Encoding variable cortical states with short-term spikepatterns

Neurons in the primary somatosensory cortex (S1) generate synchronised high-frequency (∼600 Hz) bursts in response to peripheral stimulation, and single-cell activity is locked to themacroscopic 600 Hz EEG wavelets. The mechanism of burst generation and synchronisation in S1 is not yet understood. Using a Poisson model with refractoriness that was fitted to to unit recordings from macaque monkeys, we can explain the synchronisation of neurons as the consequence of coincident synaptic inputs, while their high firing precision stems from the large input amplitude combined with a refractory mechanism. This model reproduced also the distribution of temporal spike patterns over repeated presentation of the same stimulus. In addition, the fine temporal details of the spike patterns are representative of the trial-to-trial variations in population excitability and bear upon the mean population activity. The findings are confirmed in a more detailed computational model of a neuron receiving cortical and thalamic inputs through depressing synapses. Our findings show that a simple feedforward processing of peripheral inputs could give rise to neuronal responses with non-trivial temporal and population statistics. We conclude that neural systems could use refractoriness to encode variable cortical states into stereotypical short-term spike patterns amenable to processing at neuronal time scales.