Psychedelic Information Theory

Shamanism in the Age of Reason


Frequency of gamma oscillations routes flow of information in the hippocampus

Colgin, Laura Lee, et al.; Nature 462, 353-357 (19 November 2009); doi:10.1038/nature08573

Gamma oscillations are thought to transiently link distributed cell assemblies that are processing related information1, 2, a function that is probably important for network processes such as perception1, 2, 3, attentional selection4 and memory5, 6. This 'binding' mechanism requires that spatially distributed cells fire together with millisecond range precision7, 8; however, it is not clear how such coordinated timing is achieved given that the frequency of gamma oscillations varies substantially across space and time, from approx25 to almost 150 Hz1, 9, 10, 11, 12, 13. Here we show that gamma oscillations in the CA1 area of the hippocampus split into distinct fast and slow frequency components that differentially couple CA1 to inputs from the medial entorhinal cortex, an area that provides information about the animal's current position14, 15, 16, 17, and CA3, a hippocampal subfield essential for storage of such information14, 18, 19. Fast gamma oscillations in CA1 were synchronized with fast gamma in medial entorhinal cortex, and slow gamma oscillations in CA1 were coherent with slow gamma in CA3. Significant proportions of cells in medial entorhinal cortex and CA3 were phase-locked to fast and slow CA1 gamma waves, respectively. The two types of gamma occurred at different phases of the CA1 theta rhythm and mostly on different theta cycles. These results point to routeing of information as a possible function of gamma frequency variations in the brain and provide a mechanism for temporal segregation of potentially interfering information from different sources.

Web Resource: www.nature.com

Notes and References

[1] The Norwegian University of Science and Technology (NTNU), 'How the Brain Filters out Distracting Thoughts to Focus on a Single Bit of Information'. ScienceDaily 23 November 2009.

Keywords: gamma oscillations, hippocampus, memory, recall, phase locking

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