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1.  Distinct MEG correlates of conscious experience, perceptual reversals and stabilization during binocular rivalry 
Neuroimage  2014;100(100):161-175.
During binocular rivalry, visual perception alternates spontaneously between two different monocular images. Such perceptual reversals are slowed or halted if stimuli are presented intermittently with inter-stimulus intervals larger than ~ 400 ms — a phenomenon called stabilization. Often, the neural correlates of reversal and stabilization are studied separately, and both phenomena in turn are studied separately from the neural correlates of conscious perception. To distinguish the neural correlates of perceptual content, stabilization and reversal, we recorded MEG signals associated with each in the same group of healthy humans observing repeated trials of intermittent presentation of a dichoptic stimulus. Perceptual content correlated mainly with modulation of stimulus-specific activity in occipital/temporal areas 150–270 ms after stimulus onset, possibly reflecting inhibition of the neural populations representing the suppressed image. Stability of perception reflected a gradual build-up of this modulation across at least 10 trials and was also, to some extent, associated with parietal activity 40–90 ms and 220–270 ms after stimulus onset. Perceptual reversals, in contrast, were associated with parietal (150–270 ms) and temporal (150–210 ms) activity on the trial before the reversal and a gradual change in perception-specific activity in occipital (150–270 ms) and temporal (220–420 ms) areas across at least 10 trials leading up to a reversal. Mechanistically, these findings suggest that stability of perception during rivalry is maintained by modulation of activity related to the two monocular images, and gradual adaptation of neuronal populations leads to instability that is eventually resolved by signals from parietal and late sensory cortices.
•Neural correlates of perception, reversals and stabilization were examined.•Stability of perception is maintained by modulation stimulus-specific activity.•Gradual adaptation of this modulation leads to a state of instability.•Instability is resolved by parietal/temporal sources causing perceptual reversals.
PMCID: PMC4148524  PMID: 24945667
Consciousness; Binocular rivalry; Stabilization; Perceptual reversals; MEG; Magnetoencephalography
2.  Early visual responses predict conscious face perception within and between subjects during binocular rivalry 
Journal of cognitive neuroscience  2013;25(6):969-985.
Previous studies indicate that conscious face perception may be related to neural activity in a large time window around 170-800ms after stimulus presentation, yet in the majority of these studies changes in conscious experience are confounded with changes in physical stimulation. Using multivariate classification on MEG data recorded when participants reported changes in conscious perception evoked by binocular rivalry between a face and a grating, we showed that only MEG signals in the 120-320ms time range, peaking at the M170 around 180ms and the P2m at around 260ms, reliably predicted conscious experience. Conscious perception could not only be decoded significantly better than chance from the sensors that showed the largest average difference, as previous studies suggest, but also from patterns of activity across groups of occipital sensors that individually were unable to predict perception better than chance. Additionally, source space analyses showed that sources in the early and late visual system predicted conscious perception more accurately than frontal and parietal sites, although conscious perception could also be decoded there. Finally, the patterns of neural activity associated with conscious face perception generalized from one participant to another around the times of maximum prediction accuracy. Our work thus demonstrates that the neural correlates of particular conscious contents (here, faces) are highly consistent in time and space within individuals and that these correlates are shared to some extent between individuals.
PMCID: PMC4060063  PMID: 23281780
3.  MEG activity related to conscious perception is stable within individuals across years but not between individuals 
Journal of cognitive neuroscience  2013;26(4):840-853.
Studies indicate that conscious perception is related to changes in neural activity within a time window that varies between 130-320ms after stimulus presentation, yet it is not known whether such neural correlates of conscious perception are stable across time. Here, we examined the generalization across time within individuals and across different individuals. We trained classification algorithms to decode conscious perception from neural activity recorded during binocular rivalry using MEG. The classifiers were then used to predict the perception of the same participants during different recording sessions either days or years later, as well as between different participants. No drop in decoding accuracy was observed when decoding across years compared to days, whereas a large drop in decoding accuracy was found for between-participant decoding. Furthermore, underlying percept-specific MEG signals remained stable in terms of latency, amplitude and sources within participants across years whereas differences were found in all of these domains between individuals. Our findings demonstrate that the neural correlates of conscious perception are stable across years for adults, but differ across individuals. Moreover, the study validates decoding based on MEG data as a method for further studies of correlations between individual differences in perceptual contents and between-participant decoding accuracies.
PMCID: PMC4059382  PMID: 24236699
Ambiguous perception; awareness; consciousness; magnetoencephalography; plasticity
4.  Single-subject oscillatory gamma responses in tinnitus 
Brain  2012;135(10):3089-3100.
This study used magnetoencephalography to record oscillatory activity in a group of 17 patients with chronic tinnitus. Two methods, residual inhibition and residual excitation, were used to bring about transient changes in spontaneous tinnitus intensity in order to measure dynamic tinnitus correlates in individual patients. In residual inhibition, a positive correlation was seen between tinnitus intensity and both delta/theta (6/14 patients) and gamma band (8/14 patients) oscillations in auditory cortex, suggesting an increased thalamocortical input and cortical gamma response, respectively, associated with higher tinnitus states. Conversely, 4/4 patients exhibiting residual excitation demonstrated an inverse correlation between perceived tinnitus intensity and auditory cortex gamma oscillations (with no delta/theta changes) that cannot be explained by existing models. Significant oscillatory power changes were also identified in a variety of cortical regions, most commonly midline lobar regions in the default mode network, cerebellum, insula and anterior temporal lobe. These were highly variable across patients in terms of areas and frequency bands involved, and in direction of power change. We suggest a model based on a local circuit function of cortical gamma-band oscillations as a process of mutual inhibition that might suppress abnormal cortical activity in tinnitus. The work implicates auditory cortex gamma-band oscillations as a fundamental intrinsic mechanism for attenuating phantom auditory perception.
PMCID: PMC3470708  PMID: 22975389
tinnitus; gamma oscillations; mutual inhibition; auditory cortex; magnetoencephalography

Results 1-4 (4)