ISHPSSB 2001 || Quinnipiac University, July 18-22, 2001

Memories and Molecules: Long-Term Potentiation and the Mechanisms of Memory

An understanding of the neural mechanisms of memory would be an important first step towards understanding the neural mechanisms of the mind. So it is not surprising that there is considerable controversy over the putative role of Long-Term Potentiation (LTP), a well-known form of synaptic plasticity, in the neural mechanisms of learning and memory. This symposium includes presentations by both philosophers and scientists with a common interest in evaluating the link between LTP and learning and in assessing the conceptual and evidential burdens facing any such theory. Issues to be discussed include experimentation, explanation, mechanisms, reduction, and theory structure in contemporary neuroscience and its history.

Organized by: Carl Craver

John Bickle, University of Cincinnati
"Consolidation, Long-Term Memory, and the Molecular Mechanisms of Long-Term Potentiation (LTP): A Template for Psychoneural Reductions of the Genuinely Cognitive"
Most philosophers of mind and psychology still doubt that genuinely cognitive psychological theories will be "reduced" to neurobiological counterparts: especially to counterparts from cellular and molecular neurobiology. This attitude contrasts sharply with the reductive aspirations of "mainstream" neuroscience (e.g., the "Society for Neuroscience" crowd). In this talk I'll set aside the anti-reductionist arguments typically offered and the problem of specifying the nature of "reduction" at issue. Instead I'll present recent discoveries about the molecular mechanisms of long-term potentiation, an important type of synaptic plasticity known to occur in mammalian hippocampus, cortex, and cerebellum (among many other places). These discoveries, which include retrograde transmission (from post- to pre-synaptic neurons), second messenger cascades, and protein synthesis generated by transcription and translation processes in immediate early genes, provide an accomplished neurobiological reduction of the "consolidation switch" and "long-term memory" as characterized within cognitive psychology. This reduction thus provides both a methodological and a metascientific template for additional reductions of the "genuinely cognitive" to cellular and molecular events realized in neuroanatomical pathways and tracts.

Carl Craver, Florida International University
"Consolidating LTP: Interlevel Integration in the Making of a Memory Mechanism"
The mythology surrounding the discovery of Long-Term Potentiation (LTP) has it that LTP was discovered in a reductionistically motivated experiment designed to test a hypothesis about the cellular mechanisms of memory. This myth is not only historically inaccurate; it also presents a misleading version of both discovery and theory construction in neuroscience. A more careful historical investigation reveals that the discovery of LTP was constituted by a gradual and piecemeal attempt to turn a well-known laboratory technique into piece of neuroscientific ontology. This transformation was affected by trying to integrate LTP both into lower-level molecular mechanisms (of the sort investigated by, e.g., Lynch) and into higher-level mechanisms (of the sort investigated by, e.g., Milner). This view of the history of LTP contextualizes debates over the place of LTP in learning and memory as an important upward-looking component of an interlevel theory construction process. It is only by neglecting this upward-looking component that reductionist visions of the LTP research program can appear plausible. The LTP research program, I submit, has been driven by the bidirectional goal of integrating levels (both higher and lower) into a multilevel mechanistic hierarchy rather than the unidirectional goal of reducing higher levels to ever lower levels. [ E-mail author for copy of paper ]

Louis Matzel, Rutgers University Piskataway
"Are the Biophysical Constraints on Long-Term Potentiation Compatible with the Parameters of Memory?"
Long-term potentiation (LTP) displays certain neurophysiological characteristics that are commonly cited as evidence that this form of neuronal plasticity subserves the induction and/or storage of associative memories. In particular, the associative nature (induction by conjoint pre- and postsynaptic activity) and temporal constraints on LTP, as well as its seeming persistence, suggest certain qualitative similarities between LTP and the processes that characterize associative memory. However, upon closer inspection, the actual biophysical constraints on LTP indicate that it is incompatible with the parameters of memory induction or maintenance. Here we will review evidence relevant to this incongruence, and suggest a parsimonious resolution to the problem.

Maurice Schouten, Vrije Universiteit
"Causal-Mechanical Explanations of Memory"
It has recently been suggested that the reduction of memory to molecules may already be a fait accompli. In particular, Long-Term Potentiation (LTP), and the molecular mechanisms underlying it, may (reductively) explain the psychological phenomena of learning and memory (L&M). While lower-level investigations contribute significantly to our understanding of L&M, I will also suggest that acknowledging the importance of such cross-level explanations does not in the end add up to what might be called Causal-Mechanical (C/M) Reductionism. In order to make my point, I will employ Peter Railton's notion of an "Ideal Explanatory Text". The Ideal Explanatory Text is roughly the full (law-based) causal-mechanical account of all the processes that resulted in the explanandum. Although the Ideal Explanatory Text is important as a determinant of what Railton calls "explanatory information", I will argue that it is not exhaustive of it. An important point is that in furnishing scientific explanations pragmatic considerations enter the picture. To some extent, I will here follow Van Fraassen (1981) and Garfinkel (1980). Explanation consists in concentrating attention on certain features and parts of the causal net, and this process is, to some extent, influenced by context-sensitive factors. In explanation, choices are constantly being made about what to vary and what to keep constant, that is, about where to draw the line between cause and condition. However, whereas Van Fraassen mainly emphasizes the importance of theory-external factors for making salient partitions in the causal web, I will suggest that the explanatory process appears to be driven by objective constraints. As these constraints are found across a number of levels, it can be argued that L&M research is not a show case for causal-mechanical reductionism.

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