 He even collaborated with neurophilosophers such as Patricia Churchland.In 1983, as a result of their studies of computer models of neural networks, Crick and Mitchison proposed that the function of REM sleep is to remove certain modes of interactions in networks of cells in the mammalian cerebral cortex; they called this hypothetical process 'reverse learning' or 'unlearning'.In the final phase of his career, Crick established a collaboration with Christof Koch that led to publication of a series of articles on consciousness during the period spanning from 1990 to 2005.