Regulation of spike timing in visual cortical circuits

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Abstract
In vitro, precise and reliable spike trains are obtained in response to fluctuating current waveforms injected at the soma. For aperiodic currents this is called stimulus locking; for periodic currents it is called phase locking. Across trials, stimulus-locked spike trains contain multiple distinct spike patterns that can be uncovered using analysis procedures based on clustering. In vivo, output spike trains reflect the interaction that occurs between stimulus-locked inputs and oscillatory inputs that are generated internally. As a result, precise and reliable spike trains can sometimes be obtained in response to time-varying stimulus waveforms (when the spikes are aligned to stimulus onset), or in response to cortical oscillations (when the spikes are aligned to the oscillation phase). Stimulus or phase-locked spike trains across multiple neurons can lead to synchronous spike volleys, which can propagate efficiently through dendritic action potentials that pass through the different layers of the cortex. Inhibitory interneurons can coordinate synchronous volleys in pyramidal cells. Dynamically modulated oscillations can support a flexible system for communicating through spike volleys in parallel with neural codes based on firing rates. Slow cortical oscillations set the excitability of neurons and gate the amplitude of the fast oscillations, whereas fast inhibitory oscillations can gate spike volleys or shift their time.