Learning from aversive experiences; the effect of timing
- This chapter is under construction ***************
This chapter relates some important findings from ethological observations on house mice, Mus musculus, findings that were found rather by accident. Some of the training schedules for introduction-mice did not work as expected and as was the purpose of that type of training.
While figuring out how to prevent the training schedules from turning out faulty, it was found that severely aversive experiences did not necessarily always result in avoidance behaviour. The aversive experiences training schedule could produce either stereotyped and highly predictable cowards or, on the contrary, highly skilled and less predictable heroes. These two extreme and opposite phenotypes were the result of the same training pattern, always aversive and always, at every instance, ending in outright disaster and sheer panic of the trainee.
What happened was the following.
In 1972 we were studying with ethological methods the behaviour of groups of 6 resident house mice, 4 brothers and 2 sisters from the same litter in a population cage with ample space and climbing devices, ropes, cages, sawdust, a gauze roof, escape devices, food- and drink boxes, etc. See fig. *********** We needed an extra standard social stimulus for these resident groups in order to observe the group under different circumstances, in peace and while being visited by an intruder. And that "intruder" stimulus should be as standardized as possible in order not to introduce unnecessary variation from outside sources.
Fig ************** about here.
The idea of these ethological observations of resident groups of house mice was to study differences in behaviour between male house mice that could be classified as differences in "personality". Comparing different individuals separately, we could get more reliable data on the interpersonal behaviour patterns if the stimuli from the environment under the various circumstances, would be, for the resident mice, every time the same as much as possible. One rather uniform social stimulus could be provided by introducing for a short period of time 5 to 10 minutes, an unfamiliar male introduction mouse that had been trained to react completely paranoia, and thus stereotyped, when introduced into the group of 6 residents.
What we did to make sure that the introduction mice, 60 males from a CPB's strain, would show highly similar behaviour every time when introduced for a short period of time, was giving these mice a training beforehand until their reactions after being introduced were highly stereotyped and predictable. They were in fact made completely paranoia for being introduced into such a resident population.
male intruders were introduced regularly into the population-cages for some five or ten minutes. Half of the protocols were obtained while such an intruder was present in the observation cage. In order to standardize this type of stimulus on the resident mica as much as possible, the guest-mice were trained beforehand in such a way that they showed continuous avoidance-behaviour when introduced. This was very easily realized in the following way: About 60 male trainees of the CPB's strain were weaned and isolated at the age of 21 days.
One or more weeks before they were needed to provide a standardized introduction stimulus, they were introduced every other or every second day into an unfamiliar observation cage, populated by a group of 6 resident mice, that showed territorial aggressive behaviour towards strangers. Being outnumbered at least four to one and being on foreign territory, a trainee never had a chance to win and therefore got beaten up every time when introduced. Such a trainee -introduction was stopped as soon as the trainee showed panicky behaviour such as frequently jumping high, running aroung frantically, bumping into resident mice and other objects and avoiding social contact as much as possible. The trainee was never removed before such behaviour was shown, which was always the case within a few minutes.
The trainees were often slightly wounded when introduced. After five to ten days of training, these trainees immediately showed avoidance behaviour when being introduced, even when not under attack by any resident mouse at all.
The earlier social experience of these male "trainees" consisted of ordinary maternal care in a litter until the age of 21 days, during which period of time no other adult mouse was present. After being weaned at the age of 21 days, they were kept in isolation for a shorter or longer period with water and food supplied ad libitum, and subsequently they were trained as described above.
There seemed, however, to be some sort of "critical training frequency", i.e. if the periods of rest in isolation between the training introductions were too long, the effect of the whole training was the opposite, of what was aimed at.
If a trainee was introduced for "training" once every week or once every second week instead of every day, he tended to put up extremely severe resistance . Such a male did not attack residents, refrained from "fleeing frantically" and appeared to "stand firm" when necessary. For this reason, trainees who had not been "trained" for some time became worthless for providing standardized introduction stimuli.
By manipulating only the "training-frequence" or "resting-in-isolation period", trainees could be transformed from inexperienced males into either "fearful fleeing males" or "skilled fighters".
It should be remembered that neither type of trainee was ever allowed to win a fight. During every introduction in their training period they had to fight against heavy odds. "Skilled fighters" simply managed to hold out and fight back now and then without continuously "running for their lives".
With the above described procedure trainees became either more skilled in fighting or more fearful than unexperienced males. Furthermore, inexperienced males varied more in their reaction patterns than did either of the two classes of trainees. This made sense, because the training was aimed at reducing the variation in behaviour in the first place.
Once a male had become a "skilled fighter" it was very difficult to turn him back into a "fearful fleer" again. To achieve this required a very harsh and frequent training schedule with more intense (longer) beatings and short resting periods (initially a couple of hours), but even so he would never again reach the same old reliable predicability as a "fearful fleer". The skill of fighting could apparently only be suppressed with difficulty for a limited period of time once it had been learned.
In order to find out more about this phenomenon, out of a total amount of 60 trainees, some 20 males were on purpose turned into "skilled fighters". Once we had obtained the hang of it, we could easily produce either standardized cowards or heroic fighters.
Apparently the type of (always aversive)experience in question can lead to different learning processes, depending on the input frequency of the experience. The one direction in the learning spiral leads to intensive avoidance reactions, the other direction leads to increasing skill in offering resistance.
A possible explanation of this phenomenon may be found in the influence of fearful experiences on the hormone production. Fear reduces the testosterone-level and with it probably the tendency to put up resistance when provoked (Bermond, 1977); long training intervals allow the hormone level to return to normal, but when the intervals between the fearful experiences are too short, the effects accumulate. Eleftheriou and Church demonstrated this for mice (1968), and Rose(1972) for Rhesus monkeys.
Thus the pattern in time of experiences appears to be of great importance for the eventual effect of the experience! Besides, individual mice differed in their "critical digestion-time" for this type of experience. Some males of this CPB's strain became "fighters" after three-day training intervals, whereas others remained reliable "fleeers" after five-day training intervals. So, for inexperienced males of the CPB's strain this "critical digestion time" varied between two and six days.
If males had grown up in a social group, they varied greatly in their reactions when introduced into a strange "group" as described above. In general males with a background of "normal" social experience were rather well able to hold out against such an avalanche of territorial aggression. Apparently such a "normal" social history provided ample opportunity for these mice to "digest" their aggressive encounters in such a way that they became skilled in dealing with agonistic social situations.
Conclusions
1) Male mice can easily be trained in such a way that they perform a uniform type of avoidance behaviour when introduced into a strange environment, inhabited by resident mice.
2) The training that is required for turning an inexperienced male into a "coward" is almost the same as the training needed to turn him into a "hero". The only difference is that in the former training schedule less "digestion time" is available for every experience than in the latter.
3) This "critical digestion time" or "recovery period" varies somewhat between individuals
| Previous Experience | Ability to withstand attacks from residents | Variance in behaviour during introduction | |||
|---|---|---|---|---|---|
| Grown up in a "normal"social setting | (A) | Good | Very large | ||
| Isolated from the third week on | (B) | Modest | Large | ||
| Same, but introduced with short time intervals (Cowards) | (C) | Nihil | Very small | ||
| Same, and introduced with long time intervals (Heroes) | (D) | Very good | Small | ||
