Creating a nuisance to probe the neural code

A major objective of neuroscience is to understand the neural code, namely how the patterns of neuronal signals (e.g. action potentials, membrane potential, calcium concentrations) “represent” physical objects, commands for actions, or psychological phenomena. An successful neural coding scheme has to be robust to noise (i.e. random neuronal activity). We have recently shown that using a small perturbation, an introduction of one “extra”-spike to the activity of a single neuron in the cortex, and studying the consequence of that perturbation we can obtain bounds on the level of noise in the cortex. Theoretical analysis of the data indicates that intrinsic, stimulus-independent variations in membrane potential of cortical neurons are on the order of 2.2–4.5 mV—variations that are pure noise, and so carry no information at all. Such level of noise places severe limitations on the plausibility of neural code based on precise spike timing. Using recent advances in optogentics we can extend the approach of introducing a precisely controlled perturbation. We explore how these perturbations affect the dynamics of activity in the cortex as well as theirs effect on animal performance on a task, to gain further bounds and insights on the neural code.