09. Neuroplasticity

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"Human beings are genetically programmed, programmed to learn" (F.Jacob, 1981).

1. Brain vs. Computer:

Functioning of the nervous system and a computer system that have some similarities [ 118 , 228 , 229 ]:

• Both have a binary base signal (0-1). For computers, or the current password or it does not. To the nervous system: the law of all or nothing action potentials.
• They both have a hardware part (for computer equipment and bodies for the nervous system), and a software part [ 229 ] (for senior software for the nervous system functions and IT systems) [ 228 ].

  However, the nervous system is extremely powerful on several levels:

• If we compare a transistor (core of a microprocessor, the latter being the center of computing and data processing in a computer) at a synapse since both have similar functions, we realize that in the most efficient microprocessors designed today there are only 3 billion transistors [ Wikipedia, Transistor count ]. Whereas the nervous system, 100 trillion synapses "100 000 000 000 000" is available around [ 4 , 57 ], a number of fascinating and extraordinary nerve connections in our body.
• Our brain is a supercomputer that not only has such a large number of neurons and synapses, but also manages to hit a minimum of energy: almost enough to power an ordinary lamp. If a supercomputer with the same number in transistors would be built we would have at least 100 megawatts of power to operate: enough energy to power an entire city [ 139 ]!
• Not only the brain is much higher than the number of connections and low power consumption but is also clearly much higher in the management of connections. They walk in the brain in parallel: every moment billions of information flows both. Whereas for microprocessors it is an operation mode in series, one after the other information.
• But the most extraordinary ability of the nervous system is certainly not his power. The real and undeniable power of the nervous system remains and will remain for ever its flexibility and versatility. Every day we lose around 100,000 neurons [ 111 ] and yet we continue to live as if nothing had happened, this is due to the formation of new connections that contribute to overcome the deficit. While a microprocessor is likely to fall down for the loss of a single transistor!

2. Discovery:

In 1890, the famous Russian physiologist Ivan Pavlov [ 76 ] noticed that the dogs tended to salivate before actually entering into contact with food. He then decided to investigate in more detail the (psychic secretion). He made ​​an experiment in which he announced each time the meal the dog with an audible signal. After a few days, the dog began to salivate whenever he heard the signal. Pavlov then concludes that physiological reflexes may be caused by a special brain fitness and he brought the concept (conditioned reflex [ 54 ]).   This experience had a great impact on modern neurology and psychology. Again later, the term (neuroplasticity) was invented by his student Jerzy Konorski who developed more research Pavlov. We now know that conditioned reflexes are in fact variations of a fundamental and essential property of the nervous system neuroplasticity [ 97 ].   Neuroplasticity is the brain power most remarkable and most striking, is the power to change and adapt to environmental conditions and experience. Thanks to neuroplasticity that can store, we can forget, we can learn, we can grow and can recover brain damage that can sometimes be devastating.   The discovery of Pavlov is only one example of what the nervous system is capable of. Indeed, the nervous system is constantly changing and developing, and research in this direction never cease to amaze us every day by the incredible potential of neuroplasticity.   With modern techniques such as PET (positron emission tomography [ 67 ]) and functional MRI [ 76 ], to locate the brain regions responsible for certain functions, it has been shown that each person has a particular distribution functional areas in the brain, although there are similarities in the broad strokes, but there are still some differences in the past and experience of each.   Thus, for example, a violinist has a region of the brain developed enough to the muscles that control the little finger to the detriment of the other fingers, one blind from birth or from childhood and uses the language of Braille read develops an important activity in the visual cortex even if the individual is unable to see. Whenever a region of the brain is non-functional because of an injury to a sensory apparatus or effector it sells its capital nerve cells to other brain functions. In the brain, it is not idle! !   This explains how the blind have a very fine hearing and touch, how deaf mutes develop communication skills with pretty impressive signs and how other disabilities are able to compensate for their disabilities by developing other skills.   Neuroplasticity also explains how you can become smarter with time, while we lose every day tens of thousands of neurons without being replaced!

3. Mechanisms:

Where does this flexibility and plasticity of the nervous system? In fact there are several underlying mechanisms, whether a local or global scale.

3.1. A wide synaptic (synaptic plasticity) [ 52 ]:

If you cause an action potential at a presynaptic and is repeated several times the same neuron stimulation, we note that the response of the postsynaptic neuron is growing in intensity As it therefore currently improved synaptic efficacy. If after a few days, restimulated the same presynaptic neuron we will record the post-synaptic level the same intense response. This phenomenon the long-term potentiation (LTP) [called 3 , 38 , 39 ]. Whenever a synapse is requested multiple times, it becomes more reactive and effective for a long term. This may be due to:

• Increasing secretion of neurotransmitters.
• Increasing the number of postsynaptic receptors or change their properties (phosphorylation), thus opening them will last longer.
• Or a decrease in the reuptake.

3.2. At the cellular level (neuronal plasticity) [ 74 ]:

The neuron can create new synapses (synaptogenesis) or alter the conformation of dendritic spines, which has repercussions on the amplitude of the synaptic excitation. The threshold of excitability at the cone emergence may also vary according to several factors including hormonal, and a higher threshold will make it harder to create an action potential.   But also exceptionally, there may be a low level of neurogenesis, most often at the level of the hippocampus. New neurons are born with new features.

3.3. On a global scale (brain plasticity) [ 141 ]:

There may be a reorganization of neuronal networks and redefinition of their connections. It retains Donald Hebb [ 140 ] (which is considered the father of neuroplasticity in the fifties) the phrase "That neurons fire together wire together [ 140 ] = Neurons that fire together bind together. " Every time a neural circuit is applied repeatedly, it forms a solid network that specify to perform a specific function.

4. Applications:

More and more studies focus on neuroplasticity to elucidate these mechanisms, limitations, and especially its promises. Today Neurosurgeons have increasingly knowledge to predict whether a function will be recovered after surgery on the brain or not.   This flexibility brain begins to be exploited in recent years, particularly in the area of sensory loss. Indeed, there are now devices that allow people with certain forms of blindness (see) using the language [ 97 , 141 ]: cameras placed on the forehead transmit visual data to a device that makes the language, the different light signals are converted to mechanical signals. The language is very sensitive allowing the patient to discriminate between these mechanical pixels. Over time, the brain manages to adapt to this new feature and it's visual cortex will be responsible for collecting this new modality of vision.   Another example of a patient who has lost the sense of balance after a labyrinthine toxicity due to antibiotics. It has been equipped with a device that sends the spatial location of regular vibration signals at the floor of the mouth. Gradually, the brain has adapted to this new form of reports and integrated functioning in the same way it integrates data from neurological mazes.   These very practical applications of neuroplasticity on sensory losses we prove once more that the sense organs are only means for extracting data we receive from the world. They are certainly very powerful and sophisticated, but in case of device failure, we can mitigate their loss by artificial organs (sensory substitution [ 97 ]), and the brain will take care to adapt to new ways.