Optimal Endogenous Neural Noise Speeds Reaction Time

Objective: To determine whether the detection of weak visual stimuli is facilitated by a particular level of endogenous neural noise. Method: We measured the EEG while subjects responded to the occurrence of weak luminance increments. We used independent component (IC) analysis and dipole fitting to locate the neural sources of EEG responses to the stimuli in occipital, frontal, and temporal cortex. We then determined the relationship between the variability of the frequency-specific oscillations of the relevant neural sources in the 1 sec before stimulus presentation and the RT on hit (correct detection of the increment) trials. Results: An intermediate amount of power variability yielded the fastest RTs. This nonlinear relationship was found for occipital and frontal cortical sources and was strongest for theta (4- 8 Hz) and alpha (9-14 Hz) frequencies, but was also present for gamma (30-50 Hz) in frontal cortex. Conclusion: These results support the idea that an intermediate level of endogenous neural noise optimizes the brain’s response to a weak visual stimulus.