[3] 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 wiped out or damped down by the Crick-Mitchison process making use of impulses bombarding the cortex from sub-cortical areas.
The Crick-Mitchison theory is a variant upon Hobson and McCarley's activation-synthesis hypothesis,[4] published in December 1977.
Hobson and McCarley hypothesized that a brain stem neuronal mechanism sends pontine-geniculo-occipital (or PGO) waves that automatically activate the mammalian forebrain.
[5] In the echidna, a primitive egg-laying mammal that has no REM sleep, there is a very enlarged frontal cortex.
[8] It is argued that fetuses and babies sleep so much to downgrade ("unlearn") the force of synapses present in these developmental phases.