Effets de privations sélectives en sommeil lent et en sommeil paradoxal sur l'attention automatique et sélective

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Capturing with EEG the neural entrainment and coupling underlying sensorimotor synchronization to the beat

Synchronizing movements with rhythmic inputs requires tight coup- ling of sensory and motor neural processes. Here, using a novel ap- proach based on the recording of steady-state-evoked potentials (SS-EPs), we examine how distant brain areas supporting these pro- cesses coordinate their dynamics. The electroencephalogram was recorded while subjects listened to a 2.4-Hz auditory beat and tapped their hand on every second beat. When subjects tapped to the beat, the EEG was characterized by a 2.4-Hz SS-EP compatible with beat-related entrainment and a 1.2-Hz SS-EP compatible with movement-related entrainment, based on the results of source analy- sis. Most importantly, when compared with passive listening of the beat, we found evidence suggesting an interaction between sensory- and motor-related activities when subjects tapped to the beat, in the form of 1) additional SS-EP appearing at 3.6 Hz, compatible with a nonlinear product of sensorimotor integration; 2) phase coupling of beat- and movement-related activities; and 3) selective enhancement of beat-related activities over the hemisphere contralateral to the tapping, suggesting a top-down effect of movement-related activities on auditory beat processing. Taken together, our results are compati- ble with the view that rhythmic sensorimotor synchronization is sup- ported by a dynamic coupling of sensory and motor related activities

Capturing with EEG the neural entrainment and coupling underlying sensorimotor synchronization to the beat

Synchronizing movements with rhythmic inputs requires tight coupling of sensory and motor neural processes. Here, using a novel approach based on the recording of steady-state-evoked potentials (SS-EPs), we examine how distant brain areas supporting these processes coordinate their dynamics. The electroencephalogram was recorded while subjects listened to a 2.4-Hz auditory beat and tapped their hand on every second beat. When subjects tapped to the beat, the EEG was characterized by a 2.4-Hz SS-EP compatible with beat-related entrainment and a 1.2-Hz SS-EP compatible with movement-related entrainment, based on the results of source analysis. Most importantly, when compared with passive listening of the beat, we found evidence suggesting an interaction between sensory- and motor-related activities when subjects tapped to the beat, in the form of 1) additional SS-EP appearing at 3.6 Hz, compatible with a nonlinear product of sensorimotor integration; 2) phase coupling of beat- and movement-related activities; and 3) selective enhancement of beat-related activities over the hemisphere contralateral to the tapping, suggesting a top-down effect of movement-related activities on auditory beat processing. Taken together, our results are compatible with the view that rhythmic sensorimotor synchronization is supported by a dynamic coupling of sensory and motor related activities

Optimal Eye-Gaze Fixation Position for Face-Related Neural Responses

<div><p>It is generally agreed that some features of a face, namely the eyes, are more salient than others as indexed by behavioral diagnosticity, gaze-fixation patterns and evoked-neural responses. However, because previous studies used unnatural stimuli, there is no evidence so far that the early encoding of a whole face in the human brain is based on the eyes or other facial features. To address this issue, scalp electroencephalogram (EEG) and eye gaze-fixations were recorded simultaneously in a gaze-contingent paradigm while observers viewed faces. We found that the N170 indexing the earliest face-sensitive response in the human brain was the largest when the fixation position is located around the nasion. Interestingly, for inverted faces, this optimal fixation position was more variable, but mainly clustered in the upper part of the visual field (around the mouth). These observations extend the findings of recent behavioral studies, suggesting that the early encoding of a face, as indexed by the N170, is not driven by the eyes <i>per se</i>, but rather arises from a general perceptual setting (upper-visual field advantage) coupled with the alignment of a face stimulus to a stored face template.</p></div

Heat maps for upright and inverted faces.

<p>Values of the heat maps indicate the relative strength of N170 response as a function of viewpoint (left). Bootstrap analysis was applied on the heat maps up to a p = 0.05 significance threshold (right).</p

N170 ERP responses over PO7 and PO8 scalp sites are shown as a function of eye-gaze landing positions on face stimuli.

<p>(<b>a.</b>) N170 responses recorded at fixated face regions of interest (fROIs) in upright and inverted face images. (<b>b.</b>) N170 responses elicited by fixated face regions along the vertical meridian (upper in green, middle in red, and lower in blue) in upright and inverted face images. (<b>c.</b>) N170 responses elicited by fixated face regions along the horizontal meridian (left and right visual fields).</p

Reconstruction of the time course of sources active during the N170 evoked potential using the MEM technique.

<p>Bilateral sources found in the inferior temporal gyrus exhibit higher amplitude in response to fixations at the eyes of upright faces, and at the mouth of inverted faces.</p