Science Sunday: The ontogeny of behaviour in the albino rat

Every Sunday, I'd like to post a review of an interesting peer-reviewed science article. To kick things off I'm picking an old favorite, originally posted in 1964! It is certainly well cited, Google Scholar lists the citation count at 452! Indeed this paper was a "Citation Classic" in Current Contents in 1981. At the time the lead author  Robert Bolles, was still living and stated:

"I have always believed in the idea that experimenters should look at their animals...the human eyeball is the instrument of choice if you want to observe a new phenomenon, and particularly if you want to gain a new understanding of it."

Sprague-Dawley Rat

If you have ever wondered why science uses rats the answer is that we know everything there is to know about rats. We know how they age, how they metabolize ... anything, how the respond to stress, how they develop over time, even how they laugh when tickled. Well, our understanding of rat behavior begins in antiquity but is greatly expanded by this 1964 article originally published in the journal Animal Behaviour.

In fact this article describes qualitatively the behaviors of infant rats from birth to about 24 days (rats are weened at day 21). In the first experiment, Bolles and Woods observed 13 litters with an average of 9 pups (117 pups) in their "natural" laboratory environment (cages). The animals were of the Sprague-Dawley line, which is still used today. They did use several different methods of observation and schedules of observation to arrive at a comprehensive guide to the ontogeny of lab rats.

They begin with postural observations, describing three postures that develop over time: lying, sitting and standing. Lying being the default resting position of the rat, often using other bodies for support. Sitting began on day 4 when subjects first began to lift their heads, and was fully developed by day 17 when subjects could sit and perform activities such as grooming. Also beginning on day 4 are the first attempts to support weight on the legs, and by day 10 the animals can support themselves. By day 13 they can run, by day 15 they can stand on three legs and scratch with the fourth. They can rear up on two legs with support for the front legs on day 16 and can rear independent of support (for the purpose of play-fighting with siblings) by day 18.

In similiar fashion reflexes are described. Without relating the specific timeline the reflexes are: twitiching, head waving, stretching and yawning, body flexion, righting reaction, freezing, sniffing, auditory orientation, and visual orientation. When describing startle response int he auditory orientation section there is a great footnote on the word "click:"

*The sound used was relatively well-controlled and constant, but, unfortunately rather poorly defined; it was the sound of a Parker T-Ball Jotter pen being retracted at a distance of approximately 1 foot.

Psychologists are hilarious. Also found it interesting that the animals did not freeze in fear until day 26 and they froze for approximately 15 seconds. I've never seen any rats hold still for that long unless they were sleeping. Following this functional activities are described. Here is the list: sleeping, consumatory behavior, locomotor activity, climbing, grooming, exploration  manipulation, digging, and defecation  Here the theme of development was similar as above, with rudimentary non-functional behaviors appearing first (such as scratching motion without making contact with the skin), that later developed into full-fledged adult-like behavior.

Ultimately we get a description of the social behaviors in the observed rats. Social behavior in young rats is evidenced by chasing and fighting. Bolles, and Woods observed rats begin this social play-fighting on day 14 when their eyes began to open.The activity peaks between day 20 and 30 when the whole litter engages in a high level of activity.

Table 1

In a second experiment Bolles and Woods attempt to quantify the behaviors they observed in the first experiment. Using experimental methods the authors observed 12 rats (2 each from 6 litters) and summarized their behaviors as percentages. To the right is table 1 from the paper. There are many more graphs showing the time course of the development of behaviors and it really is a fascinating reference, but I won't reproduce all of that here.

The first point of discussion and perhaps the most salient is that from these findings we can view rats as a far more social animal than might otherwise be considered. Early social interactions are to wrangle for nursing or comfort, and later become play fighting and chasing. As the authors noted this social behavior likely leads to long lasting changes in the adult organism and "offers interesting possibilities for research in this area." (See the next 50 years of rat studies for more on these possibilities)

Bolles, R., & Woods, P. (1964). The ontogeny of behaviour in the albino rat Animal Behaviour, 12 (4), 427-441 DOI: 10.1016/0003-3472(64)90062-4