The contribution of the rat to the behavioural and brain sciences is second only to that of humans, the main difference being that the contribution of the latter is frequently more voluntary. It has all started with the invasion of Europe by the brown rat (Rattus norvegi-cus). The brown rat arrived from Asia at the beginning of the eighteenth century, almost 400 years after its cousin, Rattus rattus (the black or grey rat), spread the devastating Black Death throughout the Continent. The brown rat was very successful in the new niche. The human response was to engage in extensive rat trapping, and to establish rat baiting as a popular sport. The twist in the story came when albino mutants of the brown rat were noted, isolated, and kept for entertainment. The albino rat proved to be much more tameable than the wild type. The relative docility of this mutant provided it with the opportunity for eternal fame; by 1850s, it has already been used in metabolic and genetic experiments in France. England and Germany followed right thereafter. As a matter of fact, this was the first species to be domesticated for scientific purposes (Lockard 1968; Lindsey 1979). In the 1890s, a Swiss scientist who emigrated to the USA imported the albino rat to the University of Chicago.1 At about the same time, a short-lived attempt was made to use the grey rat at Clark University (Munn 1950), but the white soon replaced the grey in Clark as well. The standardized stocks and inbred strains of laboratory rats used today were developed from the albino as well as from crosses between the albino and wild type (Lindsey 1979).
The championship of the psychology lab did not come easy to the rat. Chicks, cats, and dogs were all at one time or another effective rivals for the attention of researchers (Boakes 1984; "classical conditioning, "imprinting, "instrumental conditioning). The laboratory rat was small, cheap, easily bred and cared for, and, most importantly, smart. At Clark University, it became the subject of the first "maze experiments (Small 1901; Miles 1930). The combination of mazes and rats emerged as a real winner, shaping experimental psychology for generations to come. Rat learning "paradigms became so dominant that at a certain stage, toward the mid-twentieth century, experimental psychologists, especially in North America, became convinced that rat behaviour can faithfully "model human behaviour. Furthermore, they entertained the idea that the rat mind holds many of the clues to human psyche. '... Most of the formal underlying laws of intelligence motivation and instability can still be studied in rats ... more easily than in men ... (rats) do not go on binges the night before one has planned the experiment; they do not kill each other off in wars; they do not invent engines of destruction, and, if they did, they would not be so dumb about controlling such engines; they do not go in for either class conflicts or race conflicts; they avoid politics, economics and papers on psychology' (Tolman 1945). Whereas avoidance of politics and of papers on psychology does have some merit, the enthusiasm appears today a bit exaggerated.
The advantages of the rat for the science of memory are numerous. Some of these advantages pertain directly to the rat's ability to learn quickly in tasks which are convenient for use in the laboratory. It is especially shrewd in spatial, olfactory, and taste learning (Tolman 1948; Slotnick 1994; Biegler and Morris 1996; Schul et al. 1996). Other advantages of the rat relate to its size (not too big, not too small). But probably must important at this stage is the immense body of knowledge that has accumulated over the years on the rat's neuroanatomy, neuropharmacology, neurophysiology, and behaviour. This combination turns the rat into a prime choice for the cross-"level study of certain types of mammalian learning.
The rat, however, has at least two types of disadvantage. First, clearly, in some cognitive tasks, such as "delay tasks, which are of great importance to the understanding of primate "recognition and "recall, the rat is no rival to more advanced species such as the "monkey (Hunter 1913; Keller and Hill 1936; Steckler et al. 1998a,b). It is also debated whether it can form genuine "learning sets, a popular "criterion for rudimentary concept formation (Reid and Morris 1992; Slotnick 1994). Second, the molecular genetics of the rat is undeveloped. Transgenics were reported
(e.g. Waller et al. 1996), but no knockout technology is yet available at the time of writing. This deprives the rat of one of the most powerful tools of molecular neurobiology ("neurogenetics). So far, in this arena, the "mouse outperforms the rat, and if the latter doesn't catch up, which is rather unlikely, it will lose its hegemony in the world of mazes and puzzle boxes.
Selected associations: Maze, Model, Subject, Zeitgeist
1Whether all the albino rats later used in research in the USA indeed originated from this import is uncertain (Lindsey 1979).
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