José Antonio R. Piedrabuena -- Against the belief in neural networks

They should stop discrediting real neurons, because the brain does not only function thanks to them, and change the name of neural networks. I don't think they can be considered to be the model of any 'neural network', beyond the pure appearance and opportunistic use of the name.

We start from the fact that no artificial intelligence or neural network has the mission of coordinating, organising and maintaining all the organs of the body. By controlling all the variables of our metabolic and functional existence, while adapting to the circumstances of the environment, we maintain our personal identity, goals and complex mechanisms for the survival of the species. And for this we have a brain.

There is no resemblance between a neuron of the so-called neural networks and those we have in the body. The functional unit in the brain is not the neuron, but the sum function of the neuron, the glia, the surrounding tissue and the perivascular feet forming a set of metabolic, electrical, molecular processes whose result is the governance of the body and the mind. Glial cells (of smaller size and complexity) outnumber neurons, which I don't think is taken into account when we talk about neural networks, which give a total of about one hundred and eighty billion cells, each of which receives an average of ten thousand connections.

Neurons are all different, each region of the brain has several kinds of neurons, each one adapted in its physiology to the specific functions of the region.

An incoming stimulus can give rise to a variable infinity of responses. And as if that were not enough, the input of information can impose a particular output discharge pattern, because if a neuron receives 200,000 input connections, they all add up to signals in the cell body to become a single output signal, but no two neurons behave in the same way in terms of information output patterns. One thing to note is that the electrical and biochemical properties of the dentrites (branches through which information enters) vary from cell to cell resulting in the connections between them, synapses, differing in size, transmitter identity and transmission efficiency.

Many are rhythmically activated, some secrete hormones or neuromodulators in bursts, as in the hypothalamus, some react initially and ignore successive stimuli, and others pause and then respond, which is fundamental to successive rhythmic processes such as respiration, heart rate, some endocrine glands, biorhythms.

The incoming signals have their input in their membranes, in input and output channels, fast, electrical, or slow for other substances that have to enter conducted by transporters. A whole set of activating or braking substances are transformed into signals that have to go out through the only exit, the axon, to very precise targets or to thousands of neurons, generally in a diffuse way. All this to adapt to local requirements and demands and at different speeds.

Neurons and smaller glia cells have receptors with which they will pick up and recognise neurotransmitters, ions, hormones, nutrients, poisons, as well as identifying other members of the species.

We already know that one neuron communicates with another through a synapse. These vary widely in shape, size, identity of the neurotransmitter, efficiency of transmission; because a transmitter, depending on the nature of the components with which it interacts, can vary from one part of the brain to another and even in parts of the same neuron and produce different and even opposing actions. For example, dopamine has five different receptors or entry pores with a different stimulatory outcome. The nature of some other neurotransmitters are standard substances of life. For example, amino acids glutamate, aspartate, GABA and glycine are nutrients for the cells of the body because they function as a source of energy to make proteins, and in the brain they exert generalised messaging functions.

We have a hundred different neurotransmitters and modulators manufacturing our thoughts and emotions, activating or blocking us, such as amino acids, simple amines or molecules like adenosine and peptides, neurohormones that are waiting to be discharged, in the form of little bags, like secretory granules, which may also contain endocrine hormones. The result is our metabolic, mental, social, reproductive, peaceful or fanatical life, which will also depend on something as small as sodium, potassium, chlorine ions that transform the neurons into a charging or discharging battery that is activated when the calcium ion enters and the inside turns positive. An ion can flow out or in through a neuronal channel up to a million units per second.

We repeat that the areas through which neurons receive signals are the spines, the equivalent of the branches of trees, the trunk and the roots would be the output axon. In addition, something more complex, the spines, the branches, which in addition to receiving information have other vital tasks; they contain more than 30 proteins involved in the generation of energy and many other functions.

Responses to this barrage can range from milliseconds to days.

We can see that the brain for its sensory, motor and cognitive functions requires fast or slow but specific connections and operations to maintain all the vital constants: sleep, waking, attention, concentration, mood control, the levels of the contents of all the body's fluids and their contents, general excitability, metabolic state, command over the immune, endocrine and vascular systems, etc. And it is all mediated by different neurotransmitters, carried to their place of influence by axons through connections that can be dispersed, diffuse, meandering or localised and structured and usually deployed from the most primitive within the brain, the brainstem. Our personal and social life is commanded from the regulation, the modulation of neuromodulators produced in the second most primitive area of our brain. This area is the one that is being used so much for all the extremist, violent manifestations of behaviour outside the laws of conservation of life.

Sometimes, several thousand neurons form the centre of a system that may be diffuse, such as those in the brainstem, and do not connect one neuron to another, but pour their secretion into the liquid that bathes the entire brain and thus reaches millions of cells without synapses.

In the brainstem are the production sites of substances known to all, such as dopamine, serotonin, noradrenaline, acetylcholine, which in this case a single neuron is connected to 250,000 other neurons.

We cannot simplify this any further and move on to the other component, the thirteen families of neuroglia: the astrocytes. These also synthesise neurotransmitters, as do neurons, and up to 20 neuroactive compounds and modulate synaptic efficacy.

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