Since the normal mechanism of functioning of the system has

Since the normal mechanism of functioning of the system has not yet been discovered, any new theoretical framework of a mechanism is expected to provide an explanation for the functional role of sleep [18]. Difficulties in understanding the mechanisms of higher topotecan cost functions still continue, primarily because these functions are first-person internal sensations to which only the owner of the nervous system has access. In this context, the semblance hypothesis [19,20] that was put forward to explain the observations made from both the first- and third-person frames of reference at various levels is examined. The hypothesis was developed from the premise that the basic units of internal sensations, namely semblances, are induced as a systems property at the level of the postsynaptic terminals and occur in synchrony with extracellularly-recorded oscillating potentials of specific frequencies. To obtain an explanation for the necessity for sleep, essential conditions for the systems property of induction of semblances are examined.

Background
The quantal release of neurotransmitter molecules from the presynaptic terminal occurs all the time (tq), including during rest and sleep (Fig. 1A). The binding of these molecules to the postsynaptic membrane receptors induces a very tiny voltage that is reflected in the measured miniature postsynaptic potentials (minis) from the latter\’s neuronal soma. These quantal release-mediated potentials are continuously being induced at the postsynaptic membrane (postsynapse or dendritic spine). In addition, various stimuli from both the environment and from within the body, which arrive at the sensory receptors activate the sensory neurons, which are then transmitted through different higher neuronal orders. When this activity arrives at the presynaptic terminal, it leads to the entry of calcium into the cytoplasm that, in turn, leads to the release of a volley of neurotransmitter molecules from the presynaptic terminal into the synaptic cleft. This induces a large postsynaptic potential (Fig. 1B). Let this duration of activity-induced postsynaptic activation be (ts). The unidirectional flow of activity from the presynaptic terminal to the postsynaptic terminal at the chemical synapses can contribute to the vertical component of the extracellularly-recorded oscillatory potentials. Since recurrent collaterals do not present in sufficient numbers at different neuronal orders and since the presence of gap junctions between excitatory neurons is sparse [21], mechanisms that can contribute to the horizontal component of the oscillating potentials are yet to be discovered.
Each event or item in the environment is capable of stimulating more than one sensory system. When the event or item is close to the animal, the simultaneous arrival of these sensory inputs enables them to get associated within the animal\’s nervous system. Later, when the event or item is located away from the animal, the fastest arriving stimulus (usually visual) from the event or item induces a virtual internal sensation of the remaining stimuli from the latter. This provides the animal with a survival advantage in the environment where it has to obtain food and stay protected from its predators. These processes require a mechanism to both associatively store the information and then make internal sensations of the late-arrived or even non-arrived sensations, so that the animal can respond at appropriate times to the environmental stimuli. This is essential for both the prey and the predator to make quick internal decisions that enable them to survive in the environment. The process of associative learning during the exposure to a novel event or item was hypothesized to occur through the induction of an inter-postsynaptic functional LINK (IPL) between the simultaneously activated postsynaptic terminals at locations of convergence of different sensory stimuli [19,20] (Fig. 1C).