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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 functional LINKs (IPLs) are the key structural changes responsible for encoding learning-changes in physiological time-scales of milliseconds that can be retained for variable lengths of time. The inter-spine interaction that lead to the formation of IPLs was examined for its feasibility to have evolved through the simple steps of variation and selection. A stage of significant spine and neuronal loss during the early stages of development indicates that a corresponding stage of IPL fusion that led to neuronal loss during evolution. In the surviving cells is expected that a mechanism for stabilizing IPLs for the rest of life was triggered. This sequence of events can be achieved if the initial stage of transient inter-neuronal inter-spine fusion can trigger the lifelong expression of specific proteins that can stabilize the intermediate stage of inter-spine hemifusion. This is supported by the presence of proteins within the spines that arrest fusion between the spines. Since IPL mechanisms are expected to be utilized during every event of learning, any defect in the continued expression of proteins that stabilizes IPLs at the stage of hemifusion can lead to age-related neurodegeneration.

A realistic hope has been that from ontogeny, it may become possible to understand the steps of evolutionary changes that may assist in understanding the mechanism of nervous system functions. However, explaining how first-person internal sensations are formed in the nervous system makes this approach very difficult. In this context, if it becomes possible to derive an operational principle by using constraints from observations at different levels, then it will enable examining whether it is possible to arrive at its specific circuit features from single neuronal cells using simple steps of introducing variations and selection. In this context, semblance hypothesis is examined. Inter-neuronal inter-spine interaction leading to the formation of inter-postsynaptic functional LINK (IPL) is necessary for generating units of internal sensations and their computation. The results show its suitability as an evolved mechanism. Significant neuronal and spine loss during ontogeny indicate that following these events, IPLs resulted from the selection of a suitable variation. This can only be achieved through transient inter-neuronal inter-spine fusion, which leads to inducible molecular changes for keeping the spines separate by arresting fusion at the stage of hemifusion. The importance of sustaining this one-time induced IPL mechanism for retaining cognitive functions throughout life is discussed.

Multiple associative learning events can take place within sub-second time and the "completed" mechanism can then be used for specific memory retrieval without any lapse of time. This indicates that a biological process is completed within the matching time-scales of milliseconds that can be used for retrieving specific memory. Since qualia of working, short-term and long-term memories are same except for degradation of features in long-term memory and since every long-term memory had the capability to induce working memory immediately after learning, all memories are anticipated to get induced from a mechanism formed at the time of learning. When memories are viewed as first-person internal sensations, a derived mechanism fulfills the "completion" requirement within milliseconds that can be used to induce working memory and can be transitioned to stabilizable forms to induce short-term and long-term memories.

Possible combinations of inputs in the order of 10100 can fire (axonal spike or action potential) a neuron that has nearly 104 inputs (dendritic spines). This extreme degeneracy of inputs that can fire a neuron is associated with significant loss of information when examination is limited to neuronal firing. Excitatory postsynaptic potentials (EPSPs) propagating from remote locations on the dendritic tree attenuate as they arrive at the axon hillock depending on the distance they propagate. Moreover, some EPSPs from remote locations will not even reach the axonal hillock. In this context, an operational mechanism at the location of origin of these EPSPs is necessary to preserve information for efficient storage. Evidence can be visible as the tip of an iceberg of operational mechanisms occurring only at a narrow window when sub-threshold activated (before learning) non-firing neurons fire during memory retrieval in response to a cue stimulus. Even this observation from a set of neurons does not identify the location where information is stored due to extreme degeneracy of inputs that can contribute potentials to cross the threshold and fire those neurons. In summary, it is necessary to identify locations of specific inputs where information is expected to make changes.

Higher brain functions such as perception and memory are first-person internal sensations whose mechanisms can have options to concurrently activate motor neurons for behavioral action. By setting up all the required constraints using available information from different levels, a theoretical examination from a first-person frame of reference led to the derivation of a first-principle of the structure-function units. These units operate in synchrony with the synaptically-connected neural circuitry. These units are capable of explaining and interconnecting findings from various levels and enable triangulation of a large number of observations from both the normal and “loss of function” states of the system. Indirect evidence for the presence of a comparable circuitry in a remote species −Drosophila− suggests the universal presence of these units across the animal kingdom. The key features of the basic unit meet the expectations of the K-lines proposed for the development of artificial intelligence.