Lecture 7: dreaming
— Metzinger
— patterns of brain activity in dreaming
— the functional benefits of dreaming
— Borges
on sleep
The brain, the dynamical, self-organizing system as a whole,
activates the pilot if and only if it needs the pilot as a
representational instrument in order to integrate, monitor,
predict, and remember its own activities. As long as the pilot is
needed to navigate the world, the puppet shadow dances on the wall
of the neurophenomenological caveman's phenomenal state space. As
soon as the system does not need a globally available self-model,
it simply turns it off. Together with the model the conscious
experience of selfhood disappears. Sleep is the little brother of
death.
Metzinger (2003, p.558)
slide 2
on sleep (cont.)
"Our central hypothesis is that the executive
cognitive functions, provided by the prefrontal
cortex, are particularly sensitive to the fatigue
induced by prolonged waking. We propose that
during sleep it enjoys what is at first a passive
respite in nonrapid-eye-movement (NREM) sleep
and later, in REM sleep, a more active one.
As a consequence of deactivation of the dorsolateral
prefrontal cortex (DLPFC) during sleep, executive
functions such as self-consciousness and analytical
thought are severely impaired in NREM sleep
and are weak in REM sleep."
The prefrontal cortex in sleep
Amir Muzur, Edward F. Pace-Schott and J. Allan Hobson (2002)
slide 3
sleep states/stages
The changes in EEG activity throughout the sleep-wake cycle.
some of the relevant brain areas
Brodmann areas considered to form (a) the dorsolateral prefrontal cortex
(DLPFC; dorsal surface of the left hemisphere is shown), and (b) the ventromedial
prefrontal cortex (VMPFC; median plane cut of the right hemisphere).
DLPFC: working memory.
VMPFC: decision making; somatic marker.
Executive functions of the prefrontal cortex that are most
relevant to the self-conscious awareness: self-observation, planning,
prioritizing and decision-making.
These are, in turn, based upon more basic cognitive capacities such as
attention, working memory, temporal memory and
behavioral inhibition.
slide 5
The AIM model, after Hobson, J. Allan, Pace-Schott, E. and Stickgold,
R. (2000), DREAMING and the BRAIN: Toward a Cognitive Neuroscience of
Conscious States, Behavioral and Brain Sciences 23 (6).
The activation parameter (A) is derived from the inverse of the
voltage amplitude of the EEG which varies from 25-50 mV in waking to
150-200 mV in stage IV NREM sleep in humans (x4 range).
The input (I) source parameter can be derived from arousal threshold or
H-reflex
amplitude in humans (x4 range).
The modulatory parameter (M) is derived from the mean discharge rate of
the aminergic populations (2-4 c/s in waking, 1-2 c/s in NREM, 0.01-0.1
c/s in REM) or from the concentration of norepinephrine, serotonin or
acetylcholine in microdialysis studies (x10 range).
slide 6
the AIM model
Roughly speaking, the three posited dimensions are meant to capture respectively:
- The information processing capacity of the system (Activation);
- The degree to which the information processed comes from the outside
world and is or is not reflected in behavior (Information flow);
- The way in which the information in the system is processed
(Mode).
NE: norepinephrine;
5-HT: serotonin
(5-hydroxytryptamine).
slide 7
wakefulness, sleep, and dreaming
One use of the AIM model is to depict the highly dynamic and variable
nature of human consciousness, and thus to visually plot specific "states"
of consciousness within the state space. As an example, normal
consciousness, at the coarsest level, can be divided into the states of
waking, REM and NREM sleep. Each of these states can be characterized both
by distinct physiologies and by distinct differences in mentation.
The positions of these three states in the AIM state space, as well as the
trajectory from waking through NREM into REM sleep, are shown here.
slide 8
falling asleep
Each individual will take a unique path through the state space from
waking to NREM, depending on both the relative and absolute rates of
decline of each of the three state space parameters.
For example, if an individual is drowsy before retiring, values for "A"
and perhaps also "M" will begin to drop well before the subject even goes
to bed, while "I" remains high, placing one in the center of the back
surface of the cube.
In contrast, if an individual is quite alert when going to bed, "I" might
drop before either "A" or "M" (not shown), followed by a small drop in "A"
as alpha patterns appear in the EEG.
slide 9
sleep onset
As the subject moves from wake to sleep onset, further movement occurs
within the state space. The box labeled "Rapid" represents a possible
initial sleep onset state when the transition from waking to sleep is
precipitous following sleep deprivation. In this case, the transition
occurs before there is time for aminergic
neuromodulatory levels to decrease. As a result, the "M" function remains
on the top surface of the cube (modulation highly aminergic) while brain
activation and external inputs diminish.
In contrast, the box labeled "Slow" represents a gradual transition from
waking to sleep as might be seen in situational insomnia. In this case,
decreases in aminergic neuromodulation and external inputs might occur
prior to the decrease in brain activation. In both cases, AIM would then
move into the standard NREM position.
slide 10
lucid dreaming
Under normal circumstances, dreamers believe themselves to be awake — but
occasionally individuals become aware that they are dreaming. In this state
of "lucid dreaming" (Laberge 1990, 1992) waking insight combines with dream
hallucinosis in an intriguing and informative dissociation. We assume that
for lucidity to occur, the normally deactivated prefrontal cortex must be
reactivated but not so strongly as to suppress the pontolimbic systems
signals to it. This dissociation is represented in the AIM model by
splitting AIM so the portion representing prefrontal cortex can take a
position dissociated from that of the rest of the brain. When
this occurs, internally generated images are seen for what they are and are
not misinterpreted as coming from the outside world.
The phenomenon of lucidity clearly illustrates the always statistical and
always dissociable quality of brain-mind states. AIM accommodates these
features very well by proposing that lucid dreaming is a hybrid state
lying across the wake-REM interface.
slide 11
sleepwalking
In the REM sleep behavior disorder, the normal inhibition of
motor output during REM fails. Motor behaviors normally seen only in
waking now arise completely involuntarily and automatically during REM, and
patients physically act out their dreams. The
historically oriented reader will recognize the similarity between this
disorder and the dissociative phenomena that interested Charcot, Janet and
Freud.
During REM sleep, automatic motor cortex activation produces outputs similar
to those seen in waking, but in response to exclusively internal
inputs. Since the inhibition of spinal motorneurons usually occurs in
concert with motor cortex activation, our single "I" parameter normally
reflects the net inhibition of motor output. But in this case (as in the
case of lucid dreaming) we represent this regional dissociation by a
fragmenting of the AIM icon. In this case, the lower back quarter of the
icon, representing brainstem output systems, has moved back in the state
space toward a waking level of output. It is this dissociation
which produces the REM sleep behavior disorder.
slide 12
altered states of consciousness
Drugs which, like LSD, interfere with serotonergic neuromodulation create
dreamlike distortions of imagery and inhibit executive prefrontal cortical
functions during waking, while anticholinergics (e.g., scopolamine)
produce a delirious waking state with dream-like hallucinosis,
disorientation, anxiety and confabulation.
As seen here, scopolamine pushes AIM above the normal state space,
pharmacologically reducing the levels of cholinergic neuromodulation below
any normal physiological levels. At the same time, AIM splits as both
external and internal inputs are activated.
F: forebrain.
B: brainstem.
slide 13
AIM — a summary
Three major questions seem to us to be ripe for resolution through constructive debate:
- Are the similarities and differences in the conscious experiences of
waking, NREM, and REM sleep defined with sufficient clarity that they can
be measured objectively? If so, do the measures establish clear-cut and
major differences between the phenomenological experience of these three
physiological states ?
-
Are the similarities and differences between the brain substrates of the
states of waking, NREM, and REM sleep defined with sufficient clarity that
they can be measured objectively? If so, do the measures establish
clear-cut differences between these states at the level of brain regions,
as well as at the cellular and molecular levels?
-
To the extent that affirmative answers can be given to the two preceding
questions, can a tentative integration of the phenomenological and
physiological data be made? Can models account for the current results and
suggest experiments to clarify remaining issues?
slide 14
brain activity patterns in dreaming
During dreaming, prefrontal deactivation leads to illogical
thinking (ad hoc explanations, prominent mnemonic deficits,
bizarre uncertainties).
Hypofrontality is associated with pathological temporal limbic activation
in epilepsy; reciprocal inhibition between frontal and limbic areas has
been linked to depression and schizophrenia.
REM dreaming might be a normal physiological state that is
analogous to psychopathological conditions in which limbic hyperactivation
is combined with frontal hypoactivation.
slide 15
self-modeling robots
(A). Perform an action (initially random; later, it is the best
action found in (C)).
(B). Generate several self-models to match sensor
data collected earlier.
(C). Generate several possible actions that disambiguate competing
self-models.
(D). Use the currently best model to generate locomotion sequences
through optimization.
(E). Execute the best locomotion sequence by the physical
actuator.
(F). Continue to refine models (B), or to create new behaviors
(D).
slide 16
self-modeling robots in action
The robot performs a random action (A). A set of random models, such as
(B), is synthesized into approximate models (C). A new action is then
synthesized to maximize model disagreement and is carried out
(D), after which further modeling ensues. This cycle continues
for a fixed period or until no further model improvement is possible (E
and F).
The best model is then used to synthesize a behavior. In this case, the
behavior is forward locomotion, the first few movements of which are
shown (G to I). This behavior is then carried out (J to L).
Next, the robot suffers damage [the lower part of the right leg breaks off
(M)]. Modeling recommences with the best model so far (N), and using the
same process of modeling and experimentation, eventually discovers the
damage (O). The new model is used to synthesize a new behavior (P to R),
which is executed by the physical robot (S to U), allowing it to recover
functionality despite the unanticipated change.
slide 17
benefits of self-modeling
Distance traveled during optimized versus random behaviors.
Dots indicate the final location of the robot's center of mass, when it
starts at the origin. Red dots indicate final
positions of the physical robot when executing random
behaviors. Black dots indicate final expected positions predicted
by the 30 optimized behaviors when executed on the self-model
(Fig. 2F). Blue dots
denote the actual final positions of the physical
robot after executing those same behaviors in
reality. The behaviors corresponding to the circled
dots are depicted in Fig. 2, G to L. Squares indicate
mean final positions. Vertical and horizontal
lines indicate 2 SD for vertical and horizontal
displacements, respectively.
slide 18
America offline
Phenomenal experience during the waking state is an online
hallucination. This hallucination is online because the
autonomous activity of the system is permanently being modulated by
the information flow from the sensory organs; it is a hallucination
because it depicts a possible reality as an actual reality.
Phenomenal experience during the dream state, however, is just a
complex offline hallucination.
Metzinger (2003, p.51)
slide 19
more on lucid dreaming
LaBerge (1990): "Lucid" dreamers (the term derives from
van Eeden, 1913) report being able to freely remember the circumstances of
waking life, to think clearly, and to act deliberately upon reflection,
all while experiencing a dream world that seems vividly real.
About 20% of the population reports having lucid dreams once a month or
more.
We [LaBerge et al.] provided the necessary verification by instructing
subjects to signal the onset of lucid dreams with specific dream actions
that would be observable on a polygraph (i.e., eye movements and fist
clenches). Using this approach, LaBerge, Nagel, Dement & Zarcone (1981)
reported that the occurrence of lucid dreaming during unequivocal REM
sleep had been demonstrated for five subjects. After being instructed in
the method of lucid dream induction (MILD) described by LaBerge (1980b)
the subjects were recorded from 2 to 20 nights each. In the course of the
34 nights of the study, 35 lucid dreams were reported subsequent to
spontaneous awakening from various stages of sleep.
slide 20
some objections considered
What exactly do we mean by the assertion that lucid dreamers are 'asleep?'
Perhaps these 'dreamers' are not really dreamers, as some argued in the
last century; or perhaps this 'sleep' is not really sleep, as some have
argued in this century.
Although they know they are in the laboratory, this knowledge is a
matter of memory, not perception. Upon awakening, they report having
been totally in the dream world and not in sensory contact with the
external world.
It might be objected that lucid dreamers might simply not be attending to
the environment.
According to the reports of lucid dreamers (LaBerge, 1980a, 1985), if
they deliberately attempt to feel the bedcovers they know they are
sleeping in or try to hear the ticking of the clock they know is beside
their bed, they fail to feel or hear anything except what they find in
their dream worlds. Lucid dreamers are conscious of the absence of
sensory input from the external world; therefore, on empirical grounds,
they conclude that they are asleep.
slide 21
some objections considered
If, in a contrary case, subjects were to claim to have been awake while
showing physiological signs of sleep, or vice versa, we might have cause to
doubt their subjective reports. However, when -- as in the present case --
the subjective accounts and objective physiological measures are in clear
agreement, it is embarrassingly awkward to assert (as some critics have
done) that subjects who reported being certain that they were asleep while
showing physiological indications of unequivocal sleep were actually
awake.
The evidence is clear: lucid dreaming is an experiential and physiological
reality; though perhaps paradoxical, it is clearly a phenomenon of sleep.
slide 22
lucid dreaming occurs during tonic REM sleep
LaBerge, Levitan, and Dement (1986) analyzed physiological data from 76
signal-verified lucid dreams (SVLDs) of 13 subjects. The polysomnograms
corresponding to each of the SVLDs were scored for sleep stages and every
SVLD REM period was divided into 30 s epochs aligned with the lucidity
onset signal. For each epoch, sleep stage was scored and rapid eye
movements (EM) were counted; if scalp skin-potential responses were
observable as artifacts in the EEG, these were also counted (SP). Heart
rate (HR) and respiration rate (RR) were determined for SVLDs recorded with
these measures.
For the first lucid epoch, beginning with the initiation of the signal, the
sleep stage was unequivocal REM in 70 cases (92%). The remaining six SVLDs
were less than 30 s long and hence technically unscorable "by the
book". For these cases, the entire SVLD was scored as a single epoch; with
this modification, all SVLDs qualified as REM. The lucid dream signals
were followed by an average of 115 s (range: 5 to 490 s) of uninterrupted
REM sleep. Physiological comparison of EM, HR, RR, and SP for lucid
vs. non-lucid epochs revealed that the lucid epochs of the SVLD REM
periods had significantly higher levels of physiological activation than
the preceding epochs of non-lucid REM from the same REM period.
slide 23
initiation of lucid dreaming
Lucid dreams have been frequently reported to occur most commonly late in
the sleep cycle. A regression analysis clearly demonstrated that relative lucidity
probability was a linear function of ordinal REM period number (r = .98, p
< .0001).
There are two distinct ways in which lucid dreams are initiated. In the
usual case, subjects report having been in the midst of a dream when a
bizarre occurrence causes sufficient reflection to yield the realization
that they are dreaming. In the other, less frequent case, subjects report
having briefly awakened from a dream and then falling back asleep directly
entering the dream with no (or very little) break in consciousness. Here is
an example of a wake-initiated lucid dream:
I was lying awake in bed late in the morning listening to the sound of
running water in the adjoining bathroom. Presently an image of the ocean
appeared, dim at first like my usual waking imagery. But its vividness
rapidly increased while, at the same time, the sound of running water
diminished; the intensity of the internal image and external sound seemed
to alter inversely (as if one changed a stereo balance control from one
channel to the other). In a few seconds, I found myself at the seashore
standing between my mother and a girl who seemed somehow familiar. I could
no longer hear the sound of the bath water, but only the roar of the dream
sea....
slide 24
a typical dream-initiated lucid dream
Four channels of physiological data (central EEG [C3-A2], left and right
eye-movements [LOC and ROC], and chin muscle tone [EMG]) from the last 8
min of a 30 min REM period. Calibrations are 50 microV and 5 s.
Upon awakening the subject reported having made five eye movement signals
(labeled 1-5 in figure).
The first signal (1, LRLR) marked the onset of
lucidity. During the following 90 s the subject "flew about" exploring his
dream world until he believed he had awakened, at which point he made the
signal for awakening (2, LRLRLRLR).
After another 90 s, the subject realized he was still dreaming and
signaled (3) with three pairs of eye movements. Realizing that this was
too many, he correctly signaled with two pairs (4).
Finally, upon awakening 100 s later he signaled appropriately (5,
LRLRLRLR).
slide 25
a psychophysiological method for studying dreaming
The fact that lucid dreamers can remember to perform predetermined actions
and signal to the laboratory suggested to LaBerge (1980a) a new paradigm
for dream research: Lucid dreamers, he proposed, "could carry out diverse
dream experiments marking the exact time of particular dream events,
allowing the derivation of precise psychophysiological correlations and the
methodical testing of hypotheses".
Example: addressing the question of how long do dreams take.
Ask subjects to estimate ten second intervals (by counting, "one
thousand and one, one thousand and two, etc.") during their lucid
dreams. Time estimates during the lucid dreams were very close to the
actual time between signals.
The ratio of dreaming/reality time can be estimated as follows: have the
subjects track the tip of their fingers moving slowly left to right
during four conditions: 1) awake, eyes open; 2) awake, eyes closed
mental imagery; 3) lucid dreaming; and 4) imagination ("dream eyes
closed") during lucid dreaming. The subjects showed saccadic eye
movements in the two imagination conditions (2 and 4), and smooth
tracking eye movements during dreamed or actual tracking (conditions 1
and 3).
slide 26
sex
Sixteen channels of physiological data, including EEG, EOG, EMG,
respiration, skin conductance level (SCL), heart rate, vaginal EMG (VEMG)
and vaginal pulse amplitude (VPA), were recorded from a single subject. The
experimental protocol called for her to make specific eye movement signals
at the following points: when she realized she was dreaming (i.e., the
onset of the lucid dream); when she began sexual activity (in the dream);
and when she experienced orgasm.
The subject reported a lucid dream in which she carried out the
experimental task exactly as agreed upon. Data analysis revealed a
significant correspondence between her subjective report and all but one of
the autonomic measures; during the 15 second orgasm epoch, mean levels for
VEMG activity, VPA, SCL, and respiration rate reached their highest values
and were significantly elevated compared to means for other REM
epochs. Contrary to expectation, heart rate increased only slightly and
non-significantly.
slide 27
dreaming and reality
Although the events we appear to perceive in dreams are illusory, our
feelings in response to dream content are real. Indeed, most of the events
we experience in dreams are real; when we experience feelings, say, anxiety
or ecstasy, in dreams, we really do feel anxious or ecstatic at the
time. When we think in dreams, we really do think (whether clearly or not
is another matter). If we think in our dreams that Monday comes before
Sunday, it is not the case, as some philosophers (e.g., Malcolm, 1959)
assert, that we have only dreamed we thought; we may have thought
incorrectly (to the usual way of thinking), but thought nonetheless.
slide 28
dreaming and reality
Although the events we appear to perceive in dreams are illusory, our
feelings in response to dream content are real. Indeed, most of the events
we experience in dreams are real; when we experience feelings, say, anxiety
or ecstasy, in dreams, we really do feel anxious or ecstatic at the
time. When we think in dreams, we really do think (whether clearly or not
is another matter). If we think in our dreams that Monday comes before
Sunday, it is not the case, as some philosophers (e.g., Malcolm, 1959)
assert, that we have only dreamed we thought; we may have thought
incorrectly (to the usual way of thinking), but thought nonetheless.
Cf. Wittgenstein (On Certainty, prop. 90e):
I cannot seriously suppose that I am at this moment dreaming. Someone
who, dreaming, says "I am dreaming," even if he speaks audibly in doing
so, is no more right than if he said in his dream "it is raining," while
it was in fact raining. Even if his dream were actually connected with
the noise of the rain. [written two days before his death on April 29,
1951]
slide 29
causing a tiger
And so, as I sleep, some dream beguiles me, and suddenly I know I am
dreaming. Then I think: This is a dream, a pure diversion of my will;
and now that I have unlimited power, I am going to cause a tiger.
Oh, incompetence! Never can my dreams engender the wild beast I long
for. The tiger indeed appears, but stuffed or flimsy, or with impure
variations of shape, or of an implausible size, or all too fleeting,
or with a touch of the dog or the bird.
Jorge Luis Borges
Dreamtigers
