  In this work we reevaluate and elaborate Crick-Mitchison's proposal that
REM-sleep corresponds to a self-organized process for unlearning attractors in
neural networks. This reformulation is made at the face of recent findings
concerning the intense activation of the amygdalar complex during REM-sleep,
the role of endocannabinoids in synaptic weakening and neural network models
with itinerant associative dynamics. We distinguish between a neurological
REM-sleep function and a related evolutionary/behavioral dreaming function. At
the neurological level, we propose that REM-sleep regulates excessive
plasticity and weakens over stable brain activation patterns, specially in the
amygdala, hippocampus and motor systems. At the behavioral level, we propose
that dream narrative evolved as exploratory behavior made in a virtual
environment promoting "emotional (un)learning", that is, habituation of
emotional responses, anxiety and fear. We make several experimental predictions
at variance with those of Memory Consolidation Hipothesis. We also predict that
the "replay" of cells ensembles is done at an increasing faster pace along
REM-sleep.
