Uncertainty Promotes Neuroreductionism: A Behavioral Online Study on Folk Psychological Causal Inference from Neuroimaging Data.

INTRODUCTION: Increased efforts in neuroscience try to understand mental disorders as brain disorders. In the present study, we investigate how common a neuroreductionist inclination is among highly educated people. In particular, we shed light on implicit presuppositions of mental disorders little is known about in the public, exemplified here by the case of body integrity dysphoria (BID) that is considered a mental disorder for the first time in ICD-11. METHODS: Identically graphed, simulated data of mind-brain correlations were shown in 3 contexts with presumably different presumptions about causality. 738 highly educated lay people rated plausibility of causality attribution from the brain to mind and from mind to the brain for correlations between brain structural properties and mental phenomena. We contrasted participants' plausibility ratings of causality in the contexts of commonly perceived brain lesion-induced behavior (aphasia), behavior-induced training effects (piano playing), and a newly described mental disorder (BID). RESULTS: The findings reveal the expected context-dependent modulation of causality attributions in the contexts of aphasia and piano playing. Furthermore, we observed a significant tendency to more readily attribute causal inference from the brain to mind than vice versa with respect to BID. CONCLUSION: In some contexts, exemplified here by aphasia and piano playing, unidirectional causality attributions may be justified. However, with respect to BID, we critically discuss presumably unjustified neuroreductionist inclinations under causal uncertainty. Finally, we emphasize the need for a presupposition-free approach in psychiatry.

Measuring perceived self-location in virtual reality.

Third-person perspective full-body illusions (3PP-FBI) enable the manipulation, through multisensory stimulation, of perceived self-location. Perceived self-location is classically measured by a locomotion task. Yet, as locomotion modulates various sensory signals, we developed in immersive virtual reality a measure of self-location without locomotion. Tactile stimulation was applied on the back of twenty-five participants and displayed synchronously or asynchronously on an avatar's back seen from behind. Participants completed the locomotion task and a novel mental imagery task, in which they self-located in relation to a virtual ball approaching them. Participants self-identified with the avatar more during synchronous than asynchronous visuo-tactile stimulation in both tasks. This was accentuated for the mental imagery task, showing a larger self-relocation toward the avatar, together with higher reports of presence, bi-location and disembodiment in the synchronous condition only for the mental imagery task. In conclusion, the results suggest that avoiding multisensory updating during walking, and using a perceptual rather than a motor task, can improve measures of illusory self-location.

Putting Yourself in the Skin of In- or Out-Group Members: No Effect of Implicit Biases on Egocentric Mental Transformation.

Previous studies suggest that visual encoding of ethnicity of in-group/out-group members might influence empathy and sensorimotor sharing. Here, we investigated whether mental perspective taking, presumably a precursor of empathy, is also influenced by in-group/out-group perception and the implicit attitudes toward it. We used an embodied egocentric visual-perspective taking task, the full body rotation task (FBR), in which participants were asked to mentally rotate themselves into the position of dark- or light-skinned bodies. FBR was contrasted to a pure sensorimotor task, the hand laterality task (HLT), in which participants were asked to mentally rotate their hand to the posture of seen light- or dark-skinned hands, which does not require mental simulation of another person's perspective. We expected the FBR but not the HLT to be influenced by the skin color of the stimuli and by the individual implicit biases toward out-group members. Contrary to this hypothesis, we found that neither skin color nor implicit biases modulated reaction times (RTs) in either task. The data thus suggest that unlike other empathy tasks, skin color does not influence visuospatial perspective taking.

Suppression of the auditory N1-component for heartbeat-related sounds reflects interoceptive predictive coding.

Although many studies have elucidated the neurocognitive mechanisms supporting the processing of externally generated sensory signals, less is known about the processing of interoceptive signals related to the viscera. Drawing a parallel with research on agency and the perception of self-generated action effects, in the present EEG study we report a reduced auditory N1 component when participants listened to heartbeat-related sounds compared to externally generated sounds. The auditory suppression for heartbeat sounds was robust and persisted after controlling for ECG-related artifacts, the number of trials involved and the phase of the cardiac cycle. In addition, the auditory N1 suppression for heartbeat-related sounds had a comparable scalp distribution as the N1 suppression observed for actively generated sounds. This finding indicates that the brain automatically differentiates between heartbeat-related and externally generated sounds through a process of sensory suppression, suggesting that a comparable predictive mechanism may underlie the processing of heartbeat and action-related information. Extending recent behavioral data about cardio-visual integration, the present cardio-auditory EEG data reveal that the processing of sounds in auditory cortex is systematically modulated by an interoceptive cardiac signal. The findings are discussed with respect to theories of interoceptive awareness, emotion, predictive coding, and their relevance to bodily self-consciousness.

Listening to your heart and feeling yourself: effects of exposure to interoceptive signals during the ultimatum game.

The ultimatum game (UG) is commonly used to study the tension between financial self-interest and social equity motives. Here, we investigated whether experimental exposure to interoceptive signals influences participants' behavior in the UG. Participants were presented with various bodily sounds--i.e., their own heart, another person's heart, or the sound of footsteps--while acting both in the role of responder and proposer. We found that listening to one's own heart sound, compared to the other bodily sounds: (1) increased subjective feelings of unfairness, but not rejection behavior, in response to unfair offers and (2) increased the unfair offers while playing in the proposer role. These findings suggest that heightened feedback of one's own visceral processes may increase a self-centered perspective and drive socioeconomic exchanges accordingly. In addition, this study introduces a valuable procedure to manipulate online the access to interoceptive signals and for exploring the interplay between viscero-sensory information and cognition.

The timing of temporoparietal and frontal activations during mental own body transformations from different visuospatial perspectives.

The perspective from where the world is perceived is an important aspect of the bodily self and may break down in neurological conditions such as out-of-body experiences (OBEs). These striking disturbances are characterized by disembodiment, an external perspective and have been observed after temporoparietal damage. Using mental own body imagery, recent neuroimaging work has linked perspectival changes to the temporoparietal cortex. Because the disembodied perspective during OBEs is elevated in the majority of cases, we tested whether an elevated perspective will interfere with such temporoparietal mechanisms mental own body imagery. We designed stimuli of life-sized humans rotated around the vertical axis and rendered as if viewed from three different perspectives: elevated, lowered, and normal. Reaction times (RTs) in an own body transformation task, but not the control condition, were dependent on the rotation angle. Furthermore, RTs were shorter for the elevated as compared with the normal or lowered perspective. Using high-density EEG and evoked potential (EP) mapping, we found a bilateral temporoparietal and frontal activation at approximately 330-420 ms after stimulus onset that was dependent on the rotation angle, but not on the perspective. This activation was also found in response-locked EPs. In the time period approximately 210-330 ms we found a temporally distinct posterior temporal activation with its duration being dependent on the perspective, but not the rotation angle. Collectively, the present findings suggest that temporoparietal and frontal as well as posterior temporal activations and their timing are crucial neuronal correlates of the bodily self as studied by mental imagery.

Influence of galvanic vestibular stimulation on egocentric and object-based mental transformations.

The vestibular system analyses angular and linear accelerations of the head that are important information for perceiving the location of one's own body in space. Vestibular stimulation and in particular galvanic vestibular stimulation (GVS) that allow a systematic modification of vestibular signals has so far mainly been used to investigate vestibular influence on sensori-motor integration in eye movements and postural control. Comparatively, only a few behavioural and imaging studies have investigated how cognition of space and body may depend on vestibular processing. This study was designed to differentiate the influence of left versus right anodal GVS compared to sham stimulation on object-based versus egocentric mental transformations. While GVS was applied, subjects made left-right judgments about pictures of a plant or a human body presented at different orientations in the roll plane. All subjects reported illusory sensations of body self-motion and/or visual field motion during GVS. Response times in the mental transformation task were increased during right but not left anodal GVS for the more difficult stimuli and the larger angles of rotation. Post-hoc analyses suggested that the interfering effect of right anodal GVS was only present in subjects who reported having imagined turning themselves to solve the mental transformation task (egocentric transformation) as compared to those subjects having imagined turning the picture in space (object-based mental transformation). We suggest that this effect relies on shared functional and cortical mechanisms in the posterior parietal cortex associated with both right anodal GVS and mental imagery.