The Dreaming Glasses
R. Ernesto Blanco
Instituto de Física,
Facultad de Ingeniería, Universidad de la República
Julio Herrera y Reissig 565,
Montevideo, Uruguay,
ernesto@fisica.edu.uy
In 1983, Crick &
Mitchison proposed a function of REM
sleep as an unlearning mechanism (Ref. 1). They gives some phenomenological
implications based on neural networks theory: the developing of hallucinations
and obsessions in subjects deprived of REM sleep. This implications were not
observed in further studies. Theoretical knowledge of the spin glasses with
temperature effects is used here to explain why the implications suggested by
Crick & Mitchison could be not observed even in the case that their main
ideas could be right. Additionally I proposed here a explanation of some
characteristics of dreams imaginery and other psychological implications
derived from spin glasses models of neural networks.
In the early eighties Crick & Mitchison (Ref.
1) postulated that rapid-eye movement (REM) sleep could be a reverse learning
mechanism. This mechanism was shown as very useful in enhancing the memory
recovery performance of small networks of two states neurons with symmetric connections
(Ref. 2). The main proposal, in Crick & Mitchison words, was: “we dream in
order to forget”. Neural networks are associative memory storage device:
starting from any arbitrary state it will evolve to a stable state representing
a evokable pattern. This behaviour resembles some properties of biological neural networks. In some
simulations was seen that, while some
patterns are teached to the network, spurious ones are also created (Ref. 2).
Another observation was that different learned patterns are not equally easy to
recall. Crick & Mitchison’s hypothesis is that the spurious memories
produce hallucinatory associations. Also, the unevenness of patterns recall
(which Hopfield, Feinstein & Palmer described as the “50 % of all stimuli
remind me of sex” effect) produce
obsessions. It was observed in small networks that reverse learning equalized
the patterns recall and supressed the spurious ones (Ref. 2). A testable
prediction of Crick & Mitchison proposal is that a lack of REM sleep should
produce pathological responses such as hallucinations, delusions and
obsessions. As a biological implication they suggested that the echidna’s large
neocortex is related with lacking of REM sleep (Ref. 3): an overloading of its
neural net could be tackled by making the net bigger.
The Crick & Mitchison program (I mean: to apply simple neural networks
models in understanding dreams) lost appeal because the proposed implications
were not confirmed by experimental and clinical studies (Ref 4, 5 and 6).
However I think that developments in
the physical theory of spin glasses (Ref 7), mathematically equivalent to the
kind of neural networks that inspired the Crick & Mitchison hypothesis, can
be used to suggest a mechanism that avoid the waking hallucinations and, as by
product, qualitatively explain some aspects of the dream-work called
condensation by Sigmund Freud (Ref. 8). I assume in the following that
conscious states are in correspondence with stable states in the phase space of
a spin-glass model of a neural network. Short living states reached by the
system are considered here as an unconscious state that will evolve in a brief
time to a stable one. It was shown theoretically that for a network with
infinite number of neurons and with random noise effects (as a temperature T)
the spurious states observed in the numerical studies (Ref 2), are not random
but correspond to well-defined mixtures of a number n of the stored
patterns (Ref 9). The n=1 states, corresponding to the learned patterns,
are stable in a broad range of temperatures. The even n mixtures are
always unstable. For odd n mixtures will there be a critical temperature
below which the n-mixture states are stable. This critical temperature
is smaller when the odd n is bigger. Then can be conclude that with a
sufficiently high temperature (high levels of random noise in the system) will
not be stable all the mixture states with n>1 (spurious patterns) being
stable only the learned patterns. The previous result implies that, if Crick
& Mitchison’s interpretations of spurious patterns are right, in waking
time when there are high levels of random noise in the neural network produced
by sensorial inputs, the spurious memories are not reached as stable
(consciouss) states preventing hallucinations and delusions. The pathological
effect of the spurious patterns was predicted by Crick & Mitchison in the
less realistic approach of zero temperature used in the original Hopfield model
(Ref. 2). However when the sensorial input is strongly reduced, as in REM
sleep, those spurious states can be accesed as dream imaginery. This spurious
mixture patterns recalled the phenomena that Freud described from its clinical
and personal experience as condensation processes. More specifically he defined
them as cumulative images (Sammelbild) and mixture persons (Mischperson):
“From its own dreams each of us knows those products… I can compose a person
features from one or another, or giving the figure of one and thinking about
her in the dream with the name of other, or I can perform visually a person,
but putting her in a situation that happens with other.” (Ref 8). A
particularly simple example are the nonsense words appearing in dreams composed
by proper ones. From Freud’s studies (Ref 8) due to its rather subjective
methodology of interpretation is very difficult to quantify the number of words
involved in the construction of those nonsense words. However is possible that
carefully designed experimental studies helps to show if this words are created
from a odd or even number of proper words.
It is expected, from the point of view stated
here, that during extreme isolation and sensory deprivation, due to the
lowering of random noise as sensory inputs, the spurious patterns can be more
accesible by consciouss (stable states) process giving place to hallucinations.
This implications are consistent with the general results of the seminal work
of Bexton, Heron & Scott on sensory deprivation (Ref 10) and many further
studies. The model discussed here is
too simple in order to provide a complete explanation of the dream
psychological processes. However it provides a qualitative explanation of the
relation of random noise (temperature) and the dream imaginery that could be
further tested in properly designed experiments and confronted with more
biological based theoretical neural network models. The Crick &
Mitchinson’s predictions were not observed probably due to the temperature
effect not considered by them. I hope that their way of thinking about dreams,
including more realistic theoretical considerations, still have something to
offer in the research about psychology of dreams.
References