Memory, Consciousness, and the Brain

The end of the second millennium has coincided with significant progress in the understanding of human memory. Since the late 1950s, modern neuropsychological research has provided a considerable amount of data concerning the relation between mnesic phenomena and their neural correlates. Based on clinical and experimental observations, new concepts have been introduced and old concepts have been reformulated. Implicit expression of knowledge, or implicit memory (Milner, 1958; Warrington & Weiskrantz, 1968), short-term memory and working memory (Baddeley & Hitch, 1974), the distinction between semantic and episodic memory, among others, are now widely accepted notions. Indeed the very idea that memory is not a unitary system but one that reflects rather the interaction of different memory systems or of different memory processes probably represents the greatest achievement of the past fifty years of neuropsychological research on memory. However, the progress in the understanding of memory phenomena led to the flourishing of a number of theories and models of memory which almost invariably contain both an omission and a paradox. It is clear that any theory of memory must contain a presupposition concerning the past and its nature, since memory by definition is memory of the past. However, you can read paper after paper or book after book without finding any direct discussion or even assumption on what should be one of the very concerns in theories of memory, i.e. the nature of the past and how this is represented in our brains. The result of this omission is the paradox of the memory trace of which many theories of memory are victim. An assumption common to many old and new theories on memory is that of considering a memory as the result of the preservation of the past in the organism which remembers. Accordingly, if I now perceive an event or ob-