Mechanism, function, and computation in neural systems

• Mechanistic explanations rely on a balance between precision and abstraction that depend on the explanation's goals.
• Behavioral mechanisms are built from neural circuit computations, built in turn from algorithms, built from material.
• The myriad functions of the hippocampus and medial prefrontal cortex can be bounded by theories of computation.
• Overlapping functions of the hippocampus and prefrontal cortex are likely supported by different computations.

What constitutes a “mechanism” of behavior? In this tribute to Jerry Hogan we examine how questions of behavioral mechanism can be reframed as causes and consequences of neural circuit activity. Drawing from our work on the hippocampus and the medial prefrontal cortex we discuss the inherent difficulties of characterizing the behavioral functions of circuits that are many synapses away from sensory reception and motor/visceral expression. We briefly review the advantages of reframing a region's functions according to its computations, while also distinguishing those computations from the algorithms by which they are achieved. As an example of how these ideas can be applied, we discuss why the hippocampus and medial prefrontal cortex may have overlapping roles in memory expression in spite of being very different circuits. The present analysis draws inspiration from David Marr, whose framework for describing neural systems can be compared with Aristotle's “causes.” This article is part of a Special Issue entitled: In Honor of Jerry Hogan.