Esta mañana me asusté un poco al leer en Google News lo siguiente: "La teoría de Freud sobre la represión, validada por las técnicas de imagen cerebral". En el suplemento de Salud de El Mundo, además. Intrigado, me puse a buscar más información. Resulta que el investigador responsable del descubrimiento es John D.E. Gabrieli, jefe del Gabrieli Cognitive Neuroscience Laboratory de la prestigiosa universidad de Stanford.

Gracias al proxy de la biblioteca universitaria, pude bajar el PDF del artículo "Material-dependent and material-independent selection processes in the frontal and parietal lobes: an event-related fMRI investigation of response competition", para examinarlo con detenimiento (para el público, sólo está disponible un abstract, hay que joderse con la divulgación científica, ¿eh?). La muestra, como en muchos experimentos de neuroimagen, es muy reducida (10 sujetos, cinco mujeres y cinco hombres, todos diestros).

Se utilizó una tarea atencional bastante veterana, la tarea de los flancos de Eriksen, que data de 1934, con dos tipos de estímulos (colores y letras); en la tarea, el sujeto debe identificar una característica de un item central en una hilera de items similares. Cuando los items son iguales al central, es fácil identificar la característica de éste. Por el contrario, cuando el item central difiere de los "flankers", los sujetos tienen más dificultad en identificar la característica objetivo, puesto que hay diferentes respuestas posibles en competición. Todo esto no es una novedad: los psicólogos saben desde hace décadas que la capacidad atencional humana es bastante limitada.

Each scan included Congruent, Incongruent, and Neutral trials, along with Fixation trials. On Congruent trials, the flankers were associated with the same response as the central stimulus. However, the flanking stimuli were physically different from the target. For example, a green target might be surrounded by red flankers on a Congruent trial during the color task. On Incongruent trials, the flankers were associated with the opposite response from the target. On Neutral trials, the target was flanked by stimuli that were not associated with any response (e.g. grey circles or asterisks for the color and letter tasks, respectively).
Para el registro de neuroimagen se utilizó Resonancia Magnética Funcional. Los resultados son bastante predecibles: los ensayos "incongruentes" se ejecutaron más despacio que los neutros, por la competición de las respuestas. Esta competición activó estructuras cerebrales relacionadas con la toma de decisiones, en el lóbulo frontal. Sin embargo - y supongo que es de ahí de donde sacan los investigadores su alegría - las activaciones no fueron iguales en los dos tipos de estímulos. Esto hace que el equipo de Gabrieli hable de regiones material-independent y material-dependent, es decir, dependientes o no del material presentado.

Two material-dependent foci were observed in right lateral prefrontal cortex. One focus, centered in the inferior frontal gyrus, was more active during competition between color stimuli [...] The second focus, located in the right middle frontal gyrus, was more active during competition between letter stimuli. This site was accompanied by a similar focus in the homologous region of the left hemisphere, which was also active during response competition when the letter stimuli were used.
¿Y cuál es la conclusión de los autores?

What does material-dependence indicate about a region’s role in resolving response competition? A region that is more active for one type of stimulus material compared to another must operate on representations that are not strictly response-related, because a structure suppressing unwanted output should not be affected by the stimulus material. The presence of such regions provides empirical support for accounts of stimulus-specific interference in behavioral studies
Es decir, que el contenido estimular puede, en ocasiones, interferir en tareas de selección de la respuesta. Y Gabrieli ha presentado lo que él considera como pruebas neuropsicológicas del asunto. El segundo estudio que llevaron a cabo - aparentemente menos "serio", y que sólo está disponible - pagando - en la web de Science, se titula "Neural Systems Underlying the Suppression of Unwanted Memories", y un resumen en castellano está disponible aquí, y en inglés, aquí.

Twenty-four people, aged 19 to 31, volunteered for the experiment. Participants were given 36 pairs of unrelated nouns, such as "ordeal-roach," "steam-train" and "jaw-gum," and asked to remember them at 5-second intervals. The subjects were tested on memorizing the word pairs until they got about three-quarters of them right – a process that took one or two tries, Anderson said.

In the first set, volunteers were asked to look at the first word in the pair (presented by itself) and recall and think about the second word. In the second set, volunteers were asked to look at the first word of the pair and not recall or think of the second word. The third set of 12 word pairs served as a baseline and was not used during the brain scanning part of the experiment. The subjects were given four seconds to look at the first word of each pair 16 times during a 30-minute period.
Lamentablemente, no tengo acceso al artículo completo de Gabrieli y colaboradores, pero esta afirmación es bastante explícita:

"People's memory gets worse the more they try to avoid thinking about it," Anderson said. "If you consistently expose people to a reminder of a memory that they don't want to think about, and they try not to think about it, they actually don't remember it as well as memories where they were not presented with any reminders at all."
Una vez más, muestro mi escepticismo: para empezar, las situaciones de memoria natural son mucho más complejas, tienen contenido afectivo en mayor grado, y no se limitan a un contexto de laboratorio en el que el sujeto obedece manso las órdenes de un experimentador. ¿Qué validez ecológica tiene este estudio? Se les pidió a los sujetos que no recordaran o procesaran la segunda palabra del par. Según la hipótesis de los Niveles de Procesamiento de Craik y Lockhart (1972), el aprendizaje es más efectivo si el material se procesa de forma más profunda y rica (por ejemplo, el procesamiento semántico es más efectivo a la hora de aprender que el procesamiento visual. Así pues, ¿qué es lo que ocurrió realmente en el experimento de Gabrieli?

Hablar de represión freudiana, y desempolvar viejos conceptos psicoanalíticos puede resultar muy popular, pero hay que andar con mucho cuidado. Emoción y memoria están relacionadas, pero el tipo de relación todavía debe dilucidarse. Hacerlo en el laboratorio es muy, muy difícil.

# - Escrito por Fabrizio el 2004-01-12 a las 19:47


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Comentarios

1
De: giusec Fecha: 2004-01-13 01:34

Fabrizio, hmmm...io no recuerdo nada de nada (y esta es la razon porquè tengo el Pilot, el pocketPC, un voicerecorder, etc.etc....). Con migo no funciona el procesamiento visivo y tampoco el semantico...Soy la exceptiòn a la regla? [http://giusec.splinder.it/]



2
De: Algernon Fecha: 2004-01-13 01:48

Giusec, no creo :D



3
De: Lilly Fecha: 2019-01-14 07:58

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