Forgetting

Reverse learning is a neurobiological theory of dreams. It is like a computer that is off-line during dreaming or the REM phase of sleep. During this phase, the brain supposedly sifts through information gathered throughout the day and throws out all unwanted material. According to the theory, we dream in order to forget and this involves a process of unlearning.

The cortex cannot cope with the vast amount of information received throughout the day without developing parasitic thoughts that would disrupt the efficient organisation of memory. During REM sleep, these unwanted connections in cortical networks are supposedly wiped out or damped down by the process making use of impulses bombarding the cortex from sub-cortical areas.

Reverse learning eliminates unwanted modes of neural network interaction acquired in the adult mammal’s learning and also in the process of fetal brain growth. Therefore, there is a possibility that abnormalities of reverse learning in the fetal brain might explain some aspects of the autistic syndromes or other neurodevelopmental disorders.

The theory is a variant upon the activation-synthesis hypothesis that a brain stem neuronal mechanism sends pontine-geniculo-occipital (or PGO) waves that automatically activate the mammalian forebrain. By comparing information generated in specific brain areas with information stored in memory, the forebrain synthesizes dreams during REM sleep.

One problem for reverse-learning theory is that dreams are often organized into clear narratives or stories. It is unclear why dreams would be organized in a systematic way if they consisted only of disposable parasitic thoughts. It is also unclear why babies sleep so much, because it seems they would have less to forget.

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