An open problem a mystery

Science is driven by the unknown as much as by the known, and therefore, noting enigmas is often as useful as listing facts (ainos, Greek for 'fable', ainigma, 'to speak in riddles'). Below is a list of 10 enigmas of memory. Some refer to baffling concepts, others to technological shortcoming, and most to both. Although many investigators may agree with much of the choice, some may not. Scientific enigmas tend to reflect the "bias of their compiler. The reader is fully encouraged to expand or shrink the list unabashedly. But at least, it is a starting point.

1. What are the neuronal codes of "internal representations? This is a central issue not only in memory research, but in neuroscience at large. Without knowing in detail how models of the world are encoded in the brain, there is little hope in providing answers to many of the questions that follow.

2. What are the computational and physical changes that take place in internal representations in "acquisition and "consolidation of memory? Which of these changes are obligatory for long-term memory? Many alterations are detected in the brain after training, at the molecular, "synaptic, cellular, and "system "levels. Yet some of these alterations may not directly relate to experience-dependent modifications in internal representations (e.g. some could subserve "homeostasis). Are we currently pursuing the processes and mechanisms that are really relevant ("criterion)?

3. How are internal representations retained over time in spite of massive synaptic remodelling in the brain ("persistence)? Furthermore, there is some evidence for turnover of neurons in the mature brain ("bird-song, "hippocampus); if so, how is it that new cells integrate into existing circuits without disrupting old memories? Or do they?

4. How is complex information "retrieved from memory, frequently within a fraction of a second? And how much of retrieval is reconstruction, sometimes with doubtful faithfulness ("false memory)?

5. How much of our knowledge about the external world is due to selection by experience of pre-representations, generated by the endogenous activity of the brain? In other words, how much of our world models is encoded in our brain "a priori, and to what degree can we indeed master truly novel information and concepts?

6. Do all "percepts and thoughts leave a lingering trace in memory? If so, will we be able to tap into the latent information? Similarly, will we be able to restore "engrams once they become unretrievable?

7. Will we be able to increase significantly the physiological "capacity and performance of our memory? Will it be done by pharmacology ("nootropics), by genetic engineering ("neurogenetics), or by bionics, based on the integration of nano-chips with the central nervous system (Moravec 1988; Kuwana etal. 1995; Maher etal. 1999; Weng etal. 2001)?

8. Will we ever be able to download memories directly to and from the Web, in a non-invasive manner, hence linking our brain to a gigantic, global memory 'syncytium'? This will surely provide the term "collective memory with a new meaning. If the possibilities raised here, as well as in 7 above, ever materialize, what will be the biological, emotional, cognitive, and social price for the species and for the individual?

9. Will new types of memory systems evolve in our brain? A great variety of memory systems have already emerge in evolution, each time presumably to comply with the updated needs of the species. These systems include, among others, memory for

"skills, for space, for language, for facts, for events, for the self ("taxonomy). Some of these systems may have evolved at first in response to a certain selective pressure but later became adapted to new needs or even paved the way to new faculties and capabilities. Will new memory systems emerge to cope with the new technological environment, what will their capabilities be, and which new opportunities will they open for brain and behaviour? 10. And, finally: What is consciousness ("conscious awareness)? Similarly to enigma 1 above, this issue definitely transcends memory research, yet is intimately related to the function and mechanisms of "declarative, particularly "episodic memory, and to the role of "attention and memory in the "binding of our personality over time. Furthermore, to what degree are other species consciously aware of themselves and the world ("anthropomorphism)? Will we ever be able to really know what is it like to be a bat (Nagel 1974)? And will smart robots (Moravec 1988, Weng et al. 2001) or neuro-silicon hybrids (Kuwana et al. 1995; Maher et al. 1999) become conscious as we are? Will they have episodic, autobiographical memory, and what will it mean to them?

Scientific enigmas are there to be tackled (Duncan and Weston-Smith 1977; Doty 1998). Judging by the remarkable pace of memory research, solutions to some of the aforementioned riddles may become common knowledge sooner than imagined. Other problems, such as the consciousness one, may at the end of the day be resolved formally but resist intuition ("dimension). Note also that what an enigma is, depends on the level and resolution of the analysis. For a molecular neurobiologist, the "developmental regulation of an ion channel is a pressing enigma, as is the physiological relevance of the fMRI (functional magnetic resonance imaging) signal for the "functional neuroimaging expert. Hence, in addition to the aforementioned 'macro-enigmas', many 'micro-enigmas' are hidden in various subdisciplines of memory research. Whether they should be dubbed 'enigma' or simply 'open questions' or 'research objectives', is a matter of taste.

Before concluding, we should also remember that there is an additional type of enigma: that of not yet knowing that we do not yet know. Identifying new dimensions opens new vistas that unveil new enigmas. Even what is now deemed by us as almost trivial and even boring, may with time become a source of wonder and inspiration, if we only come to see it under fresh light. As the English author G.K. Chesterton remarked almost a century ago (cited in Gratzer 1996): 'Is ditch-water dull? Naturalists with microscopes have told me that it teems with quiet fUn'.

Selected associations: Classic, Criterion, Culture, Dimension, Homo sapiens

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