A memory system in which new patterns are stored on top of previous ones

The term had originated from Greek palimpsestos, 'scraped again' (palin, again, + psestos, scraped). It seems to have occurred first in the writings of the Roman poet Catullus (Hammond and Scullard 1970). When vellum was scarce, especially in the early middle ages, early manuscripts were erased and the writing material used again. As the removal of the original writing was seldom complete, valuable religious and classical texts have been recovered from such palimpsests (Lewis and Gibson 1900; Cuddon 1979; Shailor 1988). For example, the important mathematical text called The method, by Archimedes, was discovered in Constantinople as a tenth century manuscript on leaves of parchment over which Eastern Orthodox prayers had been added in the thirteenth century (Boyer 1989).

'Palimpsest' has been used as a "metaphor for brain and mind by Romantic writers. 'What else than a natural and mighty palimpsest is the human brain? ... Everlasting layers of ideas, images, feelings, have fallen upon your brain softly as light. Each succession has seemed to bury all that went before. And yet... not one has been extinguished... Yes, reader, countless are the mysterious hand-writing of grief or joy which have inscribed themselves successively upon the palimpsest of your brain' (De Quincey 1866). Postulated palimpsestic properties of biological memory systems were also contemplated by Freud (1925). Similarly, Gestalt psychologists have proposed that new memory records are inscribed on top of old ones (Koffka 1935).1 'Palimpsest' resurfaced in modern neurosciences with the introduction of "models of artificial neural networks (Nadal et al. 1986; Amit 1989; Amit and Fusi 1994). In subclasses of such model networks, which keep a permanent "capacity for learning, new patterns are stored on top of old ones that get progressively erased (ibid.).2

Palimpsestic memory systems may be classified into two major conceptual classes. In the first, the new memory is an autonomous representation that displaces and nullifies the old one(s). This is a 'winner-takes-all' situation. In the second, the new pattern is superimposed on the old one(s) to yield a representation that is different from both old and new (here too, with repeated learning memories may ultimately be diluted to practical extinction, but they always leave a mark on younger representations). This latter version of the concept retains more faithfully the original connotation of a palimpsest.

Ample theoretical and experimental data support the second aforementioned process in brain, i.e. new experience interacts with previous ones to generate new "internal representations. For example, "percepts interact with endogenous brain activity at any given moment ('pre-representations'; Young 1979; Heidmann et al. 1984), activity that itself is expected to be at least partially experience dependent, to yield new patterns of brain activity (e.g. Arieli et al. 1996). If this

Fig. 53 A palimpsest fragment. A Hebrew script from the tenth/eleventh century, part of a Liturgical poem (Piyut), runs on a piece of coarse vellum across an older syriac text, a chapter of Deuteronomy from the tenth century (Lewis and Gibson 1900). The Hebrew letters faded until they have become of essentially the same hue as the older Syriac ones. In palimpsests like this one the different strata of the text are easily discerned. However, in some palimpsests the new text merges with the old one and occasionally a newer text emerges. This is the idea beyond 'palimpsest' in "models of memory.

Fig. 53 A palimpsest fragment. A Hebrew script from the tenth/eleventh century, part of a Liturgical poem (Piyut), runs on a piece of coarse vellum across an older syriac text, a chapter of Deuteronomy from the tenth century (Lewis and Gibson 1900). The Hebrew letters faded until they have become of essentially the same hue as the older Syriac ones. In palimpsests like this one the different strata of the text are easily discerned. However, in some palimpsests the new text merges with the old one and occasionally a newer text emerges. This is the idea beyond 'palimpsest' in "models of memory.

indeed is the case, substantial implications emerge for both philosophical and practical issues such as the degree of objectivity of percepts and knowledge, the role of "a priori knowledge in learning, and the fidelity of memories ("false memories, "real-life memory). It also reflects on the question whether memories could indeed be utterly "forgotten.

Selected associations: A Priori, Cell assembly, Experimental extinction, False memory, Retrieval

1For more on the Gestalt, see "binding, "insight. 2It is noteworthy that 'Palimpsest' found another modern use, in the critical theory of literature and culture, to denote the thesis that literary texts are rewritten versions of earlier texts, and hence writing is rewriting, e.g. Genette (1997).

Dealing With Sorrow

Dealing With Sorrow

Within this audio series and guide Dealing With Sorrow you will be learning all about Hypnotherapy For Overcoming Grief, Failure And Sadness Quickly.

Get My Free Audio Series


Post a comment