Browsing by Author "Bosman, Conrado A."

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    Functional differences of low- and high-frequency oscillatory dynamics during illusory border perception
    (ELSEVIER, 2010) Bosman, Conrado A.; Zamorano, Francisco; Aboitiz, Francisco
    Neuronal oscillations are an essential part of several brain processes like perception, memory and attention, but little is known about the simultaneous dynamics of different frequency bands in such processes. Here, we studied the low- and high-frequency dynamics of neuronal oscillations in a task that involves covert searching and visual perception of an illusory contour figure (Kanisza square). Subjects were cued to a particular region of the space, and then a matrix of illusory contour inductors appeared. Illusory contour could appear at the cued position, in a different position or not appear at all. We analyze the condition in which an illusory contour appears and those in which the illusory borders do not appear. During the visual perception of the illusory contour, we found a significant increase in a narrow and sustained gamma frequency band (55-65 Hz). We also found a transient increase in the theta band (4-10 Hz), 0.3 s after stimuli onset. This low-frequency power increase correlates strongly with the detection of the illusory contour and it is inversely correlated with the gamma-band response. When illusory contours were absent, a sustained low-frequency response in the same frequency range was present until appearance of the motor response. The intensity of this low-frequency power response was also related to the speed of the motor response. We hypothesize that theta and gamma interact to process different aspects of the task. Gamma would be related to perception of the stimuli, while theta would be involved in search mechanisms or the initiation of a motor response. (C) 2010 Elsevier B.V. All rights reserved.
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    Increase in Beta Power Reflects Attentional Top-Down Modulation After Psychosocial Stress Induction
    (Frontiers Media S.A., 2021) Palacios García, Ismael José; Silva, Jaime; Villena González, Mario Alejandro; Campos Arteaga, German Adolfo; Artigas Vergara, Claudio; Luarte, Nicolas; Rodriguez Balboa Eugenio Fernando; Bosman, Conrado A.
    Selective attention depends on goal-directed and stimulus-driven modulatory factors, each relayed by different brain rhythms. Under certain circumstances, stress-related states can change the balance between goal-directed and stimulus-driven factors. However, the neuronal mechanisms underlying these changes remain unclear. In this study, we explored how psychosocial stress can modulate brain rhythms during an attentional task and a task-free period. We recorded the EEG and ECG activity of 42 healthy participants subjected to either the Trier Social Stress Test (TSST), a controlled procedure to induce stress, or a comparable control protocol (same physical and cognitive effort but without the stress component), flanked by an attentional task, a 90 s of task-free period and a state of anxiety questionnaire. We observed that psychosocial stress induced an increase in heart rate (HR), self-reported anxiety, and alpha power synchronization. Also, psychosocial stress evoked a relative beta power increase during correct trials of the attentional task, which correlates positively with anxiety and heart rate increase, and inversely with attentional accuracy. These results suggest that psychosocial stress affects performance by redirecting attentional resources toward internal threat-related thoughts. An increment of endogenous top-down modulation reflected an increased beta-band activity that may serve as a compensatory mechanism to redirect attentional resources toward the ongoing task. The data obtained here may contribute to designing new ways of clinical management of the human stress response in the future and could help to minimize the damaging effects of persistent stressful experiences.