Manuel Vázquez

Current Source Density Analysis of CNV During Temporal Gap Paradigm

The present report studied the contingent negative variation during Gap and Non-Gap conditions using visual stimulation and manual responses. The reaction times during the Gap condition were facilitated compared with those of the Non-Gap condition. The contingent negative variation component was obtained during the preparatory period from electrodes placed at 58 scalp sites for both Gap and Non-Gap conditions. The comparison between both conditions: Gap and non-gap did not show statistically significant differences during the preparatory period. The topography of the voltage and current source density maps showed three different foci: (i) an early negativity centred in electrodes overlying the supplementary motor area and cingulate motor areas, (ii) an activation over the primary motor cortex contralateral to the finger movement, and (iii) a bilateral activation on posterior sites. All these results suggest that the facilitation induced by the warning stimuli occurs in neural circuits that would be recruited for the subsequent processing of the imperative stimulus. The facilitation of the reaction times during the gap condition with respect to non-gap condition must be justified by neural events occurring during the gap period.

Frequency Analysis of the Eeg During Spatial Selective Attention

In this study, we recorded the event-related potentials (ERPs) elicited by stimuli appearing at attended and unattended locations. The voltage amplitudes and latencies of the P1, N1, P2, N2 and P3 visual components showed statistically significant differences in the attended condition with respect to the unattended one. The power spectral density of the EEG following stimulus onset was calculated. The difference between the spectral densities of the attended and unattended conditions was computed. Statistically significant differences were found in the decrease of alpha (9-11 Hz) and the increase of beta (15-17 Hz) frequencies during the attention condition with respect to the unattended condition. These results suggest that the arrival of a visual stimulus during the attended condition generates a complex reorganization of neuronal activity in both time and frequency domains.

Response latencies and event-related potentials during the gap paradigm using saccadic responses in human subjects

An experiment was conducted in naive human subjects to measure the time benefits of the latencies of saccadic eye movements to peripheral targets when the offset of a central fixation point precedes the switching on of the peripheral target by 200 ms. Naive subjects produced a shift advancement of the eye movement latencies to the targets with respect to when there is no such temporal gap. Simultaneously, the event-related potentials produced by visual stimuli and saccadic eye movements were recorded. The switching on of the central fixation point induced a negative component that could be considered a contingent negative variation. Subsequently, in the control non-gap condition visual evoked potentials and P300 appear. The temporal gap paradigm induced offset visual-evoked potentials and a frontal negativity; it also induced a higher P300 than the non-gap condition. The saccadic ERPs also showed a frontal negativity preceding the saccade during the gap condition. The results suggest that fast regular saccades during the gap paradigm occur by a priming of premotor and motor frontal circuits indexed by the recorded negativity during the gap paradigm.

GENDER DIFFERENCES IN EVENT-RELATED POTENTIALS DURING VISUAL-SPATIAL ATTENTION

The aim of present work is to test possible gender differences in the ERPs to the standards during the performance of a visual-spatial attention task. The sample: 20 subjects (10 women) aged 18-24. Electrodes: F3, F4, C3, C4, P3, P4, T5, T6, O1, O2. ANOVA tests were computed with the following factors: attention, gender, visual field, hemisphere, and electrodes. Results showed that men presented higher amplitudes in P1 and in P3b than did women, and women presented higher amplitudes in the temporal N1 than did men. For the P3, the amplitude in frontal-central regions for the attended condition was higher in men than in women, and men presented a gender-specific right frontal functional asymmetry that was not present in women. Since these components are related with the modulation of visual processing by the effect of spatial attention, the intra- and inter-gender differences obtained suggest possible differences in the processing of visual information in both genders. However, the fact that the brain generators could have a different orientation is also a possible explanation for the differences obtained in the ERPs in both genders

Cortical potentials during gap and non-gap paradigms using manual responses in humans☆

An experiment was conducted on naive human subjects to measure the time benefits on finger reaction times produced by the offset of a central fixation point 200 ms before the appearance of a target stimulus in the periphery. Subjects produced a shift advancement of manual reaction times. Simultaneously, the event-related potentials were recorded. The gap paradigm induced offset visual evoked potentials and a frontal negativity, it also induced a higher P300 than the non-gap condition. The results suggest that the gap promotes the speeding of the response by a cortical priming.

The gap effect during visual and auditory stimulation using manual responses

Six experiments were conducted in naive human participants to examine any facilitation produced in manual reaction time (RT) by the interposition of a temporal gap between a warning signal and an imperative signal. Peripheral visual stimuli and monoaural auditory stimuli were used as targets. Participants showed a facilitation of RTs to the targets for both auditory and visual stimuli in the five experiments in which RTs were the dependent variable. In addition, the gap effect increased over successive blocks of trials, suggesting learning. RTs were facilitated only when the gap had predictive value and was salient. Using a variable temporal gap or visual warning stimulus did not change the facilitation in RTs. A further experiment demonstrated that the gap can be perceived by the participants. The dissociation between a learned and a non-learned component in the gap effect suggests that the temporal gap induces two independent processes: warning and disengagement of attention.

Sensory and motor attentional modulation during the manual gap effect in humans: a high-density ERP study

Abstract. The present study investigated reaction time (RT) and event-related potential (ERP) differences between gap and step conditions using visual stimulation and manual responses. RTs during the gap condition were facilitated with respect to those of the step condition. The ERPs, which were obtained from electrodes placed at 58 scalp sites, showed differences when the gap and step conditions were compared for the following components: an early positive component centred at the vertex, an enhanced P1 component, a frontal negativity, a negative lateralized motor potential, and an increased P3. All these results suggest that the facilitation induced by the gap is mediated by a modulation of the neural circuits involved in sensory, motor, and cognitive functions.

Alternate response preparation in a visuomotor serial task.

The preparation of a particular motor pattern is related to the information available that enables the actor to predict the correct response to a forthcoming stimulus. In many situations, however, prediction is not possible. In such cases, the individual can guess the probable parameters of the next stimulus. The authors attempted to establish the bias in the motor intention for movement and its interaction with a possible memory trace of the stimulus-response mapping produced by the preceding stimulus. Two letters were presented bilaterally, and participants (N = 21) had to discriminate the target letter and respond with the compatible hand. The present findings support the existence of a memory trace of the previous stimulus-response mapping.

Significado funcional de los componentes de los potenciales evocados visuales en el proceso de atención al espacio y a los objetos

espanolEl proceso atencional permite seleccionar la informacion relevante. Un interrogante en este proceso cognitivo consiste en saber en que momento se realiza la seleccion dentro del procesamiento sensorial. Los estudios mediante Potenciales Evocados (PEs) han mostrado que los componentes primarios (P1 y N1) son modulados tanto por la seleccion espacial como por la del objeto. El objetivo del presente trabajo es estudiar la implicacion de los distintos componentes de los PEs en los mecanismos de atencion basados en el espacio y/o en el objeto mediante un paradigma de priming. Los resultados mostraron que la seleccion espacial modulaba la amplitud de P1, mientras que la seleccion por el objeto modulaba la de N1 y P2. El componente P3a mostro la interaccion del espacio y del objeto en el proceso de atencion. Se sugiere que el proceso atencional visual comienza la seleccion de la informacion usando claves espaciales y continua con mecanismos selectivos mas complejos basados en el espacio, en el objeto y en la interaccion de ambos. EnglishThe attentional process allows to select the relevant information. A query of this cognitive process is in what moment it is carried out the selection during the sensorial process. The studies by means of evoked potentials (ERPs) have shown that the early components (P1 and N1) are modulated by the space selection and/or by the object. The objective of the present work is the study of the implication of the different ERPs components in the mechanisms of attention for the space and for the object using a priming paradigm. The results showed that the space selection modulated the amplitude of the P1 while the selection for the form varied the amplitude of the N1 and P2 components. The P3a component showed the interaction of the space and object attention The conclusion of the present study is that the attentional visual process begins its selection of the information with space cues and it continues with refined selective mechanisms based on the space, object and its interaction