Neuronas espejo y visión... de la visión
Neuronas espejo y visión... de la visión
Interesante noticia sobre las neuronas espejo pasa Norman Holland a Psyart. Cortopego y comento:
UCLA Researchers Make First Direct Recording Of Mirror Neurons In Human Brain
Such cells appear to have wider distribution than previously thought
Mirror neurons, many say, are what make us human.
They are the cells in the brain that fire not only when we perform a particular action but also when we watch someone else perform that same action.
Neuroscientists believe this "mirroring" is the mechanism by which we can "read" the minds of others and empathize with them. It's how we "feel" someone's pain, how we discern a grimace from a grin, a smirk from a smile.
Problem was, there was no proof that mirror neurons existed — only suspicion and indirect evidence. Now, reporting in the April edition of the journal Current Biology, Dr. Itzhak Fried, a UCLA professor of neurosurgery and of psychiatry and biobehavioral sciences, Roy Mukamel, a postdoctoral fellow in Fried's lab, and their colleagues have for the first time made a direct recording of mirror neurons in the human brain.
The researchers recorded both single cells and multiple-cell activity, not only in motor regions of the brain where mirror neurons were thought to exist but also in regions involved in vision and in memory.
Further, they showed that specific subsets of mirror cells increased their activity during the execution of an action but decreased their activity when an action was only being observed.
"We hypothesize that the decreased activity from the cells when observing an action may be to inhibit the observer from automatically performing that same action," said Mukamel, the study's lead author. "Furthermore, this subset of mirror neurons may help us distinguish the actions of other people from our own actions."
The researchers drew their data directly from the brains of 21 patients who were being treated at Ronald Reagan UCLA Medical Center for intractable epilepsy. The patients had been implanted with intracranial depth electrodes to identify seizure foci for potential surgical treatment. Electrode location was based solely on clinical criteria; the researchers, with the patients' consent, used the same electrodes to "piggyback" their research.
The experiment included three parts: facial expressions, grasping and a control experiment. Activity from a total of 1,177 neurons in the 21 patients was recorded as the patients both observed and performed grasping actions and facial gestures. In the observation phase, the patients observed various actions presented on a laptop computer. In the activity phase, the subjects were asked to perform an action based on a visually presented word. In the control task, the same words were presented and the patients were instructed not to execute the action.
The researchers found that the neurons fired or showed their greatest activity both when the individual performed a task and when they observed a task. The mirror neurons making the responses were located in the medial frontal cortex and medial temporal cortex, two neural systems where mirroring responses at the single-cell level had not been previously recorded, not even in monkeys.
This new finding demonstrates that mirror neurons are located in more areas of the human brain than previously thought. Given that different brain areas implement different functions — in this case, the medial frontal cortex for movement selection and the medial temporal cortex for memory — the finding also suggests that mirror neurons provide a complex and rich mirroring of the actions of other people.
Because mirror neurons fire both when an individual performs an action and when one watches another individual perform that same action, it's thought this "mirroring" is the neural mechanism by which the actions, intentions and emotions of other people can be automatically understood.
"The study suggests that the distribution of these unique cells linking the activity of the self with that of others is wider than previously believed," said Fried, the study's senior author and director of the UCLA Epilepsy Surgery Program.
"It's also suspected that dysfunction of these mirror cells might be involved in disorders such as autism, where the clinical signs can include difficulties with verbal and nonverbal communication, imitation and having empathy for others," Mukamel said. "So gaining a better understanding of the mirror neuron system might help devise strategies for treatment of this disorder."
Other authors on the study included Arne D. Ekstrom, Jonas Kaplan and Marco Iacoboni, all of UCLA. The project was supported by the National Center for Research Resources, a component of the National Institutes of Health (NIH). The authors report no conflict of interest.
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El artículo puede leerse aquí:
Roy Mukamel, Arne D. Ekstrom, Jonas Kaplan, Marco Iacoboni, and Itzhak Fried. "Single-Neuron Responses in Humans during Execution and Observation of Actions." Current Biology 8 April 2008.
Me parece especialmente interesante que se hayan encontrado neuronas espejo en más partes del cerebro humano de las que se pensaba antes: en especial las ligadas a la visión y a la memoria. Sin conocer el estudio original, poco se puede decir, pero habría que profundizar en las implicaciones de este hallazgo para entender la percepción mutua, y también la naturaleza de la memoria como experiencia virtual. Teniendo en cuenta, además, el bien conocido hecho de que los recuerdos son parcialmente reconstruidos o "inventados" por el cerebro acudiendo a procesos cognitivos habituales y asociaciones.
En cuanto a la visión, creo que las neuronas espejo no pueden sino tener un papel muy importante en el procesamiento de la mirada ajena.
"El ojo que ves no es
ojo porque tú lo veas,
es ojo porque te ve."
—Machado dixit. En este artículo sobre las neuronas espejo de Babel's Dawn (aunque el autor no estaba muy entusiasmado con la cuestión de las neuronas espejo) observaba yo que la experiencia de la mirada ajena, en especial de la mirada humana, ha llamado con frecuencia la atención de diversos observadores (no sólo la de Sartre, atrapado en la Mirada del Otro). Ver un par de ojos es una experiencia totalmente distinta de mirar cualquier otra figura. En el momento que procesamos una mancha, etc... como dos ojos, se produce un salto perceptual bien perceptible en nuestra experiencia del objeto visto. En mi opinión (pendiente de confirmación experimental) esto se debe a la acción de las neuronas espejo. Me felicito de ver que en efecto se puede medir su actuación en diversas interacciones de gesto y mirada, pero, insisto:
—La experiencia perceptual de la mirada es distinta de cualquier otra experiencia que pueda desencadenarse con las neuronas espejo.
Y lo es, porque además del "espejo" habitual, se crea aquí un circuito reflexivo. La acción de "ver a alguien coger algo" activa determinadas neuronas espejo, OK. Pero la acción de "ver a alguien mirar algo" también lo hace —probablemente, pues esto todavía no está bien fundamentado en la literatura que conozco. "Ver a alguien mirar algo" puede parecer una acción un tanto indirecta, o de baja intensidad, pero no lo es tanto, en especial en una especie hipersocial como los humanos, donde la lectura de intenciones ajenas es tan crucial que hasta nos ha influido en el diseño del blanco de los ojos. Ver a alguien mirar algo es adivinarle las intenciones, o los deseos, o por lo menos tener algo adelantado en esa dirección. Aunque la dirección de la mirada pueda ser imprecisa, y el objeto mirado sea incierto, este objeto inmediatamente atrae nuestra mirada. Especialmente, ¿cuándo?
La respuesta es fácil. Especialmente cuando el objeto mirado somos nosotros mismos. Ahí no hay dudas ya sobre cuál pueda ser el objeto al que miran los ojos ajenos. Nuestros intereses sociales (o quizá nuestra integridad física como posibles presas) depende de la captación inmediata de esa mirada, por lo cual se trata de un mecanismo perceptual de primordial interés para su selección natural.
Y además se da la cuestión del cortocircuito reflexivo a que aludía antes. VER realizar una acción invita a recrearla "virtualmente" en las neuronas espejo de nuestro cerebro. Y a realizarla, por delegación o directamente. Ahora bien, VER realizar la acción de VER, más bien desencadena un feedback repentino entre dos sistemas cerebrales que ven y son vistos y se autoestimulan mutuamente a seguir viendo—de ahí en parte el horror a la mirada, y el reflejo también potente de apartar la mirada de otra mirada directa. Que quema como el sol.
Light seeking light doth light of light beguile:
So, ere you find where light in darkness lies,
Your light grows dark by losing of your eyes.
Study me how to please the eye indeed,
By fixing it upon a fairer eye,
Who dazzling so, that eye shall be his heed,
And give him light that it was blinded by.
Study is like the heaven's glorious sun,
That will not be deep-search'd with saucy looks...
(Love's Labour's Lost).
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