Abstract
BackgroundRecent work has indicated an increasingly complex role for astrocytes in the central nervous system. Astrocytes are now known to exchange information with neurons at synaptic junctions and to alter the information processing capabilities of the neurons. As an extension of this trend a hypothesis was proposed that astrocytes function to store information. To explore this idea the ion channels in biological membranes were compared to models known as cellular automata. These comparisons were made to test the hypothesis that ion channels in the membranes of astrocytes form a dynamic information storage device.ResultsTwo dimensional cellular automata were found to behave similarly to ion channels in a membrane when they function at the boundary between order and chaos. The length of time information is stored in this class of cellular automata is exponentially related to the number of units. Therefore the length of time biological ion channels store information was plotted versus the estimated number of ion channels in the tissue. This analysis indicates that there is an exponential relationship between memory and the number of ion channels. Extrapolation of this relationship to the estimated number of ion channels in the astrocytes of a human brain indicates that memory can be stored in this system for an entire life span. Interestingly, this information is not affixed to any physical structure, but is stored as an organization of the activity of the ion channels. Further analysis of two dimensional cellular automata also demonstrates that these systems have both associative and temporal memory capabilities.ConclusionIt is concluded that astrocytes may serve as a dynamic information sink for neurons. The memory in the astrocytes is stored by organizing the activity of ion channels and is not associated with a physical location such as a synapse. In order for this form of memory to be of significant duration it is necessary that the ion channels in the astrocyte syncytium be electrically in contact with each other. This function may be served by astrocyte gap junctions and suggests that agents that selectively block these gap junctions should disrupt memory.
Highlights
Recent work has indicated an increasingly complex role for astrocytes in the central nervous system
This paper examines the possible role of ion channels in storing information in astrocytes
This form of information processing by ion channels is remarkably similar to models known as cellular automata [18,19]
Summary
Recent work has indicated an increasingly complex role for astrocytes in the central nervous system. As an extension of this trend a hypothesis was proposed that astrocytes function to store information To explore this idea the ion channels in biological membranes were compared to models known as cellular automata. Until recently astrocytes were considered to play no more than a supportive role for neurons in the central nervous system This view has been supplanted by a more active participation of astrocytes in information processing, where the astrocytes receive and respond to (page number not for citation purposes). A sixteen unit one dimensional cellular automaton was constructed using binary units and Wolfram's rule number 232 This rule is illustrated at the bottom of the figure where the three squares on top are the current states of three adjacent units and the single square below is the resultant state of the middle unit during the iteration. Starting at R0 the units no longer change state indicating that all information about R1 is lost
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