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Wednesday, June 13, 2012

Beha'aloscha, Bamidbar 11:6. Tired of Mahn: Orienting, Habituation, Sensory-Specific Satiety, Ruchnius and Gashmius.

Most people will find this post boring.  I find the question fascinating, possibly a key to the nature of human motivation, but that's just my opinion.

How would you like to eat the same food for forty years?  Let's say that the food could have different flavors, even different textures, but it always looked the same, and only changed when thought about some other specific food while you were eating it.  But when you ate it without the hineni muchan, without imagination, it would always taste and feel the same, kind of like shortbread cookies.  Would you enjoy it much?  

The fact is that we experience a decline in appetite when that appetite is satisfied repeatedly in the same manner.  We're all familiar with this phenomenon.  Although some people, particularly children with food obsessions, can eat and will only eat one or two foods for years- with one of my children, it was Cheerios and macaroni and cheese, and by the end of Pesach he lost lost ten percent of his body weight- for most people, repeatedly eating one food results in not only diminished enjoyment, but even disgust.

This is not specific to eating.  It applies just as well to sexual relations and to music.  Passionate affairs inevitably cool, and listening to the same music over and over has been used by the military as a form of torture.  There are so many words to describe it- bored, jaded, world-weary, ennui.....

Why is this so?  The food tastes the same as it did before, you're the same person, so why don't you enjoy it as much as you did in the beginning?  The pate de foie gras is still exactly the same as when you tasted it and swooned from pleasure.  Your taste buds are the same.  The ambiance is the same.  What's the problem?  The spouse is the same, why are you bored, why are you looking at another person whose only distinction is that she is not the one to whom you've been married for seven years?  What does boredom have to do with physical enjoyment?  

And given that this is a reality, we need to kler a Chkira: 
However it works, what is the underlying logic?  Is novelty a necessary component of enjoyment?  Or does repetitiveness work against pleasure?  

There are two mechanisms that psychologists have studied that bear upon this question.  (I) is Orienting/Habituation and the other (II) is Sensory-Specific Satiety.  Following brief discussions, we will talk about (III) why the Ribono shel Olam was angered by the complaints about the Mahn.

Orienting responses are heightened sensitivity experienced by an organism when exposed to a new or changing stimulus. Orienting responses can result in overt, observable behaviors as well as psychophysiological responses such as EEG activity and undergo habituation with repeated presentation of the eliciting stimulus.

The importance of mind over stomach was demonstrated in 1998 in a striking experiment with two men whose mental functions were normal except for a severe form of amnesia. They were unable to remember an event for more than a minute. Their eating habits were studied on several days by researchers, led by Paul Rozin at the University of Pennsylvania, who created a rather extended lunch period.

After each man ate his lunch, the food was cleared. In a few minutes, a researcher appeared with an identical meal and announced, “Here’s lunch.” The men always ate up without any complaint about feeling full. Then, after the food was cleared and another few minutes passed, a third lunch was served, and the men always dug into it, too.In fact, one of them stood up after his third lunch of the day and announced that he would “go for a walk and get a good meal.” Asked what he planned to eat, he replied, “Veal parmigiana” — the same food he had just had for lunch. When the researchers tried the same experiment on a control group with normal memories, the people all refused a second lunch. They, unlike the men with amnesia, consistently felt less hungry after eating, but the sensation apparently wasn’t just coming from their stomachs, as the researchers concluded.
“Nonphysiological factors seem to be of major importance in the onset and cessation of normal eating,” Dr. Rozin and his colleagues wrote in  Psychological Science. “The results suggest that one of the principal nonphysiological factors is memory for what has recently been eaten.”

I would put it this way.  It seems that after eating a particular food, the memory of satiety is imprinted more strongly than the memory of the appetite.  With repeated experiences of the satiety brought about by eating this food, the sense of not being hungry becomes a conditioned reflex.  A nafka minah would be that according to this model, habituation would not occur unless the person ate to full satisfaction.  A person who every day eats a particular food but not to satisfaction will never tire of eating it.

The other is Sensory-Specific Satiety- that eating will decrease appetite selectively- a person will be satiated for one food but not for others: For item A, I have no appetite.  For item B, I'm hungry.  There is an aphorism for this in many languages, such as (Eiruvin 82b)  רווחא לבסימא שכיח.  In English, the expression is, as Dr. Rolls says,  New meat begets a new appetite.

The following is an excerpt 
from a paper by Dr. Barbara Rolls, "Sensory-specific Satiety" NUTRITION REVIEWS VOL. 44, NO. 3/MARCH 1986, in which she discusses a concept in which her peers (e.g., Dr. Paul Rozin, who was kind enough to send me the information) consider her pre-eminent.  Dr. Rolls is the author of a series of popular weight management books titled "Volumetrics."

Monotony in the Diet 
Up to this point we  have been considering hedonic responses to foods during a meal and for  several  hours  after  a  meal.  Let  us look beyond  daily consumption and consider changes in food preference that can develop over longer periods. People tire  of  particular foods and this, of course, means that they stop eating them. There is  little understanding of why  the  preference for particular foods  declines over time, but one obvious possibility is that eating a food too often can affect acceptance. 

Studies of the effects of consumption of monotonous army rations indicate that  repeated presentation of some foods can lead to a very persistent decrease in the pleasantness of  these foods.  For  example,  with  repeated consumption canned meats became very un- palatable and continued to be disliked for 3 to 6 months after the study. Canned meats were not rated as very palatable at the start of the study, and the effects of repeated consumption appear  to be  different  for  staple foods and foods of initial high palatability. For example, in the army studies repeated consumption did not change  the  palatability  of  desserts, sweets, canned fruits, cereal, or staples such as dairy products, bread, or coffee.  We also found no decline in the rating of pleasantness of the taste, appearance, texture, or smell or either a confectionery or a savory corn snack after they had been eaten every day for 3 weeks. 

Moskowitz has described time preference curves for different food types. These indicate that foods not consumed for about 3 months are highly desired,  but those eaten the  day before may not be desired at all. Foods such as meat and shellfish, foods with a heavy fat content, or foods that carry the meal such as the entree have steep curves and are greatly desired if  not eaten for  a very long period, but recent consumption eliminates the desire for such foods. Items that do not carry the meal and do not have a high fat or  protein content such as bread, salad, potatoes, and some desserts have a much flatter function and can be eaten every day with no loss of preference. (emphasis mine.)

A recent study of food preference of Ethiopian refugees illustrates the importance of understanding the effects of  monotony on food intake. The refugees reported that the taste of the three foods that they had been eating for approximately  6 months  was  less pleasant than  that  of  three new foods. Refugees who had been eating the usual diet for only 2 days found its taste as pleasant as that of the new foods. The monotonous diet affected the refugees in that they would often trade the staple diet for small quantities of less nutritious foods, and they  would stop preparing the  monotonous foods adequately. This effect could possibly have been overcome by the simple expedient of adding spices to vary the flavor, as is the practice when people subsist on diets consisting primarily of one food such as rice. It appears that decreases in palatability can extend beyond a meal to affect general acceptability of  some foods. It seems unlikely, however, that  this  is the same phenomenon as sensory-specific satiety. Sensory-specific satiety occurs rapidly after eating, and tends to be fairly short-term. 

The food industry refers to decreases in acceptance of  foods in the long term as “wear-out.’’ It seems likely that wear- out is partly due to cognitive satiety. That is, a person knows a lot of a particular food has been  consumed and  desires a change.  It is possible that eating too much  of  a food  or being forced to  eat  a food  can contribute to cognitive satiety. Supporting this cognitive hypothesis is the finding that, in a study of factors affecting food monotony, self-selection of  the items to be included in a repetitive diet reduced dissatisfaction with the diet. Thus overall satisfaction with a 3-day, self-planned menu cycle was the same as with a 6-day cycle chosen by someone else. Making people eat foods that they  have  not selected themselves can decrease the preference for those foods. (emphasis mine)  This is supported  by  studies  of  young children,  in which foods they were  forced to  eat to  gain rewards  decreased  in  preference. Clearly, much more work is needed to understand what makes foods change in desirability. Variety, Monotony, and Body Weight Body  weight maintenance may  depend to some extent on the availability of a varied and palatable diet. 

In studies of the effects of consumption of  a monotonous liquid diet, it was found that both obese and normal-weight individuals voluntarily  restricted intake and  lost  weight. There is also some evidence that if freely available diets are varied and palatable there may be excessive weight gain. In studies of  caloric regulation  in  obese  and  normal- weight subjects confined  to  the hospital, a plentiful and varied supply of food led to over- eating and weight gain over 3- to 6-day period . It is difficult to conduct long-term controlled studies of the effects of variety and palatability on human body weight.  It  is therefore worth considering the literature on animals. 

In recent years there have been several reports of obesity in rats given free access to  a variety of  palatable, high-energy  food.  In most  of  these studies the obesity could have been due to the high palatability and high energy content of the foods as well as their varied sensory properties. However, in one study the effect of  variety per se was examined by using foods of similar energy  density which were eaten  in  similar amounts in pilot studies (ie, they appeared to be of similar palatabilities). Rats were offered either laboratory chow alone, chow plus one palatable food, or chow plus three palatable foods (cookies, crackers, chocolate)  in  succession (changed every  12 hours), or  simultaneously, for 7 weeks. All rats offered the palatable foods ate more than the chow-fed controls. Rats given the simultaneous but not the successive variety ate more than the other palatable food groups and had significantly greater body weight gains and more body fat at the end of  the 7 weeks. Thus the effect of  variety on food intake can extend beyond a single meal and can contribute to the development of  obesity. 

It seems likely that, in affluent societies where there is continual appetite stimulation by both successive and simultaneous variety within and between meals, there will be little opportunity to compensate for overeating due to variety without conscious limitation of intake. Mechanisms of Sensory-specific Satiety Is the  decrease in the palatability of  foods that accompanies consumption simply  because of sensory adaptation or habituation? In other words,  does the perceived intensity of foods decrease with consumption? In a study conducted by Mower et al on the effect of  a meal  on  olfactory stimuli, decreases  were found in the pleasantness of  the  odors, but there were no changes in the perceived intensity  of  the stimuli. In another study  it was found that the decrease in the pleasantness of the taste  of  particular foods  was  associated with only minor changes in the intensity of the taste of those  It would not be adaptive to have food consumption lead to a decreased ability to taste foods. Indeed, we all know that we  can still taste and smell foods after they have  been consumed.  It  is  more  likely that sensory-specific satiety involves a change in a mechanism concerned particularly with the reward or hedonic value of food. 

Electrophysiological studies of brain cells in monkeys are  clarifying  the mechanisms  of sensory-specific satiety. The electrical activity of  single cells has been recorded while mon- keys ate particular foods  to  satiety.  When recordings were  made  in  areas of  the  brain concerned with the sensory analysis off  taste stimuli (the nucleus tractus solitarius and the opercular cortex) or visual stimuli (the inferior visual temporal cortex and the amygdala), satiety  had no  effect  on  the responses of  the This finding is in marked contrast to the effects of  consumption on cells in the lateral hypothalamus, an  area  of  the  brain involved in the control of  motivational state and reward. It  was  found that  when  a  monkey was hungry, cells in the lateral hypothalamus responded to the sight or taste of food, but as it consumed a food the neurons became less responsive to it and acceptance for that food gradually decreased. However, if the monkey was then offered another food, the neuron responded and the monkey then accepted this food. Thus, sensory-specific satiety does not appear to be  related to  changes in  sensory processing of  responses to foods, but it is related to brain areas controlling motivation and the reward value of foods. 

To further define the neuronal basis of   sensory-specific satiety, Rolls and colleagues followed taste processing from the primary (opercular) taste cortex into a secondary gustatory area in the caudolateral orbitofrontal cortex, which  in turn  has  connections to  the  lateral hypothalamus.  Sensory-specific satiety  is paralleled by the responses of single neurons in this caudolateral orbitofrontal cortex taste area. A neurophysiological basis for  this,  in terms of altering responsiveness of specifically tuned neurons in this area of gustatory cortex as a food is eaten, has been proposed.  It is likely that cognitions contribute to sensory-specific satiety. People seem to learn how much of  a  particular food they  can eat  in a meal.  It  may  be that when this  limit is exceeded, food  becomes unpleasant. Learning about the  caloric value  of  foods and appropriate amounts for  consumption depends on the sensory properties of the foods. Since cognitions about foods depend on sensory properties  of  foods,  it will  be difficult to  determine whether sensory-specific satiety and cognitive satiety are distinct phenomena. 

During consumption of  a food the pleasantness of  its taste, appearance, smell, and texture  decrease.  The  pleasantness  of  other foods not consumed decreases much less or remains unchanged. Such responses to foods occur  very  rapidly, within  2  minutes after a meal, and appear to depend more on the sensory properties of  foods than the caloric content, hence the term “sensory-specific satiety.” Sensory-specific satiety helps to  ensure the consumption of  a varied, and therefore  balanced, diet. Thus, when a variety of  foods is available, there will  be a tendency to switch from one food to another because of  the decrease in palatability in any one food after consumption. Sensory-specific satiety can also affect the amount of  food consumed in a meal, so that the more varied a meal, the greater the intake will be. Since sensory-specific satiety is one of many factors controlling food intake and selection, its influence depends on the  context in which eating takes place. An understanding of factors  that affect the hedonic response to foods is important, for this response potentially influences both appetite and the acceptability of foods.

Considering these realities, it is not surprising that we found the Mahn unappetizing after a while.  The reaction was natural and expectable, perhaps inevitable.  In fact, in Devarim (8:16) it says   המאכלך מן במדבר אשר לא ידעון אבתיך למען ענתך ולמען נסתך להיטבך באחריתך  , He fed you the Mahn in the that you would suffer and to test you so that you would benefit in the end.     The Gemara (Yoma 74b) says 
המאכילך מן במדבר למען ענותך רבי אמי ורבי אסי חד אמר אינו דומה מי שיש לו פת בסלו למי שאין לו פת בסלו וחד אמר אינו דומה מי שרואה ואוכל למי שאינו רואה ואוכל אמר רב יוסף מכאן רמז לסומין שאוכלין ואין שבעין אמר אביי הלכך מאן דאית ליה סעודתא לא ליכלה אלא ביממא that the people did not enjoy the Mahn as they would regular food, either because it didn't look like food, and appearance is an important part of gustatory satisfaction, or because they never had tomorrow's food in the pantry.  I would say that equally problematic was the sameness of the Mahn, the constant repetition.  Even if it did taste different, it was the same old thing every day.  It was missing the sizzle, the excitement of newness.  Just like a blind person is not as satisfied as a sighted person, because he is missing the visual aspect, so too the sameness of appearance caused boredom and ultimately disgust.  So what was the Ribono shel Olam's kpeida?  Why was He angered? 

I'd like to think about the fact of our abhorrence of sameness, how boredom subverts pleasure and drives us to seek new experiences, even if they are absolutely not better than what we've had before.  Irrespective of Darwinian necessities (ensuring a varied diet, fathering children with many women,) or physiological mechanisms (altering responsiveness of specifically tuned neurons), let's assume there's an intentional spiritual component in this phenomenon.  In the section I emphasized above, Moskowitz's observation, we note that the problem only occurs in foods "with a heavy fat content or foods that carry the meal".  But there does not seem to be any such phenomenon in foods that "do not carry the meal or do not have a heavy fat or protein content."  Similarly, see Rolls' reference to the difference between self-planned repetitive menus and menus planned by someone else.  These strongly imply a predominant mental component in this phenomenon.  Let's further assume that the disgust with the Mahn bespoke an extreme spiritual flaw on the part of Klal Yisrael.  The question then becomes, what, exactly, was that flaw?

to be continued

I don't have time to finish this, so here's what I'm thinking.
This problem is intensified where the foods have a high fat content, or carry the meal, or are imposed externally.  The common denominator is the attitude of eating to satisfy the nefesh ha'be'hamis- self-indulgence.  Hashem created us with a hatred for stagnation, and this emotion should serve a desire to grow in ruchnius, to never be satisfied, to feel impatience and disdain for what we've already achieved, because of a burning desire to accomplish more.  For the Dor Hamidbar to allow infantile impulse for self-indulgence to redirect this spiritual drive toward a desire for new food meant that they didn't appreciate what it meant to eat the Mahn, which was the food of Malachim and enabled them to grow in havanas hatorah.  It was, basically, Me'ilah.

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