24 de enero de 2013

Eat Less by Altering Your Food Memories

Hunger is affected by how much you think you ate.

If you made a New Year’s resolution a few weeks ago, you probably decided to get fit or lose weight – two goals that pretty unavoidably involve a pledge to eat less. Perhaps you’ve stuck with it so far, through some combination of brute will, guilt, and the deployment of winning slogans at spots of greatest temptation. But unless you’re one of the rare successful long-term dieters, your assault on adiposity will be short lived. Sooner or later, you’ll find your way back to foods that are sweet, fat, and synthetically tinted.

Why do we eat bad stuff, and too much of it?

Naturally, “because we’re hungry and it tastes good” is an answer, but this just begs the deeper question of what call, exactly, we’re answering when we relent to hunger. Is hunger just the stomach’s empty light, pinging the brain with motivation to refill the tank?  Maybe hunger works more like a balance sheet, telling us how many calories we should seek out, relative to how many we have in the bank. Or perhaps hunger is opportunism, indulged in any case where the expected ‘taste-payoff’ is high enough.

In fact, all of these are known and well-studied facets of the drive experienced as hunger, and they all speak to the idea of appetite as a complex regulatory process.

According to a recent study in PLOS One, however, by Jeffrey Brunstrom and his colleagues, hunger is also a trick of memory.  In effect, these scientists argue that the remembrance of meals past can help fill an empty belly.

What makes this work especially interesting is that it cleanly demarcates a psychologically complex component of hunger. Naturally, we suspect that our thoughts about food must surely play a role in our eating (and overeating) decisions. But nailing these processes down has been trickier than, say, identifying the peptides and hormones that enhance or suppress appetite. By understanding the hunger’s cognitive components better, we might come up with more effective mind hacks to limit overeating.

Early evidence that memory plays a role in eating came from subjects whose memory was impaired. More specifically, both amnesic rats and people with damage to the hippocampus – a key structure in memory formation – tend to eat in short sporadic bouts, rather than in a few concentrated meals. If you put food in front of an amnesic person, they’re almost always game to eat, whether their last large meal was 5 minutes ago, or 5 hours ago. Other evidence for the “memory for eating” idea comes from memory cueing experiments. If people who are about to eat are given reminders of their previous meal (as opposed to reminders of a meal from long ago), they tend to eat smaller portions. In other words, we seem to keep tabs on what we’ve eaten not just by computing signals of physical fullness – which are presumably unperturbed in all of these cases -- but also by keeping a mental tally of what was eaten when. It’s as if you have a vigilant inner parent, reminding you that “you just ate 15 minutes ago – how could you possibly be hungry!”

While interesting, these experiments have their problems. In the amnesic studies, for example, it’s dangerous to infer too much about normal brain function from behaviors that are the product of a damaged brain. Likewise, its unclear what the memory cueing experiments tell us about normal, everyday eating, since we’re not typically given overt reminders of our previous meals. In order to test if the memory of a previous meal comes unbidden, and has effects on subsequent eating, you have to perturb that memory in a normal individual. But how do you do this?

Basically, you trick people, and you do it in a carefully controlled way. In Brunstrom’s experiment, this was done using a device with an infomercial-worthy name: the self-refilling soup bowl apparatus. Experimental subjects would approach the otherwise normal looking soup bowl, and were told to eat what was in it (creamed tomato, for the curious). Half of the subjects were shown a small portion of soup (300 mL, or about one and a quarter cups), and the other half was shown a considerably larger portion (500 mL, a bit more than two cups). 

What the subjects didn’t see, however was that the soup bowl was rigged up to system of unseen tubes and valves that let the experimenters covertly add or take away soup as people ate. Some subjects ate an amount of soup equal to what they were presented with (either the small or the large portion), but others ate a different amount from what they saw. In these ‘incongruous’ cases, people thought they consumed the large portion, but really ate the small portion, or vice versa. With this setup, the experimenters could then test how hungry the subjects were some time later, and tease apart the purely physiological aspects of hunger (having to do with the volume consumed) from the cognitive aspects of hunger (having to do with impressions and judgments about what was consumed).

The first result is that there’s no fooling your stomach immediately after a meal. When tested shortly after eating the soup, subjects who had eaten the larger portion were more sated than those who had eaten the smaller portion, and it mattered comparatively little how much people thought they ate. Two cups is more than one cup, and your stomach gets it right, despite any visual trickery.

Two and three hours after eating, however, a different sort of pattern emerged. The subjects were all hungrier, of course, but their hunger had little to do with the volume of soup they had actually eaten. Instead, it was what they remembered seeing in the bowl that mattered. In fact, those who ate the small portion and thought it was large were more sated than those who ate the large portion and thought it was small. When it comes to the feeling of fullness, the eyes are more important than the stomach.

Overall, this work helps clear up our thinking on an important component of hunger that’s historically been tough to study. Of course, this doesn’t say that hunger is the same thing as a memory of having eaten (or rather, having not eaten). Just that our drive to eat can be biased by memory, as well as possibly the contexts in which we encounter food.  On the practical front, this work also opens the door for some possible cognitive-based approaches to dieting. Memory is notoriously fickle, and we may be able to use this to our advantage to enhance our feelings of fullness. In fact, previous work has already suggested that distracted, or “mindless” eating leads people to feel hungry, while more deliberate and mindful eating leads people to feel full. One possibility is that deliberative eating leads to stronger food-associated memories, in turn providing a stronger antidote against future hunger.

So when you sit down for your next meal, pay close attention and remember what you eat – you may pull off that New Year’s resolution yet.

Tomado de: http://www.scientificamerican.com/article.cfm?id=eat-less-by-altering-your-food-memories&page=2

15 de enero de 2013

Los insectos saben contar

Descubren que algunos insectos disponen de un mecanismo para contar. Esta habilidad cognitiva hasta ahora se creía exclusiva de los vertebrados.

Investigadores de la Universitat de València (UV) han descubierto que algunos insectos disponen de un sofisticado mecanismo para contar, una habilidad cognitiva que hasta ahora se creía exclusiva de los animales vertebrados.

Es una de las conclusiones a la que ha llegado un grupo de científicos del Institut Cavanilles de Biodiversitat i Biologia Evolutiva de la UV y de la Universidad de Oxford en un trabajo publicado en la revista Frontiers in Psychology, según una nota de prensa de la Universitat.

El estudio revela que el macho del 'tenebrio molitor', comúnmente conocido como escarabajo de la harina, es capaz de contar el número de machos rivales con los que compite por una hembra antes de aparearse.

De este modo, los machos de esta especie ajustan el tiempo dedicado a vigilar las hembras tras la cópula en función del número de rivales presentes.

Así, los mecanismos basales en los que se sustenta la habilidad humana para contar están más extendidos en el reino animal de lo sospechado, sostiene la investigación.

'Dura competición' para fecundar

Según explican los expertos, los machos de este coleóptero se enfrentan a una "dura competición" por fecundar a las hembras ya que, tras el apareamiento, corren el riesgo de que otros machos rivales copulen con la misma hembra y desplacen su esperma por completo.

Para que el esperma de un macho esté a salvo, es decir, quede almacenado por la hembra, hacen falta entre siete y diez minutos, un período clave en el que este escarabajo permanece "alerta" y dedica más o menos tiempo a "guardar" a la hembra según la cantidad de competidores que haya en las inmediaciones.

"Cuando hay pocos rivales y el riesgo de que un segundo macho desplace su esperma es muy bajo, los machos abandonan a la hembra a los pocos segundos de terminar la cópula para buscar alimento u otras hembras", expone Pau Carazo, uno de los científicos del estudio.

Sin embargo, conforme se incrementa la densidad promedio de machos en las inmediaciones y el riesgo de que la hembra se aparee con un segundo macho, los machos van aumentando, a su vez, el tiempo que permanecen con la hembra tras la cópula, con el fin de evitar que ésta copule con otros y asegurarse de que su esperma no se pierde.

Experimentos recientes

Los resultados de experimentos recientes, como los publicados por este mismo grupo de la Universitat de València en 2009, ya habían puesto de manifiesto que algunas especies de insectos son capaces de estimar el número de objetos de un grupo de forma aproximada.

Esta habilidad resulta muy ventajosa en multitud de contextos, según los expertos, que citan el ejemplo de que, cuando un insecto tiene que decidir qué planta visitar, es muy beneficioso saber cuál contiene más flores.

Se pensaba que los mecanismos cognitivos que los insectos empleaban para estimar el número de objetos en un grupo tenían poco que ver con lo que entendemos normalmente por contar.

El trabajo de la Universitat de València, sin embargo, sugiere que los escarabajos de la harina son capaces de determinar el número de individuos en un grupo sin utilizar variables continuas; reconocen individualmente a cada individuo y acumulan en su memoria el número de individuos distintos que se encuentran para valorar el número total de ellos presentes en su entorno más inmediato.

Tomado de: http://www.elmundo.es/elmundo/2013/01/15/valencia/1358267103.html

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