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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 (ß) 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 ß. 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 ß increased in the four leads; in Pre, ß 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.

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BACKGROUND: Berger related the EEG with cognition; we are attempting to identify which rhythms and circuits participate in habituation, a learning that decreases responses to meaningless stimuli which, changed the absolute power (AP) of EEG oscillations. OBJECTIVE: To characterize habituation, analyzing the AP of four rhythms in lateral regions of both hemispheres (BH), proposing that their diminution, desynchronization (D), means activation whereas their increase, synchronization (S), means inhibition. MATERIAL AND METHODS: qEEG analysis in 83 college students, in waking state with closed eyes, and photostimulated (RPh). The used UAMI/Yáñez software identifies RPh signals and takes 2-s samples before (Pre) and during RPh; the Welch periodogram integrates the AP of the four rhythms. We calculated the average AP (AAP) in Pre and RPh per frequency in bipolar lateral leads per hemisphere. AAP differences were evaluated with the Wilcoxon tests correcting with Bonferroni for repeated samples. Applying the linear regression model, we plotted the AAP distribution slopes during Pre and RPh. RESULTS: We established the differences of the AP of the four rhythms within each hemisphere and between both hemispheres (BH). During PRE, AAP of δ and θ increased whereas α and ß decreased. RPh increased the AAP (p = 0.01) of the four rhythms in fronto-frontal (FF) leads; the increase in δ persisted in fronto-temporal (FT) and temporo-occipital (TO), whereas ß's increase persisted in all leads. The AAP of α decreased with the first RPh (D) increasing with the following ones; its slope starts with desynchronization and ends with synchronization. Theta followed a D/S pattern in temporal leads. Beta followed and ascending (S) slope in all leads. CONCLUSIONS: Habituation results from the D/S of a in all cortical regions, of θ in temporal, of δ in frontal regions and ß in all regions. Synchronization reflects hyperpolarization of neuronal membranes, decreasing their activity.

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Las confabulaciones o “mentiras honestas” como las define Marcovich, constituyen un fenómeno complejo cuyo estudio y conceptualización ha ido evolucionando en el último siglo. Inicialmente se consideró a las confabulaciones como un fenómeno eminentemente amnésico con alteraciones principales en la recuperación de la información. Sin embargo la investigación de distintos cuadros clínico-patológicos, ha demostrado que en las confabulaciones interviene una amplia red de procesos cognoscitivos, involucrándose procesos tales como el funcionamiento ejecutivo, emociones, motivación y temporalidad; adicionándose a los subsistemas de memoria ampliamente descritos en la literatura. El presente trabajo constituye una revisión sobre los principales tipos y modelos explicativos de las confabulaciones así como de los avances en la neuropatología de las mismas. Asimismo, se realiza una breve descripción de las confabulaciones en algunos de los principales cuadros nosológicos como son el Síndrome de Korsakoff, la Enfermedad de Alzheimer y la esquizofrenia; resaltando las características compartidas y distintivas entre los distintos cuadros. En forma anexa se describe la relevancia de las emociones en la naturaleza y contenido de las confabulaciones como una posible forma adicional para su caracterización, conceptualización y comprensión. Por último se hace énfasis en la participación del neuropsicólogo durante el proceso de valoración y análisis clínico como parte fundamental en la exploración de rutina e investigación clínica.

The confabulations or "honest lies" as defined by Marcovich, are complex phenomena whose study and conceptualization has been changed in the last century. Initially it was thought confabulation as an eminently amnestic phenomenon with major alterations on the information retrieval; nevertheless, from the research in different clinical and pathological studies, today it is known that the confabulation involved an extensive network of cognitive processes such as executive functioning, emotions, motivation and temporality in addition to the memory subsystems widely described in the literature. The present work constitutes a review of the principal types and confabulation’s explanatory models, including also advances in the neuropathology of them. Likewise, there is a brief description of the confabulations in some of the main nosological tables such as Korsakoff's syndrome, Alzheimer’s disease and schizophrenia, highlighting the shared and distinctive features between them. It also describes the relevancy of emotions in the nature and content of the confabulations as a possible additional form for its characterization, conceptualization and understanding. Finally, it emphasizes the participation of neuropsychologist during clinical assessment as a fundamental part in the routine examination and clinical research.

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