How to find decision makers in neural circuits?

Neural circuits often face the problem of classifying stimuli into discrete groups and making decisions based on such classifications. Neurons of these circuits can be distinguished according to their correlations with different features of stimulus or response, which allows defining sensory or motor neuronal types. In this study we define the third class of neurons, which is responsible for making decision. We suggest two descriptions for contribution of units to decision making: first, as a spatial derivative of correlations between neural activity and the decision; second, as an impact of variability in a given neuron on the response. These two definitions are shown to be equivalent, when they can be compared. We also suggest an experimental strategy for determining contributions to decision making, which uses electric stimulation with timevarying random current.