Noriaki Kanayama

Agency over a phantom limb and electromyographic activity on the stump depend on visuomotor synchrony : a case study

Most patients, post-amputation, report the experience of a phantom limb. Some even sense voluntary movements when viewing a mirror image of the intact limb superimposed onto the phantom limb. While delayed visual feedback of an action is known to reduce a sense of agency, the effect of delayed visual feedback on phantom motor sensation (i.e., sense of controlling a phantom limb) has not been examined. Using a video-projection system, we examined the effect of delayed visual feedback on phantom motor sensation in an upper-limb amputee (male; left upper-limb amputation). He was instructed to view mirrored video images of his intact hand clasping and unclasping during a phantom limb movement. He then rated the intensity of the phantom motor sensation. Three types of hand movement images were presented as follows: synchronous, asynchronous with a 250-ms delay, and asynchronous with a 500-ms delay. Results showed that phantom motor sensation decreased when the image was delayed by 250 and 500 ms. However, when we instructed the patient to adjust the phase of phantom limb movement to that of the image with a 500-ms delay, phantom motor sensation increased. There was also a positive correlation between intensity of phantom motor sensation and electromyographic (EMG) activity on deltoids at the patient’s stump. These results suggest that phantom motor sensation and EMG activity on the stump depend on visuomotor synchrony and top-down effects.

Tuning of temporo-occipital activity by frontal oscillations during virtual mirror exposure causes erroneous self-recognition

Self‐face recognition, a hallmark of self‐awareness, depends on ‘off‐line’ stored information about ones face and ‘on‐line’ multisensory‐motor face‐related cues. The brain mechanisms of how on‐line sensory‐motor processes affect off‐line neural self‐face representations are unknown. This study used 3D virtual reality to create a ‘virtual mirror’ in which participants saw an avatars face moving synchronously with their own face movements. Electroencephalographic (EEG) analysis during virtual mirror exposure revealed mu oscillations in sensory‐motor cortex signalling on‐line congruency between the avatars and participants’ movements. After such exposure and compatible with a change in their off‐line self‐face representation, participants were more prone to recognize the avatars face as their own, and this was also reflected in the activation of face‐specific regions in the inferotemporal cortex. Further EEG analysis showed that the on‐line sensory‐motor effects during virtual mirror exposure caused these off‐line visual effects, revealing the brain mechanisms that maintain a coherent self‐representation, despite our continuously changing appearance.

Top down influence on visuo-tactile interaction modulates neural oscillatory responses

Multisensory integration involves bottom-up as well as top-down processes. We investigated the influences of top-down control on the neural responses to multisensory stimulation using EEG recording and time-frequency analyses. Participants were stimulated at the index or thumb of the left hand, using tactile vibrators mounted on a foam cube. Simultaneously they received a visual distractor from a light emitting diode adjacent to the active vibrator (spatially congruent trial) or adjacent to the inactive vibrator (spatially incongruent trial). The task was to respond to the elevation of the tactile stimulus (upper or lower), while ignoring the simultaneous visual distractor. To manipulate top-down control on this multisensory stimulation, the proportion of spatially congruent (vs. incongruent) trials was changed across blocks. Our results reveal that the behavioral cost of responding to incongruent than congruent trials (i.e., the crossmodal congruency effect) was modulated by the proportion of congruent trials. Most importantly, the EEG gamma band response and the gamma-theta coupling were also affected by this modulation of top-down control, whereas the late theta band response related to the congruency effect was not. These findings suggest that gamma band response is more than a marker of multisensory binding, being also sensitive to the correspondence between expected and actual multisensory stimulation. By contrast, theta band response was affected by congruency but appears to be largely immune to stimulation expectancy.

Neural overlap between resting state and self-relevant activity in human subcallosal cingulate cortex – Single unit recording in an intracranial study

High activity of the default mode network (DMN) has been proposed to be central in processing self-relevant events. Thus far, this hypothesis of DMN function has not been tested directly using neurophysiological techniques. To test for the link between frontal midline DMN activity and self-relevant processing we measured neuronal activity (single-neurons firing rates) in human subcallosal cingulate cortex (SCC) in the course of Deep Brain Stimulation surgery. We find that firing rates in SCC did not change during the presentation of specifically self-relevant stimuli when compared to the preceding pre-stimulus resting state level. In contrast, we observed significant changes in firing rates during other names in SCC. Such rest-self overlap seems to be specific for SCC since increase in firing rates in response to self-relevant stimuli were observed in another region, the subthalamic nucleus, in a group of Parkinson patients receiving deep brain stimulation surgery. These results suggest specific relationship between resting state and self-related activity, rest-self overlap, in specifically SCC as core region of the default-mode network.

Multisensory processing and neural oscillatory responses: separation of visuotactile congruency effect and corresponding electroencephalogram activities.

By using electroencephalogram, we aimed at identifying the neural oscillations corresponding to two subcomponents of the visuotactile congruency process, facilitation and interference effects. The participants identified the location of the tactile stimulus presented at their index finger or thumb while ignoring simultaneous visual stimuli presented at the same (congruent) or different (incongruent) finger. Significant differences in reaction time were found between the congruent or incongruent condition and the unimodal baseline condition, indicating two different effects of visuotactile interaction. Electroencephalogram results showed significant increases in the &ggr;-band response in the congruent condition and in the &thetas;-band response in the incongruent condition. These results suggest two systems of multisensory interaction.

Cortical EEG components that reflect inverse effectiveness during visuotactile integration processing

Multisensory integration is required to interpret information from multiple senses and then produce the appropriate behavioral output. Inverse effectiveness, a phenomenon in which weaker stimuli induce greater activation of multisensory neurons than do stronger stimuli, is an essential component of multisensory integration. The superior colliculus is especially abundant in multisensory neurons with properties of inverse effectiveness. However, multisensory neurons are distributed throughout the brain, suggesting that a wide range of brain regions are involved in generating multisensory behavior in addition to the superior colliculus. In this study, we aimed to use scalp EEG to elucidate the cortical responses that respond to multisensory stimuli according to the principle of inverse effectiveness. By modulating the intensity of the tactile aspect of a simultaneous visuotactile stimulus, we explored the time-frequency component of scalp EEG waveforms produced during multi-sensory stimulation. Using this method, we determined the relative values and temporal dynamics of the increment of power spectrum (event-related spectrum perturbation) and phase coherence across trials (e.g., inter-trial phase coherency) produced by multisensory stimulation compared to unisensory stimulation. In the somatosensory and anterior cingulate cortices, we observed significant differences in the inter-trial phase coherence of the theta band oscillation 200-400 ms post-stimulus, in response to visuotactile (multisensory) and tactile (unisensory) stimulation, while no differences were found in later time windows and other cortical areas. These results suggest that inverse effectiveness is an important aspect of multi-sensory processing in the somato-sensory and frontal cerebral cortices.

“Cutaneous Rabbit” Hops Toward a Light: Unimodal and Cross-Modal Causality on the Skin

Our somatosensory system deals with not only spatial but also temporal imprecision, resulting in characteristic spatiotemporal illusions. Repeated rapid stimulation at the wrist, then near the elbow, can create the illusion of touch at intervening locations along the arm (as if a rabbit is hopping along the arm). This is known as the “cutaneous rabbit effect” (CRE). Previous studies have suggested that the CRE involves not only an intrinsic somatotopic representation but also the representation of an extended body schema that includes causality or animacy perception upon the skin. On the other hand, unlike other multi-modal causality couplings, it is possible that the CRE is not affected by concurrent auditory temporal information. The present study examined the effect of a simple visual flash on the CRE, which has both temporal and spatial information. Here, stronger cross-modal causality or correspondence could be provided. We presented three successive tactile stimuli on the inside of a participant’s left arm. Stimuli were presented on the wrist, elbow, and midway between the two. Results from our five experimental manipulations suggest that a one-shot flash enhances or attenuates the CRE depending on its congruency with cutaneous rabbit saltation. Our results reflect that (1) our brain interprets successive stimuli on the skin as motion in terms of time and space (unimodal causality) and that (2) the concurrent signals from other modalities provide clues for creating unified representations of this external motion (multi-modal causality) as to the extent that “spatiotemporal” synchronicity among modalities is provided.Our somatosensory system deals with not only spatial but also temporal imprecision, resulting in characteristic spatiotemporal illusions. Repeated rapid stimulation at the wrist, then near the elbow, can create the illusion of touch at intervening locations along the arm (as if a rabbit is hopping along the arm). This is known as the “cutaneous rabbit effect” (CRE). Previous studies have suggested that the CRE involves not only an intrinsic somatotopic representation but also the representation of an extended body schema that includes causality or animacy perception upon the skin. On the other hand, unlike other multi-modal causality couplings, it is possible that the CRE is not affected by concurrent auditory temporal information. The present study examined the effect of a simple visual flash on the CRE, which has both temporal and spatial information. Here, stronger cross-modal causality or correspondence could be provided. We presented three successive tactile stimuli on the inside of a participant’s left arm. Stimuli were presented on the wrist, elbow, and midway between the two. Results from our five experimental manipulations suggest that a one-shot flash enhances or attenuates the CRE depending on its congruency with cutaneous rabbit saltation. Our results reflect that (1) our brain interprets successive stimuli on the skin as motion in terms of time and space (unimodal causality) and that (2) the concurrent signals from other modalities provide clues for creating unified representations of this external motion (multi-modal causality) as to the extent that “spatiotemporal” synchronicity among modalities is provided.

Causal Dynamics of Scalp Electroencephalography Oscillation During the Rubber Hand Illusion

Rubber hand illusion (RHI) is an important phenomenon for the investigation of body ownership and self/other distinction. The illusion is promoted by the spatial and temporal contingencies of visual inputs near a fake hand and physical touches to the real hand. The neural basis of this phenomenon is not fully understood. We hypothesized that the RHI is associated with a fronto-parietal circuit, and the goal of this study was to determine the dynamics of neural oscillation associated with this phenomenon. We measured electroencephalography while delivering spatially congruent/incongruent visuo-tactile stimulations to fake and real hands. We applied time–frequency analyses and calculated renormalized partial directed coherence (rPDC) to examine cortical dynamics during the bodily illusion. When visuo-tactile stimulation was spatially congruent, and the fake and real hands were aligned, we observed a reduced causal relationship from the medial frontal to the parietal regions with respect to baseline, around 200xa0ms post-stimulus. This change in rPDC was negatively correlated with a subjective report of the RHI intensity. Moreover, we observed a link between the proprioceptive drift and an increased causal relationship from the parietal cortex to the right somatosensory cortex during a relatively late period (550–750xa0ms post-stimulus). These findings suggest a two-stage process in which (1) reduced influence from the medial frontal regions over the parietal areas unlocks the mechanisms that preserve body integrity, allowing RHI to emerge; and (2) information processed at the parietal cortex is back-projected to the somatosensory cortex contralateral to the real hand, inducing proprioceptive drift.

Development of Embodied Sense of Self Scale (ESSS): Exploring Everyday Experiences Induced by Anomalous Self-Representation.

The scientific exploration of the self has progressed, with much attention focused on the Embodied Sense of Self (ESS). Empirical studies have suggested the mechanisms for self-representation. On the other hand, less attention has been paid to the subjectivity itself of the self. With reference to previous studies, the current study collected items that reflect the ESS and statistically extracted three factors for it: Ownership, Agency, and Narrative. The developed questionnaire [Embodied Sense of Self Scale (ESSS)] showed good enough validity and reliability for practical use. Furthermore, ESSS discriminated schizophrenia, a disorder of the ESS, from controls. We discuss the factorial structure of ESS and the relationship among factors on the basis of the current results.

Post-response βγ power predicts the degree of choice-based learning in internally guided decision-making.

Choosing an option increases a person’s preference for that option. This phenomenon, called choice-based learning (CBL), has been investigated separately in the contexts of internally guided decision-making (IDM, e.g., preference judgment), for which no objectively correct answer exists, and externally guided decision making (EDM, e.g., perceptual decision making), for which one objectively correct answer exists. For the present study, we compared decision making of these two types to examine differences of underlying neural processes of CBL. As IDM and EDM tasks, occupation preference judgment and salary judgment were used, respectively. To compare CBL for the two types of decision making, we developed a novel measurement of CBL: decision consistency. When CBL occurs, decision consistency is higher in the last-half trials than in first-half trials. Electroencephalography (EEG) data have demonstrated that the change of decision consistency is positively correlated with the fronto-central beta–gamma power after response in the first-half trials for IDM, but not for EDM. Those results demonstrate for the first time the difference of CBL between IDM and EDM. The fronto-central beta–gamma power is expected to reflect a key process of CBL, specifically for IDM.