|
“Dreams are a brief
madness and madness a long dream.”
– Schopenhauer
INTRODUCTION
Dreams
have been defined as “a series of images, ideas, emotions, and sensations
occurring involuntarily in the mind during certain stages of sleep”
(American Heritage Dictionary, 1992). There has long been the assumption
that there was an intimate relationship between dreams and mental
disorders. Epigrammatic statements that if “we could find out about dreams
we could find out about insanity” (Jackson,
1958) and that if we “let the dreamer walk around and act like a person
awake…we [would] have the clinical picture of dementia praecox” (Jung,
1960) reflect the conviction about the close relationship between dreams
and profound emotional disturbance. This view enlivened efforts to study
dreaming to gain insights into the problems of the mentally ill. Also, the
study of the phenomenology of dreaming combined with a study of the
physiology of the dreaming brain affords a unique nature-made opportunity
to develop a cognitive neuroscience of brain-mind states.
HISTORICAL ASPECTS
Sigmund Freud and his interpretation of dreams
Freud (1900) believed that dreams were "delusions and illusions of a
psychosis" and "...the royal road to knowledge of the
unconscious activities of the mind."
In his magnum opus, Die Traumdeutung (The Interpretation of
Dreams), free associations to dream images were used as guides to the
discovery of forgotten memories of traumatic experiences of early life.
Freud regarded these as playing a major role in the pathogenesis of
neurotic symptoms and related clinical disorders. Recovery of these
repressed memories into consciousness was considered as playing an
important role in treatment. Freud theorized that the manifest
(superficial) content of the dream had no significance because it was a
mask for underlying (unconscious) issues of the dream, and that the latent
content contained unconscious wishes or fantasies. The wish that excites
the dream arises from the day residue and is greatly reinforced by
memories of childhood. He termed "...the unconscious mental operations by which the latent
dream content is transformed into the manifest dream..." as dream work,
and added that it involved four key mechanisms – condensation,
displacement, symbolic representation and secondary revision.
The discovery of REM sleep
Shortly after Freud’s death, the study of dreaming from the perspective of
neuroscience began in earnest. In 1953 Aserinsky and Kleitman discovered
the REM state which occurs periodically (in 90 minute cycles) throughout
sleep, and occupies approximately 25% of our sleeping hours. The REM phase
of sleep differs from the NREM phase by the presence of an intensely
desynchronized pattern of cortical electrical activity resembling that of
waking life, atony of the postural muscles, rapid eye movements and the
appearance in the visual system of single-phase waves (known as ponto-geniculo-occipital (PGO) waves) and
neurovegetative storms characterized by respiratory and cardiac
arrhythmia.
Aserinsky and Kleitman suspected that the REM state was the external
manifestation of the subjective dream state. That suspicion was soon
confirmed experimentally by Aserinsky and Kleitman (1955) and Dement and
Kleitman (1957). In 1962 Jouvet discovered that REM (and therefore
dreaming) was produced by a small region of cells in the pons (Jouvet and
Jouvet, 1963). The duration of an individual REM episode was correlated
with the quantity of the dream material collected (Wolpert and Trosman,
1958), the quantity of eye movements with the dream contents (Dement and
Wolpert, 1958), and the specific direction of eye movements with the
spatial organization of the dream events (Dement, 1965). According to the reciprocal interaction model of McCarley
and Hobson (1975), REM sleep – and therefore dreaming- is triggered by
cholinoceptive and/or cholinergic “REM- on” cells, and terminated by
aminergic (noradrenergic and serotonergic) inhibitory “REM off” cells. The
REM on cells are localized principally in the mesopontine tegmentum and
the REM off cells in the nucleus locus coeruleus and dorsal raphe nucleus.
Subjects awakened from REM sleep report that they were dreaming in as many
as 95% of awakenings, while NREM sleep yields dream reports at a rate of
only 5-10% of awakenings (Gillin et al, 2000). Furthermore, the spatial
structuring of the dreams, the level of personal participation of the
dreamer, the number of words used to tell the dream, and certain
characteristics of the dream itself, such as bizarreness, were found to be
greater in REM than in NREM phases (Mancia, 1999).
THEORIES OF DREAMING
The activation-synthesis hypothesis
Hobson
and McCarley (1977) presented a neurophysiological model of the dream
process that seriously challenged Freud's theory on virtually every point.
In REM sleep, they said, the ascending cholinergic PGO waves stimulate
higher midbrain and forebrain cortical structures, producing rapid eye
movements and rapidly spreading activation over the association cortex, in
which memory traces are stored (activation: first half of the theory). The
forebrain attempts to make sense of this random activation and it
synthesizes dream images to fit the patterns of internally generated
stimulation. According to their theory, the dream images and experiences,
having been randomly generated, do not in and of themselves have or convey
any meaning. To make sense of the experience, the dreamer, on awakening,
“edits” the storyline to make at least a modicum of sense of it
(synthesis: the second half of the theory). According to the theory, the
dream report is regarded merely as a work sample, reflecting the dreamer’s
way of dealing with affect and disturbing ideas. Regarded in this way, the
dream can be secondarily useful to the clinician in his or her attempts to
understand the patient’s mind (cognitive styles, defenses, and the like)
but has no relevance to unconscious mental events or meanings.
The neuropsychological -
psychoanalytic model of Mark Solms
Solms (1997, 2000)
reports that 200 of his 332 patients with brain lesions reported no
changes in dreaming, revealing that the dorsolateral prefrontal cortex,
the sensorimotor cortex, and the primary visual cortex are not necessary
for dreaming. Solms had 112 patients with forebrain lesions who had lost
dreaming. None of them had brainstem injuries, showing that REM sleep is
not sufficient for dreaming. This observation is supported by the fact
that temporal lobes seizures can cause dreaming in NREM sleep and the
evidence from NREM awakenings in sleep laboratory studies which suggest
that brainstem stimulation and REM are not necessary for dreaming (Domhoff
& Schneider, 1999). There were only two forebrain lesion sites that Solms
found to be associated with a cessation of dreaming. One was located in
the occipitotemporal junction. This finding correspond with 13 cases that
go back to the 1880s in the neurological literature (Domhoff, 2001). The
other site was the bilateral ventromesial quadrant of the frontal lobes
involving interruption of the mesocortical-mesolimbic dopaminergic system
of the ventromedial forebrain. Solms strengthened his argument by drawing
on the reports of the complete loss of dreaming in 70-90% of the patients
with schizophrenia and other who were leucotomized in the 1940s(Frank,
1950). This system of fibre tracts is the one identified by Panksepp
(1998) as the “curiosity-interest-expectancy” command system of the
ventral forebrain, the system associated with instinctual appetitive
craving states. Solms concludes that this is neuroscientific evidence for
Freud’s hypothesis that dreams are motivated phenomena, driven by our
wishes. (Interestingly, the positive symptoms of schizophrenia are widely
thought to result from overactivity of this system). Solms also adds that
REM only causes dreaming via the intermediary of this motivational
mechanism, and that a variety of other triggers, like stimulant drugs,
seizures, etc. have a similar activating effects on this mechanism. All
these triggers of dreams actually create a state of arousal during sleep,
and Solms claims that this supports Freud’s hypothesis that dreams are a
response to something which disturbs sleep.
Solms hypothesizes that the initiating mechanisms of the neural network
for dream generation are probably located in the temporal-limbic region
and argues that this area provides the "affective arousal”. PET scan
studies show that limbic, paralimbic, inferior parietal and
occipito-temporal areas are active during REM sleep (Braun et al., 1997;
1998), and support many parts of Solms' overall viewpoint.
AIM; a new state space
model
The AIM model (Hobson
1990, Kahn et al, 1997) proposes that conscious states are in large part
determined by three independent processes, namely the level of brain
activation (“A”), the origin of inputs (“I”) to the activated areas, and
the relative levels of activation of aminergic (noradrenergic and
serotonergic) and cholinergic neuromodulators (“M”). The model proposes
that the universe of possible brain-mind states can be construed as a
three-dimensional state-space, with axes A, I, and M (activation, input
and mode). Hobson et al (2000) update the activation-synthesis model as
follows: (1) High levels of cortical activation (“A”) are a correlate of
the mind’s ability to access and manipulate significant amounts of stored
information from the brain during dream synthesis; (2) The blockade of
external sensory input and its functional replacement by internally
generated REM sleep events such as PGO waves (internal sources of “I”)
provide the specific activation of sensory and affective centers that
prime the cortex for dream construction; and (3) The shift of the brain
from aminergic to cholinergic neuromodulation (“M”) alters the mnemonic
capacity of the brain-mind and reduces the reliability of cortical
circuits, increasing the likelihood of bizarre temporal sequences and
associations which are uncritically accepted as waking reality when we are
dreaming. Hobson (1994) even suggests that similar chemical mechanisms may
underlie major psychotic symptoms that share formal features with
dreaming.
Hobson et al (2000)
explains the distinctive aspect of dream cognition at the level of the
brain as follows: (1) the intense and vivid hallucinosis is due to
autoactivation of the visual brain by pontine activation processes
impinging initially at the level of unimodal visual association cortex and
heteromodel parietal areas subserving spatial cognition. (2) the intense
emotions are due to activation of the amygdala and more medial limbic
structures. The emotional salience of dream imagery is possibly due to the
activation of the paralimbic cortices by the amygdala and other
subcortical limbic structures. (3) the delusional belief that we are
awake, the lack of directed thought, the loss of self-reflective
awareness, and the lack of insight about illogical and impossible dream
experiences are due to the combined and possibly related effects of
aminergic demodulation and the selective inactivation of the dorsolateral
prefrontal cortices. (4) the bizarre cognition of dreaming is due to an
orientational instability caused by the chaotic nature of the pontine
inactivation process, its sporadic engagement of association cortices, the
absence of frontal cortical monitoring, and episodic memory deficits that
are, in part, due to failures of aminergic neuromodulation.
Computational neurocognitive model by Antrobus
Antrobus (1991) also sees the dream as a product of cortical activation
and attributes the particular qualitative aspects of REM sleep mentation
to the interpretation of spontaneous activity by the cortex in the absence
of external afferent input during a time of high sensory threshold. In
this context, he has applied neural network model principles to simulate
the characteristics of dreaming (Antrobus, 1997). Connectionist models are
based on the assumption that traditional features – those we can
consciously identify and name – are learned as a part of a longer sequence
that starts with microfeatures, which are the smallest units of neural
network models and are not cognitively penetrable, and moves through
increasingly abstract feature-detecting neural networks, leading to
networks that recognize, spatially locate, name, and determine the meaning
of the object or event that possesses the features (McClelland et al,
1995). Rumelhart et al (1986) demonstrated that when a feature is
represented by a cluster of interrelated neural units, it requires the
activation of only a few units in the cluster to activate the entire
feature cluster. Similarly, activation of only a few features of an object
or an event may be sufficient to fully activate all of the feature
clusters that express that object or event. Furthermore, because the
microfeatures are smaller than features, the units can be combined to form
novel features, objects and events. For eg., “flat surface” may be
experienced as “table top,” but if it is “irregularly shaped,” the dreamer
may conclude that he or she is “at the circus,” where such shapes are more
common (Antrobus, 2000).
The functional state-shift hypothesis
Based
on EEG, Koukkou and Lehmann (1983) proposed that the brain states during
sleep in adults correspond functionally with waking states during
childhood and dreams constitute the state-dependent retrieval of memories
of the past. Authors cited evidence supporting this notion stating that
greatest interhemispheric coherence is observed during REM phases,
indicating a higher interhemispheric transfer. This translated to
increased access of the adult dominant (left) hemisphere to memory
material stored in the right hemisphere in early childhood, before
functional left dominance was established, and the possibility of
verbalization of material generated in the right hemisphere, which might
be dominant during dreaming.
The reverse learning theory
In
this theory (Crick and Mitchinson 1983, 1995), memory in the brain is
compared to simple models of associative nets. When such a net gets
overloaded, it easily starts to produce outputs that are combinations of
actually stored associations. In order to make storage more efficient and
avoid overloading, a process of reverse learning can be used. The net is
disconnected from its normal inputs and outputs, and random input is given
to it. The associations that this random input produces are consequently
weakened, and the process is repeated many times with different kinds of
random input. According to Crick and Mitchinson (1983, 1995) this is
loosely analogous to what happens in the brain during REM sleep: the brain
is disconnected from its usual inputs and outputs, and PGO-waves provide
it with more or less random input. The theory explains why REM dreams are
full of bizarre intrusions, consisting of mixtures of features previously
stored in memory.
The cognitive psychological model
Foulkes (1982) suggest that dreaming depends upon abilities to organize
experiences in memory and to access and reorganize those experiences
independently of external environmental stimulation.
Foulkes (1985) has put forward a cognitive theory of dreaming. He proposes
that dreaming originates in diffuse, more or less random activation of
semantic and episodic memory during sleep.
This cognitive approach does not rely on specific physiological events to
dream features and considers dreaming to be a form of thinking. This model
is consistent with the suggestion by the neurophysiologists Llinas and
Pare’ (1991) that REM sleep and associated dreams may be interpreted as a
state of modified attention, directed not outwards but inwards, towards
the subject’s own memories.
The neurocognitive theory
Foulkes (1999) reported that only 20-30% of REM period awakenings lead to
dream reports in children aged 3-5 years and that the dreams of children
under age 5 are bland and static in content, suggesting that dreaming is a
cognitive achievement that develops gradually over the first 8 or 9 years
of life. A rigorous system of content analysis (Hall & Van de Castle,
1966; Domhoff, 1996) demonstrated the repetitive nature of much dream
content and showed that the dream content in general is continuous with
waking conceptions and emotional preoccupations (the continuity
hypothesis). Based on these findings, and the already mentioned studies of
Solms (2000) that imply the contours of the neural network necessary for
dreaming, Domhoff (2001) postulates that dreaming is best understood as a
developmental cognitive achievement that depends upon the maturation and
maintenance of a specific network of forebrain structures.
Theories of Dreaming – A Critical Appraisal
The Activation Synthesis Hypothesis:
Hobson and McCarley’s (1977) ‘Activation
Synthesis Hypothesis’ has been contested in quite a few ways. First, it
has been said that dreams indistinguishable from the dreams of REM sleep,
can occur in the absence of REM sleep (Vogel, 1978) and REM sleep can
occur in the absence of dreaming (Frank, 1950). Solms (2000) has found
that patients with pontine lesions and an absence of REM sleep do report
dreaming. Moreover visual imagery persists during REM sleep when there are
no eye movements and therefore no PGO bursts (Antrobus, 2000).
Nevertheless, the assumptions by Hobson and McCarley that the production
of dream imagery is dependent on an activated brain and that this
activation is controlled by periodic pontine activation (in REM sleep) are
fundamental components of any theory of dreaming.
The Neuropsychological – Psychoanalytic Model:
According to Hobson (2000) Solms’ theory is an attempt to resuscitate
Freud’s dream theory. Positive emotions like elation, joy etc. do not
qualify as unconscious Freudian wishes and they certainly do not need
disguise. Solms rules out brain stem as source of dreams but his own
mesolimbic dopaminergic system (mediator of wishes) has its origin in
brain stem. Moreover dopaminergic output changes the least between NREM
and REM sleep. In addition REMs occur not only in REM sleep but also in
stage I and II NREM sleep albeit at a lower level. In the last its
doubtful that the patients with pontine lesions severe enough to eliminate
REM sleep could be conscious enough to report dreaming (Hobson, 1999).
The Reverse Learning Theory:
Crick and Mitchison’s reverse learning theory does not even try to explain
the narrative aspect of REM dreams. It does not assign any independent
function to the phenomenology of dreaming; phenomenal dream images merely
reflect the functioning of a memory cleaning process (Revonsuo, 2000).
Computational Neurocognitive Model:
This attractive model by Antrobus depending on neuronal interconnections
does not make it clear as to how the cortical activation during sleep
could be selectively stimulating a neuronal network to make a coherent
dream.
FUNCTIONS OF DREAMING
The function of dreaming
has remained a mystery for a very long time. Based on the fact that the
amount and proportion of REM sleep decreases throughout life, Roffwarg et
al (1966) suggested that REM sleep may play an important role in the
development of the brain, providing an internal source of intense
stimulation which would facilitate the myelination of the infant's nervous
system. Dreaming sleep has been shown to play a general role in reducing
brain excitability (Cohen and Dement, 1965).
According to Hartmann
(1973), REM sleep helps us to adapt to our environments by improving our
mood, memory, and other cognitive functioning through restoring certain
neurochemicals that are depleted in the course of waking mental activity.
Cartwright and Lamberg, (1992) have proposed the cognitive,
problem-solving view according to which there is a considerable
continuity between waking and sleeping thought. They believe that dreams
allow people to engage in creative thinking about problems because dreams
are not restrained by logic or realism.
Kramer
(1993) proposed “the selective mood regulatory function of
dreaming”. He suggested that the affective state of the dreamer covaries
with the content of the dream and that changes in dreams across the night
may contribute to the dreamer’s coping capacity.
Revonsuo (2000)has put forward the threat
simulation theory, which states that the
biological function of dreaming is the simulation of threatening waking
events and the repeated rehearsal of threat perception and threat
avoidance responses, which would have been valuable for the development
and maintenance of threat avoidance skills during human evolutionary
history.
Vertes and Eastman (2000)
proposes that the primary function of REM sleep is to provide periodic
endogenous stimulation to the brain which serves to maintain minimum
requisite levels of CNS activity throughout sleep, and that REM is the
mechanism used by brain to ensure and promote recovery from sleep.
According to Staunton
(2001) the two constants in the dreaming process are that the dreamer is
always present as first person observer and that there is always a
topographical setting. Based this, he proposes that a major function of
REM sleep is the development and maintenance of a sense of personal
identity.
Dream in memory consolidation
The
hypothesis that REM sleep plays a role in learning and memory processing
at several levels is supported by an extensive body of research which
indicate that the learning tasks that require significant concentration or
the acquisition of unfamiliar skills is followed by increased REM sleep
and the studies which show that memory for certain types of learning is
impaired by subsequent REM deprivation (LaBerge, 1985). Recent evidences
include the REM-dependent developmental wiring of binocular cells in
visual cortex, procedural learning of a visual discrimination task and the
development of problem-solving skills (Seigel, 2001). Studies suggest that
REM might modify neocortical networks in general, rather than simply those
involved in procedural learning (Stickgold et al, 2001). During REM sleep,
neuronal ensembles in hippocampal and neocortical areas are thought to
‘replay’ neural activity associated with the encoding of novel stimuli,
and this reactivation occurs in phase with neural oscillations (theta and
gamma rhythms), which are thought to induce long-term potentiation (Titone,
2002).
But, numerous studies have shown that depriving animals of REM sleep has
no effect on learning or memory. Although other reports have shown that
REM deprivation disrupts memory, many of them have been questioned based
on stressful REM deprivation techniques, which could cause performance
deficits rather than memory impairment per se (Vertes, 2000). TCAs are
known to suppress REM sleep without any impairment of memory or learning.
Recent functional imaging studies of human brain activity in REM sleep
reveal patterns of activity that are consistent with dream processes but
not with memory consolidation (Jones, 1998).
METHODS FOR COLLECTING DREAM REPORTS
There
are several factors that may influence the content of the dream reports
regardless of which collection method is used. They include-the
instructions given to the dreamer for making the report, the nature of the
interpersonal situation if the report is verbal and the degree of
anonymity available to the subject. These problems can be mitigated by
collecting dream reports with a standardized interview protocol or written
form using subjects whose participation is voluntary and allowing
anonymity to the participants. Following are some methods to collect dream
reports:
Sleep Laboratories
Sleep
laboratories provide the opportunity for collecting a large representative
sample of a person’s dream life under controlled conditions. Awakenings
during REM periods maximize the probability of recall making it possible
to collect as many as four or five dream narratives in a single night. The
dream reports in laboratory don’t differ greatly from those written down
by the same subjects at home (Domhoff and Schineider, 1999). The
differences if any are less of aggression and sexuality in laboratory
reports (Domhoff and Kamiya, 1964).
Psychotherapy Relationship
Such
relationships provide the occasion for the creation of dream journals that
include dreams reported in therapy as well as those written outside of
therapy. They have a virtue of rich accompanying biographical and fantasy
material. However not all psychotherapists (except Jungians) make use of
dreams. Moreover patients are a small and unrepresentative sample of the
population (Domhoff, 2000).
Dream Journals
They
are a form pf personal document. They are non-reactive archival sources
that have not been influenced by the purposes of the investigators who
analyze them. They are extremely valuable in establishing consistency in
what people dream about. However they may have drawbacks like people may
not provide the whole of their records or may not be willing to reply to
inferences about their personal life based on a blind analysis of the
journal’s contents. Moreover such records may have gaps or omissions.
Group Settings
The
most objective and structured context for the efficient and inexpensive
collection of large samples of dream reports is the classroom, where
reports can be written by anonymous subjects who reveal only there age and
gender (Hall, 1951). The main drawback of this method is that it is
usually not possible to collect much personality or cognitive information
about the people providing the dream reports.
METHODS FOR ANALYZING DREAM CONTENT
The
four general methods for analyzing dream content (Domhoff, 2000) are:
Free Association Method
Introduced by Freud, it consists of instructing dreamers to say whatever
comes in their minds about each element of the dream. However in
psychotherapy setting where the dreamer is already well known to the
analyst, the actual meaning of the dream can easily be contaminated.
Metaphoric Analysis
Symbolic interpretations are used as supplement to free associations in
the analysis of dreams in psychotherapy settings and in some studies of
dream journals. The symbols that are said to stand for parts of the mind
or the mind as a whole are all based on common metaphors. For example, the
equation of “psyche” and “house” in Jungian theory is based on the
conceptual metaphor “the mind is a container”. There are several problems
with metaphoric analysis. First, there is as yet no systematic evidence of
how many dreams are metaphoric in nature. Second, more than one metaphor
may be possibly applied to some dreams. Third, if they are metaphoric, the
dreams often rely on personal metaphors based on past experiences.
Thematic Analysis
It
involves repeatedly reading through a dream series to see if one or more
themes emerge. Sometimes the search is made easier by the presence of one
or more spotlight dreams that seem to contain the theme in an obvious
fashion. However the findings tend to be unique to each dreamer, allowing
little opportunity for generalizations across dreamers. Moreover they do
not go far in terms of detailed statements about dreams content that can
be tested on new dream samples.
Quantitative Approaches
They
are also called ‘content analysis’. The major task here is the creation of
carefully defined categories that lead to the same results when used by
different investigators and that yield findings that relate to other
variables.
The
set of nominal categories developed by Hall and Van de castle (Schneider
and Domhoff, 2002) is the most comprehensive and widely used empirical
system of content analysis. Its original 10 general categories include
characters, social interactions, activities, misfortunes and good
fortunes, successes and failures, emotions, settings and objects,
descriptive elements, elements from the past, and food and eating. The
reliability of coding for this system is good. It includes norms for young
men and women that have been replicated several times. The content analyst
must be blind about the dreamer to guard against biases.
|
