'This is what I see in my dreams about final exams: /Two monkeys, chained to the floor, sit on the windowsill/ The sky behind them flutters,/The sea is taking its bath./The exam is History of Mankind./I stammer and hedge./One monkey stares and listens with mocking disdain,/the other seems to be dreaming away—/But when it's clear I don't know what to say/He prompts me with a gentle/Clinking of his chain' (Szymborska 1995). It is the appreciation that monkeys are our closest phylogenetic relatives and share some of our intimate biological secrets, that fuels Szymborska's irony. Among all the species around us, the monkey's brain resembles ours the most. It is there that we often go in search for the rudiments of our higher cognitive faculties ("a priori, "declarative memory). 'Plato', remarked Darwin (1838a), "... says in 'Phaedo' that our 'necessary ideas' arise from the preexistence of the soul, are not derivable from experience—read monkeys for preexistence". And he also noted, musing relativity in the universe: 'If all men were dead then monkeys make men.—Men makes angles' (Darwin 1838b).
Monkeys belong to the order Primates, which has two major suborders (Bennett etal. 1995): The Prosimii ('pre' or 'early' monkeys) and the Anthropoidea ('human-like'). In general, prosimians have a long, wet nose, slightly sideways eyes, prominent muzzle and brow whiskers, and large mobile ears. Many of them are nocturnal species that rely on smell and hearing. Anthropoids have flatter faces, a dry short nose, no prominent whiskers, forward-facing eyes, and they rely mostly on vision. The prosimians and the anthropoids each are further classified into suborders: The prosimi-ans into the Lemuriforms and the Lorisiformes, and the anthropoids into the Platyrrhini ('broad nose', New World Monkeys) and the Catarrhini ('hooked nose', Old World monkeys, apes and humans). The term 'monkey' is conventionally reserved to denote only the long-tailed, medium-sized primates, always excluding the anthropoids apes and humans, and frequently excluding also the prosimians. This classification also fits the term 'nonhominoid primates'. The monkey species most commonly used in medical and biological research are the macaques, which are Old World monkeys. They include the rhesus, Macaca mulatta (Bourne 1975), the Japanese macaque, Macaca fuscata, and the cynomolgus monkey, Macaca fascicularis. But other species are used as well.
Monkeys became occasional pets since times unknown. Their resemblance to humans also led to their use in early anatomical investigations (Morris and Morris 1966). They were among the first species to be systematically used in the early days of brain research and experimental psychology. Generally speaking, monkeys are employed in neurobiology for four main purposes:
1. As "models for human brain pathology. The contribution of the monkey to our understanding of the consequences of brain damage cannot be underestimated. The effect of circumscribed brain lesions on monkey's physiology and behaviour was systematically studied already more than a century ago (Brown and Schafer 1888). These studies have led to the discovery that the temporal lobe (Kluver and Bucy 1938) and frontal lobe (Jacobsen and Nissen 1937; Pribram et al. 1952; Fuster 2000b) play a key part in higher brain function, learning, memory, and cognition ("cortex, "limbic system, "working memory). In recent decades, extensive efforts have been devoted to the development of monkey models of human "amnesia. This has led to remarkable sophistication in lesion techniques on the one hand and behavioural testing on the other (e.g. Mishkin 1982; Zola-Morgan and Squire 1985; "delay tasks). Attempts to resolve the debate over the obligatory role ("criterion) of "hippocampus, "amygdala, and various adjacent cortical areas in memory are still largely based on lesions in monkeys (e.g. Suzuki et al. 1993). Even the fast developments in the "functional neuroimaging of human brain do not yet provide a satisfactory alternative.
2. As "systems for the investigation of the role of discrete brain areas and circuits in normal physiology and behaviour, of the alteration of these roles with development and experience, and, ultimately, of the nature of neural codes and "internal representations. Such research programmes rely on a variety of neuronal activity recording methods, including the use of single and multiple invasive electrodes as well as invasive or noninvasive functional neuroimaging, combined with behavioural protocols on the one hand and with modelling on the other (e.g. Miller and Desimone 1994; Vaadia et al. 1995; Britten et al. 1996; Goldman-Rakic 1996; Georgopoulos 1996; Malonek and Grinvald 1996; Nudo et al. 1996; Tanaka 1997; Logothetis et al. 1999).
3. As systems for exploring the capability and applicability of top-notch research and clinical methods, before they can be safely applied to humans (e.g. Logothetis et al. 1999).
4. Monkeys as well as hominoid primates are used to unveil the evolution of human cognitive abilities, including social interactions, self-recognition, tool usage, communication and language, and even rudimentary math (Anderson 1990; Greenfield and Savage-Rumbaugh 1993; Swartz 1997; Brannon and Terrace 1998; Kawai and Matsuzawa 2000; Ramus et al. 2000; on the criticism of the studies of human language in the apes, see Pinker 1994; "anthropomorphism).
Although monkeys are indispensable for multiple facets of brain research, they are not the easiest species to use in the laboratory. They require special handling, infrastructure, attitude, and quality time. They learn at a very slow rate some tasks that look so simple to humans; it may take many months to a year to teach a monkey to master certain "instrumental tasks. This may attest to the remoteness of the experimental protocols from "real life. The frustrated investigator should also ask himself or herself how long would it take for a naive, perplexed human "subject to acquire such tasks in the complete absence of verbal instructions. On top of it all, monkeys are prone to evoke human-like emotions, which may give rise under certain conditions to hesitations and scruples on the side of some human experimenters. Monkeys are also quick to draw the aggression of the so-called 'animal-rights' group. Whoever subjects animals to invasive manipulations should always keep in mind ample respect for the well-being of the other species; in the case of the monkey, this is even more so warranted.
Selected associations: Amnesia, Anthropomorphism, Declarative memory, Model, Subject
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Have you ever been envious of people who seem to have no end of clever ideas, who are able to think quickly in any situation, or who seem to have flawless memories? Could it be that they're just born smarter or quicker than the rest of us? Or are there some secrets that they might know that we don't?