Effects of the synaptic transmission's dynamics on possible neural codes.

To examine the effects of paired pulse facilitation, long-term synaptic modifications as well as spike frequency adaptation on neural signal transmission, a simple model was applied. This way various input-output properties of the model units were described. Particularly, the transmission of the mean and S.D. of the simulated synaptic currents were studied. The results indicate that the transfer of the mean value of the membrane currents cannot be described in terms of synaptic weights. So firing rate can hardly be an efficient neural code, especially for adaptive channels of the central nervous system (CNS). On the contrary, the transfer of S.D. of synaptic currents behaves in accordance with the synaptic weights. So it is supported that S.D. of the synaptic currents is a biological relevant subclass of the variation codes [see Perkel, H., Bullock, T.H., 1968. Neurol coding. Neurosci. Res. Program Bull. 6, 221-344]. It is discussed how this code can be established and how it works.