John Bickle

David Marr's three-level method for completely understanding a cognitive system and the importance he attaches to the computational level are so familiar as to scarcely need repeating. Fewer seem to recognize that Marr defends his famous method by criticizing the “reductionistic approach.” This sets up a more interesting relationship between Marr and reductionism than is usually acknowledged. I argue that Marr was correct in his criticism of the reductionists of his time—they were only describing, not explaining. But a careful metascientific account of reductionistic neuroscience over the past two decades reveals that Marr's criticisms no longer have force. Contemporary neuroscience now explains cognition directly, although in a fashion—causal-mechanistically—quite different than Marr recommended. So while Marr was correct to reject the reductionism of his day and offer an alternative method for genuinely explaining cognition, contemporary cognitive scientists now owe us a new defense of Marr's famous method and the advantages of its explanations over the type now pursued successfully in current reductionist neuroscience. There are familiar reasons for thinking that this debt will not be paid easily.

Over the past three decades, philosophy of science has grown increasingly “local.” Concerns have switched from general features of scientific practice to concepts, issues, and puzzles specific to particular disciplines. Philosophy of neuroscience is a natural result. This emerging area was also spurred by remarkable recent growth in the neurosciences. Cognitive and computational neuroscience continues to encroach upon issues traditionally addressed within the humanities, including the nature of consciousness, action, knowledge, and normativity. Empirical discoveries about brain structure and function suggest ways that “naturalistic” programs might develop in detail, beyond the abstract philosophical considerations in their favor. The literature distinguishes “philosophy of neuroscience” and “neurophilosophy.” The former concerns foundational issues within the neurosciences. The latter concerns application of neuroscientific concepts to traditional philosophical questions. Exploring various concepts of representation employed in neuroscientific theories is an example of the former. Examining implications of neurological syndromes for the concept of a unified self is an example of the latter. In this entry, we will assume this distinction and discuss examples of both.

A number of influences have combined to make reductionism an unpopular position in recent philosophy of mind and psychology. Davidson’s Principle of the Anomalousness of the Mental, the multiple realizability arguments of Putnam, Fodor, and others, and attempts to characterize supervenience or dependency as the appropriate nonreductive relation to seek between psychological and physical kinds are the most well-known objections. And these have found their mark. Being a psychophysical reductionist nowadays, as Jaegwon Kim aptly puts it, “is a bit like being a logical positivist or a member of the Old Left—an aura of doctrinaire naiveté hangs over such a person”.

Philosophers and psychologists seeking an accessible introduction to current neuroscience will find much value in this volume. Befitting the neuroscientific focus on sensory processes, many essays address explicitly the binding problem. Theoretical and experimental work pertaining to the “temporal synchronicity” solution is prominent. But there are also some surprising implications for current philosophical concerns, such as the intemalism/extemalism debate about representational content, epistemological realism, a “bottom-up” approach to naturalizing intentionality, Humean concerns about the self, and implications from phantom-limb phenomena. Higher-level theorists about the mind ignore results like these from current neuroscience at their own peril, at least from the point of view of discourse worthy of serious attention as the sciences of the mind/brain push forward into the 21st century.

Social cognition, cognitive neuroscience, and neuroethics have reached a synthesis of late, but some troubling features are present. The neuroscience that currently dominates the study of social cognition is exclusively cognitive neuroscience, as contrasted with the cellular and increasingly molecular emphasis that has gripped mainstream neuroscience over the past three decades. Furthermore, the recent field of molecular and cellular cognition has begun to unravel some molecular mechanisms involved in social cognition, especially pertaining to the consolidation of memories of particular conspecific organisms. Some new experimental techniques for positive interventions into these hypothesized mechanisms offer opportunities for establishing direct causal linkages between intra-neuronal molecular events and the behaviors used to measure social cognitive phenomena. Predicted results from an experiment described below also cast doubt on the application of the “extended mind” approach from recent cognitive science to ground the neuroscience of social cognition. Since neuroethics relies heavily on our best neuroscience of social cognition, that field may soon need to extend its attention beyond cognitive neuroscience, and into neuroscience’s cellular and molecular mainstream

This chapter argues that much discussion between philosophers and neuroscientists is infected by philosophical assumptions about the nature of reduction. Instead we should pursue an unbiased examination of the methods used throughout relevant areas of neuroscience. The chapter focuses on reductionist work in the neurobiological discipline of molecular and cellular cognition. It is argued that reduction is a matter of causal intervention into low level mechanisms, and tracking of the effects of these interventions through levels. When interventions provide evidence that activity in the proposed reductive mechanism co-varies reliably with activity in the target property, such that appealing to higher-level mechanisms will not add any extra explanatory power, reduction can succeed. This is explicitly contrasted with functionalisation and a posteriori approaches to reduction.

This book precis describes the motives behind my recent attempt to bring to bear “ruthlessly reductive” results from cellular and molecular neuroscience onto issues in the philosophy of mind. Since readers of this journal will probably be most interested in results addressing features of conscious experience, I highlight these most prominently. My main challenge is that philosophers (even scientifically-inspired ones) are missing the nature and scope of reductionism in contemporary neuroscience by focusing exclusively on higher-level cognitive neuroscience, and ignoring the discipline's cell-physiological and molecular-biological core.

In their review essay (published in this issue), Looren de Jong and Schouten take my 2003 book to task for (among other things) neglecting to keep up with the latest developments in my favorite scientific case study (memory consolidation). They claim that these developments have been guided by psychological theorizing and have replaced neurobiology's traditional 'static' view of consolidation with a 'dynamic' alternative. This shows that my 'essential but entirely heuristic' treatment of higher-level cognitive theorizing is a mistaken view of actual scientific practice. In response I contend that, on the contrary, a closer look at the memory reconsolidation following reactivation experiments and data suggests (1) a less revolutionary judgment about the proposed alternative, and (2) a now-complete reliance on ruthlessly reductive experimental methods from cellular and molecular neuroscience. These conclusions save the heuristic status I propose for higher-level investigations of behavior and brain. I close with a brief comment on their further charge that I 'sell out' philosophy of science to factual developments in science itself.

Psychoneural reduction is under attack again, only this time from a former ally: cognitive neuroscience. It has become popular to think of the brain as a complex system whose theoretically important properties emerge from dynamic, non-linear interactions between its component parts. ``Emergence'' is supposed to replace reduction: the latter is thought to be incapable of explaining the brain qua complex system. Rather than engage this issue at the level of theories of reduction versus theories of emergence, I here emphasize a role that reductionism plays – and will continue to play – even if neuroscience adopts this ``complex systems'' view. In detailed investigations into the function of complex neural circuits, certain questions can only be addressed by moving down levels and scales. This role for reduction also finds a place for approaches that dominate mainstream neuroscience, like the widespread use of experimental techniques and theories from molecular biology and biochemistry. These are difficult to reconcile with the anti-reductionist sentiments of the ``complex systems'' branch of cognitive neuroscience.

The structuralist program has developed a useful metascientific resource: ontological reductive links (ORLs) between the constituents of the potential models of reduced and reducing theories. This resource was developed initially to overcome an objection to structuralist ``global'' accounts of the intertheoretic reduction relation. But it also illuminates the way that concepts at a higher level of scientific investigation (e.g., cognitive psychology) become ``structured through reduction'' to lower-level investigations (e.g., cellular/molecular neuroscience). After (briefly) explaining this structuralist background, I demonstrate how this resource illuminates an actual, emerging scientific example: the link between the psychological concept of a ``consolidation switch'' from short-term to long-term memory and the cellular/molecular mechanisms of the transition from early- to late-phases of long-term potentiation (LTP) (an important type of synaptic plasticity in mammalian hippocampus and cortex).

Many believe that phenomenology is an uneasy fit with the notion that consciousness is simply produced by physical manipulations. This chapter takes one of the most provocative examples of this type of manipulation — cortical microstimulation leading to seemingly random conscious states such as the image of one's grandmother or a musical melody — and shows that such phenomena are not only consistent with Husserlian phenomenology, but actually underscore the importance of Husserl's careful distinctions. It guards against conflating ‘physical’ with ‘empirically observable’ by falling into the natural attitude and unwarrantedly equating the ‘perceived object’ with the corresponding ‘physical object’ that supposedly causes the perception, and then equating both of those with the ‘intentional’ object. There can be an intentional object with no physical object, and subserved only by a physical brain event. But this does not detract from the intentional meaning of the object-as-experienced. In this kind of example, it shows more clearly than ever Husserl's distinction between the noesis and the noema within each intentional experience.