'Classic' in its classical sense is borrowed from the Romans. 'Classici' were citizens who possessed a substantial income. The word was used also to refer to the armed forces, and 'classicum' was the trumpet call signalling the battle. The Latin author Aulus Gellius (second century ad) was probably the first to refer to writers of worth and distinction as classic writers (Saint-Beuve 1850). The French philologist Littre later adapted the term to refer to literary works 'used in the classes of colleges and schools' (Harvey 1937). 'Classical' then became the adjective used when reference was made to the arts and literature of ancient Greece and Rome;
with time it also came to denote formative periods in other segments of "culture, such as Western music in the last half of the eighteenth century, or physics before relativity and quantum mechanics. Strictly speaking, 'classics' are works of letters produced in the 'classical', Greek- Roman period, and 'classic' is a signal work in any discipline and period (Burchfield 1996), but this distinction is not usually honoured in daily language.
What are the "criteria for a 'classic'? High quality is of course a must, but is not enough. The work must also exert a strong impact, either explicit or implicit, on later generations. Hence, it must withstand the test of time. It is therefore good practice to refrain from crowning pieces of work as 'classic', be they as impressive as they are, before they pass the judgement of at least a few scientific generations. A reasonable estimate of a generation time in the neuroscience is 8-10years; a time window of >30 years seems therefore sufficient to judge the impact of publications on the field. Admittedly, by choosing to label as 'classic' signal works published at least 30 years ago, one surely minimizes the number of enemies among his or her contemporaries. But the latter argument is of course merely a fringe benefit. Not all selections of 'classic' publications in the life sciences follow the test-of-time rule. M.H. Green (1991) compiled 'classic' publications in molecular biology over the period 1958-88, i.e. up to 2-3 years earlier. Peters (1959) covered genetics during the period 1865-1955, i.e. up to 3-4years earlier. And Shaw etal. (1990), compiled a reprint volume of 82 influential publications in the neurobiology of learning and memory, including papers published only a year or two earlier. The stand taken here is that there is no need to rush.
The method of choosing 'classic' publications in science is another issue. One way is by vox populi, i.e. citations. This is now common in other areas of culture as well, e.g. poetry (Harmon 1998). However, citation indices have their own pitfalls, including the tendency to cite 'trendy spikes' or mundane methods in overcrowded fields. At the end of the day, selection of a short-list of'classics' in a scientific discipline boils down to a mix of a few unchallenged choices, strong professional "bias, and an unavoidable touch of idiosyncrasy. It does mean, of course, that different people will generate somewhat different lists (e.g. Baddeley 1994). But this only adds to the fun. Having said all that, here is a biased canonic list, limited "a priori to 10 items only, although a few additional ones are actually sneaked-in in the process. This selection unavoidably leaves aside very important publications by very influential authors, including, among others, Pavlov ("classical conditioning), Thorndike ("instrumental conditioning),
Skinner ("behaviourism), and Konorski (*plasticity).Yet the list does not refer to the corpus of authors, but rather to selected, individual papers or books; and in any case, one must make decisions, even if painful. The list is arranged chronologically:
1. St Augustine's philosophy of memory, book 10 in his autobiographical Confessions (~400). Augustine (354-430), a prominent Christian philosopher (Colish 1997), and a marvellous writer, composed his autobiography in the service of theology. Embedded in it is a gem of introspective psychology. Augustine was not the first in antiquity to write about memory,1 but his treatise is probably the most readable and surely the most poetic. Those who take the joy of reading Augustine's philosophy of memory, especially chapters 8-19 in book 10, will encounter reference to issues of "taxonomy, "metamemory, "binding, problems of "retrieval and "forgetting, imagery, and more. Augustine is included in this list to remind us that as far as the phenomenology of memory is concerned, although we have perfected it tremendously, we did not invent the wheel.
2. James' The principles of psychology (1890). The bible of Western psychology, James' tour de force still provides not only an object of intellectual admiration but also a rich source of inspiration. When many later works in psychology are analysed, they appear to contain "palimpsestic fragments that trace back to James. In three studies conducted to establish a consensual list of psychology's great books, polling colleges and professional psychologists, The principles received the highest rating (Norcross and Tomcho 1994).
3. Experimental study of the mental processes of the rat, by Small (1901). Fans and slaves of "mazes, please note: here it all started, in a small-scale model of the Londonian Hampton Court Labyrinth, copied from the Encyclopaedia Britannica (Fig. 46, p.156). This is a perfect example of the importance of matching a "subject with an "assay in the field of memory research. In such matching, ethology could always provide the guide to success: as Small put is, to rodents, maze experiments are 'couched in a familiar language'. Since then, mazes have become the most popular tool to measure the memory of the most popular species of laboratory animals.
4. Remembering, a study in experimental and social psychology by Bartlett (1932). This is the epitome of the attempt to understand human memory in real life. Bartlett became disappointed with the investigation of the memory of nonsense material under artificial conditions, a "paradigm introduced by Ebbingahus
(1885) at the birth of quantitative experimental psychology. Instead, he started to use "methods that unveil how the memory of meaningful items works in normal conditions and surroundings. 'Remembering is a function of daily life. So our memories are constantly mingled with our constructions, are perhaps themselves to be treated as constructive in character. It is true that they claim the confirmation of past, perceptual, personal experience; but the claim must not, psychologically speaking, be taken too seriously...' (Bartlett 1932,p. 16). It took almost half a century before this view has started to infiltrate the "zeitgeist of memory research at large ("false memory, "real-life memory, "retrieval). By the way, part I of Remembering is a source of inspiration for perceptual and memory experiments to try on family and friends.
5. Hebb's The organization of behavior (1949). Another holy scripture of modern neuroscience, and probably the most cited and influential publication on neural "plasticity and memory in the past 50 years. Judging by the trends in the field, it is likely to remain the most cited classic for generations to come. A uniquely coherent conceptual statement, The organization of behavior maintains an extensive dialogue with earlier literature (with primary sources as well as the excellent textbook of Hilgard and Marquis, 1940). The organization of behavior is mostly cited for two notions: "cell assemblies and their maturation, and, most of all, Hebb's postulate of learning ("algorithm). Hebb was rather astonished to see that this postulate gained so much popularity, as he himself did not consider it as his most original contribution (Milner 1986). Nevertheless, the crispness ofthe formulation, and its integration in a creative exposition of a theory of brain function, clearly justify the naming of the postulate as 'Hebbian'.
6. The formation of learning sets, by Harlow (1949). This is an outstanding example of the ability to extract new "levels of information from a seemingly simple experimental set-up. No big grants were required to make the breakthrough here. Harlow shows how by using discrimination tasks, one could unveil not only the ad-hoc "performance of the "subject, but also learn about the ability of that subject to learn how to learn and form rudimentary concepts ("learning set).
7. The magical number seven, plus or minus two: Some limits on our capacity for processing information, by Miller (1956). Here is a title that has become a legend. This work is a decedent of earlier attempts to quantify universals of human memory (e.g.
Ebbinghuas 1885; Jacobs 1887). It is anchored in the concepts and measures of information theory, and demonstrates that the brain is an information processing system of limited "capacity. Although Miller's intention was not to determine a precise value, his estimate of short-term memory capacity of seven-plus-or-minus-two chunks became almost a mantra (not without challenges; e.g. Baddeley 1994).
8. Loss of recent memory after bilateral hippocampal lesions, by Scoville and Milner (1957). This is the beginning of a major chapter in the research on "amnesia, on the role of medial temporal lobe in "consolidation and memory, and on the "taxonomy of memory. The real hero is the amnesic patient, H.M., unfortunately unaware of his profound continual role in modern neuroscience. The incentive for many studies on human amnesics, primate models of amnesia ("delay task, "monkey), and the role of the "hippocampus in learning, could be traced to Scov-ille and Milner's report. It is a classic case of a fruitful interaction of the clinic with basic research (Code et al. 1996; Corkin et al. 1997; Milner et al. 1998).
9. The information available in brief visual presentations, Sperling (1960). In this condensation of his Ph.D. thesis, a beautiful example of a smart and focused experimental design and execution, Sperling demonstrates the existence of an 'iconic memory' store, or "phase, which lasts for a fraction of a second to a few seconds at most. The giants on the shoulders of which this study is standing are duly accredited in the monograph, something to be longed for in many papers nowadays. Sperling's paper boosted the whole field of'immediate' or 'sensory' memory (for a perspective 40 years later, see Dosher and Sperling 1998).
10. This place is reserved to three papers, each published by an independent research team. These papers promoted what was later to become a most productive chapter in the molecular biology of learning: investigation of the role of macromolecular synthesis and growth in consolidation and long-term memory. Taken together, the studies of Flexner et al. (1963), Agranoff and Klinger (1964), and Barondes and Cohen (1966), have demonstrated that inhibition of protein synthesis during or immediately after training prevents the formation of long-term memory, without affecting short-term memory. These papers complement each other in their experimental details. They have paved the way to decades of research on neuronal proteins, genes, plasticity, and memory. By doing so, they have contributed remarkably to an important ingredient in the current neurobiological
zeitgeist (*CREB, *development, *immediate-early genes, *late response genes, *protein synthesis). Close contenders for this slot are McGaugh (1966), a well-cited epitome of the view that the *engram is not completed when training is over ^consolidation); and Kandel and Spencer (1968), a manifesto of the *reductionist, cellular approach to learning and a harbinger of the highly successful research program on Aplysia.
Naturally, because of the aforementioned self-imposed criterion of a 30-year moratorium on canonization, this list does not refer to many developments that have revolutionized memory research in recent years. It is indeed rather tempting to single out already at this stage some more recent papers, in disciplines ranging from molecular neurobiology to cellular physiology, neu-roanatomy, imaging, behaviour, and psychophysics, which are almost certain to withstand the test of time and compete for a respectable seat in the classics pantheon. At the same time, however, it is also tempting to suggest that many of the older papers cited above will retain their status in years to come. In the highly dynamic field of memory research, keeping the classics list short is bound to become only more and more difficult with time.
Selected associations: Bias, Culture, Insight, Paradigm, Persistence
1Two other notable examples are Aristotle's On memory, and Quintillian's On the education of the orator (first century ad; ^consolidation).
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