Physical space containing multiple potential routes to a goal at least one of which is productive or optimal

Mazes (amasian, 'to confound' in old English) are for some current students of learning what the pen is for a literary critic: indispensable but occasionally abused. Although employed mainly to probe the memory of rodents (Olton 1979), over the years, mazes have been applied to the analysis of other species as well, ranging from flies (Dudai 1988) to monkeys (Murray et al. 1988) and humans (Woodworth and Schlosberg 1954). The systematic use of mazes in the psychological laboratory was initiated by Kline in Clark University in 1898. He was searching for an appropriate "system to experiment on 'the migratory impulse vs. the love of home' (the title of his PhD thesis, admittedly rather poetic). The idea to use the laboratory "rat and the maze for 'home finding' experiments was suggested to him by Sanford (Miles 1930). Furthermore, Sanford suggested specifically to model the Hampton Court Garden labyrinth in London for these experiments. Up to that stage all this had nothing to do with learning research. But soon after, Small (1901), in the same department, started to use the Hampton Court maze for learning experiments. With time, rats in mazes became highly popular in studies of behaviour and learning. By the 1930s-1950s,they almost monopolized experimental psychology. The contemporary "zeitgeist culminated in "paradigmatic statements such as 'everything important in psychology (except such matters as building of a super-ego.) can be investigated in essence through... determinants of rat behavior at a choice point in the maze' (Tolman 1938).

There was reason behind the mazomania. Against a background of some rather artificial and sometimes bizarre paradigms of "instrumental learning, mazes have provided a reproducible experimental environment adapted to the rodent sensory-motor ecological disposition: '(for the rat)', said Small (1901), '.the experiments were couched in a familiar language'. Inter alia, mazes became a major test ground for two rivalling types of theories in the psychology of learning. One, the stimulus-response (S-R) type, trusted that whatever an animal learns is due to "reinforcement by trial and error of atomistic sensory stimulus-motor response connections. The other type of theory was cognitive, claiming that with experience, animals accumulate structured bodies of knowledge that they use to construe, react to, and even anticipate the world. Hence, whereas the first type of theories denied the existence of inferred mental processes that bridge S to R ("behaviourism), the second type deemed such internal intervening processes as obligatory; and whereas S-R theories portrayed laboratory animals as having a somewhat impoverished picture of their milieu, the cognitive theories were ready to endow them with a much more intricate psyche (Boakes 1984).

Proponents of the cognitive view have tried to convince themselves and their opponents that when a rat runs a maze, its behaviour reflects a molar cognitive purpose (as opposed to reacting to local cues like a kinesthetic automaton). The innate predisposition of the rat to navigate in space ("a priori), combined with the varied complexity of the task and the substantial number of response strategies permitted in certain mazes, rendered maze paradigms especially fit to be used in the attempts to resolve the aforementioned debate (e.g. Tolman 1938; Olton 1979). The maze studies matured into a dynamic, multifaceted research field, addressing cognitive "maps and brain regions that retain "engrams of such maps. Sophisticated cellular physiology, molecular biology, and computational science now permit, for the first time, attempts to close the gap between the observed behaviour, the postulated cognitive maps, the circuits that are assumed to encode the maps, and the cellular and molecular mechanisms that embody the "internal representation in these circuits (e.g. Burgess and O'Keefe 1996; Wilson and Tonegawa 1997; "reduction).

Mazes come in many variants. A convenient distinction is between 'defined paths' and 'open-field' mazes. The former (definition 1) have bordered passages and cul-de-sacs as intuitively expected of labyrinths. The passages could be delineated by walls (in which case it is an 'alley maze') or by elevated paths ('elevated maze', with the dead ends being the termination of the elevated alley into open space rather than a wall; Olton 1979). Alternatively, mazes may have no defined physical paths within the maze enclosure (conforming to the more inclusive definition 2 above). Such mazes are thus of an 'open-field' type.1 The term 'enclosed' or 'closed' field is sometimes used to denote defined paths mazes within a closed environment (Hebb and Williams 1946), but this is questionable because unless virtual (Maguire et al. 1998), all mazes are enclosed in physical space in one way or another. In their shape, defined path mazes range from a straightforward I, T, or Y, useful for example in simple discrimination or avoidance tasks, to more complex multiple-arm radial mazes, permitting sophisticated spatial and "working memory tests (Olton and Samuelson 1976; see also example in "habit). An 'open-field' type of maze that has gained impressive usefulness and popularity in recent years is the water maze (also known as the 'Morris maze'; Morris 1981). In this type of maze rodents are trained to escape from water on to a hidden platform located within a large unobstructed pool (for earlier variants of water mazes, although with defined paths, see Glaser 1910; Rosvold and Mirsky 1954). The 'Morris

maze' has been seminal in reinforcing the notion that rodents can form stable overall spatial maps of their milieu, independent of local cues (Morris 1981). It has also been instrumental in analysing the function of the "hippocampus in learning and memory, as well as the relevance of "long-term potentiation to behavioural plasticity (e.g. Bannerman et al. 1995; Wilson and Tone-gawa 1997). Many other types of maze are, however, highly useful as well in such studies (e.g. O'Keefe and Speakman 1987; Markus et al. 1995).

The rapid and impressive advances in molecular neurobiology in general, and in mice "neurogenetics in particular, have promoted the popularity of mazes among neurobiologists at large, because mazes could provide a seemingly simple learning "assay. Thus, it has become almost routine for new transgenic and knockout mice to be declared either smart or stupid on the basis of passing or flunking the test in the water maze. However, the simplicity of the procedures facing the experimenter may mask the complexities facing the mouse (e.g. Bannerman et al. 1995; Day et al. 1999). It may also blur the finesse of species-specific innate behaviours (Wolfer et al. 1998). A maze is clearly not an instant assay kit, and the experimenter should devote ample attention to the "performance of the "subject and to what this performance really means.

Selected associations: Assay, Hippocampus, Map, Mouse, Rat, Paradigm

1For a beautiful distinction between alley and open field mazes in fiction, see Borges (1949).

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