Calvin, W. H. (1994). Compressing the cerebral code: Hebbian cell assemblies may be concentrated into a hexagonal macrocolumn. Society for Neuroscience Abstracts 20:315.what follows is the handout for the poster as presented seven months later.
Copyright 1994 by W. H. Calvin.
University of Washington
Department of Psychiatry and Behavioral Sciences, Box 351800
Seattle, Washington 98195-1800 USA
Hebb's Cell-assembly postulates that recalling a memory involves reconstituting the activity pattern present at input, a pattern involving many neurons. Just as a bar code can uniquely represent a banana with an arbitrary pattern that looks nothing like a banana, so one expects the cerebral code for banana to be a pattern of activity in a number of cortical neurons. In long-term memory, this pattern is surely a spatial pattern of connection strengths (not unlike a washboarded road). Recalling the memory, however, involves recreating a spatiotemporal pattern (not unlike a bouncing car driving over the washboarded road, or a phonograph needle vibrating in the grooves), as any output (pronunciation, limb movement) involves creating a spatiotemporal pattern of activity in motorneuron pools.
But recall presumably does not involve recreating the exact spatiotemporal pattern of activity at the time of memorization, not that of the entire brain. What is the minimal Hebbian cell assembly? How many neurons? Extending over what distances in cerebral cortex? How is redundancy achieved?
In the present Darwin Machine model, insights from the periodic nature of the horizontal connectivity of the superficial pyramidal neurons are used to predict a triangular mosaic of synchronized neurons at 0.5 mm spacings. Like the unit pattern of mosaic wallpaper, the largest unique spatial pattern would be contained in a 0.5 mm hexagon -- despite initial separations of the activated feature detectors that span much longer distances. The initial representation appears to be collapsed by end-around overwriting into a compact one that has an inherent error-correction feature. This candidate seems worthy of the name Cerebral Code.
Because each pyramid sends horizontal axons in many directions, simultaneous arrivals may recruit a 3rd and 4th pyramid at 0.5mm from the synchronized parental pair. A triangular mosaic of synchronized superfic- ial pyramids thus can temporarily form, extending for some mm (Calvin, Soc. Neurosci. Abstr.'92). At least at the V1-V2 border, the intrinsic horizontal connections change in character and in length, suggesting that mosaics might stay confined to the parent architectonic area, spreading to other areas only via the U-fibers of white matter.
More general background can be found in:
William H. Calvin and George A. Ojemann.Conversations with Neil's Brain: The Neural Nature of Thought and Language (Addison-Wesley, 1994).
William H. Calvin, "The emergence of intelligence," Scientific American 271(4):100-107 (October 1994).
Mailing address: University of Washington, Box 351800, Seattle WA 98195-1800 USA.
A list of my other books and articles can be found here. .....[Jump to Top]
Revised 27 Jan 95 WHC
[Current references to Darwin Machines and cerebral codes]