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Vadakkan KI.2019. A derived mechanism of nervous system functions shows features capable to have evolved and provides a testable explanation for age-related neurodegeneration. PeerJ Preprints7:e27458v4https://doi.org/10.7287/peerj.preprints.27458v4
By viewing memories as first-person internal sensations, it was possible to derive a potential mechanism of nervous system functions. Accordingly, a spectrum inter-postsynaptic (inter-dendritic spine) functional LINKs (IPLs) are the key structural changes responsible for encoding learning-changes in physiological time-scales of milliseconds that can be retained for different lengths of time and can be used for inducing first-person inner sensation of memory. The objective of this study was to examine a) where preconditions existed for an accident to trigger sparking of internal sensations, b) what conditions might have promoted the formation and selection of IPLs, and c) how the synaptically-connected neuronal circuitry accommodated the formation of IPLs through the simple steps of variations and selection. Sequence of events during the development of the nervous system was examined for the feasible sequence of steps that led to the formation of IPLs and optimization of the system. A stage of significant spine loss and neuronal death during the early stages of development indicate about a corresponding stage of inter-spine fusion that led to neuronal loss during evolution. When the generation of internal sensations by the IPLs started to become advantageous to the system, it started preserving the circuitry by developing an adaptation to prevent inter-spine fusion. This can be achieved only if a stage of transient inter-neuronal inter-spine fusion "turn on" certain mechanism to prevent the intermediate stage of inter-spine hemifusion from progressing to fusion. In summary, the derived IPL mechanism is capable to have evolved. An adaptation to prevent IPL hemifusion from progressing to fusion is a likely evolutionary adaptation. Since the IPL mechanism is utilized during every event of learning, any age-related factors that weaken the maintenance of this adaptation to prevent IPL fusion can lead to neurodegeneration.
A figure was replaced with a new figure and modified figure legend. Substantive evidence for the claims made in the work is added to section 4.3 of this version. Five new references are added.