Abstract

Neural oscillations have been suggested to be involved in basic mechanisms which allow the synchronization of neural activity within and across brain regions. Neural entrainment has been defined as the synchronization of neural responses to an external stimulus. Perceptual detection of target stimuli presented right after the entrainment offset, depends on the time between the entrainment offset and the target presentation. These results suggested that entrainment persists after visual stimulation removal. We tested this hypothesis by characterizing the generation and persistence of steady-state visual evoked potentials (SSVEP) in 24 healthy volunteers. SSVEP were elicited by visual stimuli modulated in amplitude using the subject’s resting-state peak frequency. The electrophysiological signal was narrow-band filtered (± 1Hz around the entrainer frequency) and the envelope of the resulting signal was calculated using a Hilbert transform. The period between the stimulus offset and the time at which the brain oscillations returned to the pre-stimulus stage was defined as the duration of the entrainment persistence. Neural generators involved in the entrainment persistence were estimated using low resolution electromagnetic tomography analysis (LORETA). Our results demonstrate that visual entrainment can be generated using continuous amplitude-modulated sinusoidal stimulation. More important, visual entrainment can persist up to 400 ms after the stimulus offset, which corresponds to 4 cycles for 10-Hz stimulation. The neural entrainment was associated with the increased activation of the visual primary cortex (bilateral) and temporal and parietal areas involved in processing temporal and spatial visual information (left hemisphere). Occipital, temporal and parietal activations decreased after the entrainer offset. Nevertheless, significant increased activity of frontal areas was obtained during the persistence stage, mainly in the superior and medial frontal gyri. Our results suggest that persistence of the neural entrainment is mediated by fronto-occipital connections which might modulate the detection of target stimuli after the entrainer offset.