The Syncytial Theory of Consciousness

1. Complex bidirectional communication exists between astrocytes and neurons at each active tripartite synapse. 2. Individual astrocyte domains monitor and integrate excitatory and inhibitory synaptic information throughout the territory occupied. 3. Individual human astrocyte domains interact with up to 2 million excitatory and inhibitory synapses with multiple origins and neurotransmitter profiles. 4. Astrocytes alter structural and functional properties of presynaptic and postsynaptic elements that affect long term potentiation or depression. 5. Astrocytes, along with microglia, modify neuronal networks through synaptogenesis and synapse elimination throughout the lifespan. 6. Astrocyte domains form a functional astroglial syncytium through gap junction intercellular channels that transmit electrical and chemical signals throughout the neocortex. 7. From an evolutionary perspective, human astrocytes, unlike neurons, have undergone dramatic exaptations including vastly enlarged protoplasmic astrocytes as well as three unique human/primate-specific astrocytes. 8. Human exapted astrocytes significantly enhance learning and memory in mice chimeras. 9. A recent study demonstrates rapid electrical signaling from one group of neurons to another through a bridge of syncytial astrocytes. This strongly supports the astroglial syncytium as a structure for rapid long-range signaling on a timescale required for binding widespread regions of the brain into consciousness. Conclusion: Conscious expression occurs in the human astroglial syncytium. The syncytium also provides mechanisms for encoding and storing memories that return into consciousness as needed.