Astrocyte domains and the three-dimensional and seamless expression of consciousness and explicit memories

The expression of consciousness and the site of memory storage within the brain are unknown despite over a century of intense empirical scrutiny. Recent anatomical studies show that human protoplasmic astrocytes form innumerable uniform polyhedral tessellating domains that are arranged three-dimensionally. This complex geometric structure provides a matrix for seamless and three-dimensional expression of consciousness and explicit memories. These studies, in conjunction with physiological data, demonstrate how this may be achieved: 1. Individual protoplasmic astrocytes occupy separate three-dimensional non overlapping (i.e., tessellating) territories known as domains. Thus, billions of contiguous and continuous domains tile mammalian cortical gray matter. 2. Each domain subtends approximately 90,000 rodent and 2,000,000 human tripartite synapses that signal to perisynaptic astrocyte processes which encode and integrate synaptic information. Neuron to astrocyte signalling is as rapid as neuron to neuron signaling. 3. Astrocytes are exquisitely sensitive to neural activity and distinguish synapse from numerous afferent pathways with different neurotransmitters or neuromodulators. Therefore, synaptic information is dynamically integrated within a global matrix of tessellating astrocyte domains. 4. Astrocytes of the sensory cortex respond to peripheral stimulation in vivo, and some have the ability to distinguish sensory input in more refined detail than surrounding neurons (e.g., visual cortex). Additionally, astrocytes of the cortex and cerebellum react in concert with activity of awake and behaving animals. 5. Domains are extensively interconnected by gap junctions that transmit molecules, many important for information processing and transcription, through complex syncytial networks. This adds an additional level of complexity to interactions between astrocyte domains that may extend over large areas including the entire neocortex. Hypothesis: Consciousness is seamlessly expressed in a three-dimensional matrix consisting of billions of tessellating cortical astrocyte domains that bind attended sensory information. The temporal sequence (stream of consciousness) depends on the global distribution of sequential neural activity. The matrix may also be utilized to encode and store explicit memories. (C) 2013 The Author. Published by Elsevier Ltd. All rights reserved.