Các phản ứng thần kinh, và mối quan hệ của nó với kích thích, là hoàn toàn được đặc trưng bởi sự phân bố xác suất của các lần tăng đột biến như là một chức năng của kích thích. Nếu thế hệ tăng đột biến có thể được mô tả như một quá trình | 34 Neural Encoding I Firing Rates and Spike Statistics independent-spike code correlation code independentneuron code Independent-Spike Independent-Neuron and Correlation Codes The neural response and its relation to the stimulus is completely characterized by the probability distribution of spike times as a function of the stimulus. If spike generation can be described as an inhomogeneous Poisson process this probability distribution can be computed from the time-dependent firing rate r t using equation . In this case r t contains all the information about the stimulus that can be extracted from the spike train and the neural code could reasonably be called a rate code. Unfortunately this definition does not agree with common usage. Instead we will call a code based solely on the time-dependent firing rate an independent-spike code. This refers to the fact that the generation of each spike is independent of all the other spikes in the train. If individual spikes do not encode independently of each other we call the code a correlation code because correlations between spike times may carry additional information. In reality information is likely to be carried both by individual spikes and through correlations and some arbitrary dividing line must be established to characterize the code. Identifying a correlation code should require that a significant amount of information be carried by correlations say as much as is carried by the individual spikes. A simple example of a correlation code would be if significant amounts of information about a stimulus were carried by interspike intervals. In this case if we considered spike times individually independently of each other we would miss the information carried by the intervals between them. This is just one example of a correlation code. Information could be carried by more complex relationships between spikes. Independent-spike codes are much simpler to analyze than correlation codes and most work on neural coding
