Desynchronization/synchronization of parasagittal EEG rhythms during habituation to photostimulation in adults.

INTRODUCTION Learning by habituation implies a gradual diminution of the organism's responses to non-relevant stimuli. These responses, resulting from electrical oscillations of the brain, can be analyzed through quantitative electroencephalography (qEEG). OBJECTIVE To characterize the absolute power (AP) in the range of delta (δ), theta (θ), alpha (α), beta (β) in cortical parasagittal regions during habituation to photostimulation (RPh). MATERIAL AND METHODS We studied 81 undergraduate students. The EEG was recorded in a Nicolet; awake subjects with closed eyes were photostimulated (5 Hz for 2 s, 20 times, RPh). The UAMI/Yáñez program identifies the RPh signal, chooses and collects 2-sec samples before (Pre) and during RPh, and instruments the Welch periodogram, which integrates the absolute power (AP) of δ, θ, α, and β. We calculated the average AP (AAP) in Pre and RPh per frequency and lead. AAP differences were assessed with non-parametric tests. Linear regression was used to plot the AAPs of each Pre and each RPh sample, representing the resulting slope with its statistical significance. RESULTS RPh increased the AAP of δ in frontal and frontocentral leads of both hemispheres, and its slopes were ascendant. AAP of θ increased in fronto-frontal and diminished in the other three leads, its slopes were ascendant in right central parietal and parieto-occipital leads. AAP of α increased in fronto-frontal leads, did not change in fronto-central, and diminished in the other leads; its slopes were descendent in Pre and ascendant in RPh in both hemispheres. AAP of β increased in the four leads; in Pre, β slopes were descendent in parieto-occipital leads of both hemispheres. During RPh, δ slopes were ascendant in right parieto-central and in both parieto-occipital leads. CONCLUSION The progressive diminution of alpha's desynchronization, which ends in synchronization, is probably due to hyperpolarization of neuronal membranes and represents habituation. This is complemented with synchronization of the delta rhythm in anterior cortical areas and of theta and beta in areas of the right hemisphere.