Bronnen bij Neurologie: spiegelneuronen
Spiegelneuronen zijn ontdekt door de Italianen Giacomo Rizzolatti, Leonardo
Fogassi en Vittorio Gallese tijdens onderzoek naar de werking van
individuele neuronen bij makaken. Het bleek dat sommige neuronen niet alleen
vuurden tijdens het uitvoeren van een bepaalde actie, zoals het grijpen van
een voorwerp op tafel, maar ook als iemand anders dat voorwerp greep.
Kennelijk werd deze actie in het apenbrein nagespeeld - gespiegeld. Onder
een deel van het overzichtsartikel in Scientific American over hun
zeer belangwekkende onderzoek - de tekst bevat verkleinde versies van de met
tekst toegelichte illustraties, die hyperlinks zijn naar de grotere,
leesbare, versies (Scientific American, nov. 2006, door Giacomo Rizzolatti, Leonardo Fogassi
en Vittorio Gallese):
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Overview | Meeting the minds
■ Subsets of neurons in human and monkey brains respond when an individual
performs certain actions and also when the subject observes others
performing the same movements.
■ These "mirror neurons" provide a direct
internal experience, and therefore understanding, of another person's act,
intention or emotion.
■ Mirror neurons may also underlie the
ability to imitate another's action, and thereby learn, making the mirror
mechanism a bridge between individual brains for communication and
connection on multiple levels.
Mirrors in the mind
A special class of brain cells reflects the outside world, revealing a new
avenue for human understanding, connecting and learning
Tussentitels: The pattern of activity was a true representation in the
brain of the act
itself, regardless of who was performing it.
When people use the expression "I feel your pain," they
may not realize how literally it could be true.
John
watches Mary, who is grasping a flower. John knows what Mary is doing - she
is picking up the flower - and he also knows why she is doing it. Mary is
smiling at John, and he guesses that she will give him the flower as a
present. The simple scene lasts just moments, and John's grasp of what is
happening is nearly instantaneous. But how exactly does he understand Mary's
action, as well as her intention, so effortlessly?
A decade ago most neuroscientists and psychologists would have
attributed an individual's understanding of someone else's actions and,
especially, intentions to a rapid reasoning process not unlike that used to
solve a logical problem: some sophisticated cognitive apparatus in John's
brain elaborated on the information his senses took in and compared it with
similar previously stored experiences, allowing John to arrive at a
conclusion about what Mary was up to and why.
Although such complex deductive operations probably do occur in some
situations, particularly when someone's behavior is difficult to decipher,
the ease and speed with which we typically understand simple actions suggest
a much more straightforward explanation. In the early 1990s our research
group at the University of Parma in Italy, which at the time included
Luciano Fadiga, found that answer somewhat accidentally in a surprising
class of neurons in the monkey brain that fire when an individual performs
simple goal-directed motor actions, such as grasping a piece of fruit. The
surprising part was that these same neurons also. fire when the individual
sees someone else perform the same act. Because this newly discovered subset
af cells seemed to directly reflect acts performed by another in the
observer's brain, we named them mirror neurons.
Much as circuits of neurons are believed to store specific memories
within the brain, sets of mirror neurons appear to encode templates for
specific actions. This property may allow an individual not only to perform
basic motor procedures without thinking about them but also to comprehend
those acts when they are observed, without any need for explicit reasoning
about them. John grasps Mary's action because even as it is happening before
his eyes, it is also happening, in effect, inside his head. ...
Instant Recognition
Our
research group was not seeking to support or refute one philosophical
position or another when we first noticed mirror neurons. We were studying
the brain's motor cortex, particularly an area called F5 associated with
hand and mouth movements, to learn haw commands to perform certain actions
are encoded by the firing patterns of neurons. Far this purpose, we were
recording the activity of individual neurons in the brains of macaques. Our
laboratory contained a rich repertoire of stimuli for the monkeys, and as
they performed various actions, such as grasping for a toy or a piece of
food, we could see that distinct sets of neurons discharged during the
execution of specific motor acts.
Then we began to notice same thing strange: when one of us grasped a piece
of food, the monkeys' neurons would fire in the same way as when the monkeys
themselves grasped the food. At first we wandered whether this phenomenon
could be the result of same trivial factor, such as the monkey performing an
unnoticed movement while observing our actions. Once we managed to rule out
this possibility and others, including food expectation by the monkeys, we
realized that the pattern of neuron activity associated with the observed
action was a true representation in the brain of the act itself, regardless
of who was performing it. ...
... To test whether mirror neurons play a role in understanding an
action rather than just visually registering it, we assessed the neurons'
responses when the monkeys could comprehend the meaning of an action without
actually seeing it. If mirror neurons truly mediate understanding, we
reasoned, their activity should reflect the meaning of the action rather
than its visual features. We therefore carried out two series of
experiments.
First we tested whether the F5 mirror neurons could "recognize" actions
merely from their sounds. We recorded the mirror neurons while a monkey was
observing a hand motor act, such as ripping a sheet of paper or breaking a
peanut shell, that is accompanied by a distinctive sound. Then we presented
the monkey with the sound alone. We found that many F5 mirror neurons that
had responded to the visual observation of acts accompanied by sounds also
responded to the sounds alone, and we dubbed these cell subsets audiovisual
mirror neurons.
Next we theorized that if mirror neurons are truly involved in understanding
an action, they should also discharge when the monkey does not actually see
the action but has sufficient clues to create a mental representation of it.
Thus, we first showed a monkey an experimenter reaching for and grasping a
piece of food. Next, a screen was positioned in front of the monkey so that
it could not see the experimenter's hand grasping the food but could only
guess the action's conclusion. Nevertheless, more than half the F5 mirror
neurons also discharged when the monkey could just imagine what was
happening behind the screen.
These experiments confirmed, therefore, that the activity of mirror
neurons underpins understanding of motor acts: when comprehension of an
action is possible on a nonvisual basis, such as sound or mental
representation, mirror neurons do still discharge to signal the act's
meaning.
Following these discoveries in the monkey brain, we naturally wondered
whether a mirror neuron system also exists in humans. We first obtained
strong evidence that it does through a series of experiments that employed
various techniques for detecting changes in motor cortex activity. As
volunteers observed an experimenter grasping objects or performing
meaningless arm gestures, for example, increased neural activation in their
hand and arm muscles that would be involved in the same movements suggested
a mirror neuron response in the motor areas of their brains. Further
investigations using different external measures of cortical activity, such
as electroencephalography, also supported the existence of a mirror neuron
system in humans. ...
These encouraging results suggested a mirror mechanism at work in the
human brain as well but still did not fully reveal its scope. If mirror
neurons permit an observed act to be directly understood by experiencing it,
for example, we wondered to what extent the ultimate goal of the action is
also a component of that "understanding."
On Purpose
Returning to our example of John and Mary, we said John knows both that Mary
is picking up the flower and that she plans to hand it to him. Her smile
gave him a contextual clue to her intention, and in this situation, John's
knowledge of Mary's goal is fundamental to his understanding of her action,
because giving him the flower is the completion of the movements that make
up her act.
When we perform such a gesture ourselves, in reality we are performing a
series of linked motor acts whose sequence is determined by our intent: one
series of movements picks the flower and brings it to one's own nose to
smell, but a partly different set of movements grasps the flower and hands
it to someone else. Therefore, our research group set out to explore whether
mirror neurons provide an understanding of intention by distinguishing
between similar actions with different goals.
For this purpose, we returned to our monkeys to record their parietal
neurons under varying conditions. In one set of experiments, a monkey's task
was to grasp a piece of food and bring it to its mouth. Next we had the
monkey grasp the same item and place it into a container. Interestingly, we
found that most of the neurons we recorded discharged differently during the
grasping part of the monkey's action, depending on its final goal. This
evidence illustrated that the motor system is organized in neuronal chains,
each of which encodes the specific intention of the act. We then asked
whether this mechanism explains how we understand the intentions of others.
We tested the same grasping neurons for their mirror properties by having a
monkey observe an experimenter performing the tasks the monkey itself had
done earlier. In each instance, most of the mirror neurons were activated
differently, depending on whether the experimenter brought the food to his
mouth or put it in the container. The patterns of firing in the monkey's
brain exactly matched those we observed when the monkey itself performed the
acts - mirror neurons that discharged most strongly during grasping-to-eat
rather than grasping-to-place did the same when the monkey watched the
experimenter perform the corresponding action.
A strict link thus appears to exist between the motor organization of
intentional actions and the capacity to understand the intentions of others.
When the monkeys observed an action in a particular context, seeing just the
first grasping component of the complete movement activated mirror neurons
forming a motor chain that also encoded a specific intention. Which chain
was activated during their observation of the beginning of an action
depended on a variety of factors, such as the nature of the object acted on,
the context and the memory of what the observed agent did before.
To see whether a similar mechanism for reading intentions exists in
humans, we teamed with Marco Iacoboni and his colleagues at the University
of California, Los Angeles, for a functional magnetic resonance imaging
(fMRI) experiment on volunteers. ...
Given that humans and monkeys are social species, it is not difficult to
see the potential survival advantage of a mechanism, based on mirror
neurons, that locks basic motor acts onto a larger motor semantic network,
permitting the direct and immediate comprehension of others' behavior
without complex cognitive machinery. In social life, however, understanding
others' emotions is equally important. Indeed, emotion is often a key
contextual element that signals the intent of an action. That is why we and
other research groups have also been exploring whether the mirror system
allows us to understand what others feel in addition to what they do.
Connect and Learn
As with actions, humans undoubtedly understand emotions in more than one
way. Observing another person experiencing emotion can trigger a cognitive
elaboration of that sensory information, which ultimately results in a
logical conclusion about what the other is feeling. It may also, however,
result in direct mapping of that sensory information onto the motor
structures that would produce the experience of that emotion in the
observer. These two means of recognizing emotions are profoundly different:
with the first, the observer deduces the emotion but does not feel it; via
the second, recognition is firsthand because the mirror mechanism elicits
the same emotional state in the observer. Thus, when people use the
expression "I feel your pain" to indicate both comprehension and empathy,
they may not realize just how literally true their statement could be.
A paradigmatic example is the emotion of disgust, a basic reaction whose
expression has important survival value for fellow members of a species. In
its most primitive form, disgust indicates that something the individual
tastes or smells is bad and, most likely, dangerous. Once again using fMRI
studies, we collaborated with French neuroscientists to show that
experiencing disgust as a result of inhaling foul odorants and witnessing
disgust on the face of someone else activate the same neural structure - the
anterior insula - at some of the very same locations within that structure
[see box]. These results indicate that populations of mirror neurons in the
insula become active both when the test participants experience the emotion
and when they see it expressed by others. In other words, the observer and
the observed share a neural mechanism that enables a form of direct
experiential understanding.
Tania Singer and her colleagues at University College London found
similar matches between experienced and observed emotions in the context of
pain. In that experiment, the participants felt pain produced by electrodes
placed on their hands and then watched electrodes placed on a test partner's
hand followed by a cue for painful stimulation. Both situations activated
the same regions of the anterior insula and the anterior cingulate cortex in
the subjects.
Taken together, such data strongly suggest that humans may comprehend
emotions, or at least powerful negative emotions, through a direct mapping
mechanism involving parts of the brain that generate visceral motor
responses. Such a mirror mechanism for understanding emotions cannot, of
course, fully explain all social cognition, but it does provide for the
first time a functional neural basis for some of the interpersonal relations
on which more complex social behaviors are built. It may be a substrate that
allows us to empathize with others, for example. ...
Many laboratories, including our own, are continuing to explore these
questions ... Recent evidence indicates, in fact, that the mirror mechanism
also plays a role in the way we initially learn new skills.
Although the word "ape" is often used to denote mimicry, imitation is
not an especially well developed ability among nonhuman primates. It is rare
in monkeys and limited in the great apes, including chimpanzees and
gorillas. For humans, in contrast, imitation is a very important means by
which we learn and transmit skills, language and culture. Did this advance
over our primate relatives evolve on the neural substrate of the mirror
neuron system? Iacoboni and his group provided the first evidence that this
might be the case when they used fMRI to observe human subjects who were
watching and imitating finger movements. Both activities triggered the IFG,
part of the mirror neuron system, in particular when the movement had a
specific goal.
In all these experiments, however, the movements to be imitated were simple
and highly practiced. What role might mirror neurons play when we have to
learn completely new and complex motor acts by imitation? To answer this
question, Giovanni Buccino at our university and collaborators in Germany
recently used fMRI to study participants imitating guitar chords after
seeing them played by an expert guitarist. While test subjects observed the
expert, their parietofrontal mirror neuron systems became active. And the
same area was even more strongly activated during the subjects' imitation of
the chord movements. Interestingly, in the interval following observation,
while the participants were programming their own imitation of the guitar
chords, an additional brain region became active. Known as prefrontal area
46, this part of the brain is traditionally associated with motor planning
and working memory and may therefore play a central role in properly
assembling the elementary motor acts that constitute the action the subject
is about to imitate.
Many aspects of imitation have long perplexed neuroscientists, including
the basic question of how an individual's brain takes in visual information
and translates it to be reproduced in motor terms. If the mirror neuron
system serves as a bridge in this process, then in addition to providing an
understanding of other people's actions, intentions and emotions, it may
have evolved to become an important component in the human capacity for
observation-based learning of sophisticated cognitive skills.
Scientists do not yet know if the mirror neuron system is unique to
primates or if other animals possess it as well. ...
Only a decade has passed since we published our first discoveries about
mirror neurons, and many questions remain to be answered, including the
mirror system's possible role in language, one of humanity's most
sophisticated cognitive skills. The human mirror neuron system does include
Broca's area, a fundamental language-related cortical center. And if, as
some linguists believe, human communication first began with facial and hand
gestures, then mirror neurons would have played an important role in
language evolution. In fact, the mirror mechanism solves two fundamental
communication problems: parity and direct comprehension. Parity requires
that meaning within the message is the same for the sender as for the
recipient. Direct comprehension means that no previous agreement between
individuals - on arbitrary symbols, for instance - is needed for them to
understand each other. The accord is inherent in the neural organization of
both people. Internal mirrors may thus be what allow John and Mary to
connect wordlessly and permit human beings in general to communicate on
multiple levels. |
De basale concepten.
Een toepassing hiervan in het patroon van
sociale interactie is zichtbaar in het volgende artikel (Volkskrant.nl, 20-08-2009, ANP):
In beide artikelen wordt een verband gelegd tussen gereken
in dit soort capaciteiten en het verschijnsel van autisme. Maar recente
onderzoeken laten zien dat er diverse soorten van autisme zijn, zodat het
misschien slechts één van de factoren is.
Een heel aparte toepassing
is deze (de Volkskrant, 27-08-2009, door Malou van Hintum):
Het verband is dus nog nauwer dan het eerste artikel
verondersteld. Niet alleen van het visuele systeem naar de neuronen, maar
ook direct door naar het motorische systeem hoewel dit systeem zelf niet
geactiveerd wordt. Wat een bevestiging is van de hoge mate van integratie
van de diverse systemen in zowel het brein als samen met het lichaam.
Het blijkt ook op hoog niveau te werken (de Volkskrant, 12-03-2011, door Mark Mieras):
Hetgeen dus slaat op behoorlijk hoog in het bewustzijn.
Een bevestiging van de relatie met autisme (de Volkskrant, 03-05-2011, van verslaggeefster Maud Effting):
Of de koppeling met de rest van de hersens werkt op één of
andere manier niet goed.
Wat ook meer wijst op een probleem met de samenwerking tussen
spiegelprocessen en de rest dan met de werking van de losse processen op
zich.
Of dat ze steeds beter wisten hoe te antwoorden.
Een probleem is hier spiegelneuronen zouden kunnen zijn ontstaan.
Daarvoor is een evolutionair proces nodig. Hier een mogelijke fase in dat
proces (de Volkskrant, 13-08-2011, door Marcus Werner):
Dat bijvoorbeeld vogels op elkaar letten volgt uit het
zwermgedrag. Dat kan gesimuleerd worden met simpele modellen bestaande uit
bewegende elementen, waarbij ieder element beweegt in een richting naar
aanleiding van wat zijn buren doen - wat alleen kan door "op elkaar te
letten".
Vanaf welke processen er steeds meer voordeel zit in het leren afkijken bij
de ander, zodat er uiteindelijk gespecialiseerde onderdelen voor komen:
spiegelneuronen.
Een onweerlegbaar bewijs van hoe sterk de werking van dit proces is (www.fsw.leidenuniv.nl
, 26-11-2013.
):
Oftewel: men dacht dat het een min-of-meer rationeel
proces was. Dat is het natuurlijk niet. Het is op zijn minst iets dat plaats
vindt in de emotionele hersenen, en als je het kan koppelen aan beweging,
ook met een component in het reflexmatige systeem:
En waarom is het zo sterk verankerd:
Tja, soms kunnen ook psychologen, net als sociologen, onderzoek doen naar
wat een een beetje gezond verstand zegt. Moet je wel zo veel gezond verstand
hebben om te beseffen dat het menselijke denken en handleen gewoon "een
soort machine" is.
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