Traveling EEG slow oscillation along the dorsal attention network initiates spontaneous perceptual switching

An ambiguous figure such as the Necker cube causes spontaneous perceptual switching (SPS). The mechanism of SPS in multistable perception has not yet been determined. Although early psychological studies suggested that SPS may be caused by fatigue or satiation of orientation, the neural mechanism of SPS is still unknown. Functional magnetic resonance imaging (fMRI) has shown that the dorsal attention network (DAN), which mainly controls voluntary attention, is involved in bistable perception of the Necker cube. To determine whether neural dynamics along the DAN cause SPS, we performed simultaneous electroencephalography (EEG) and fMRI during an SPS task with the Necker cube, with every SPS reported by pressing a button. This EEG–fMRI integrated analysis showed that (a) 3–4 Hz spectral EEG power modulation at fronto-central, parietal, and centro-parietal electrode sites sequentially appeared from 750 to 350 ms prior to the button press; and (b) activations correlating with the EEG modulation traveled along the DAN from the frontal to the parietal regions. These findings suggest that slow oscillation initiates SPS through global dynamics along the attentional system such as the DAN

Necker cube reversals during long-term EEG recordings: Sub-bands of alpha activity

Reversible figures, such as the Necker cube, make tip a well-known class of visual phenomena in which an invariant stimulus pattern gives rise to at least two different perceptual interpretations. A better understanding of the neurophysiological processes underlying perceptual reversals might help to disentangle bottom-up from top-clown influences on multistable perception. Recently, we reported alpha activity decrease during multistable visual perception. The aim of the present study was to define more specifically the functional roles of the EEG alpha hand during the perception of Necker cube reversals by Subdividing the extended alpha band into three sub-bands (lower-1 alpha, lower-2 alpha, upper alpha). We employed a long-term recording condition, during which 10 healthy participants observed the Necker cube for approximately 60 min and responded by pressing a button to any perceived reversal. The results showed a reversal induced alpha desynchronization for the lower alpha hands, with the lower-2 alpha clesynchronization differing across the time course of the experiment. The upper alpha band demonstrated no reliable effects. It is concluded that the lower-1 alpha desynchronization reflects ail automatic arousal reaction which triggers attentional processing in a bottom-up manner, whereas the lower-2 alpha desynchronization is related to attentional processes that are achieved by top-down control with limited resources. The lack of reliable effects ill the Upper alpha hand is presumably due to the relatively low semantic task demands in Figure reversal. (c) 2005 Elsevier B.V. All rights reserved

Auditory on- and off-responses and alpha oscillations in the human EEG

In the present study, the wide band alpha and sub-bands of alpha in the auditory on- and off-responses to different stimulation frequencies were evaluated. Auditory on- and off-responses of 12 healthy volunteers (average 17 years. old) were recorded from five locations (Fz, Cz, Pz, P3, and P4). The auditory stimuli of 80 dB SPL and 1000 ms duration were delivered at six different stimulation frequencies (f1-f6; 0.2, 0.6, 1, 2, 3, and 4 kHz, respectively). In using individual alpha frequency (IAF) as individual anchor point, wide band alpha and three different alpha frequency sub-bands with a bandwidth of 2 Hz each were defined: lower-1 alpha, lower-2 alpha, and upper alpha. The Root Mean Square (RMS) values of the alpha frequency bands were computed for two time periods: +/-3 sd around the mean peak latency of the auditory on-responses (t1-on and t2-on) and a time window of the same length of the auditory off-responses (t1-off and t2-off). The alpha RMS values of both on- and off responses showed significant differences between t1 and t2 periods on wide band, lower-1 and lower-2 alpha bands, especially at 0.2, 0.6, 1, 2, and 3 kHz stimulation frequencies in all recording places. Amplitudes in anterior locations (Fz, Cz) were higher than the others. These observations may provide a preliminary but nonetheless important understanding of how information may be processed in the brain

N2 and P3 components of event-related potential in first-episode schizophrenic patients: scalp topography, medication, and latency effects

Auditory N2 and P3 components of event-related potentials were assessed in first-episode schizophrenic and normal control subjects (n = 12/group). P3 amplitude was decreased in the patients most prominently over the frontal areas in contrast to a widespread P3 amplitude decrease reported in chronic schizophrenia. Moreover, frontal attenuation of P3 amplitude was greater in the non-medicated compared with medicated patients, a finding that suggests frontal areas are primarily affected at the onset of the first schizophrenic episode. Prolongation of N2 and P3 latencies was also observed in the patients, which indicates that stimulus classification and memory updating processes were slowed even in early stages of schizophrenia. These findings indicate that first-episode schizophrenic patients produce N2 and P3 abnormalities that are distinct from those in chronic patients, and that psychotropic medication can attenuate event-related potential effects in specific ways. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved