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While the contingent negative variation (CNV) has been the subject of extensive research over the last fifty years, the maximum duration during which such cortical negativity can be maintained has, to the best of our knowledge, never been systematically explored. Participants were presented with the classic S1-S2 paradigm task, where a warning stimulus (S1) acts as a cue for the appearance of an imperative stimulus (S2). A fast motor response was required upon S2 arrival. Inter-stimulus intervals (ISIs) of 2.5, 5, 7.5 and 10 s duration were presented in blocked fashion. Data was analysed using both EEG referenced to linked mastoids and the current source density (CSD) technique, which maximizes the cortical origin of the measured voltage. Mean late CNV (lCNV) amplitude was found to be significantly higher for fast reaction time (RT) trials when CSD data was split according to the median into 'fast' and 'slow' RT halves. Post-hoc comparisons showed that this RT effect was particularly strong for the 10 s condition. This may be explained by the lack of an lCNV component and thus of cortical negativity prior to S2 in the 10 s condition. Our results suggest that intervals of a duration between 7.5 and 10 s represent the upper boundary during which the lCNV component can be elicited.

The Necker-Zeno model of bistable perception provides a formal relation between the average duration of meta-stable percepts (dwell times T) of ambiguous figures and two other basic time scales (t(0), ΔT) underlying cognitive processing. The model predicts that dwell times T covary with t(0), ΔT or both. We tested this prediction by exploiting that observers, in particular experienced meditators, can volitionally control dwell times T. Meditators and non-meditators observed bistable Necker cubes either passively or tried to hold their current percept. The latencies of a centro-parietal event-related potential (CPP) were recorded as a physiological correlate of t(0). Dwell times T and the CPP latencies, correlated with t(0), differed between conditions and observer groups, while ΔT remained constant in the range predicted by the model. The covariation of CPP latencies and dwell times, as well as their quadratic functional dependence extends previous psychophysical confirmation of the Necker-Zeno model to psychophysiological measures.

Environmental information available to our senses is incomplete and to varying degrees ambiguous. It has to be disambiguated in order to construct stable and reliable percepts. Ambiguous figures are artificial examples where perception is maximally unstable and alternates between possible interpretations. Tiny low-level changes can disambiguate an ambiguous figure and thus stabilize percepts. The present study compares ERPs evoked by ambiguous stimuli and disambiguated stimulus variants across three visual categories: geometry (Necker cube), motion (stroboscopic alternative motion stimulus, SAM) and semantics (Boring's old/young woman). We found that (a) disambiguated stimulus variants cause stable percepts and evoke two huge positive ERP excursions (Cohen's effect sizes 1-2), (b) the amplitudes of these ERP effects are inversely related to the degree of stimulus ambiguity, and (c) this pattern of results is consistent across all three tested visual categories. This generality across visual categories points to mechanisms at a very abstract (cognitive) level of processing. We discuss our results in the context of a high-level Bayesian inference unit that evaluates the reliability of perceptual processing results, given a priori incomplete, ambiguous sensory information. The ERP components may reflect the outcome of this reliability estimation.

The belief in free will has been frequently challenged since Benjamin Libet published his famous experiment in 1983. Although Libet's experiment is highly dependent upon subjective reports, no study has been conducted that focused on a first-person or introspective perspective of the task. We took a neurophenomenological approach in an N=1 study providing reliable and valid measures of the first-person perspective in conjunction with brain dynamics. We found that a larger readiness potential (RP) is attributable to more frequent occurrences of self-initiated movements during negative deflections of the slow cortical potentials (SCP). These negative deflections occur in parallel with an inner impulse reported by an expert meditator which may in turn lead to a voluntary act. We demonstrate in this proof-of-principle approach that the first-person perspective obtained by an expert meditator in conjunction with neural signal analysis can contribute to our understanding of the neural underpinnings of voluntary acts.

It has been repeatedly shown that specific brain activity related to planning movement develops before the conscious intention to act. This empirical finding strongly challenges the notion of free will. Here, we demonstrate that in the Libet experiment, spontaneous fluctuations of the slow electro-cortical potentials (SCPs) account for a significant fraction of the readiness potential (RP). The individual potential shifts preceding self-initiated movements were classified as showing a negative or positive shift. The negative and positive potential shifts were analyzed in a self-initiated movement condition and in a no-movement condition. Comparing the potential shifts between both conditions, we observed no differences in the early part of the potential. This reveals that the apparently negative RP emerges through an unequal ratio of negative and positive potential shifts. These results suggest that ongoing negative shifts of the SCPs facilitate self-initiated movement but are not related to processes underlying preparation or decision to act.

In an fMRI study, effects of contingency awareness on conditioned responses were assessed in three groups comprising 118 subjects. A differential fear-conditioning paradigm with visual conditioned stimuli, an electrical unconditioned stimulus and two distractors was applied. The instructed aware group was informed about the contingencies, whereas the distractors prevented contingency detection in the unaware group. The third group (learned aware) was not informed about the contingencies, but learned them despite the distractors. Main effects of contingency awareness on conditioned responses emerged in several brain structures. Post hoc tests revealed differential dorsal anterior cingulate, insula and ventral striatum responses in aware conditioning only, whereas the amygdala was activated independent of contingency awareness. Differential responses of the hippocampus were specifically observed in learned aware subjects, indicating a role in the development of contingency awareness. The orbitofrontal cortex showed varying response patterns: lateral structures showed higher responses in instructed aware than unaware subjects, the opposite was true for medial parts. Conditioned subjective and electrodermal responses emerged only in the two aware groups. These results confirm the independence of conditioned amygdala responses from contingency awareness and indicate specific neural circuits for different aspects of fear acquisition in unaware, learned aware and instructed aware subjects.

Recent research suggests that our sense of time intervals in the range of seconds is directly related to activity in the insular cortex, which contains the primary sensory area for interoception. We therefore investigated whether performance in a duration reproduction task might correlate with individual interoceptive awareness and with measurable changes in autonomic activity during the task. Thirty-one healthy volunteers participated in an interoceptive (heartbeat) perception task and in repeated temporal reproduction trials using intervals of 8, 14, and 20s duration while skin conductance levels and cardiac and respiratory periods were recorded. We observed progressive increases in cardiac periods and decreases in skin conductance level during the encoding and (less reliably) the reproduction of these intervals. Notably, individuals' duration reproduction accuracy correlated positively both with the slope of cardiac slowing during the encoding intervals and with individual heartbeat perception scores. These results support the view that autonomic function and interoceptive awareness underpin our perception of time intervals in the range of seconds.

This study investigates the effect of awareness of stimulus contingencies on BOLD responses within the amygdala, the orbitofrontal, and the occipital cortex, and on differential skin conductance responses (SCRs) during fear conditioning. Of two geometric figures, the paired conditioned stimulus (CS+) predicted an electrical stimulus (unconditioned stimulus = UCS), whereas the unpaired conditioned stimulus (CS-) was not followed by the UCS. Awareness of stimulus contingencies was manipulated experimentally, creating an aware and an unaware group: a distracter figure and a working memory task were introduced to conceal the stimulus contingencies of the conditioning paradigm, hence preventing contingency detection in the unaware group. The aware group was informed beforehand about the relation between CS+, CS-, and UCS. Differential SCRs were only obtained in the aware but not in the unaware group. Conversely, we observed enhanced responses of the amygdala, the orbitofrontal, and the occipital cortex to the CS+ in the unaware group only. Thus, we found a dissociation of SCR differentiation and the activation of a neural fear network depending on the presence or absence of awareness. These results support a model of fear conditioning that distinguishes between a more cognitive level of learning, reflected in contingency awareness and differential SCRs, and the awareness independent activation of a fear network.

Two correlates of outcome processing in the orbitofrontal cortex (OFC) have been proposed in the literature: One hypothesis suggests that the lateral/medial division relates to representation of outcome valence (negative vs. positive), and the other suggests that the medial OFC maintains steady stimulus-outcome associations, whereas the lateral OFC represents changing (unsteady) outcomes to prepare for response shifts. These two hypotheses were contrasted by comparing the original with the inverted version of the Iowa Gambling Task in an event-related functional magnetic resonance imaging experiment. Results showed (1) that (caudo) lateral OFC was indeed sensitive to the steadiness of the outcomes and not merely to outcome valence and (2) that the original and the inverted tasks, although both designed to measure sensitivity for future outcomes, were not equivalent as they enacted different behaviors and brain activation patterns. Results are interpreted in terms of Kahneman and Tversky's prospect theory suggesting that cognitions and decisions are biased differentially when probabilistic future rewards are weighed against consistent punishments relative to the opposite scenario [Kahneman, D., & Tversky, A. Choices, values, and frames. American Psychologist, 39, 341-350, 1984]. Specialized processing of unsteady rewards (involving caudolateral OFC) may have developed during evolution in support of goal-related thinking, prospective planning, and problem solving.

Global variations of BOLD-fMRI signal are often considered as nuisance effects. This unwanted source of variance is commonly eliminated using proportional global signal scaling (PGSS). However, application of PGSS relies on the assumption that global variations of BOLD signal and experimental conditions are uncorrelated. It has been shown for cognitive tasks that the unjustified application of PGSS might greatly distort statistical results. The present study examined this issue in the domain of emotion research. Specifically, fMRI data were obtained in a block-design, while 21 subjects passively viewed high and low emotionally arousing pleasant, unpleasant, and neutral pictures. Violations of the orthogonality assumption were found for analyses of emotional pictures high in arousal, causing dramatically different outcomes when compared to analyses performed without PGSS. Application of PGSS was associated with attenuated emotional activation in visual cortical areas, insensitivity to emotional activations in limbic and paralimbic regions, and widely distributed artificial deactivations. In contrast, the orthogonality assumption was not violated for low arousing emotional materials. Thus, the validity of using PGSS varied as a function of the emotional arousal of the stimuli. Taken together, the unwarranted use of PGSS might contribute to conflicting results in affective neuroscience fMRI studies, in particular with respect to limbic and paralimbic structures.