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Resumen Introducción. La comprensión del lenguaje está determinada por diversos procesos, entre los que se encuentra el reconocimiento léxico. Según el modelo conexionista, este reconocimiento se genera por activación mediante el emparejamiento de la información acumulada y por la inhibición de las entradas léxicas que compiten por activación. Objetivo. Determinar las diferencias temporales y espaciales de procesamiento entre las incongruencias léxicas semánticamente relacionadas a un contexto lingüístico oracional y las no relacionadas a través de mediciones electrofisiológicas de potenciales relacionados a eventos (PRE). Materiales y métodos. Se realizó la medición de los PRE en 10 sujetos sanos por medio de un paradigma de 240 oraciones en español agrupadas de la siguiente manera: 80 oraciones congruentes, 80 con incongruencias dentro del campo léxico y 80 con incongruencias fuera del campo léxico. Resultados. Se observó una diferencia estadística en la latencia de aparición del componente N400 entre las dos condiciones. Por su parte, se encontró una mayor activación del precúneo, del giro orbitofrontal, del giro angular y del giro supramarginal en la condición de incongruencia fuera del campo léxico. Conclusión. Se identificaron diferencias temporales y espaciales (activación del precúneo, del giro orbitofrontal, del giro angular y del giro supramarginal) entre el procesamiento de las incongruencias léxicas y no léxicas.

Abstract Introduction: Language understanding depends on several processes, including lexical recognition. According to the connectionist model, this recognition is generated by activation through the matching of accumulated information and by the inhibition of lexical entries that compete for activation. Objective: To determine, through electrophysiological measurements of event-related potentials (ERP), temporal and spatial processing differences between lexical inconsistencies semantically related to a sentence linguistic context and those that are unrelated. Materials and methods: ERPs were measured in 10 healthy subjects by means of a 240 Spanish sentences paradigm grouped as follows: 80 congruent sentences, 80 sentences with lexical incongruities, and 80 with non-lexical incongruities. Results: A statistical difference was found in the latency of appearance of the N400 component between both conditions. On the other hand, a greater activation of the precuneus, the orbitofrontal gyrus, the angular gyrus and the supramarginal gyrus was observed in the non-lexical incongruity condition. Conclusion: There are temporal and spatial (activation of the precuneus, the orbitofrontal gyrus, the angular gyrus and the supramarginal gyrus) differences between the processing of lexical inconsistencies and the processing of non-lexical inconsistencies.

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Neural entrainment is the synchronization of neural activity to the frequency of repetitive external stimuli, which can be observed as an increase in the electroencephalogram (EEG) power spectrum at the driving frequency, -also known as the steady-state response. Although it has been systematically reported that the entrained EEG oscillation persists for approximately three cycles after stimulus offset, the neural mechanisms underpinning it remain unknown. Focusing on alpha oscillations, we adopt the dynamical excitation/inhibition framework, which suggests that phases of entrained EEG signals correspond to alternating excitatory/inhibitory states of the neural circuitry. We hypothesize that the duration of the persistence of entrainment is determined by the specific functional state of the entrained neural network at the time the stimulus ends. Steady-state visually evoked potentials (SSVEP) were elicited in 19 healthy volunteers at the participants' individual alpha peaks. Visual stimulation consisted of a sinusoidally-varying light terminating at one of four phases: 0, π/2, π, and 3π/2. The persistence duration of the oscillatory activity was analyzed as a function of the terminating phase of the stimulus. Phases of the SSVEP at the stimulus termination were distributed within a constant range of values relative to the phase of the stimulus. Longer persistence durations were obtained when visual stimulation terminated towards the troughs of the alpha oscillations, while shorter persistence durations occurred when stimuli terminated near the peaks. Source localization analysis suggests that the persistence of entrainment reflects the functioning of fronto-occipital neuronal circuits, which might prime the sensory representation of incoming visual stimuli based on predictions about stimulus rhythmicity. Consequently, different states of the network at the end of the stimulation, corresponding to different states of intrinsic neuronal coupling, may determine the time windows over which coding of incoming sensory stimulation is modulated by the preceding oscillatory activity.

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The amplitude of auditory steady-state responses (ASSRs) generated in the brainstem of rats exponentially decreases over the sequential averaging of EEG epochs. This behavior is partially due to the adaptation of the ASSR induced by the continuous and monotonous stimulation. In this study, we analyzed the potential clinical relevance of the ASSR adaptation. ASSR were elicited in eight anesthetized adult rats by 8-kHz tones, modulated in amplitude at 115 Hz. We called independent epochs to those EEG epochs acquired with sufficiently long inter-stimulus interval, so the ASSR contained in any given epoch is not affected by the previous stimulation. We tested whether the detection of ASSRs is improved when the response is computed by averaging independent EEG epochs, containing only unadapted auditory responses. The improvements in the ASSR detection obtained with standard, weighted and sorted averaging were compared. In the absence of artifacts, when the ASSR was elicited by continuous acoustic stimulation, the computation of the ASSR amplitude relied upon the averaging method. While the adaptive behavior of the ASSR was still evident after the weighting of epochs, the sorted averaging resulted in under-estimations of the ASSR amplitude. In the absence of artifacts, the ASSR amplitudes computed by averaging independent epochs did not depend on the averaging procedure. Averaging independent epochs resulted in higher ASSR amplitudes and halved the number of EEG epochs needed to be acquired to achieve the maximum detection rate of the ASSR. Acquisition protocols based on averaging independent EEG epochs, in combination with appropriate averaging methods for artifact reduction might contribute to develop more accurate hearing assessments based on ASSRs.

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Generation of the auditory steady state responses (ASSR) is commonly explained by the linear combination of random background noise activity and the stationary response. Based on this model, the decrease of amplitude that occurs over the sequential averaging of epochs of the raw data has been exclusively linked to the cancelation of noise. Nevertheless, this behavior might also reflect the non-stationary response of the ASSR generators. We tested this hypothesis by characterizing the ASSR time course in rats with different auditory maturational stages. ASSR were evoked by 8-kHz tones of different supra-threshold intensities, modulated in amplitude at 115 Hz. Results show that the ASSR amplitude habituated to the sustained stimulation and that dishabituation occurred when deviant stimuli were presented. ASSR habituation increased as animals became adults, suggesting that the ability to filter acoustic stimuli with no-relevant temporal information increased with age. Results are discussed in terms of the current model of the ASSR generation and analysis procedures. They might have implications for audiometric tests designed to assess hearing in subjects who cannot provide reliable results in the psychophysical trials.

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OBJECTIVE: The maturation pattern of the envelope following response (EFR) was described using rats as an experimental model. DESIGN: EFRs were recorded in animals at different postnatal ages (15, 20, 25, 35, and 70 postnatal days) in response to broadband noise (BBN) and tones of 8000 and 4000 Hz modulated in amplitude using a continuous sweep of modulation frequencies. Responses were analysed in the 90-190 Hz modulation frequency (MF) range. STUDY SAMPLE: Forty individuals (eight individuals for each age bracket) were included in the present study. RESULTS: During maturation, the MF at which the maximum amplitude was obtained (BMF, best modulation frequency) shifted to higher values when animals were stimulated with tones. At the same time, the amplitude of the response at the BMF increased. For every group of animals, the amplitude of the response continuously decreased for MFs higher than the BMF. However, less steep decreases of amplitude were obtained as animals became adults. CONCLUSIONS: These results provide normative data regarding the maturation of the EFR in rats. They provide information for the development of predictor models to estimate the temporal resolution of the auditory system during maturation.

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