Spontaneous activity competes externally evoked response in sensory cortex

The activity state of neuronal populations is key to understanding information processing in the brain. Most of our knowledge about sensory processing and perception comes from studying local changes in firing rates and local field-potentials (LFP) evoked by external stimuli. However, most of the cortical activity is generated intrinsically, can originate spontaneously in almost any cortical area, and spreads globally. The relationship between spontaneous activity and perception is largely unclear. Here we show that high levels of spontaneous activity in the beta-band (15-30 Hz) predict reduced detection, and that this influence can be overridden by stimulus-intensity adjustment. We found that vibro-tactile stimulation of the forepaw of behaving rats evokes a robust modulation of event-related field potentials and firing rates, reflected in power in low (3-10 Hz) and high (95-120 Hz) frequencies of the LFP, independent of detection. Only beta shows higher power prior and during undetected stimuli, and anti-correlates with firing rate. LFP oscillations in 15-120 Hz appear as short-high-power bursts, and by applying burst-rate detection algorithm in real-time, we found that changing the vibration amplitude according to beta-burst-rate can adjust beta’s impact on detection bi-directionally. This result is supported by the finding that while in all bands bursts indicate transient synchronization of cell assemblies, only beta bursts are followed by a reduction in firing rate. Our results reveal that beta-bursts reflect increased spontaneous synchrony and predict reduced detection, suggesting a dynamic state that competes with the detection of external stimuli.