Healthy wild-type animals generally display a percentage of alternation around 70–75%, far above chance level (50%). Percentages of alternation across the test trials are calculated as an index of working memory.
#Hamster maze study series#
A series of test trials is then carried out (usually from 5 to 12, depending on the protocol), with an intertrial interval (ITI) that can range from virtually zero to 20, 40 or even 60 s. After the entrance a guillotine door is shut down and the animal is confined in the chosen arm for a fixed amount of time (for example 30 s), at the end of which it is removed and newly placed in the start arm with all the doors raised for the test trial.
#Hamster maze study trial#
Regarding the murine procedure, in the sample trial mice are released in the stem of the T-maze (the start arm) and let free to choose one the two lateral goal arms to explore. Over the past century, spontaneous alternation has been found in a wide variety of mammalian species, including rats 6, mice 14, hamsters 15, guinea pigs 16, rabbits 17, gerbils 18, ferrets 19, opossums 20, marmosets 21 and cats 22, and also in non-mammals such as pill bugs 23, garden woodlice 24, marine crabs 25, fruit flies 26, 27, goldfish 28 and zebrafish 29. In both cases (innate novelty-seeking behaviour or innate shifting behaviour), during the task, in order to successfully alternate choices across trials, an animal has to remember which arm had been visited in the previous trial, which makes spontaneous alternation T-maze an optimal test for spatial working memory. For example, visiting a place that contains a food reward leads to a win-shift behaviour, while visiting a place that does not contain food leads to a loose-shift behaviour. An alternative explanation for alternation is that mice have an innate tendency to shift. Since this behaviour does not require pre-training and relies merely on the natural attraction of rodents for novelty, alternation has been defined as spontaneous. In the third trial, when both arms have been visited, the arm with the highest degree of novelty (the arm explored longer ago) is preferred. After a first choice in the sample trial, in the second trial the arm which has not been previously explored is preferred. Basically, spontaneous alternation T-maze is based on the natural tendency of rodents to prefer exploring a novel arm over a familiar one, which induces them to alternate the choice of the goal arm 6, 10, 11, 12, 13. This phenomenon was better defined and investigated in the 1930s by Wayne Dennis (1905–1976) 7, 8, 9, who also coined the expression “spontaneous alternation” 10. In the 1920s, Edward Tolman (1886–1959) applied the T-maze to the study of rodent cognition and was the first to report the phenomenon of spontaneous alternation 6. A first T-maze apparatus was designed at the beginning of the 1910s by Robert Yerkes (1876–1956) at Harvard University for the study of invertebrate cognition, in particular learning processes in the earthworm 5.
The T-maze is a T-shaped apparatus allowing a choice between two opposite arms. One of the most well-established tests of spatial working memory is the spontaneous alternation T-maze. Since the pioneering studies of Willard Stanton Small (1870–1943) at the end of the 1890s 4 mazes have been widely employed in behavioural neuroscience to investigate experimentally memory processes through animal models, in particular rodents, such as mice and rats. In particular, spatial working memory designates temporary spatial information needed to carry out a specific behaviour. On the other hand, on the basis of its content, memory can likewise be divided into several subtypes, including visual, auditory, tactile, olfactory, gustatory, interoceptive and spatial. Its capacity is limited, as well as its duration, and its usefulness is strictly related to the execution of a specific task. The concept of working memory partially overlaps the one of STM and although many authors subsequently utilized the expressions as synonyms, working memory actually refers more specifically to a cognitive buffer that stores information and permits its manipulation to guide decision-making and behaviour 3. The expression “working memory” was first coined by George Armitage Miller (1920–2012), Eugene Galanter (1924–2016) and Karl Pribram (1919–2015) in their seminal book Plans and the Structure of Behavior in reference to a memory store for action plans 2. On the basis of the duration of its retention, we can distinguish between short-term memory (STM), which ranges from seconds to minutes, and long-term memory (LTM), which is characterized by a duration of days, years or even decades. Importantly, memory is not a unique faculty but can be subdivided into different subsystems. Memory can be broadly defined as the persistence of previously acquired information 1.
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