18 de diciembre de 2013

Las personas con hipertimesia también crean recuerdos falsos

Las personas que padecen hipertimesia, un síndrome que causa una memoria autobiográfica muy superior a la normal, también se pueden ver afectadas por recuerdos falsos. Estas mentiras se originan en el cerebro por la asociación de objetos, la valoración personal de eventos pasados o por la propia imaginación.

Un reciente estudio ha comparado las capacidades de memoria de 38 personas normales con otras 20 que padecían hipertimesia. Les hicieron pasar una serie de pruebas para medir la distorsión de la memoria, incluido un test en el que se induce a los participantes a informar erróneamente sobre un accidente de avión inexistente. Los autores no encontraron ninguna diferencia entre el grupo de estudio y el de control.  Tanto las personas con hipertimesia como aquellas con una capacidad de recuerdo normal poseían la misma susceptibilidad a los recuerdos falsos.

Un estudio anterior había demostrado que la tendencia a generar recuerdos verdaderos y falsos se relaciona con las diferencias individuales en la sustancia blanca cerebral, una parte del sistema nervioso central compuesta de fibras nerviosas cubiertas de mielina.



12 de diciembre de 2013

¿Memoria fotográfica?

Tomar fotografías durante la visita a un museo puede deteriorar los recuerdos precisos.


En la actualidad, durante la visita a un museo o a un monumento, resulta habitual encontrar nativos y foráneos con la cámara digital o el teléfono inteligente en mano para apuntar y disparar sobre alguna pieza de arte u objeto histórico. La memoria del dispositivo retiene la imagen. Mas ¿permanecen los elementos retratados también en la memoria del visitante?

Aunque fotografiar parece una buena manera de preservar el momento en el recuerdo, durante una visita al museo puede ser más aconsejable dejar la fotografía para más tarde, según una reciente investigación. «A menudo la gente saca su cámara, casi sin pensar, para capturar un momento, hasta el punto de que se están perdiendo cuanto sucede justo frente a ellos», indica Linda Henkel, de la Universidad de Fairfield y autora del estudio.

Recuerdos más vagos

Con el fin de averiguar el grado en que la captura fotográfica de eventos influye en su recordación posterior, Henkel llevó a un grupo de universitarios de visita a un museo. Pidió a unos cuantos de ellos que utilizaran la cámara para tomar nota de los objetos que veían; otros tan solo debían contemplar las piezas expuestas. Al día siguiente se puso a prueba la memoria de los voluntarios. 

Según se descubrió, los participantes que habían retratado las obras de arte con la cámara eran menos precisos en el reconocimiento de las piezas que habían visto en comparación con aquellos que «solo» las habían observado. Por otra parte, los primeros no fueron capaces de responder a tantas preguntas acerca de los detalles visuales de los objetos. En palabras de Henkel, se trata de un «efecto de deterioro por la toma de fotografías». Según explica: «Cuando las personas confían en la tecnología para que recuerde por ellos, contando con que la cámara grabará el evento y así no deben reparar en él plenamente, puede ejercer un impacto negativo en el recuerdo de la experiencia».

En un segundo ensayo, a parte de confirmarse los primeros resultados, se halló que el uso del zum de la cámara para fotografiar los detalles de un objeto, puede preservar en la memoria la pieza en su conjunto, no la particularidad retratada. «Estos resultados demuestran que el "ojo de la mente" y el ojo de la cámara no son lo mismo».


Con todo, la mayoría de los visitantes de museos probablemente argumenten que toman imágenes para mirarlas  con tranquilidad más tarde. Ahora bien, ¿ayuda a la recordación el hecho de revisar las fotografías que se han tomado? El reciente estudio sugiere que así es, pero solo si la persona se tomó en su momento el tiempo necesario para fijarse en el objeto. «La investigación ha sugerido que el volumen y la falta de organización de fotografías digitales desalienta a muchas personas a acceder a ellas y recordarlas», apunta Henkel «Con el fin de recordar, debemos acceder e interactuar con las fotografías, en lugar de, simplemente, acumularlas», concluye.

Tomado de: http://www.investigacionyciencia.es/noticias/memoria-fotogrfica-11664

4 de diciembre de 2013

TED Talks Education (9 talks)

How can we create an education system that works for kids, instead of against them? Watch eight inspiring talks (and one beautiful performance) from TED's May 2013 PBS special, given in their entirety.

Para ver los videos haga clic AQUI
Subtituladas al español.


3 de diciembre de 2013

How your "working memory" makes sense of the world

video

Fearful memories haunt mouse descendants

Genetic imprint from traumatic experiences carries through at least two generations.

Certain fears can be inherited through the generations, a provocative study of mice reports1. The authors suggest that a similar phenomenon could influence anxiety and addiction in humans. But some researchers are sceptical of the findings because a biological mechanism that explains the phenomenon has not been identified.

According to convention, the genetic sequences contained in DNA are the only way to transmit biological information across generations. Random DNA mutations, when beneficial, enable organisms to adapt to changing conditions, but this process typically occurs slowly over many generations.

Yet some studies have hinted that environmental factors can influence biology more rapidly through 'epigenetic' modifications, which alter the expression of genes, but not their actual nucleotide sequence. For instance, children who were conceived during a harsh wartime famine in the Netherlands in the 1940s are at increased risk of diabetes, heart disease and other conditions — possibly because of epigenetic alterations to genes involved in these diseases2. Yet although epigenetic modifications are known to be important for processes such as development and the inactivation of one copy of the X-chromsome in females, their role in the inheritance of behaviour is still controversial.

Kerry Ressler, a neurobiologist and psychiatrist at Emory University in Atlanta, Georgia, and a co-author of the latest study, became interested in epigenetic inheritance after working with poor people living in inner cities, where cycles of drug addiction, neuropsychiatric illness and other problems often seem to recur in parents and their children. “There are a lot of anecdotes to suggest that there’s intergenerational transfer of risk, and that it’s hard to break that cycle,” he says.

Heritable traits

Studying the biological basis for those effects in humans would be difficult. So Ressler and his colleague Brian Dias opted to study epigenetic inheritance in laboratory mice trained to fear the smell of acetophenone, a chemical the scent of which has been compared to those of cherries and almonds. He and Dias wafted the scent around a small chamber, while giving small electric shocks to male mice. The animals eventually learned to associate the scent with pain, shuddering in the presence of acetophenone even without a shock.

This reaction was passed on to their pups, Dias and Ressler report today in Nature Neuroscience1. Despite never having encountered acetophenone in their lives, the offspring exhibited increased sensitivity when introduced to its smell, shuddering more markedly in its presence compared with the descendants of mice that had been conditioned to be startled by a different smell or that had gone through no such conditioning. A third generation of mice — the 'grandchildren' — also inherited this reaction, as did mice conceived through in vitro fertilization with sperm from males sensitized to acetophenone. Similar experiments showed that the response can also be transmitted down from the mother.

These responses were paired with changes to the brain structures that process odours. The mice sensitized to acetophenone, as well as their descendants, had more neurons that produce a receptor protein known to detect the odour compared with control mice and their progeny. Structures that receive signals from the acetophenone-detecting neurons and send smell signals to other parts of the brain (such as those involved in processing fear) were also bigger.

The researchers propose that DNA methylation — a reversible chemical modification to DNA that typically blocks transcription of a gene without altering its sequence — explains the inherited effect. In the fearful mice, the acetophenone-sensing gene of sperm cells had fewer methylation marks, which could have led to greater expression of the odorant-receptor gene during development.

But how the association of smell with pain influences sperm remains a mystery. Ressler notes that sperm cells themselves express odorant receptor proteins, and that some odorants find their way into the bloodstream, offering a potential mechanism, as do small, blood-borne fragments of RNA known as microRNAs, that control gene expression.

Contentious findings

Predictably, the study has divided researchers. “The overwhelming response has been 'Wow! But how the hell is it happening?'" says Dias. David Sweatt, a neurobiologist at the University of Alabama at Birmingham who was not involved in the work, calls it “the most rigorous and convincing set of studies published to date demonstrating acquired transgenerational epigenetic effects in a laboratory model".

However, Timothy Bestor, a molecular biologist at Columbia University in New York who studies epigenetic modifications, is incredulous. DNA methylation is unlikely to influence the production of the protein that detects acetophenone, he says. Most genes known to be controlled by methylation have these modifications in a region called the promoter, which precedes the gene in the DNA sequence. But the acetophenone-detecting gene does not contain nucleotides in this region that can be methylated, Bestor says. "The claims they make are so extreme they kind of violate the principle that extraordinary claims require extraordinary proof,” he adds.

Tracy Bale, a neuroscientist at the University of Pennsylvania in Philadelphia, says that researchers need to “determine the piece that links Dad's experience with specific signals capable of producing changes in epigenetic marks in the germ cell, and how these are maintained”.

“It's pretty unnerving to think that our germ cells could be so plastic and dynamic in response to changes in the environment,” she says.

Humans inherit epigenetic alterations that influence behaviour, too, Ressler suspects. A parent’s anxiety, he speculates, could influence later generations through epigenetic modifications to receptors for stress hormones. But Ressler and Dias are not sure how to prove the case, and they plan to focus on lab animals for the time being.

The researchers now want to determine for how many generations the sensitivity to acetophenone lasts, and whether that response can be eliminated. Scepticism that the inheritance mechanism is real will likely persist, Ressler says, “until someone can really explain it in a molecular way”, says Ressler. “Unfortunately, it’s probably going to be complicated and it’s probably going to take a while.”

Tomado de: http://www.nature.com/news/fearful-memories-haunt-mouse-descendants-1.14272?WT.ec_id=NEWS-20131203
Nature doi:10.1038/nature.2013.14272