Synaptic transmission in the neocortex is dynamic, such that the magnitude of the post-synaptic response changes with the history of the pre-synaptic activity. Therefore, each response carries information about the temporal structure of the preceding pre-synaptic input spike train. We quantitatively analyze the information about the previous inter-spike intervals, contained in single responses of dynamic synapses, using methods from information theory applied to phenomenological models of depressing and facilitating synapses. We show that for any given dynamic synapse, there exists an optimal frequency of pre-synaptic spike firing for which the information context is maximal; simple relation between this optimal frequency and the synaptic parameters is derived. Depressing neocortical synapses are optimized for coding temporal information at low firing rates of 0.5-5Hz, characteristic for the spontaneous activity of cortical neurons, and carry significant information about the timing of up to four preceding pre-synaptic spikes. Facilitating synapses, on the other hand, are optimized for higher pre-synaptic rates of 9-70Hz and can represent the timing of over 8 pre-synaptic spikes.