Short abstract
I argue that the popular neural coding metaphor is often misleading. First, the “neural code” often spans both the experimental apparatus and the brain. Second, a neural code is information only by reference to something with a known meaning, which is not the kind of information relevant for a perceptual system. Third, the causal structure of neural codes (linear, atemporal) is incongruent with the causal structure of the brain (circular, dynamic). I conclude that a causal description of the brain cannot be based on neural codes, because spikes are more like actions than hieroglyphs.
Long abstract “Neural coding” is a popular metaphor in neuroscience, where objective properties of the world are communicated to the brain in the form of spikes. Here I argue that this metaphor is often inappropriate and misleading. First, when neurons are said to encode experimental parameters, the neural code depends on experimental details that are not carried by the coding variable. Thus, the representational power of neural codes is much more limited than generally implied. Second, neural codes carry information only by reference to things with known meaning. In contrast, perceptual systems must build information from relations between sensory signals and actions, forming a structured internal model. Neural codes are inadequate for this purpose because they are unstructured. Third, coding variables are observables tied to the temporality of experiments, while spikes are timed actions that mediate coupling in a distributed dynamical system. The coding metaphor tries to fit the dynamic, circular and distributed causal structure of the brain into a linear chain of transformations between observables, but the two causal structures are incongruent. I conclude that the neural coding metaphor cannot provide a basis for theories of brain function, because it is incompatible with both the causal structure of the brain and the informational requirements of cognition.
