The neural system somehow gives rise to a sense of being and Self. Does this immense phenomenon result from the particular activity of specific cells interconnected in certain circuitry in the innermost place of a brain? If this is factual, our task is to discover the shape of this activity, the structure of a neuronal circuit, characteristics of corresponding neurons and, may be, other non-neuronal cells and their location in the brain. This, by the way, is just the problem that neuroscience really tries to solve. Now, let us this problem is already solved. And our response is this: the sense of being arises, when at least 14 glutamatergic neurons located in the 5th layer of the medial prefrontal cortex, connected by means of electrical synapses in a circuit together with 21 astrocytes and generates synchronous activity in a 7-band. Might we, after all, say that now the sense of being is clear for us? Definitely not. We hoped to realize why our Self possesses a mysterious free will, how it is continued in time, restricted in space and located in our body. And, mainly, how one guesses that one is alive and why this is so valuable? In the end, any living cell possesses aspiration to life. At least it behaves as if it does aspire. Desire to live is the core sense and it somehow connects with the sense of being.
The death and birth of neurons is a normal process in brain. The nervous system is a central regulator of an organismal life span, and brain performance is accompanied by neuronal birth and death [157, 1350]. During ontogenesis, axons emit signals that play a role in target field development and these signals regulate target cell proliferation, differentiation and survival. Target-derived molecules, such as neurotrophins, transport also in a retrograde fashion along axons to bring neurotrophin molecules from postsynaptic cell populations (both neurons and glia) to presynaptic cell bodies [687]. Cells in the brain of adults die and are born, too. These processes are non-uniform: neurons that are in close contact may elicit markedly different responses to increasing age that can result in the loss of specific populations of neurons [1379]. For instance, the rat supraoptic nucleus does not loose neurons in old age [396].
In the adult mammalian brain, neurons and glial cells are continuously passed away and generated in retina, olfactory bulb, inferior olive, cerebellum, thalamus, locus coeruleus, hippocampus and neocortex [492, 1216, 332] and, possibly, in other areas. The number of new generated cells (glia, and, in a larger proportion, inhibitory interneurons releasing GABA) decline during several weeks, but a smaller percentage of them continue to survive. In olfactory bulb of adults, approximately 1% of the total interneurons die and are added each day [332, 759]. Therefore, cellular birth and death may somehow participate in cerebral function. The number of neurons in a nervous system depends on environmental circumstances [943, 797]. In addition, the location of neurons that are particularly vulnerable to injury suggests that damage to neurons may participate in the control of behavior. Emotional, homeo-static, perceptive and motor centers such as the cortex, hippocampus, specific hypothalamic nuclei, amygdala, medulla, and cerebellum are more sensitive than other brain area to metabolic stress [1228]. It is tempting to speculate that the sensitivity of these nervous centers to injurious factors is not only an aggravating opportunity, but is essential for the fulfillment of higher neural functions.
