Single neurons in the thalamus and subthalamic nucleus process cardiac and respiratory signals in humans.

Visceral signals are constantly processed by our central nervous system, enable homeostatic regulation, and influence perception, emotion, and cognition. While visceral processes at the cortical level have been extensively studied using non-invasive imaging techniques, very few studies have investigated how this information is processed at the single neuron level, both in humans and animals. Subcortical regions, relaying signals from peripheral interoceptors to cortical structures, are particularly understudied and how visceral information is processed in thalamic and subthalamic structures remains largely unknown. Here, we took advantage of intraoperative microelectrode recordings in patients undergoing surgery for deep brain stimulation (DBS) to investigate the activity of single neurons related to cardiac and respiratory functions in three subcortical regions: ventral intermedius nucleus (Vim) and ventral caudalis nucleus (Vc) of the thalamus, and subthalamic nucleus (STN). We report that the activity of a large portion of the recorded neurons (about 70%) was modulated by either the heartbeat, the cardiac inter-beat interval, or the respiration. These cardiac and respiratory response patterns varied largely across neurons both in terms of timing and their kind of modulation. A substantial proportion of these visceral neurons (30%) was responsive to more than one of the tested signals, underlining specialization and integration of cardiac and respiratory signals in STN and thalamic neurons. By extensively describing single unit activity related to cardiorespiratory function in thalamic and subthalamic neurons, our results highlight the major role of these subcortical regions in the processing of visceral signals.

Robotically-induced auditory-verbal hallucinations: combining self-monitoring and strong perceptual priors.

BACKGROUND: Inducing hallucinations under controlled experimental conditions in non-hallucinating individuals represents a novel research avenue oriented toward understanding complex hallucinatory phenomena, avoiding confounds observed in patients. Auditory-verbal hallucinations (AVH) are one of the most common and distressing psychotic symptoms, whose etiology remains largely unknown. Two prominent accounts portray AVH either as a deficit in auditory-verbal self-monitoring, or as a result of overly strong perceptual priors. METHODS: In order to test both theoretical models and evaluate their potential integration, we developed a robotic procedure able to induce self-monitoring perturbations (consisting of sensorimotor conflicts between poking movements and corresponding tactile feedback) and a perceptual prior associated with otherness sensations (i.e. feeling the presence of a non-existing another person). RESULTS: Here, in two independent studies, we show that this robotic procedure led to AVH-like phenomena in healthy individuals, quantified as an increase in false alarm rate in a voice detection task. Robotically-induced AVH-like sensations were further associated with delusional ideation and to both AVH accounts. Specifically, a condition with stronger sensorimotor conflicts induced more AVH-like sensations (self-monitoring), while, in the otherness-related experimental condition, there were more AVH-like sensations when participants were detecting other-voice stimuli, compared to detecting self-voice stimuli (strong-priors). CONCLUSIONS: By demonstrating an experimental procedure able to induce AVH-like sensations in non-hallucinating individuals, we shed new light on AVH phenomenology, thereby integrating self-monitoring and strong-priors accounts.

The diagnostic performance of functional dopaminergic scintigraphic imaging in the diagnosis of dementia with Lewy bodies: an updated systematic review.

INTRODUCTION: Dopaminergic scintigraphic imaging is a cornerstone to support the diagnosis in dementia with Lewy bodies. To clarify the current state of knowledge on this imaging modality and its impact on clinical diagnosis, we performed an updated systematic review of the literature. METHODS: This systematic review was carried out according to PRISMA guidelines. A comprehensive computer literature search of PubMed/MEDLINE, EMBASE, and Cochrane Library databases for studies published through June 2022 was performed using the following search algorithm: (a) "Lewy body" [TI] OR "Lewy bodies" [TI] and (b) ("DaTscan" OR "ioflupane" OR "123ip" OR "123?ip" OR "123 ip" OR "123i-FP-CIT" OR "FPCIT" OR "FP-CIT" OR "beta?CIT" OR "beta CIT" OR "CIT?SPECT" OR "CIT SPECT" OR "Dat?scan*" OR "dat scan*" OR "dat?spect*" OR "SPECT"). Risk of bias and applicability concerns of the studies were evaluated using the QUADAS-2 tool. RESULTS: We performed a qualitative analysis of 59 studies. Of the 59 studies, 19 (32%) addressed the diagnostic performance of dopamine transporter imaging, 15 (25%) assessed the identification of dementia with Lewy bodies in the spectrum of Lewy body disease and 18 (31%) investigated the role of functional dopaminergic imaging in distinguishing dementia with Lewy bodies from other dementias. Dopamine transporter loss was correlated with clinical outcomes in 19 studies (32%) and with other functional imaging modalities in 15 studies (25%). Heterogeneous technical aspects were found among the studies through the use of various radioligands, the more prevalent being the [123I]N­ω­fluoropropyl­2ß­carbomethoxy­3ß­(4­iodophenyl) nortropane (123I-FP-CIT) in 54 studies (91.5%). Image analysis used visual analysis (9 studies, 15%), semi-quantitative analysis (29 studies, 49%), or a combination of both (16 studies, 27%). CONCLUSION: Our systematic review confirms the major role of dopaminergic scintigraphic imaging in the assessment of dementia with Lewy bodies. Early diagnosis could be facilitated by identifying the prodromes of dementia with Lewy bodies using dopaminergic scintigraphic imaging coupled with emphasis on clinical neuropsychiatric symptoms. Most published studies use a semi-quantitative analytical assessment of tracer uptake, while there are no studies using quantitative analytical methods to measure dopamine transporter loss. The superiority of a purely quantitative approach to assess dopaminergic transmission more accurately needs to be further clarified.

Behavioral and neurophysiological evidence for altered interoceptive bodily processing in chronic pain.

Whereas impaired multisensory processing of bodily stimuli and distorted body representation are well-established in various chronic pain disorders, such research has focused on exteroceptive bodily cues and neglected bodily signals from the inside of the body (or interoceptive signals). Extending existing basic and clinical research, we investigated for the first time interoception and its neurophysiological correlates in patients with complex regional pain syndrome (CRPS). In three different experiments, including a total of 36 patients with CRPS and 42 aged-gender matched healthy controls, we measured interoceptive sensitivity (heart beat counting task, HBC) and neural responses to heartbeats (heartbeat evoked potentials, HEPs). As hypothesized, we observed reduced sensitivity in perceiving interoceptive bodily stimuli, i.e. their heartbeat, in two independent samples of CRPS patients (studies 1 and 2). Moreover, the cortical processing of their heartbeat, i.e. the HEP, was reduced compared to controls (study 3) and reduced interoceptive sensitivity and HEPs were related to CRPS patients' motor impairment and pain duration. By providing consistent evidence for impaired processing of interoceptive bodily cues in CRPS, this study shows that the perceptual changes occurring in chronic pain include signals originating from the visceral organs, suggesting changes in the neural body representation, that includes next to exteroceptive, also interoceptive bodily signals. By showing that impaired interoceptive processing is associated with clinical symptoms, our findings also encourage the use of interoceptive-related information in future rehabilitation for chronic pain.

Audio-Tactile and Peripersonal Space Processing Around the Trunk in Human Parietal and Temporal Cortex: An Intracranial EEG Study.

Interactions with the environment happen within one's peripersonal space (PPS)-the space surrounding the body. Studies in monkeys and humans have highlighted a multisensory distributed cortical network representing the PPS. However, knowledge about the temporal dynamics of PPS processing around the trunk is lacking. Here, we recorded intracranial electroencephalography (iEEG) in humans while administering tactile stimulation (T), approaching auditory stimuli (A), and the 2 combined (AT). To map PPS, tactile stimulation was delivered when the sound was far, intermediate, or close to the body. The 19% of the electrodes showed AT multisensory integration. Among those, 30% showed a PPS effect, a modulation of the response as a function of the distance between the sound and body. AT multisensory integration and PPS effects had similar spatiotemporal characteristics, with an early response (~50 ms) in the insular cortex, and later responses (~200 ms) in precentral and postcentral gyri. Superior temporal cortex showed a different response pattern with AT multisensory integration at ~100 ms without a PPS effect. These results, represent the first iEEG delineation of PPS processing in humans and show that PPS and multisensory integration happen at similar neural sites and time periods, suggesting that PPS representation is based on a spatial modulation of multisensory integration.

Neural Sources and Underlying Mechanisms of Neural Responses to Heartbeats, and their Role in Bodily Self-consciousness: An Intracranial EEG Study.

Recent research has shown that heartbeat-evoked potentials (HEPs), brain activity in response to heartbeats, are a useful neural measure for investigating the functional role of brain-body interactions in cognitive processes including self-consciousness. In 2 experiments, using intracranial electroencephalography (EEG), we investigated (1) the neural sources of HEPs, (2) the underlying mechanisms for HEP generation, and (3) the functional role of HEPs in bodily self-consciousness. In Experiment-1, we found that shortly after the heartbeat onset, phase distributions across single trials were significantly concentrated in 10% of the recording sites, mainly in the insula and the operculum, but also in other regions including the amygdala and fronto-temporal cortex. Such phase concentration was not accompanied by increased spectral power, and did not correlate with spectral power changes, suggesting that a phase resetting, rather than an additive "evoked potential" mechanism, underlies HEP generation. In Experiment-2, we further aimed to anatomically refine previous scalp EEG data that linked HEPs with bodily self-consciousness. We found that HEP modulations in the insula reflected an experimentally induced altered sense of self-identification. Collectively, these results provide novel and solid electrophysiological evidence on the neural sources and underlying mechanisms of HEPs, and their functional role in self-consciousness.

Self-Grounded Vision: Hand Ownership Modulates Visual Location through Cortical ß and γ Oscillations.

Vision is known to be shaped by context, defined by environmental and bodily signals. In the Taylor illusion, the size of an afterimage projected on one's hand changes according to proprioceptive signals conveying hand position. Here, we assessed whether the Taylor illusion does not just depend on the physical hand position, but also on bodily self-consciousness as quantified through illusory hand ownership. Relying on the somatic rubber hand illusion, we manipulated hand ownership, such that participants embodied a rubber hand placed next to their own hand. We found that an afterimage projected on the participant's hand drifted depending on illusory ownership between the participants' two hands, showing an implication of self-representation during the Taylor illusion. Oscillatory power analysis of electroencephalographic signals showed that illusory hand ownership was stronger in participants with stronger α suppression over left sensorimotor cortex, whereas the Taylor illusion correlated with higher ß/γ power over frontotemporal regions. Higher γ connectivity between left sensorimotor and inferior parietal cortex was also found during illusory hand ownership. These data show that afterimage drifts in the Taylor illusion do not only depend on the physical hand position but also on subjective ownership, which itself is based on the synchrony of somatosensory signals from the two hands. The effect of ownership on afterimage drifts is associated with ß/γ power and γ connectivity between frontoparietal regions and the visual cortex. Together, our results suggest that visual percepts are not only influenced by bodily context but are self-grounded, mapped on a self-referential frame. SIGNIFICANCE STATEMENT: Vision is influenced by the body: in the Taylor illusion, the size of an afterimage projected on one's hand changes according to tactile and proprioceptive signals conveying hand position. Here, we report a new phenomenon revealing that the perception of afterimages depends not only on bodily signals, but also on the sense of self. Relying on the rubber hand illusion, we manipulated hand ownership, so that participants embodied a rubber hand placed next to their own hand. We found that visual afterimages projected on the participant's hand drifted laterally, only when the rubber hand was embodied. Electroencephalography revealed spectral dissociations between somatic and visual effects, and higher γ connectivity along the dorsal visual pathways when the rubber hand was embodied.

Transient Modulations of Neural Responses to Heartbeats Covary with Bodily Self-Consciousness.

UNLABELLED: Recent research has investigated self-consciousness associated with the multisensory processing of bodily signals (e.g., somatosensory, visual, vestibular signals), a notion referred to as bodily self-consciousness, and these studies have shown that the manipulation of bodily inputs induces changes in bodily self-consciousness such as self-identification. Another line of research has highlighted the importance of signals from the inside of the body (e.g., visceral signals) and proposed that neural representations of internal bodily signals underlie self-consciousness, which to date has been based on philosophical inquiry, clinical case studies, and behavioral studies. Here, we investigated the relationship of bodily self-consciousness with the neural processing of internal bodily signals. By combining electrical neuroimaging, analysis of peripheral physiological signals, and virtual reality technology in humans, we show that transient modulations of neural responses to heartbeats in the posterior cingulate cortex covary with changes in bodily self-consciousness induced by the full-body illusion. Additional analyses excluded that measured basic cardiorespiratory parameters or interoceptive sensitivity traits could account for this finding. These neurophysiological data link experimentally the cortical mapping of the internal body to self-consciousness. SIGNIFICANCE STATEMENT: What are the brain mechanisms of self-consciousness? Prominent views propose that the neural processing associated with signals from the internal organs (such as the heart and the lung) plays a critical role in self-consciousness. Although this hypothesis dates back to influential views in philosophy and psychology (e.g., William James), definitive experimental evidence supporting this idea is lacking despite its recent impact in neuroscience. In the present study, we show that posterior cingulate activities responding to heartbeat signals covary with changes in participants' conscious self-identification with a body that were manipulated experimentally using virtual reality technology. Our finding provides important neural evidence about the long-standing proposal that self-consciousness is linked to the cortical processing of internal bodily signals.

Interoceptive signals impact visual processing: Cardiac modulation of visual body perception.

Multisensory perception research has largely focused on exteroceptive signals, but recent evidence has revealed the integration of interoceptive signals with exteroceptive information. Such research revealed that heartbeat signals affect sensory (e.g., visual) processing: however, it is unknown how they impact the perception of body images. Here we linked our participants' heartbeat to visual stimuli and investigated the spatio-temporal brain dynamics of cardio-visual stimulation on the processing of human body images. We recorded visual evoked potentials with 64-channel electroencephalography while showing a body or a scrambled-body (control) that appeared at the frequency of the on-line recorded participants' heartbeat or not (not-synchronous, control). Extending earlier studies, we found a body-independent effect, with cardiac signals enhancing visual processing during two time periods (77-130 ms and 145-246 ms). Within the second (later) time-window we detected a second effect characterised by enhanced activity in parietal, temporo-occipital, inferior frontal, and right basal ganglia-insula regions, but only when non-scrambled body images were flashed synchronously with the heartbeat (208-224 ms). In conclusion, our results highlight the role of interoceptive information for the visual processing of human body pictures within a network integrating cardio-visual signals of relevance for perceptual and cognitive aspects of visual body processing.

Distinct vestibular effects on early and late somatosensory cortical processing in humans.

In non-human primates several brain areas contain neurons that respond to both vestibular and somatosensory stimulation. In humans, vestibular stimulation activates several somatosensory brain regions and improves tactile perception. However, less is known about the spatio-temporal dynamics of such vestibular-somatosensory interactions in the human brain. To address this issue, we recorded high-density electroencephalography during left median nerve electrical stimulation to obtain Somatosensory Evoked Potentials (SEPs). We analyzed SEPs during vestibular activation following sudden decelerations from constant-velocity (90°/s and 60°/s) earth-vertical axis yaw rotations and SEPs during a non-vestibular control period. SEP analysis revealed two distinct temporal effects of vestibular activation: An early effect (28-32ms post-stimulus) characterized by vestibular suppression of SEP response strength that depended on rotation velocity and a later effect (97-112ms post-stimulus) characterized by vestibular modulation of SEP topographical pattern that was rotation velocity-independent. Source estimation localized these vestibular effects, during both time periods, to activation differences in a distributed cortical network including the right postcentral gyrus, right insula, left precuneus, and bilateral secondary somatosensory cortex. These results suggest that vestibular-somatosensory interactions in humans depend on processing in specific time periods in somatosensory and vestibular cortical regions.

Semantic Relations between Visual Objects Can Be Unconsciously Processed but Not Reported under Change Blindness.

Change blindness-the failure to detect changes in visual scenes-has often been interpreted as a result of impoverished visual information encoding or as a failure to compare the prechange and postchange scene. In the present electroencephalography study, we investigated whether semantic features of prechange and postchange information are processed unconsciously, even when observers are unaware that a change has occurred. We presented scenes composed of natural objects in which one object changed from one presentation to the next. Object changes were either semantically related (e.g., rail car changed to rail) or unrelated (e.g., rail car changed to sausage). Observers were first asked to detect whether any change had occurred and then to judge the semantic relation of the two objects involved in the change. We found a semantic mismatch ERP effect, that is, a more negative-going ERP for semantically unrelated compared to related changes, originating from a cortical network including the left middle temporal gyrus and occipital cortex and resembling the N400 effect, albeit at longer latencies. Importantly, this semantic mismatch effect persisted even when observers were unaware of the change and the semantic relationship of prechange and postchange object. This finding implies that change blindness does not preclude the encoding of the prechange and postchange objects' identities and possibly even the comparison of their semantic content. Thus, change blindness cannot be interpreted as resulting from impoverished or volatile visual representations or as a failure to process the prechange and postchange object. Instead, change detection appears to be limited at a later, postperceptual stage.

Spatiotemporal brain dynamics of emotional face processing modulations induced by the serotonin 1A/2A receptor agonist psilocybin.

Emotional face processing is critically modulated by the serotonergic system. For instance, emotional face processing is impaired by acute psilocybin administration, a serotonin (5-HT) 1A and 2A receptor agonist. However, the spatiotemporal brain mechanisms underlying these modulations are poorly understood. Here, we investigated the spatiotemporal brain dynamics underlying psilocybin-induced modulations during emotional face processing. Electrical neuroimaging analyses were applied to visual evoked potentials in response to emotional faces, following psilocybin and placebo administration. Our results indicate a first time period of strength (i.e., Global Field Power) modulation over the 168-189 ms poststimulus interval, induced by psilocybin. A second time period of strength modulation was identified over the 211-242 ms poststimulus interval. Source estimations over these 2 time periods further revealed decreased activity in response to both neutral and fearful faces within limbic areas, including amygdala and parahippocampal gyrus, and the right temporal cortex over the 168-189 ms interval, and reduced activity in response to happy faces within limbic and right temporo-occipital brain areas over the 211-242 ms interval. Our results indicate a selective and temporally dissociable effect of psilocybin on the neuronal correlates of emotional face processing, consistent with a modulation of the top-down control.

Invisible visual stimuli elicit increases in alpha-band power.

The cerebral cortex responds to stimuli of a wide range of intensities. Previous studies have demonstrated that undetectably weak somatosensory stimuli cause a functional deactivation or inhibition in somatosensory cortex. In the present study, we tested whether invisible visual stimuli lead to similar responses, indicated by an increase in EEG alpha-band power-an index of cortical excitability. We presented subliminal and supraliminal visual stimuli after estimating each participant's detection threshold. Stimuli consisted of peripherally presented small circular patches that differed in their contrast to a background consisting of a random white noise pattern. We demonstrate that subliminal and supraliminal stimuli each elicit specific neuronal response patterns. Supraliminal stimuli evoked an early, strongly phase-locked lower-frequency response representing the evoked potential and induced a decrease in alpha-band power from 400 ms on. By contrast, subliminal visual stimuli induced an increase of non-phase-locked power around 300 ms that was maximal within the alpha-band. This response might be due to an inhibitory mechanism, which reduces spurious visual activation that is unlikely to result from external stimuli.

Numerosity estimation of virtual humans as a digital-robotic marker for hallucinations in Parkinson's disease.

Hallucinations are frequent non-motor symptoms in Parkinson's disease (PD) associated with dementia and higher mortality. Despite their high clinical relevance, current assessments of hallucinations are based on verbal self-reports and interviews that are limited by important biases. Here, we used virtual reality (VR), robotics, and digital online technology to quantify presence hallucination (vivid sensations that another person is nearby when no one is actually present and can neither be seen nor heard) in laboratory and home-based settings. We establish that elevated numerosity estimation of virtual human agents in VR is a digital marker for experimentally induced presence hallucinations in healthy participants, as confirmed across several control conditions and analyses. We translated the digital marker (numerosity estimation) to an online procedure that 170 PD patients carried out remotely at their homes, revealing that PD patients with disease-related presence hallucinations (but not control PD patients) showed higher numerosity estimation. Numerosity estimation enables quantitative monitoring of hallucinations, is an easy-to-use unobtrusive online method, reaching people far away from medical centers, translating neuroscientific findings using robotics and VR, to patients' homes without specific equipment or trained staff.

Phantom Boarder Relates to Experimentally-Induced Presence Hallucinations in Parkinson's Disease.

Background: Phantom boarder (PB) is the sensation that someone uninvited is in the patient's home despite evidence to the contrary. It is mostly reported by patients with neurodegenerative disorders such as Alzheimer's disease, dementia with Lewy bodies or Parkinson's disease (PD). Presence hallucination (PH) is frequent in neurodegenerative disease, shares several aspects with PB, and is the sensation that someone is nearby, behind or next to the patient (when nobody is actually there). Recent work developed a sensorimotor method to robotically induce PH (robot-induced PH, riPH) and demonstrated that a subgroup of PD patients showed abnormal sensitivity for riPH. Objective: We investigated if PD patients with PB (PD-PB) would (1) show elevated sensitivity for riPH that (2) is comparable to that of patients reporting PH, but not PB (PD-PH). Methods: We studied the sensitivity of non-demented PD patients in a sensorimotor stimulation paradigm, during which three groups of patients (PD-PB; PD-PH; PD patients without hallucinations, PD-nPH) were exposed to different conditions of conflicting sensorimotor stimulation. Results: We show that PD-PB and PD-PH groups had a higher sensitivity to riPH (compared to PD-nPH). PD-PB and PD-PH groups did not differ in riPH sensitivity. Together with interview data, these behavioral data on riPH show that PB is associated with PH, suggesting that both share some underlying brain mechanisms, although interview data also revealed phenomenological differences. Conclusions: Because PD-PB patients did not suffer from dementia nor delusions, we argue that these shared mechanisms are of perceptual-hallucinatory nature, involving sensorimotor signals and their integration.

Noise in brain activity engenders perception and influences discrimination sensitivity.

Behavioral and brain responses to identical stimuli can vary with experimental and task parameters, including the context of stimulus presentation or attention. More surprisingly, computational models suggest that noise-related random fluctuations in brain responses to stimuli would alone be sufficient to engender perceptual differences between physically identical stimuli. In two experiments combining psychophysics and EEG in healthy humans, we investigated brain mechanisms whereby identical stimuli are (erroneously) perceived as different (higher vs lower in pitch or longer vs shorter in duration) in the absence of any change in the experimental context. Even though, as expected, participants' percepts to identical stimuli varied randomly, a classification algorithm based on a mixture of Gaussians model (GMM) showed that there was sufficient information in single-trial EEG to reliably predict participants' judgments of the stimulus dimension. By contrasting electrical neuroimaging analyses of auditory evoked potentials (AEPs) to the identical stimuli as a function of participants' percepts, we identified the precise timing and neural correlates (strength vs topographic modulations) as well as intracranial sources of these erroneous perceptions. In both experiments, AEP differences first occurred ~100 ms after stimulus onset and were the result of topographic modulations following from changes in the configuration of active brain networks. Source estimations localized the origin of variations in perceived pitch of identical stimuli within right temporal and left frontal areas and of variations in perceived duration within right temporoparietal areas. We discuss our results in terms of providing neurophysiologic evidence for the contribution of random fluctuations in brain activity to conscious perception.

Spatio-temporal brain dynamics mediating post-error behavioral adjustments.

Optimal behavior relies on flexible adaptation to environmental requirements, notably based on the detection of errors. The impact of error detection on subsequent behavior typically manifests as a slowing down of RTs following errors. Precisely how errors impact the processing of subsequent stimuli and in turn shape behavior remains unresolved. To address these questions, we used an auditory spatial go/no-go task where continual feedback informed participants of whether they were too slow. We contrasted auditory-evoked potentials to left-lateralized go and right no-go stimuli as a function of performance on the preceding go stimuli, generating a 2 × 2 design with "preceding performance" (fast hit [FH], slow hit [SH]) and stimulus type (go, no-go) as within-subject factors. SH trials yielded SH trials on the following trials more often than did FHs, supporting our assumption that SHs engaged effects similar to errors. Electrophysiologically, auditory-evoked potentials modulated topographically as a function of preceding performance 80-110 msec poststimulus onset and then as a function of stimulus type at 110-140 msec, indicative of changes in the underlying brain networks. Source estimations revealed a stronger activity of prefrontal regions to stimuli after successful than error trials, followed by a stronger response of parietal areas to the no-go than go stimuli. We interpret these results in terms of a shift from a fast automatic to a slow controlled form of inhibitory control induced by the detection of errors, manifesting during low-level integration of task-relevant features of subsequent stimuli, which in turn influences response speed.

Auditory perceptual decision-making based on semantic categorization of environmental sounds.

Discriminating complex sounds relies on multiple stages of differential brain activity. The specific roles of these stages and their links to perception were the focus of the present study. We presented 250 ms duration sounds of living and man-made objects while recording 160-channel electroencephalography (EEG). Subjects categorized each sound as that of a living, man-made or unknown item. We tested whether/when the brain discriminates between sound categories even when not transpiring behaviorally. We applied a single-trial classifier that identified voltage topographies and latencies at which brain responses are most discriminative. For sounds that the subjects could not categorize, we could successfully decode the semantic category based on differences in voltage topographies during the 116-174 ms post-stimulus period. Sounds that were correctly categorized as that of a living or man-made item by the same subjects exhibited two periods of differences in voltage topographies at the single-trial level. Subjects exhibited differential activity before the sound ended (starting at 112 ms) and on a separate period at ~270 ms post-stimulus onset. Because each of these periods could be used to reliably decode semantic categories, we interpreted the first as being related to an implicit tuning for sound representations and the second as being linked to perceptual decision-making processes. Collectively, our results show that the brain discriminates environmental sounds during early stages and independently of behavioral proficiency and that explicit sound categorization requires a subsequent processing stage.

Neuroscience robotics for controlled induction and real-time assessment of hallucinations.

Although hallucinations are important and frequent symptoms in major psychiatric and neurological diseases, little is known about their brain mechanisms. Hallucinations are unpredictable and private experiences, making their investigation, quantification and assessment highly challenging. A major shortcoming in hallucination research is the absence of methods able to induce specific and short-lasting hallucinations, which resemble clinical hallucinations, can be elicited repeatedly and vary across experimental conditions. By integrating clinical observations and recent advances in cognitive neuroscience with robotics, we have designed a novel device and sensorimotor method able to repeatedly induce a specific, clinically relevant hallucination: presence hallucination. Presence hallucinations are induced by applying specific conflicting (spatiotemporal) sensorimotor stimulation including an upper extremity and the torso of the participant. Another, MRI-compatible, robotic device using similar sensorimotor stimulation permitted the identification of the brain mechanisms of these hallucinations. Enabling the identification of behavioral and a frontotemporal neural biomarkers of hallucinations, under fully controlled experimental conditions and in real-time, this method can be applied in healthy participants as well as patients with schizophrenia, neurodegenerative disease or other hallucinations. The execution of these protocols requires intermediate-level skills in cognitive neuroscience and MRI processing, as well as minimal coding experience to control the robotic device. These protocols take ~3 h to be completed.

Neural signatures of visuo-motor integration during human-robot interactions.

Visuo-motor integration shapes our daily experience and underpins the sense of feeling in control over our actions. The last decade has seen a surge in robotically and virtually mediated interactions, whereby bodily actions ultimately result in an artificial movement. But despite the growing number of applications, the neurophysiological correlates of visuo-motor processing during human-machine interactions under dynamic conditions remain scarce. Here we address this issue by employing a bimanual robotic interface able to track voluntary hands movement, rendered in real-time into the motion of two virtual hands. We experimentally manipulated the visual feedback in the virtual reality with spatial and temporal conflicts and investigated their impact on (1) visuo-motor integration and (2) the subjective experience of being the author of one's action (i.e., sense of agency). Using somatosensory evoked responses measured with electroencephalography, we investigated neural differences occurring when the integration between motor commands and visual feedback is disrupted. Our results show that the right posterior parietal cortex encodes for differences between congruent and spatially-incongruent interactions. The experimental manipulations also induced a decrease in the sense of agency over the robotically-mediated actions. These findings offer solid neurophysiological grounds that can be used in the future to monitor integration mechanisms during movements and ultimately enhance subjective experience during human-machine interactions.