Friday, April 27, 2012

Conditioned Cues Elicited Feeding in Sated Rats

    This is the second week of my blog and I have another exciting article to talk about.  For anyone with access, the article is here. The title of the article is Conditioned Cues Elicited Feeding in Sated Rats: A Role for Learning in Meal Initiation.  The article talks about Pavlovian conditioning influencing rats to eat even while they are full (satiatied), if they have learned the cues that signal food.  The procedure for this experiment was to take seven male rats, housed individually and carry out two phases: conditioning and testing.  During conditioning a 4.5 minute conditioned stimulus (CS+) consisting of a buzzer and a light presented together, was presented before every meal.  The '+' sign in this experiment, as professor Blaisdell taught us, means that the US (the food) will actually be appearing in this experiment, and is signaled by the CS.  The meal, which was composed of 8ml of a liquid diet (some type of evaporated milk) was delivered to the mice during the last 30 seconds of the CS+.  Rats received six meals in a day, 3.5 hours apart.  A CS- of a pure tone was presented at the midpoint of every inter-meal interval.  As we learned the '-' sign in this case signals that no food will be paired with the stimulus, and it was meant to condition the rats to learn that feeding had ended, at least for some period of time.  Once the rats had been conditioned to a stimuli and knew which stimuli were meant to signal food, they were tested in a subsequent experiment.  The conditioned simuli were presented and the responses of the rats measured.  The most important observation of this experiment was that feeding responses were made to the CS+ during testing on all 21 days, EVEN WHILE THE RATS WERE SATIATED!   In further testing, where rats were tested with the conditioned stimuli and then later allowed to feed on a food bottle for a free period of time, the experimenters discovered some very shocking results.  The rats would eat when presented with the previously conditioned stimuli, but they would limit their food intake from a food bottle when the signal was not present.  This goes to show that rats had learned to eat only in the presence of specific signals, and did not eat simply because food was readily available; the rats also ate while satiated if the signals were presented.  As the text itself has explained:  Once an association has been learned between signals for food and a meal, stimuli retain their ability to influence feeding for protracted periods and even under a state, satiation, that might be expected to minimize the impact of such events.
   Although it is possible for people to eat when hungry (this experiment has not directly disproved that explanation), it is more logical to think of eating as a complex process that incorporates learned procedures and extenuating circumstances that influence our ability to ingest foods.  It is interesting to see that an energy deficiency is NOT the dominating factor in causing someone to eat, contrary to what the major thinking has been for as long as I have known.  I mean, most people that I talk to would say that they eat because they think they are hungry, but little do they know that there are external cues and conditioned stimuli that can influence their conditioned response to eat, without them even knowing.  In the experiment with rats, the conditioned stimuli to signal food were a light and a buzzer, but in real life the stimuli that have conditioned many of us takes on different forms.  Think about when we decide to eat.  If you are out with friends, the social cues around us, such as friends ordering food, the smell of food in a restaurant, people enjoying their food, will all elicit cues for you to order food and eat, even if you are not hungry (much like the rats in this experiment).
     The example that I think of with my own life, is the time of day that elicits cues for eating. I have associated the time of 12-1 o'clock with eating lunch and 5'oclock with eating dinner.  Regardless of what time I wake up, when those times roll around, my brain will be alerted and want to eat a meal... To clarify this point, during the summer I often wake up around 12 o'clock and will start my day off with eating lunch, and then eat a dinner around 5 p.m.  On the other hand, during the school year, I wake up at a more respectable time of 10 o'clock and begin my day with a breakfast, eat lunch around 3 p.m., but when 5 p.m. rolls around I immediately begin thinking about eating again even though I am full from eating just two hours ago (much like the satiated rats in the experiment).  The same processes are at work with conditioning rats to eat at the sight of a light and the tone of a buzzer, with conditioning humans to eat at cues of time or external signals.  Sometimes we both do things that don't make sense based on needs, we do things because we have become accustomed and learned to do them by association.
     In rats, much like in real life, once an association has been made, it is hard to counteract those effects and unlearn or extinguish those associations.  We often do not eat when we have an energy depletion, mostly because we have associated quicker, easier cues to the desire to eat.  I imagine this to be a biological effect, because food was very limited in our ancestors.  In other words, since food was not always available for our predecessors, it is easier to learn associations and cues that will make us want to eat even when we are not particularly hungry.  Our genetic makeup predisposes us to want to eat and take in nutrients for the possibility (usually a reality in our ancestors) that food would not be available at a later time.  In other words: we are predisposed to take advantage of the food that is available now at an earlier time.  This explanation, however, is not supported by the finding that rats limit their food intake when presented with a feeding bottle.  If it was an evolutionary limitation explanation, as I proposed, then we probably should have seen the rats eat a lot of food, unconditionally, while sated, but even when the learned cues were not presented.
    This is just my opinion on the matter.  Going out on a limb and saying that there is a biological and genetic basis to the ease of association and learning may be completely incorrect or it may be right on point.   That is up to you to let me know in the comments.  I would love some feedback.

Thanks for reading! Look out for my next post very shortly!

Thursday, April 19, 2012

A Pavlovian approach to the problem of obesity

To whom it may concern.  This is my personal blog, created for the dissemination of thoughts and analysis of various research papers over an eight week span.  Every week I will be analyzing one or several papers on the general idea of learning as it deals with eating behaviors.  I will attempt to focus on issues dealing with obesity/uncontrolled-eating, etc. but as I research these topics, I may drift from this topic and write about whatever interests me under the general umbrella of learning and eating.  I want to thank Professor Blaisdell, who is my honors contract advisor and teacher of Psychology 110 at UCLA for proposing the idea of writing in a weekly blog.  It is a fascinating concept that I am undertaking as an experimental project for these next eight weeks, while keeping an open mind of the possibility of writing beyond that time span.
       And now to get to the real issue at hand, I will be giving my feedback on an article I came across on google scholar known as "A Pavlovian approach to the problem of obesity".  Article 1 on obesity.  I recommend reading the article first before continuing on.
       I believe that the problem of over-eating stemming from associated learning of sweet-tasting food and high calories is an interesting take, but one that should be tested on humans, now that some evidence has arisen in rats.  The test these experimenters conducted was to make two groups, one consistent with sweet-taste and high calories, and the other an inconsistent association, with sweet-taste but lower calories (non-caloric saccharin was used). Once these connections were trained and established for ten days, the rats ate lab-chow for one whole day, then starved overnight so that they would be hungry for the next day of testing. After the overnight starvation, the rats were all offered a sweet tasting high-calorie chocolate pre-meal, followed by lab chow for 1 hour.  What the experimenters are hoping to see here is a difference in controlling caloric intake between the consistent and inconsistent groups because the rats in the 'consistent' group made an association between sweet food and high calories.  The experiments showed that the consistent group rats consumed less of the lab chow in the 1 hour after the pre-meal in order to compensate for that heavy caloric intake.  The rats in the 'inconsistent' group ate a considerably greater quantity of the lab chow after the pre-meal than the rats in the 'consistent' group.  This is an interesting finding because it is seen so readily in our every day life.  We see people taking in a variety of foods such as candies that are very-sweet and high calories, but also foods that are sweet but low in calories like diet-coke, vitamin-water zero, some breakfast bars (nutrigrain bars) or something like sweet potatoes.  This creates an 'inconsistent' association between sweetness and calories that may cause people to underestimate how many calories they are actually taking in while eating sweet and sugary foods.  As a result of the breakdown of the predictive relationships between sweetness and calories, people begin to over-indulge in sweet foods such as cakes, ice creams, etc.  People may not regulate how much they take in of the sweet foods just as the 'inconsistent' rats in the experiment did not regulate how much of the lab chow they ate, because they did not think they had taken in so many calories with the pre-meal.
         The second experiment aimed to see if similar restrictions are made when rats are tricked into thinking they are taking in a low-calorie, low-viscosity drink which actually had the same calories and nutritional value as a high-viscosity substance.  The association has been made that low-viscosity drinks are relatively low in calories, while high-viscosity ones are high in calories, stemming from time spent breastfeeding.  Rats in one group that drank the low-viscosity drink (made this way by adding water) ended up drinking more and gaining more weight than the rats who drank highly viscous drinks (made this way by adding nonmetabolizable guar) showing that they could not regulate the calories they took in, as they had done with the sweet foods.  The problem I see with this experiment that the researchers did not adress is the ease with which we consume low-viscous foods compared to high-viscous ones.  Talking from personal experience, I would definitely prefer to drink multiple cups of chocolate milk because of convenience and speed, compared to eating (or trying to gulp down) multiple cups of chocolate pudding which takes longer to enjoy and can be more effortful.  The association in my mind is not as clear between viscosity and calories, and the reason behind my choice is one of convenience, speed, and simply a preference, which are not adressed in this paper.  As wikipedia defines viscosity: "Put simply, the less viscous the fluid is, the greater its ease of movement (fluidity)"... I prefer to consume foods that flow easily into my mouth, rather than wait for something like honey to flow out slowly. However, If the findings of this study are found to be true in a test with human experiments, it is clear to see the reasons why.  Once again, this can be seen in every day situations where people have lost that connection between viscosity and calories, because of the plethora of foods which we consume, some of which have been artificially modulated to adjust for calories or viscosity.  Something like Coca-Cola is not very viscous, but contains many calories and disrupts that learned association that people may have from breastfeeding.
     In conclusion, I just wanted to say a few words about societal overeating habits.  I have personally dealt with issues of overeating throughout my life and I want to say that all people have different preferences for different tastes and foods, usually overlooking the need to balance caloric intake.  Despite having an association with calories and certain types of food, there are so many factors at play when eating food that may have gone overlooked in this study.  Until this can be replicated in trials with hundreds of human participants, I will take the results with a grain of salt.  I can see strong support in every day life for the issues that the researchers were getting at, while there is more convincing evidence here for the sweetness/caloric association disruption than the viscosity.
    In any event this is just a rough first trial at keeping a blog, as I hope to polish up my writing from week to week and possibly give more elaborate analyses as we study these topics further in class and as I look at more research articles.  Thank you for reading.


testing out my new blog to see if my message posts work.