Neuroscience: Qualitative Overview of Population Neurodynamics

Neuroscience: Qualitative Overview of Population Neurodynamics

The estimates of the number of neurons in a cubic millimeter of cortex range from 104 to 106 and from 103 to 105 for the number of synaptic connections on each dendritic tree. The typical sensory input for a conditioned stimulus is carried by a parallel array of an immeasurably large number of receptor axons and the motor outflow for a typical conditioned response, a fraction of a second later, is carried in parallel by an immeasurably large number of motor axons. The networks of model neurons are constructed by induction that represent the actions of a small subset of neurons on the implicit assumption that what the other (unobserved) neurons are doing during a perceptual act or a conditioned reflex is not important for the activity of the observed subset. This approach might be called statistical mechanics of brain function, comparable to the study of molecules in an ideal gas in terms of their kinetic energy, position, and collision rates.