Carl F. Craver

Thinking about mechanisms

The concept of mechanism is analyzed in terms of entities and activities, organized such that they are productive of regular changes. Examples show how mechanisms work in neurobiology and molecular biology. Thinking in terms of mechanisms provides a new framework for addressing many traditional philosophical issues: causality, laws, explanation, reduction, and scientific change.

When mechanistic models explain

Not all models are explanatory. Some models are data summaries. Some models sketch explanations but leave crucial details unspecified or hidden behind filler terms. Some models are used to conjecture a how-possibly explanation without regard to whether it is a how-actually explanation. I use the Hodgkin and Huxley model of the action potential to illustrate these ways that models can be useful without explaining. I then use the subsequent development of the explanation of the action potential to show what is required of an adequate mechanistic model. Mechanistic models are explanatory.

Integrating psychology and neuroscience: functional analyses as mechanism sketches

We sketch a framework for building a unified science of cognition. This unification is achieved by showing how functional analyses of cognitive capacities can be integrated with the multilevel mechanistic explanations of neural systems. The core idea is that functional analyses are sketches of mechanisms, in which some structural aspects of a mechanistic explanation are omitted. Once the missing aspects are filled in, a functional analysis turns into a full-blown mechanistic explanation. By this process, functional analyses are seamlessly integrated with multilevel mechanistic explanations.

The Explanatory Force of Dynamical and Mathematical Models in Neuroscience: A Mechanistic Perspective

We argue that dynamical and mathematical models in systems and cognitive neuroscience explain (rather than redescribe) a phenomenon only if there is a plausible mapping between elements in the model and elements in the mechanism for the phenomenon. We demonstrate how this model-to-mechanism-mapping constraint, when satisfied, endows a model with explanatory force with respect to the phenomenon to be explained. Several paradigmatic models including the Haken-Kelso-Bunz model of bimanual coordination and the difference-of-Gaussians model of visual receptive fields are explored.

Interlevel Experiments and Multilevel Mechanisms in the Neuroscience of Memory

The dominant neuroscientific theory of spatial memory is, like many theories in neuroscience, a multilevel description of a mechanism. The theory links the activities of molecules, cells, brain regions, and whole organisms into an integrated sketch of an explanation for the ability of organisms to navigate novel environments. Here I develop a taxonomy of interlevel experimental strategies for integrating the levels in such multilevel mechanisms. These experimental strategies include activation strategies, interference strategies, and additive strategies. These strategies are mutually reinforcing, providing a kind of interlevel and intratheoretic robustness that has not previously been recognized.

Strategies in the interfield discovery of the mechanism of protein synthesis

Abstract In the 1950s and 1960s, an interfield interaction between molecular biologists and biochemists integrated important discoveries about the mechanism of protein synthesis. This extended discovery episode reveals two general reasoning strategies for eliminating gaps in descriptions of the productive continuity of mechanisms: schema instantiation and forward chaining/backtracking. Schema instantiation involves filling roles in an overall framework for the mechanism. Forward chaining and backtracking eliminate gaps using knowledge about types of entities and their activities. Attention to mechanisms highlights salient features of this historical episode while providing general reasoning strategies for mechanism discovery.

Mechanisms and natural kinds

It is common to defend the Homeostatic Property Cluster (HPC) view as a third way between conventionalism and essentialism about natural kinds (Boyd, 1989, 1991, 1997, 1999; Griffiths, 1997, 1999; Keil, 2003; Kornblith, 1993; Wilson, 1999, 2005; Wilson, Barker, & Brigandt, forthcoming). According to the HPC view, property clusters are not merely conventionally clustered together; the co-occurrence of properties in the cluster is sustained by a similarity generating (or homeostatic) mechanism. I argue that conventional elements are involved partly but ineliminably in deciding which mechanisms define kinds, for deciding when two mechanisms are mechanisms of the same type, and for deciding where one particular mechanism ends and another begins. This intrusion of conventional perspective into the idea of a mechanism raises doubts as to whether the HPC view is sufficiently free of conventional elements to serve as an objective arbiter in scientific disputes about what the kinds of the special sciences should be.

Future decision-making without episodic mental time travel

Deficits in episodic memory are associated with deficits in the ability to imagine future experiences (i.e., mental time travel). We show that K.C., a person with episodic amnesia and an inability to imagine future experiences, nonetheless systematically discounts the value of future rewards, and his discounting is within the range of controls in terms of both rate and consistency. Because K.C. is neither able to imagine personal uses for the rewards nor provide a rationale for selecting larger future rewards over smaller current rewards, this study demonstrates a dissociation between imagining and making decisions involving the future. Thus, although those capable of mental time travel may use it in making decisions about future rewards, these results demonstrate that it is not required for such decisions.

Dissociations in future thinking following hippocampal damage: evidence from discounting and time perspective in episodic amnesia.

Recollecting past experiences and imagining future experiences activate a common set of brain regions that includes the hippocampus (Schacter, Addis, & Buckner, 2007), and both functions are impaired in people with compromised hippocampal function (Klein, Loftus, & Kihlstrom, 2002; Tulving, 1985). These findings indicate a role for the hippocampus that extends beyond declarative memory. However, a case study revealed that a person with extensive medial temporal lobe (MTL) damage and episodic amnesia was able to forgo smaller, immediate rewards for a larger future payoff to a degree similar to control participants (Kwan et al., 2012). This finding suggests that typical regard for the future does not depend on hippocampal integrity. To test this hypothesis, the current study examined the nature and limits of the role of the hippocampus in future thinking and decision making in amnesic individuals with hippocampal damage and associated impairments in episodic memory and future imagining. The amnesic individuals were administered a delay discounting task to assess valuation of future rewards, a probability discounting task to assess risk taking, and the Zimbardo Time Perspective Inventory to assess personal orientation toward the past, present, and future. Comparisons with demographically matched controls indicated that aspects of temporal thought and future-oriented decision making are preserved in individuals with hippocampal amnesia despite their inability to imagine themselves in detailed future events. Thus, even extensive MTL damage and the resulting episodic amnesia do not preclude prudent decision making, including consideration of future financial outcomes and personal identification with the past and future.

Physical Law and Mechanistic Explanation in the Hodgkin and Huxley Model of the Action Potential

Hodgkin and Huxley’s model of the action potential is an apparent dream case of covering‐law explanation in biology. The model includes laws of physics and chemistry that, coupled with details about antecedent and background conditions, can be used to derive features of the action potential. Hodgkin and Huxley insist that their model is not an explanation. This suggests either that subsuming a phenomenon under physical laws is insufficient to explain it or that Hodgkin and Huxley were wrong. I defend Hodgkin and Huxley against Weber’s heteronomy thesis and argue that explanations are descriptions of mechanisms.