Pre-stimulus gamma power in human posteromedial cortex shows supra-modal mechanisms in predicting the amplitude and latency of task-induced suppression

Upon repetitively performing the same well-practiced task on identical bottom-up stimuli, our performance still varies. Although it has been well documented that elevated pre-stimulus baseline activity in the human default-mode network impairs the subsequent task performance, it remains unknown (i) the fine-grained temporal dynamics and (ii) whether the underlying neural dynamics are supra-modal or modality-specific. We utilized intracranial recordings in the human posteromedial cortex (PMC) during a simple visual and an auditory detection task. Our findings suggested that the pre-stimulus gamma power in PMC predicted the subsequent task performance. Critically, the higher the pre-stimulus gamma power, the longer it took for it to be suppressed, and the less suppressed it was during the task performance, which eventually resulted in deleterious effects on task performance, i.e. longer reaction times. These fine-grained temporal dynamics were consistent between the visual and auditory simple detection task. In addition, a direct comparison between the visual and auditory modality showed that the between-modality difference emerged during the recovery period from the maximal gamma suppression back to the baseline. Taken together, the present results contribute novel spatio-temporal mechanisms in human PMC on how simple detection performance varies across multiple repetitions, irrespective of the sensory modality involved.

Neural correlates of temporal integration and segregation in metacontrast masking: A phenomenological study

Temporal integration and segregation have been investigated both in the research on the temporal mechanisms in visual perception and in the research on visual masking. Although both research lines share theoretical, methodological, and empirical similarities, there is little overlap between them and their models of temporal processing are incompatible. As a first step toward the unification of both lines of research, we investigated the electrophysiological correlates of temporal integration and segregation in a metacontrast masking paradigm. Participants reported in each trial whether they perceived the target-mask sequence as a simultaneous or temporally segregated percept while their EEG was recorded. A comparison of both temporal report categories resulted in an ERP difference after stimulus presentation (200-450 ms) that closely resembles the contour integration negativity. Moreover, we found that phase states were shifted between perceptual report categories in the alpha (450-250 ms) and beta (225-125 ms) frequency band before stimulus presentation and induced a sinusoidal periodicity in later temporal report proportions. Thus, we show that neural correlates of temporal integration and segregation can be generalized to metacontrast masking. These findings emphasize the potential role of temporal mechanisms in the emergence of the masking phenomenon. Additionally, our findings validate our phenomenological approach by demonstrating similar neural correlates of temporal integration and segregation as in performance-based tasks. Future research may profit from our phenomenological approach to disentangle the (neural) interplay between temporal and masking mechanisms.

Predictive physiological anticipatory activity preceding seemingly unpredictable stimuli: An update of Mossbridge et al's meta-analysis

Background: This is an update of the Mossbridge et al’s meta-analysis related to the physiological anticipation preceding seemingly unpredictable stimuli which overall effect size was 0.21; 95% Confidence Intervals: 0.13 - 0.29

Methods: Nineteen new peer and non-peer reviewed studies completed from January 2008 to June 2018 were retrieved describing a total of 27 experiments and 36 associated effect sizes.

Results: The overall weighted effect size, estimated with a frequentist multilevel random model, was: 0.28; 95% Confidence Intervals: 0.18-0.38; the overall weighted effect size, estimated with a multilevel Bayesian model, was: 0.28; 95% Credible Intervals: 0.18-0.38.

The weighted mean estimate of the effect size of peer reviewed studies was higher than that of non-peer reviewed studies, but with overlapped confidence intervals: Peer reviewed: 0.36; 95% Confidence Intervals: 0.26-0.47; Non-Peer reviewed: 0.22; 95% Confidence Intervals: 0.05-0.39.

Similarly, the weighted mean estimate of the effect size of Preregistered studies was higher than that of Non-Preregistered studies: Preregistered: 0.31; 95% Confidence Intervals: 0.18-0.45; No-Preregistered: 0.24; 95% Confidence Intervals: 0.08-0.41.

The statistical estimation of the publication bias by using the Copas selection model suggest that the main findings are not contaminated by publication bias.

Conclusions: In summary, with this update, the main findings reported in Mossbridge et al’s meta-analysis, are confirmed.

Ongoing Slow Fluctuations in V1 Impact on Visual Perception

The human brain’s ongoing activity is characterized by intrinsic networks of coherent fluctuations, measured for example with correlated functional magnetic resonance imaging signals. So far, however, the brain processes underlying this ongoing blood oxygenation level dependent (BOLD) signal orchestration and their direct relevance for human behavior are not sufficiently understood. In this study, we address the question of whether and how ongoing BOLD activity within intrinsic occipital networks impacts on conscious visual perception. To this end, backwardly masked targets were presented in participants’ left visual field only, leaving the ipsi-lateral occipital areas entirely free from direct effects of task throughout the experiment. Signal time courses of ipsi-lateral BOLD fluctuations in visual areas V1 and V2 were then used as proxies for the ongoing contra-lateral BOLD activity within the bilateral networks. Magnitude and phase of these fluctuations were compared in trials with and without conscious visual perception, operationalized by means of subjective confidence ratings. Our results show that ipsi-lateral BOLD magnitudes in V1 were significantly higher at times of peak response when the target was perceived consciously. A significant difference between conscious and non-conscious perception with regard to the pre-target phase of an intrinsic-frequency regime suggests that ongoing V1 fluctuations exert a decisive impact on the access to consciousness already before stimulation. Both effects were absent in V2. These results thus support the notion that ongoing slow BOLD activity within intrinsic networks covering V1 represents localized processes that modulate the degree of readiness for the emergence of visual consciousness.

Spontaneous activity in default-mode network predicts ascription of self-relatedness to stimuli

Spontaneous activity levels prior to stimulus presentation can determine how that stimulus will be perceived. It has also been proposed that such spontaneous activity, particularly in the default-mode network (DMN), is involved in self-related processing. We therefore hypothesised that pre-stimulus activity levels in the DMN predict whether a stimulus is judged as self-related or not. Participants were presented in the MRI scanner with a white noise stimulus that they were instructed contained their name or another. They then had to respond with which name they thought they heard. Regions where there was an activity level difference between self and other response trials 2 s prior to the stimulus being presented were identified. Pre-stimulus activity levels were higher in the right temporoparietal junction, the right temporal pole and the left superior temporal gyrus in trials where the participant responded that they heard their own name than trials where they responded that they heard another. Pre-stimulus spontaneous activity levels in particular brain regions, largely overlapping with the DMN, predict the subsequent judgement of stimuli as self-related. This extends our current knowledge of self-related processing and its apparent relationship with intrinsic brain activity in what can be termed a rest-self overlap.

Prestimulus default mode activity influences depth of processing and recognition in an emotional memory task

Low self-referential thoughts are associated with better concentration, which leads to deeper encoding and increases learning and subsequent retrieval. There is evidence that being engaged in externally rather than internally focused tasks is related to low neural activity in the default mode network (DMN) promoting open mind and the deep elaboration of new information. Thus, reduced DMN activity should lead to enhanced concentration, comprehensive stimulus evaluation including emotional categorization, deeper stimulus processing, and better long-term retention over one whole week. In this fMRI study, we investigated brain activation preceding and during incidental encoding of emotional pictures and on subsequent recognition performance. During fMRI, 24 subjects were exposed to 80 pictures of different emotional valence and subsequently asked to complete an online recognition task one week later. Results indicate that neural activity within the medial temporal lobes during encoding predicts subsequent memory performance. Moreover, a low activity of the default mode network preceding incidental encoding leads to slightly better recognition performance independent of the emotional perception of a picture. The findings indicate that the suppression of internally-oriented thoughts leads to a more comprehensive and thorough evaluation of a stimulus and its emotional valence. Reduced activation of the DMN prior to stimulus onset is associated with deeper encoding and enhanced consolidation and retrieval performance even one week later. Even small prestimulus lapses of attention influence consolidation and subsequent recognition performance.

Predictive physiological anticipation preceding seemingly unpredictable stimuli: a meta-analysis

This meta-analysis of 26 reports published between 1978 and 2010 tests an unusual hypothesis: for stimuli of two or more types that are presented in an order designed to be unpredictable and that produce different post-stimulus physiological activity, the direction of pre-stimulus physiological activity reflects the direction of post-stimulus physiological activity, resulting in an unexplained anticipatory effect. The reports we examined used one of two paradigms: (1) randomly ordered presentations of arousing vs. neutral stimuli, or (2) guessing tasks with feedback (correct vs. incorrect). Dependent variables included: electrodermal activity, heart rate, blood volume, pupil dilation, electroencephalographic activity, and blood oxygenation level dependent (BOLD) activity. To avoid including data hand-picked from multiple different analyses, no post hoc experiments were considered. The results reveal a significant overall effect with a small effect size [fixed effect: overall ES = 0.21, 95% CI = 0.15-0.27, z = 6.9, p < 2.7 × 10(-12); random effects: overall (weighted) ES = 0.21, 95% CI = 0.13-0.29, z = 5.3, p < 5.7 × 10(-8)]. Higher quality experiments produced a quantitatively larger effect size and a greater level of significance than lower quality studies. The number of contrary unpublished reports that would be necessary to reduce the level of significance to chance (p > 0.05) was conservatively calculated to be 87 reports. We explore alternative explanations and examine the potential linkage between this unexplained anticipatory activity and other results demonstrating meaningful pre-stimulus activity preceding behaviorally relevant events. We conclude that to further examine this currently unexplained anticipatory activity, multiple replications arising from different laboratories using the same methods are necessary. The cause of this anticipatory activity, which undoubtedly lies within the realm of natural physical processes (as opposed to supernatural or paranormal ones), remains to be determined.