.
9 A more fine-grained categorization of the NREM phase can be done based on EEG, EOG,
and EMG patterns. For details see Tononi (2009).
−Broadmann area 46 (See Braun et al (1997, table 1 p.1177)).
During REM sleep some areas are even more active than in wakefulness,
especially the limbic areas. In the cortex, the areas receiving strong inputs from
the amygdale, like the anterior cingulate and the parietal lobe, are also activated
(Maquet et al (1996, table 1 p.164)). On the other hand, the rest of the parietal
cortex, the precuneus and the posterior cingulate are relatively inactive (Braun
et al. (1997, table 2 p.1178)).
What is relevant for this discussion is that there is a selective deactivation
(compared with wakefulness) of the dlPFC (Braun et al (1997); Maquet et al
(1996, 2005); Muzur et al (2002)) during REM phase.10 Specifically, Maquet et
al. showed a very significant reduction in the activity of the area identified by
Lau and Passingham (left dorsolateral prefrontal cortex).
All of these regional activations and inactivations are consistent with the
differences in mental states between sleep and wakefulness (see Schwarz and
Maquet (2002); Tononi (2009)). In particular, the deactivation of the dlPFC,
which is associated with executive abilities such as expectancy, volitional
control and working memory in wakefulness (Fuster (2008)), fits in well with the
common loss of self-reflective awareness and rational control in dreams (Kahn
(2007)).
According to Lau and Passingham's experiment, the neural correlate of HOTs
lies in the dlPFC; there is an increase in its activity when subjects report having
seen the stimulus in comparison with the situation in which they report not
having seen it and having guessed −despite the lack of difference in their
performance in both situations. If HOTs were constitutive of phenomenal
consciousness we would expect its neural correlate to be active during dreams.
However, empirical evidence suggests the opposite. Given these elements the
reader can easily anticipate my argument against HOT theories.
4 The Argument
In this section I present the argument against HOT theories in more detail.
Let me start with a simple argument against cognitive theories of consciousness
in general. I call 'cognitive theories of consciousness' those theories that
10 In the Maquet et al. study, subjects were controlled for dreaming (the subject maintained
steady REM sleep during scanning and recalled dreams upon awakening). This control is
missing in the Braun et al. study.
maintain that the cognitive accessibility that underlies reporting is constitutive of
phenomenal consciousness. One example of such cognitive theories is, as we
have seen, Rosenthal's HOT theory. Another example is Michael Tye's PANIC
theory (Tye (1997, 2002)). According to Tye, phenomenally conscious mental
states are states whose content is Poised, in the sense that it is available to
first-order belief-forming and behavior-guiding systems; Abstract, meaning that
the intentional content is not individuated by the particular things represented;
and Non-conceptual in the sense that it is not structured into concepts. Contrary
to HOT, PANIC is a first-order theory. It does, however, endorse the claim that
phenomenal consciousness depends on the cognitive accessibility underlying
our ability to report −on the plausible assumption that it is the same one as the
one that underlies belief-forming and behavior-guiding.
The argument against cognitive theories of consciousness has the form of a
reductio ab adsurdum:
(Anti-Cognitive)
1. Phenomenal consciousness depends on the cognitive accessibility that
underlies reporting.
2. The cognitive accessibility that underlies reporting, in the case of visual
experiences, depends on the left dorsolateral prefrontal cortex (dlPFC).
3. dlPFC is necessary11 for phenomenally conscious visual experiences
(From 1 and 2).
4. We have phenomenally conscious visual experiences during the REM
phase of sleep.
5. dlPFC is deactivated during the REM phase of sleep.
6. dlPFC is not necessary for phenomenally conscious visual experiences
(From 4 and 5).
________________
7. Phenomenal consciousness does not depend on the cognitive
accessibility that underlies reporting (From 1-6).
Premise 1 is the common claim of what I have called cognitive theories of
consciousness and the assumption of the argument. Premise 2 is supported by
Lau & Passingham's experiment. As I have presented it, the neural correlate of
the difference between subjects reporting seeing the target stimuli and not
seeing it is in the left dorsolateral prefrontal cortex. (3) follows from these two
premises.
11 Modal claims in this argument are obviously to be read as restricted to beings like us in
worlds with the same laws as the actual one.
It is hard to deny that we have conscious experiences during sleep and that
those experiences include conscious visual experiences. These experiences
typically happen during the REM phase of sleep (4). However, as we have
seen, there is empirical evidence showing a selective deactivation of the dlPFC
during the REM phase (5). (4) and (5) together suggest that the activation of the
dlPFC is not required for having a phenomenally conscious experience and lead
us to the claim that the dlPFC is not necessary for consciousness (6).
(3) and (6) are contradictory claims, what lead us to reject premise 1, QED.
This argument might, however, be invalid. The reason is that one can deny that
(6) follows from the conjunction of (4) and (5). This possibility is explored by Lau
himself. According to Lau's theory (Lau (2008)), the role of dlPFC is to work as a
Bayesian decision system that tries to make accurate judgments about the
inputs of the sensory cortex. The increase in the noise signals in the sensory
cortex during REM phase in comparison to NREM, accompanied by a
deactivation of the dlPFC, explains dreams as a malfunction of the decision
system.
By this definition, one hallucinates while dreaming; in dreams
we consciously perceive stimuli that are not really there...
Dreams are more likely to be reported during a stage of sleep
that is characterized by rapid eye movement (REM), and brain
activity of relatively high frequency and intensity. Let us
assume that the overall signal during REM-sleep is higher. If
the brain maintains the same criterion for detection over
alternations of REM and non-REM sleep, it would be predicted
that false positives are a lot more likely during REM-sleep,
because of the higher signal intensity. (op.cit., p.41)
Dreams are for Lau similar to hallucinations. According to Lau, during sleep the
dlPFC is deactivated and, therefore, malfunctioning, making the wrong
judgments.12 Lau can, hence, accept (4) and (5) while resisting (6): the dlPFC is
malfunctioning due to its deactivation, but its judgments, right or wrong, are still
required for phenomenal consciousness.
In order to properly evaluate Lau's claim, further details about how the decision
12 Lau has maintained, in private conversation, that, contrary to HOT, the under-activation of
the dlPFC during REM phase is favorable to his theory because in dreams perceptual
judgments are wrong.
mechanism is supposed to work and how the decrease of activity in the dlPFC
is related to this mechanism need to be added. We need an explanation of how
the decrease in the activity of the dlPFC during REM is related to the failure to
set an appropriately high criterion during REM sleep so that one mis-classifies
noise as stimuli. (op.cit, p.41). Such an explanation has to be compatible with
the fact that the perceptual certainty, which according to Lau corresponds to
phenomenal consciousness, is accompanied with an increase in the activity of
the dlPFC in the original experiment. It is an open question whether a
satisfactory answer can be provided and an empirical issue whether the dlPFC
works in this way. If Lau were right then (Anti-Cognitive) would be an invalid
argument.
This line of reasoning can be endorsed by defenders of first-order cognitive
theories like Tye's PANIC. It seems reasonable to think of the dlPFC as a filter.
A state would be available for reporting −and hence poised− if the dlPFC let its
content go through; in other words, if the dlPFC decides that the signal arriving
corresponds to sensory input and not to noise. A similar reply could be provided
by a particular kind of Higher-Order Theory, call it Indexical Higher-Order
Representational Theory (IHOR). According to IHOR, in the case of visual
conscious experiences, the first-order state with the content *SQUARE* is
accompanied by a higher-order indexical thought, encoded in the dlPFC, with
the content I SEE THIS pointing to the first-order one.1314
This strategy is, however, not available for HOT theories. According to HOT
theories, the higher-order state is not indexical as in IHOR, but something like I
SEE A SQUARE in the previous example. If dlPFC encodes HOTs, we would
expect an increase in its activity as the content of conscious phenomenology
increases, because we would expect more frequent updates in the
13
If one is interested in this strategy, one would have to elaborate on the mechanisms on
which such a demonstration would rely.
14
Those willing to endorse Lau's model of cognitive accessibility will maintain that there
are two states involved. The relation between these two states distinguishes higher-order and
first-order theories. Lau and Passingham (2006) seem to be silent among the two kinds of
theories.
On the one hand, a first-order theory maintains that there is a merely causal relation
between the two states, which we can call ANIC and PANIC taking Tye's theory as a model, and
that both states have the same intentional object, say the square.
On the other hand, IHOR maintains that the relation between a first-order and the
higher-order one is not only causal but intentional. Whereas the first-order state has the square
as its object, the higher-order one has the first-order one as its intentional object. IHOR has to
make room for cases in which there is no first-order state, cases of misrepresentation. It is
unclear to me what would be the phenomenology of cases in which the demonstration fails and
there is no first-order state the higher-order one is pointing to. For a discussion on related issues
derived of such an intentional relation see Block (2011); Rosenthal (2011); Weisberg (2011).
corresponding HOTs. HOT theory seems to be committed to the claim that there
is a monotonic relation between the content of conscious experiences and the
activity of the neural correlate of HOTs. It is, therefore, unable to accommodate
the data about the brain activity during dreams as we have just seen, blocking
thereby the inference from (4) and (5) to (6) in the argument.
In the next section I will discuss possible replies that the defender of HOT
theories can endorse against the argument and offer a rejoinder.
5 Replies
5.1 HOTs have a Different Neural Correlate during Dreams
One possible way to resist the argument would be to maintain that HOTs have
two different neural correlates. During wakefulness, dlPFC is the neural
correlate for visual HOTs, whereas during sleep HOTs have a different neural
correlate. This way, one blocks step 3 in (Anti-Cognitive), because, in spite of
the fact that the cognitive accessibility that underlies reporting in the case of
visual experiences depends on the dlPFC, it only does so during wakefulness
and, therefore, it is not true that the activity of the dlPFC is necessary for
conscious visual experiences (3).
That kind of dissociation seems, however, implausible. Having another area
responsible for HOTs during dreams would require a functional duplication and
mutual exclusion. Imagine that we have another area that is the neural correlate
of dreams during sleep,15 let me refer to this area as 'the sleep neural correlate
of HOT '(SNCHOT). When we have a visual experience during wakefulness, the
neural correlate of the corresponding HOT is in the dlPFC, and not SNCHOT,
which is not differentially activated as the fMRI in the Lau and Passingham's
experiment shows. On the other hand, during dream experiences, dlPFC is
deactivated and the neural correlate of the HOT would be SNCHOT. The
question is: why do we need SNCHOT?
REM sleep seems to be exclusive to marsupial and placental mammals (Winson
(1993)). It is, therefore, reasonable to assume that the only organisms capable
of dreams are those at the top of the pyramid of evolution. The plausibility of
SNCHOT depends on the function of dreams during sleep; a function that
should require HOTs. If dreams have no function, it seems unreasonable to
15
A plausible candidate could be the anterior cingulate. As we have seen this area is
strongly activated during the REM phase. Furthermore, the anterior cingulate communicates to
the relevant sensory and limbic areas.
assume that changes in brain activity during REM phase appear to give rise to
HOTs in other areas that were not present during wakefulness, and the only
area they are present during wakefulness seems to be the dlPFC.
Most of the theories of dreaming yield dreams as epiphenomenal.16 This has
been explicitly claimed by Flanagan:
[Dreams are] a likely candidate for being given
epiphenomenalist status from an evolutionary point of
view. P-dreaming [phenomenal experiences during sleep]
is an interesting side effect of what the brain is doing, the
function(s) it is performing during sleep. To put it in slightly
different terms: p-dreams, despite being experiences, have
no interesting biological function. I mean in the first
instance that p-dreaming was probably not selected for,
that p-dreaming is neither functional nor dysfunctional in
and of itself (Flanagan (1995, p.9)).
Sometimes it is held that dreams are the result of noise activity or a by-product
of the changes in brain activity during sleep. This option is considered by the
Activation-Synthesis theory (Hobson and McCarley (1977)), where dreams are
the result of the forebrain responding to random activity initiated at the
brainstem, the improved AIM (Activation, Input-ouput gating, Modulation) model
(Muzur et al (2002)) or by Lau (2008), as we have just seen.
Solms (1997) has recently defended the Freudian view that the function of
dreams is to protect sleep. However, Solms does not attribute any functions to
the content of dreams, and therefore HOTs, and he also regards dreams as
hallucinations that the weakened frontal reflective systems mistake for real
perception.
Other theories maintain that dreams have a function in memory processing
(Crick and Mitchison (1983); Foulkes (1985); Hobson et al (1994)), in which
case there is no function for HOTs and dreams merely reflect the corresponding
memory processing −processes that do not require any HOT.
One exception is Revonsuo (2000).17 According to him, the function of dreams
16
In the intended sense here, something is epiphenomenal if and only if it lacks biological
function. This sense should be contrasted with the sense in which something is epiphenomenal
if and only if it lacks causal impact whatsoever.
For a review of these epiphenomenal theories see Revonsuo (2000).
17
See also Franklin and Zyphur (2005) for an extension of Revonsuo's proposal.
is to simulate threatening events and to rehearse threat perception and threat
avoidance . But this function can also be performed during wakefulness, so the
same structures that we use while we are awake could be used during sleep.
As long as one cannot make the case for the function of HOTs in dreams, and I
seriously doubt that it can be made, we have no additional reason for defending
the possibility of having an additional neural structure, SNCHOT, which differs
from dlPFC. There seems to be no reason for a duplication of the HOT
machinery. If this is right, and dlPFC is the neural correlate of HOTs responsible
for visual experiences, then we have good reasons for believing that there are
no visual HOTs during dreams and therefore a good support for (3).
An alternative objection would deny that we have phenomenally conscious
experiences during sleep. This is the next objection I am going to consider.
5.2 We do not have Conscious Experience during Dreams
A different possibility to block the argument is to reject premise (4). The
common sense position maintains that dreams are conscious experiences; a
position that has been maintained by philosophers, psychologists and
neuroscientists, but not without exception.
The common sense position has been famously rejected by Malcolm (1959)
who asserts that it leads to conceptual incoherency ...the notion of a dream as
an occurrence that is logically independent of the sleeper's waking impression
has no clear sense. (op.cit., p. 70). Malcolm maintains that we have no reason
to believe the reports given by awakened subjects, for there is no way to verify
them: they could be cases of 'false memory'.18 It could be that processes during
REM phase are all non-conscious and that on awakening there is a HOT
targeting the content of memory and thereby making it conscious.
Whereas Malcolm denies that there are dreams, Dennett (1976) has defended a
skeptical position. Dennett presents an alternative account in which dreams
could be unconscious memory loading processes.19 According to Dennett,
before establishing whether dreams are conscious we need an empirical theory
of dreams and that it is an open, and theoretical question whether dreams fall
inside or outside the boundary of experience (op.cit., p.170-71). Dennett goes a
step further, claiming that we have some empirical evidence indicating that
18
Rosenthal, in conversation, points in this direction.
19
It is not worth discussing the value of the proposal itself, for it is only intended to
present a skeptical argument showing that there can be alternative explanations to dreamer's
reports when awakened.
dreams are not conscious experiences, for they fail to satisfy well confirmed
conditions for conscious experience like the activation of the reticular formation
(op.cit., p.163).
This position has been challenged by Revonsuo (1995) who provides empirical
evidence to the effect that there is in fact activity of the reticular formation and
important neurophysiological similarity between dreaming and wakefulness.
From the standpoint of the thalamocortical system, the overall
functional states present during paradoxical sleep and
wakefulness are fundamentally equivalent, although the
handling of sensory information and cortical inhibition is
different in the two states... That is, paradoxical sleep and
wakefulness are seen as almost identical intrinsic functional
states in which subjective awareness is generated. (Llinas
and Pare (1991, p. 522), quoted in Revonsuo (1995))
Unfortunately that would not impress my opponent. According to HOT theory,
consciousness necessitates the presence of a HOT; HOTs are absent during
dreams, so dreams are unconscious experiences.
Skepticism about dreams being phenomenally conscious experiences is based
on the fact that the access to dreams is retrospective: we recall the dream when
we are awakened and we have no reason for trusting these reports. There are
cases, however, in which some people are aware of being dreaming. This is the
case of lucid dreams. In lucid dreams, the dreamer is able to remember the
circumstances of normal life and to act deliberately upon reflection.
Although lucid dreams have been reported since Aristotle, many have had their
doubts about the reality of these episodes. Dennett endorses this skepticism; he
considers that the report of lucid dreams is consistent with the hypothesis that
dreams are unconscious episodes and that the subject is dreaming that she is
aware of being dreaming. The empirical evidence suggests, nonetheless, that
Dennett's hypothesis is wrong.
During REM sleep all skeletal muscle groups except those that govern eye
movements and breathing are profoundly inhibited (LaBerge (2000)); this fact
makes it very difficult to collect evidence in favor of lucid dreams beyond
subjects’ reports upon awaking. Nevertheless, Rowarg et al (1962) showed that
some of the eye movements of REM sleep correspond to the reported direction
of the dreamer's gaze. Based on this evidence, LaBerge et al. (1981) could
provide evidence in favor of lucid dreams. They trained subjects and asked
them to make distinctive patterns of voluntary eye movements when they
realized they were dreaming. These prearranged eye movement signals were
recorded by the polygraph records during REM, proving that subjects had
indeed been lucid during uninterrupted REM sleep. Furthermore, LaBerge and
Dement (1982) recorded lucid dreamers who were asked to either hold their
breath or breath rapidly (in their lucid dreams), marking the interval of altered
respiration with eye movement signals. The subjects reported having
accomplished the agreed-upon tasks a total of nine times, and in every case, a
judge was able to correctly predict, on the basis of the polygraph recordings,
which of the two patterns had been executed. These results have been
replicated by other laboratories. (For a review see LaBerge (1988)).
The experiments on lucid dreams provide evidence that we have conscious
experiences during sleep, and give us the opportunity to record reports to that
effect. The main reason for skepticism is dissolved: there are conscious dreams.
In lucid dreams, subjects can report having an experience. One might be willing
to concede that, independently of the preferred theory of consciousness, when
subjects report having an experience they are entertaining a HOT. In this case,
if dlPFC is the neural correlate of HOTs we should expect an increase in its
activity in these cases.
Some authors have hypothesized that the deactivation of the dlPFC observed
during REM sleep does not occur during lucid dreams. Dreams are conscious
experiences characterized, among other things, by reduced voluntary control
and reflective thought. These characteristics fit well, as we have seen (Fuster
(2008)), with the independent hypothesis that the dlPFC is involved in volitional
control and self-monitoring. For this reason, a reactivation of the dlPFC is
expected during lucid dreams (Hobson et al (2000); Kahn and Hobson (2005);
Tononi (2009)). Preliminary empirical evidence for this hypothesis has been
obtained from a recent study by Voss et al (2009). This study shows that lucid
dreaming
in
trained
participants
is
associated
with
increasing
electroencephalography (EEG) power, especially in the 40-Hz range, over
frontal regions during REM sleep. Furthermore, Wehrle et al (2005, 2007) use
fMRI to study brain regional activation during lucid dreams and show that in
lucid dreams not only frontal but also temporal and occipital regions are highly
activated in comparison to non-lucid dreams. Hobson (2009) also refers to
preliminary fMRI data gathered by M. Czisch, R. Wehrle and M. Dresler showing
that dream lucidity is correlated with increased activation of the cortical areas
including the dlPFC.20
20
I am not sure about how to make this reactivation of the dlPFC compatible with Lau's
hypothesis about the role of the dlPFC in dreams. Recall that this hypothesis might be endorsed
by other cognitive theories, such as PANIC, to block my argument.
My opponent can still try to resist the argument by maintaining that we have
conscious experiences during lucid dreams but not during ordinary dreams, for
only during lucid dreams can the subject report on them (according to her,
reporting is inextricably linked to HOTs). However, distinguishing lucid dreams
from other dreams in such a way that there is phenomenology associated to the
former but not to the latter seems to be something of a reach.
6 Conclusions
Some philosophers have argued that phenomenal consciousness requires a
certain form of Awareness, and that this Awareness depends on the cognitive
accessibility that underlies reporting. Higher-Order Thought theories of
consciousness are an example of this position.
Lau and Passingham's experiment provides good evidence for believing that the
neural correlate of the reporting access to our visual conscious experiences
depends on the dorsolateral prefrontal cortex (dlPFC). This would be,
accordingly, the most plausible candidate to be the neural correlate of visual
HOTs. The evidence seems to suggest that visual HOTs are not necessary for
consciousness, because their neural correlate is highly deactivated during the
phenomenally conscious experiences we have when we sleep: dreams.
I have argued that we have no reason to believe that visual HOTs are
implemented by another area during sleep. The defender of HOT theory can
embrace a skeptical position as to whether we have conscious dreams. This
position, which runs against common sense, has been refuted by empirical
evidence (lucid dreams).
The position remaining for HOT theory is a not very plausible one, according to
which, there would be an ontological dichotomy with regard to dreams (some
dreams are phenomenologically conscious and others are not).21
21
draft.
I am very grateful to David Pineda and Rubén Sebastián for comments on a previous
A previous version of this paper was presented on the 3rd Consciousness Online
Conference and the LOGOS's GRG. An earlier ancestor was presented in the Cognitive Science
talks at CUNY Graduate Center in summer 2010. I am very grateful to Marc Artiga, Richard
Brown, Jake Berger, Michal Klincewicz, Stevan Harnad, Marta Jorba, Hakwan Lau, Dan Lopez
de Sa, Pete Mandik, Manolo Mart“nez, Myrto Mylopoulos, David Rosenthal, and very especially
to Josh Weisberg, Matthew Ivanowich and two anonymous referees for their comments.
Financial support for this work was provided by the Committee for the University and
research of the department of Innovation, Universities and Company of the Catalonia
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