What is the neuroscience definition? Neuroscience is the scientific study of the nervous system, both in structure and function, from the molecular to the organ level, such as the brain, or even the whole organism.
Understanding the relationship between the brain and the mind is both a scientific and a philosophical problem. The strong relationship between physical brain matter and the mind is easily evidenced by the impact that physical brain changes have on the mind, such as head trauma or psychotropic use.
Until the end of the twentieth century, the mind-body problem was one of the central debates in the history of philosophy and consisted in considering the way in which the brain and the mind could be connected.
Three major schools of thought existed on this question: dualism, materialism, and idealism:
– Dualism postulates that the mind exists independently of the brain;
– Materialism postulates, for its part, that the mental phenomenon is identical to the neuronal phenomenon;
– Idealism postulates that only the mental phenomenon exists.
In addition to these philosophical questions, this hypothesis of the relationship between the mind and the brain raised a great number of scientific questions, such as the relationship between mental activity and brain activity, the mechanism of action of drugs on cognition, or still the correlation between neurons and consciousness.
Historically, many philosophers thought it inconceivable that cognition could be put in place by a physical substance such as brain tissue. Philosophers like Patricia Churchland have postulated that the interaction between drugs and the mind is an indicator of the intimate relationship between brain and mind but that the two entities are distinct.
Since the advent of neuroscience, and the work of many international research teams, this issue is no longer relevant in science. Antonio Damasio, in his book The Error of Descartes in particular, shows that body and mind function inseparably. He also explains that reasoning, memorizing, acquiring new learning cannot be done without integrating emotions into processes.
I – Neuroscience Definition
If the study of the brain is old, the word neurosciences are recent, it dates from the 70s. It refers to all the scientific and medical disciplines studying the nervous system (including psychiatry, and clinical psychology according to the terminology of the European Union). The researchers are neuroscientists.
The various levels of brain analysis can be defined in increasing order of complexity: molecular, cellular, integrated (systems), behavioral and cognitive.
Molecular neurobiology: study of different molecules that allow brain function, for example, messengers allowing communications between neurons, molecules that control inputs and outputs, neuron growth substances …
Cellular neurobiology: study of neuron properties, its development…
Integrated neuroscience: The study of neuronal systems that form particular sets, such as sensory systems, or the motor system. These circuits allow the reception of sensory information, their analysis, or also decide and order the movements.
Behavioral neuroscience: these correspond to a more global level of study, the search for the biological bases of behavior.
Some examples of questions posed by behavioral neuroscience are:
– The role of neuronal systems in the development of integrated behaviors,
– The neurobiological bases of memory,
– The modes of action of the drugs which modify the mood, the psyche, the behaviors,
– The formation of dreams.
Previously we spoke of Psychophysiology or physiological Psychology: a study of the physiological bases of the psyche. Thus the program of the degree in psychology included until the 1994 reform physiological psychology, now replaced by behavioral neuroscience.
There is, therefore, a double approach:
– Psychobiological researching the biological bases of behavior (is the title of Rosenzweig’s new book);
– Psychological: a study of mental functioning, psyche…
Cognitive Neuroscience Definition
Study of the neural mechanisms of mental activities such as language, mental representations, consciousness, or in more general terms the relations between brain and thought. They are part of the cognitive sciences, including cognitive psychology, artificial intelligence, and robotics.
Ultimately, What Is Neuroscience?
The field of neuroscience research is a transdisciplinary field: biology, chemistry, mathematics, bioinformatics, and neuropsychology are used in neuroscience. The conceptual and methodological arsenal of neuroscience goes hand in hand with a variety of approaches in the study of the molecular, cellular, developmental, neuroanatomical, neurophysiological, cognitive, genetic, evolutionary, computational or neurological aspects of the nervous system.
Neuroscience definition is often presented in terms of cognitive neuroscience, especially brain imaging: some applications of cognitive neuroscience can be used in economics, finance, marketing, law, and artificial intelligence.
The neurosciences have made extraordinary progress over the past fifteen years, as evidenced by the Nobel Prize in Medicine awarded in October 2000 to three specialists in this field. The term neuroscience appeared (in the English language) at the end of the 1960s to designate the branch of biological sciences which is interested in the study of the nervous system and more particularly from the electrophysiological point of view, as the work illustrates future Nobel laureates David Hubel and Torsten Wiesel record the electrical responses of the neurons of the cat’s visual cortex according to the images presented to him.
II – History of Neurosciences
1 – Neuroscience Definition and History – Brain Localizations
The brain was not considered an important organ, it was rather the heart, but not always.
Thus Tutankhamun (3300 years ago) had in his tomb jars containing his stomach, liver, lungs, and intestines but not the brain that was thrown for embalming.
Until the rebirth, it was forbidden on pain of excommunication to dissect the human body, at this time the anatomical observation resumes and the main parts of the brain are named (see eg Vesalus, 1543).
At this time the brain function is interpreted according to a hydraulic or “pneumatic” model. The material support of psychic processes is considered to be constituted by the liquid of the cerebral cavities circulating along the nerves.
With Descartes, and its 17th-century machine animals, the mechanistic vision of brain function begins to emerge, it takes off with the Phenology of Gall: Study of character and dominant faculties according to the shape of the skull (Phrenos: intelligence in Greek) also called craniology. [Do not confuse craniology with anthropometry that aims to measure the various parts of the human body, nor with morphopsychology “study of the correspondences between psychology and morphological types or predominance in humans”]
For Gall, it is the cortex which is fundamental, and it assigns to each of the human faculties a particular location. Gall establishes a topographic map of the skull, supposing that it is a reflection of the brain surface. By collecting the skulls of famous men and criminals or mentally ill he develops the phrenology that allows by a simple examination of the reliefs of the cranial box the analysis of 35 intellectual functions such as intelligence, aggression, hope confidence, patriotism, home instinct, flight aptitude, etc. See also in Saché in the castle of Balzac an engraving of 1896 entitled “The phenologiscope cranioscope”.
At the same time, some doctors like Flourens develop opposing theories, considering that the properties of the brain are based on its globality, without precise anatomical locations. It is striking that the highly speculative character of Gall’s ideas did not prevent their success and their use until the middle of the 19th century. It remains traces since we still talk about the math bump!
It was Broca who in 1861 was going to provide partial confirmation of Gall’s hypotheses, with the post-mortem anatomical study of certain patients, in particular, Mr “Tan-Tan”. This one understands the meaning of the words but can only repeat one syllable “Tan” embellished with “Sacred name of God”. At the dissection of the brain of this patient, he discovers a part between the eyebrow and the left temple which is injured (frontal lobe) and thus corresponds to the pronunciation of the words. The center of the language (now called Broca’s area) is located in the left hemisphere and its lesion causes motor aphasia (the patient speaks incomprehensible gibberish, but he understands what he is told).
Localization theses were later to be widely confirmed, with, for example, another center of language, that of understanding this time. Shortly after Broca, the German Carl Wernicke (1848-1905) identifies a second area (this time temporo-parietal) involved in a language with a patient who is unable to understand the meaning of words and utters meaningless sentences (eg “Shop to eat street on a copper candlestick or”). Since then, we have been talking about Wernicke’s aphasia: a voluble language with words but no understandable sentences.
The areas of sensory systems, areas of association, and motor areas are known at the level of the cortex. At the subcortical level, the afferent sensory and motor relay areas have been located. The fragmentation is increasing; we know 32 zones in the visual cortex. Lesions of the V4 area in front of the occipital cortex cause achromatopsia (no color vision). In reality, complex processes are not only localized but divided into interacting systems. The visual system includes 12 successive stages and 187 connections between all these visual areas! Neurophysiology is interactionist.
For example, we have discovered that the visual (occipital) and touch (parietal) areas are connected and that the birth blind has an occipital area that is activated during Braille reading. If we inactivate the occipital cortex of these blind, they make many mistakes in reading braille. “To see with the fingers” would have a biological basis and one can imagine that these blind people realize real mental images. It is the same for the deaf who “read” the language with their auditory area. These data confirm the extraordinary malleability of the human brain and its compensation capabilities.
2. Neuroscience Definition and History – The Neuron
The nerve fiber is known from the beginning of the microscope around 1700. The organization of nervous tissue has been the subject of a major controversy from the 1870s, a controversy that will not be definitively closed until after 1950 with the discovery of the electron microscope. For some (reticularists) the nerve cells form a continuous network like the blood system. For the others (neuronists) the neurons are independent units in contiguity with each other. The psychiatrists of the time are doing anatomy work, so Freud in 1882 publishes works in support of the reticularist thesis. At this time, various arguments are already in the direction of the neuronist thesis, in particular, the study of neuronal degeneration, but it is after 1950 that this thesis will be definitively adopted with the observation of the ultrastructure of the synapse. Nerve tissue forms an extraordinarily complex network with 30 to 100 billion neurons and 1 billion possible connections and 600 million synapses per mm! We also know now that this network is flexible and adaptable unlike a network of telephone cables.
It has always been considered that the number of neurons was fixed at birth. It seems that this dogma is not totally true since neurons of the hippocampus are able to multiply in the adult monkey and man.
Another peculiarity of the nervous tissue is the presence of glial feeder cells whose role is very important, whether during development, as the immune system or survival. Microglia cells are responsible for immunity but also secrete neurons survival factors. The AIDS virus that affects the immune system leads at the end of life to cognitive dysfunction and early dementia; it does not attack neurons but microglia cells that produce inflammatory cytokines (intracellular messengers) and toxic molecules for neurons.
3 – Neuroscience Definition and History – Brain Electricity
This is the work of Galvani who in 1791 really opened the way to a correct explanation of nervous functioning by experimentation on the frog. It shows that muscle contraction is triggered by electricity from the brain and circulating along the nerves.
Helmotz in the 19th century shows that electrical signals propagate at a speed of 50 to 100 m / s.
In 1930 the German Berger highlights the electrical signals emitted by the brain (EEG).
In 1959 Hodgkin and Huxley discovered the mechanisms of propagation of the nerve impulse, this one is related to movements of ions Na + and K +, one speaks about sodium pump which allows the exit of the sodium and the entry of potassium. We now know that these fluxes are possible thanks to ion channels.
The size of the electrical pulse (it is the action potential PA) is standard, the coding of the information is done by the rhythm of PA.
4 – Neuroscience Definition and History – Neuromediators and Neurochemistry
At the beginning of the century, adrenaline and acetylcholine (ACh) are the first two neuromediators identified at the peripheral level. It was only in the 1940s that we discovered ACh in the brain. With the discovery of the fine structure of the synapse, it is shown that the transmission is electrochemical with a chemical mediator. The identification of neuromediators and their pathways in the brain begins. The era of neurochemistry is primed.
The neurotransmitter (or neuromediator) will be called a chemical substance released by the presynaptic element after stimulation that activates postsynaptic receptors. About 50 neuromediators intervene in the chemical communication between neurons, several coexist sometimes in the same neuron.
The neurotransmitter binds to a receptor protein of the postsynaptic membrane, called a receptor. The first discovered receptor was that of ACh on the torpedo (electric fish), it was called the nicotine receptor because nicotine has the same effects as ACh, it is a cerebral stimulant. The neuromediator and the receiver work a bit like a key in a lock. Various substances can block the lock, for example, curare which selectively blocks nicotinic receptors and causes motor paralysis and death by asphyxiation. Other substances do not trigger action potential but changes in the permeability of the postsynaptic membrane, we speak of neuromodulator. This is the case of serotonin, which may be neurotransmitter or neuromodulator depending on the case. We are currently discovering a large number of receptors; we already know 14 serotonin receptors.
GABA is an inhibitory neurotransmitter (the binding of GABA on the receptor causes the opening of the chlorine channels, and thus the hyperpolarization of the cell by the entry of Cl ions. Sometimes there is a second intracellular messenger, such as cAMP (cyclic AMP, Adenosine MonoPhosphate).