Search

In recent years, several ERP components have been identified as potential neural correlates of consciousness (NCC), including early negativities and late positivities. Based on experiments in the visual modality, it has recently been shown that awareness is often confounded with reporting it, possibly overestimating the NCC. It is unknown whether similar constraints also exist in the auditory modality. In order to address this gap, we presented spoken words in a sustained inattentional deafness paradigm. Electrophysiological responses were obtained in three physically identical experimental conditions that differed only with respect to the participants' instructions. Participants were either left uninformed or informed about the presence of spoken words while confronted with an auditory distractor task (U/I condition), informed about the words while exposed to the same task as before (I condition), or requested to respond to the now task-relevant speech stimuli (TR condition). After completion of the U/I condition, only informed participants reported awareness of the words. In ERPs, awareness of words in the U/I and I condition was accompanied by an anterior auditory awareness negativity (AAN). Only when stimuli were task-relevant, i.e., during the TR condition, late positivities emerged. Taken together, these results indicate that early negativities but not late positivities index awareness across sensory modalities. Thus, they provide evidence for a recurrent processing framework, which highlights the importance of early sensory processing in conscious perception.

Several regions of the frontal cortex interact with striatal and amygdala regions to mediate the evaluation of reward-related information and subsequent adjustment of response choices. Recent theories discuss the particular relevance of dorsal anterior cingulate cortex (dACC) for switching behavior; consecutively, ventromedial prefrontal cortex (VMPFC) is involved in mediating exploitative behaviors by tracking reward values unfolding after the behavioral switch. Amygdala, on the other hand, has been implied in coding the valence of stimulus-outcome associations and the ventral striatum (VS) has consistently been shown to code a reward prediction error (RPE). Here, we used fMRI data acquired in humans during a reversal task to parametrically model different sequences of positive feedback in order to unravel differential contributions of these brain regions to the tracking and exploitation of rewards. Parameters from an Optimal Bayesian Learner accurately predicted the divergent involvement of dACC and VMPFC during feedback processing: dACC signaled the first, but not later, presentations of positive feedback, while VMPFC coded trial-by-trial accumulations in reward value. Our results confirm that dACC carries a prominent confirmatory signal during processing of first positive feedback. Amygdala coded positive feedbacks more uniformly, while striatal regions were associated with RPE.

It is as yet unknown if behavioral and neural correlates of performance monitoring in socially anxious individuals are affected by whether feedback is provided by a person or a computer. This fMRI study investigated modulation of feedback processing by feedback source (person vs. computer) in participants with high (HSA) (N=16) and low social anxiety (LSA) (N=16). Subjects performed a choice task in which they were informed that they would receive positive or negative feedback from a person or the computer. Subjective ratings indicated increased arousal and anxiety in HSA versus LSA, most pronounced for social and negative feedback. FMRI analyses yielded hyperactivation in ventral medial prefrontal cortex (vmPFC)/anterior cingulate cortex (ACC) and insula for social relative to computer feedback, and in mPFC/ventral ACC for positive relative to negative feedback in HSA as compared to LSA. These activation patterns are consistent with increased interoception and self-referential processing in social anxiety, especially during processing of positive feedback. Increased ACC activation in HSA to positive feedback may link to unexpectedness of (social) praise as posited in social anxiety disorder (SAD) psychopathology. Activation in rostral ACC showed a reversed pattern, with decreased activation to positive feedback in HSA, possibly indicating altered action values depending on feedback source and valence. The present findings corroborate a crucial role of mPFC for performance monitoring in social anxiety.

The spatio-temporal neural basis of earliest differentiation between emotional and neutral facial expressions is a matter of debate. The present study used concurrent electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) in order to investigate the ‘when’ and ‘where’ of earliest prioritization of emotional over neutral expressions. We measured event-related potentials (ERPs) and blood oxygen dependent (BOLD) signal changes in response to facial expressions of varying emotional intensity and different valence categories. Facial expressions were presented superimposed by two horizontal bars and participants engaged in a focal bars task (low load, high load), in order to manipulate the availability of attentional resources during face perception. EEG data revealed the earliest expression effects in the P1 range (76–128 ms) as a parametric function of stimulus arousal independent of load conditions. Conventional fMRI data analysis also demonstrated significant modulations as a function of stimulus arousal, independent of load, in amygdala, superior temporal sulcus, fusiform gyrus and lateral occipital cortex. Correspondingly, EEG-informed fMRI analysis revealed a significant positive correlation between single-trial P1 amplitudes and BOLD responses in amygdala and lateral posterior occipital cortex. Our results are in line with the hypothesis of the amygdala as fast responding relevance detector and corresponding effects in early visual face processing areas across facial expressions and load conditions.

In recent years continuous flash suppression (CFS) has become a popular "blinding" technique for the investigation of nonconscious affective processing since it elicits potent and long-lasting suppression of conscious visual perception. While the majority of studies provides some positive evidence for nonconscious affective processing, there are also studies reporting their absence. Several methodological variations may give rise to this discrepancy: with respect to the experimental paradigm these variations pertain to the likelihood of residual stimulus visibility on the level of individual participants and single trials. Concerning the statistical analysis they relate to the procedures applied to assess whether detection performance is at chance level and whether the outcome measure does or does not depend on the affective stimulus category. In the present study we determined individual eye dominance and individual stimulus contrast in pretests, measured objective and subjective awareness online and applied Bayesian statistics to estimate the likelihood for the null hypothesis. Event-related potentials (ERPs) were measured while participants were subjected to fearful, happy, and neutral faces in a conscious as well as in a nonconscious CFS condition. In the conscious condition, expected emotion effects were observed in the ERP components N170/EPN and LPP. However, despite high statistical power, no effects of emotional expression were found in the nonconscious condition and the absence of nonconscious affective processing under the tested conditions was substantially more likely than its presence. We discuss whether CFS disrupts affective processing completely if thoroughly applied or whether positive and negative findings should be integrated under a two-threshold framework of nonconscious processing.

An influential framework suggests that the central nucleus of the amygdala (CeA) is involved in phasic responses to threat, while the bed nucleus of the stria terminalis (BNST) mediates sustained anxiety. However, this model has been questioned, proposing that the role of the BNST is not limited to sustained threat contexts. Rather, amygdala and BNST also seem to work in concert in the processing of discrete and briefly presented threat-related stimuli, likely dependent on inter-individual differences in anxiety. A direct test of this assumption with sufficient experimental power is missing in human research and the degree to which individual differences in trait anxiety moderate phasic responses and functional connectivity of amygdala and BNST during threat processing remains unclear. The current event-related functional magnetic resonance imaging (fMRI) study investigated activation and connectivity of amygdala and BNST, as well as modulating effects of trait anxiety, during processing of briefly presented threat-related relative to neutral standardized pictures in 93 psychiatrically healthy individuals. Both amygdala and BNST activation was increased during presentation of threat-related relative to neutral pictures. Furthermore, functional connectivity between BNST and amygdala in response to threat was positively associated with trait anxiety. These findings suggest that amygdala and BNST form a functional unit during phasic threat processing whereby their connectivity is shaped by inter-individual differences in trait anxiety.

A recent study in monkeys showed that averted gaze displayed by conspecifics activates the amygdala regardless of the valence of facial expression (angry, neutral, appeasing). In contrast to this result, previous findings on amygdala activation to gaze information in humans have been mainly interpreted in terms of threat-related processing of facial signals. In the present event-related functional magnetic resonance imaging study with humans, we investigated brain responses to angry, happy, and neutral faces with either direct or averted gaze. Averted versus direct gaze induced increased amygdala responses regardless of facial expression. This finding suggests a critical role of the amygdala in gaze processing independently of the valence of facial expression. Furthermore, the effect of gaze on amygdalar responses seems to be preserved across nonhuman and human primates.

Thermal and nociceptive cutaneous stimuli activate the brain via two types of nerve fibers, slightly myelinated Adelta-fibers with moderate conduction velocity and unmyelinated C-fibers with slow conduction velocity. Differences in central processing upon selective stimulation of these two fiber types in healthy human subjects still remain poorly understood. By means of event-related functional magnetic resonance imaging the present study investigated brain activation in response to stimulation of Adelta- and C-fibers in healthy subjects. We used the stimulation of tiny skin areas to perform a selective stimulation upon cutaneous C-fibers. Besides similar activation in several brain areas in response to both kinds of stimulation, we observed pronounced brain activation to selective C-fiber stimulation as compared to Adelta-fiber stimulation in the right frontal operculum and anterior insula. Based on a putative function of these structures we suggest that the C-fiber system might be engaged in homeostatic and interoceptive functions in a manner other than the Adelta-fiber system, producing a signal of greater emotional salience.

Anticipatory anxiety during expectation of phobogenic stimuli is an integral part of abnormal behaviour in phobics. The neural basis of anticipatory anxiety in specific phobia is unknown. Using functional magnetic resonance imaging (fMRI), we explored brain activation in subjects with spider phobia and in non-phobic subjects, while participants anticipated the presentation of either neutral or phobogenic visual stimuli. Subjective ratings indicated that anticipation of phobia-related stimuli was associated with increased anxiety in phobics but not in healthy subjects. FMRI results showed increased activation of the dorsal anterior cingulate cortex (ACC), insula, thalamus, and visual areas in phobics compared to controls during anticipation of phobia-relevant versus anticipation of neutral stimulation. Furthermore, for this contrast, we found also increased activation of the bed nucleus of the stria terminalis (BNST). This particular finding supports models, which propose, based on animal experiments, a critical involvement of the BNST in anticipatory anxiety. Finally, correlation analysis revealed that subjective anxiety of phobics correlated significantly with activation in rostral and dorsal ACC and the anterior medial prefrontal cortex. Thus, activation in different ACC regions and the medial prefrontal cortex seems to be specifically associated with the severity of experienced anticipatory anxiety in subjects with spider phobia.

Visual perceptual load has been shown to modulate brain activation to emotional facial expressions. However, it is unknown whether cross-modal effects of visual perceptual load on brain activation to threat-related auditory stimuli also exist. The current fMRI study investigated brain responses to angry and neutral voices while subjects had to solve an easy or a demanding visual task. Although the easy visual condition was associated with increased activation in the right superior temporal region to angry vs. neutral prosody, this effect was absent during the demanding task. Thus, our results show that cross-modal perceptual load modulates the activation to emotional voices in the auditory cortex and that high visual load prevents the increased processing of emotional prosody.

It is still a matter of debate under which conditions the neural processing of emotional stimuli can occur without conscious awareness. Using functional magnetic resonance imaging, we investigated brain responses to highly arousing threat-related versus neutral pictures which were presented very briefly during two backward-masking conditions resulting in either subliminal or supraliminal stimulus processing. Signal detection analysis confirmed the successful experimental manipulation of awareness that effectively prevented stimulus recognition during the subliminal condition. Participants showed stronger responses of the amygdala and extrastriate visual cortex during the supraliminal, but not during the subliminal condition. These results suggest that the processing of highly arousing visual threat requires conscious awareness during backward masking. This contradicts the assumption of pervasive neural responses to emotional stimuli.

The evaluation of emotional stimuli is based on different levels of information processing, ranging from rather automatic processes to focused attention to the emotional relevance of stimuli. The role of specific brain areas for these processes is a matter of debate. In this event-related fMRI study, we varied the information processing mode of participants exposed to aversive and neutral pictures. Based on four different tasks, participants' attentional focus onto the emotional quality of the stimuli and the own emotional involvement was increased systematically across tasks. Regardless of task, stronger activation to threatening vs. neutral pictures was found in several regions such as the amygdala, anterior insula, anterior cingulate cortex, primary somatosensory cortex and medial prefrontal cortex. However, there was a parametric increase of activation with increasing attention to one's own emotion specifically in the right posterior insula and right primary and secondary somatosensory cortex, i.e. in areas implicated in self-awareness of a person's own body. These findings are in accordance with theories suggesting a crucial role of the perception of bodily states for emotional experiences.

The time course of amygdala activation during aversive conditioning is a matter of debate. While some researchers reported rapid habituation, others found stable or no amygdalar responses to conditioned stimuli at all. In the present event-related fMRI study, we investigated whether the activity of the amygdala during aversive conditioning depends on attentional conditions. Subjects underwent aversive delay conditioning by pairing an electrical shock (unconditioned aversive stimulus) with a visual conditioned stimulus (CS+). For each singular presentation of the CS+ or a nonconditioned visual stimulus (CS-), subjects attended in random order to features that either differed between both stimuli (identification task) or that did not differ (distraction task). For the identification task trials, increased responses of the left amygdala to CS+ versus CS- were rapidly established but absent at the end of the conditioning trials. In contrast, under the distraction condition, amygdala activation to CS+ versus CS- was present during the late but not the early phase of conditioning. The results suggest that the time course of amygdala activity during aversive associative learning is strongly modulated by an interaction of attention and time.

Little is known about the effects of successful psychotherapy on brain function in subjects with anxiety disorders. The present study aimed to identify changes in brain activation following cognitive-behavioral therapy (CBT) in subjects suffering from specific phobia. Using functional magnetic resonance imaging (fMRI), brain activation to spider videos was measured in 28 spider phobic and 14 healthy control subjects. Phobics were randomly assigned to a therapy-group (TG) and a waiting-list control group (WG). Both groups of phobics were scanned twice. Between scanning sessions, CBT was given to the TG. Before therapy, brain activation did not differ between both groups of phobics. As compared to control subjects, phobics showed greater responses to spider vs. control videos in the insula and anterior cingulate cortex (ACC). CBT strongly reduced phobic symptoms in the TG while the WG remained behaviorally unchanged. In the second scanning session, a significant reduction of hyperactivity in the insula and ACC was found in the TG compared to the WG. These results propose that increased activation in the insula and ACC is associated with specific phobia, whereas an attenuation of these brain responses correlates with successful therapeutic intervention.