Thursday, April 13, 2006

Memory Consolidation

Research on REM sleep suggests that there is a biologically relevant reason for dreaming. The revised version of the Hobson-McCarley activation synthesis hypothesis acknowledges the deep psychological core of dreams. In its present truncated form, the hypothesis of random brain stem activation has little explanatory or predictive power.

The Crick-Mitchison hypothesis provides a function for REM sleep—reverse learning—but it does not apply to narrative, only to the bizarre elements of the dream. What this implies with regard to REM processing in lower species must be defined before the theory can be evaluated further. In addition, the Crick-Mitchison hypothesis as applied to the hippocampus would suggest that neurons fire randomly during REM sleep, providing reverse learning. Instead, in my experiment on the neurons that coded space, these neurons fired selectively, implying an orderly processing of memory.

Recently Avi Karni and his colleagues at the Weizmann Institute of Science in Israel were able to show that memory processing occurs in humans during REM sleep. In their experiment, individuals learned to identify particular patterns on a screen. The memory of this skill improved after a night with REM sleep. When the subjects were deprived of REM sleep, memory consolidation did not occur. This study is an important breakthrough and opens a particularly promising field for exploration.

Further study will continue to elucidate the meaning of dreams. In particular, an experiment is needed to determine whether eliminating theta rhythm during REM sleep alone results in a memory deficit. Because theta rhythm has not been demonstrated in primates, it may have disappeared as vision replaced olfaction as the dominant sense. An equivalent neural mechanism may exist in the hippocampus that periodically activates the NMDA receptor. These studies in animals and others to come in humans will probe fundamental aspects of memory processing and the neuroscientific basis of human psychological structure.
*David Jones; Derived apart from Jonathan Winson  and internet database.

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