Effects of prism adaptation and visual scanning training on perceptual and response bias in unilateral spatial neglect.

In some patients with unilateral spatial neglect, symptoms reflect impaired lateralized spatial attention and representation (perceptual bias) whereas in others the inability to respond to stimuli located in contralesional space (response bias). Here, we investigated whether prismatic adaptation (PA) and visual scanning training (VST) differentially affect perceptual and response bias and whether rehabilitation outcome depends on the type of bias underlying symptoms. Two groups of neglect patients in the subacute phase were evaluated before, immediately after, and two weeks following 10 days of PA (n = 9) or VST (n = 9). Standard neuropsychological tests (i.e., Behavioural Inattentional Test, Diller cancellation test, and Line Bisection test) were administered to assess neglect symptoms, while the Landmark task was used to disentangle perceptual and response biases. Performance on the Landmark task revealed that PA was more effective in improving the perceptual bias, while VST mainly modulated the response bias. Neuropsychological tests performance suggested that VST is better suited to modulate neglect in patients with response bias, while PA may be effective in patients with both types of bias. These findings may offer novel insights into the efficacy of PA and VST in the rehabilitation of perceptual and response biases in patients with neglect.

Modulation of Motor Awareness: A Transcranial Magnetic Stimulation Study in the Healthy Brain.

Previous studies on the mechanisms underlying willed actions reported that the premotor cortex may be involved in the construction of motor awareness. However, its exact role is still under investigation. Here, we investigated the role of the dorsal premotor cortex (PMd) in motor awareness by modulating its activity applying inhibitory rTMS to PMd, before a specific motor awareness task (under three conditions: without stimulation, after rTMS and after Sham stimulation). During the task, subjects had to trace straight lines to a given target, receiving visual feedback of the line trajectories on a computer screen. Crucially, in most trials, the trajectories on the screen were deviated, and to produce straight lines, subjects had to correct their movements towards the opposite direction. After each trial, participants were asked to judge whether the line seen on the computer screen corresponded to the line actually drawn. Results show that participants in the No Stimulation condition did not recognize the perturbation until 14 degrees of deviation. Importantly, active, but not Sham, rTMS significantly modulated motor awareness, decreasing the amplitude of the angle at which participants became aware of the trajectory correction. These results suggest that PMd plays a crucial role in action self-monitoring.

Modulation of vestibular input by short-term head-down bed rest affects somatosensory perception: implications for space missions.

Introduction: On Earth, self-produced somatosensory stimuli are typically perceived as less intense than externally generated stimuli of the same intensity, a phenomenon referred to as somatosensory attenuation (SA). Although this phenomenon arises from the integration of multisensory signals, the specific contribution of the vestibular system and the sense of gravity to somatosensory cognition underlying distinction between self-generated and externally generated sensations remains largely unknown. Here, we investigated whether temporary modulation of the gravitational input by head-down tilt bed rest (HDBR)-a well-known Earth-based analog of microgravity-might significantly affect somatosensory perception of self- and externally generated stimuli. Methods: In this study, 40 healthy participants were tested using short-term HDBR. Participants received a total of 40 non-painful self- and others generated electrical stimuli (20 self- and 20 other-generated stimuli) in an upright and HDBR position while blindfolded. After each stimulus, they were asked to rate the perceived intensity of the stimulation on a Likert scale. Results: Somatosensory stimulations were perceived as significantly less intense during HDBR compared to upright position, regardless of the agent administering the stimulus. In addition, the magnitude of SA in upright position was negatively correlated with the participants' somatosensory threshold. Based on the direction of SA in the upright position, participants were divided in two subgroups. In the subgroup experiencing SA, the intensity rating of stimulations generated by others decreased significantly during HDBR, leading to the disappearance of the phenomenon of SA. In the second subgroup, on the other hand, reversed SA was not affected by HDBR. Conclusion: Modulation of the gravitational input by HDBR produced underestimation of somatosensory stimuli. Furthermore, in participants experiencing SA, the reduction of vestibular inputs by HDBR led to the disappearance of the SA phenomenon. These findings provide new insights into the role of the gravitational input in somatosensory perception and have important implications for astronauts who are exposed to weightlessness during space missions.

Can static Rorschach stimuli perceived as in motion affect corticospinal excitability?

It has been proposed that seeing human movement or activity (M), while trying to say what the static Rorschach inkblot design look like, is accompanied by Mirror Neuron System (MNS)-like mirroring activity in the brain. The present study aimed to investigate whether the Rorschach cards eliciting M responses could affect the excitability of the motor cortex by recording motor evoked potentials (MEPs) elicited by single-pulse TMS over the primary motor cortex (M1). We hypothesized that Rorschach inkblot stimuli triggering the viewer's experience of human movement would increase corticospinal excitability. Twenty-one healthy volunteers (15 women) participated in the preliminary experiment, while another different sample of twenty-two healthy participants (11 women) ranging in age from 21 to 41 years was enrolled in the main experiment. Our results showed that the Rorschach cards known to be associated with a high number of M responses elicited human movement both as automatic internal sensations and as verbal production of responses involving human movement. However, contrary to our hypothesis, the reported internal feeling of human movement had no corresponding physiological counterpart, as the amplitude of MEPs did not increase. Possible and innovative explanations for the involvement of bottom-up and top-down processes were provided.

Virtual reality rehabilitation for unilateral spatial neglect: A systematic review of immersive, semi-immersive and non-immersive techniques.

INTRODUCTION: In recent decades, new virtual reality (VR)-based protocols have been proposed for the rehabilitation of Unilateral Spatial Neglect (USN), a debilitating disorder of spatial awareness. However, it remains unclear which type of VR protocol and level of VR immersion can maximize the clinical benefits. To answer these questions, we conducted a systematic review of the use of VR for the rehabilitation of USN. METHOD: Studies between 2000 and 2022 that met the inclusion criteria were classified according to their research design and degree of immersion (non-immersive, NIVR; semi-immersive, SIVR; immersive, IVR). RESULTS: A total of 375 studies were identified, of which 26 met the inclusion criteria. Improvements were found in 84.6% of the reviewed studies: 85.7% used NIVR, 100% used SIVR and 55.6% used IVR. However, only 42.3% of them included a control group and only 19.2% were randomized control trials (RCT). CONCLUSION: VR protocols may offer new opportunities for USN rehabilitation, although further RCTs are needed to validate their clinical efficacy.

Investigating the Origin of TMS-evoked Brain Potentials Using Topographic Analysis.

The combination of transcranial magnetic stimulation (TMS) and electroencephalography (EEG) represents an increasingly popular tool to non-invasively probe cortical excitability in humans. TMS-evoked brain potentials (TEPs) are composed of successive components reflecting the propagation of activity from the site of stimulation, thereby providing information on the state of brain networks. However, TMS also generates peripherally evoked sensory activity which contributes to TEP waveforms and hinders their interpretation.In the present study, we examined whether topographic analysis of TEPs elicited by stimulation of two distinct cortical targets can disentangle confounding signals from the genuine TMS-evoked cortical response. In 20 healthy subjects, TEPs were evoked by stimulation of the left primary motor cortex (M1) and the left angular gyrus (AG). Topographic dissimilarity analysis and microstate analysis were used to identify target-specific TEP components. Furthermore, we explored the contribution of cortico-spinal activation by comparing TEPs elicited by stimulation below and above the threshold to evoke motor responses.We observed topographic dissimilarity between M1 and AG TEPs until approximately 80 ms post-stimulus and identified early TEP components that likely reflect specific TMS-evoked activity. Later components peaking at 100 and 180 ms were similar in both datasets and attributed to sensory-evoked activity. Analysis of sub- and supra-threshold M1 TEPs revealed a component at 17 ms that possibly reflects the cortico-spinal output of the stimulated area. Moreover, supra-threshold M1 activation influenced the topography of almost all later components. Together, our results demonstrate the utility of topographic analysis for the evaluation and interpretation of TMS-evoked EEG responses.

Improvement of Impulsivity and Decision Making by Transcranial Direct Current Stimulation of the Dorsolateral Prefrontal Cortex in a Patient with Gambling Disorder.

Gambling disorder (GD) is a form of behavioral addiction. In recent years, it has been suggested that the application of transcranial Direct Current Stimulation (tDCS) to the dorsolateral prefrontal cortex (DLPFC), which plays a key role in top-down inhibitory control and impulsivity, may represent a new therapeutic approach for treating addictions. Here we investigated the effectiveness of a novel low dose tDCS protocol (i.e. six sessions of right anodal/left cathodal tDCS for 20 min, with a current intensity of 1 mA) applied to DLPFC in a patient with GD. To evaluate the effect of the proposed intervention, cognitive, psychological and behavioural evaluations were performed at different time points, pre and post intervention. The results showed improvement of impulsivity, decision making, and cognitive functioning after tDCS intervention. Findings of the present study suggest that low doses of right anodal/left cathodal tDCS to DLPFC may effectively improve gambling behaviour. They also suggest to carefully evaluate the effects of this tDCS polarity on the patient's emotional state. The current protocol warrants further investigation in large groups of patients, as it may provide relevant insights into the design of effective, low dose treatments of gambling disorder.

When Right Goes Left: Phantom Touch Induced by Mirror Box Procedure in Healthy Individuals.

In the present article, we investigated the possibility of inducing phantom tactile sensations in healthy individuals similar to those that we observed in patients after stroke. On the basis of previous research, we assumed that manipulating visual feedbacks may guide and influence, under certain conditions, the phenomenal experience of touch. To this aim, we used the Tactile Quadrant Stimulation (TQS) test in which subjects, in the crucial condition, must indicate whether and where they perceive a double tactile stimulation applied simultaneously in different quadrants of the two hands (asymmetrical Double Simultaneous Stimulation trial, Asym-DSS). The task was performed with the left-hand out of sight and the right-hand reflected in a mirror so that the right-hand reflected in the mirror looks like the own left-hand. We found that in the Asym-DSS trial, the vision of the right-hand reflected in the mirror and stimulated by a tactile stimulus elicited on the left-hand the sensation of having been touched in the same quadrant as the right-hand. In other words, we found in healthy subjects the same phantom touch effect that we previously found in patients. We interpreted these results as modulation of tactile representation by bottom-up (multisensory integration of stimuli coming from the right real and the right reflected hand) and possibly top-down (body ownership distortion) processing triggered by our experimental setup, unveiling bilateral representation of touch.

Zero gravity induced by parabolic flight enhances automatic capture and weakens voluntary maintenance of visuospatial attention.

Orienting attention in the space around us is a fundamental prerequisite for willed actions. On Earth, at 1 g, orienting attention requires the integration of vestibular signals and vision, although the specific vestibular contribution to voluntary and automatic components of visuospatial attention remains largely unknown. Here, we show that unweighting of the otolith organ in zero gravity during parabolic flight, selectively enhances stimulus-driven capture of automatic visuospatial attention, while weakening voluntary maintenance of covert attention. These findings, besides advancing our comprehension of the basic influence of the vestibular function on voluntary and automatic components of visuospatial attention, may have operational implications for the identification of effective countermeasures to be applied in forthcoming human deep space exploration and habitation, and on Earth, for patients' rehabilitation.

Right and left inferior frontal opercula are involved in discriminating angry and sad facial expressions.

BACKGROUND: Neuroimaging studies suggest that the inferior frontal operculum (IFO) is part of a neuronal network involved in facial expression processing, but the causal role of this region in emotional face discrimination remains elusive. OBJECTIVE: We used cathodal (inhibitory) tDCS to test whether right (r-IFO) and left (l-IFO) IFO play a role in discriminating basic facial emotions in healthy volunteers. Specifically, we tested if the two sites are selectively involved in the processing of facial expressions conveying high or low arousal emotions. Based on the Arousal Hypothesis we expected to find a modulation of high and low arousal emotions by cathodal tDCS of the r-IFO and the l-IFO, respectively. METHODS: First, we validated an Emotional Faces Discrimination Task (EFDT). Then, we targeted the r-IFO and the l-IFO with cathodal tDCS (i.e. the cathode was placed over the right or left IFO, while the anode was placed over the contralateral supraorbital area) during facial emotions discrimination on the EFDT. Non-active (i.e. sham) tDCS was a control condition. RESULTS: Overall, participants manifested the "happy face advantage". Interestingly, tDCS to r-IFO enhanced discrimination of faces expressing anger (a high arousal emotion), whereas, tDCS to l-IFO decreased discrimination of faces expressing sadness (a low arousal emotion). CONCLUSIONS: Our findings revealed a differential causal role of r-IFO and l-IFO in the discrimination of specific high and low arousal emotions. Crucially, these results suggest that cathodal tDCS might reduce the neural noise triggered by facial emotions, improving discrimination of high arousal emotions but disrupting discrimination of low arousal emotions. These findings offer new insights for treating clinical population with deficits in processing facial expressions.

I'm a believer: Illusory self-generated touch elicits sensory attenuation and somatosensory evoked potentials similar to the real self-touch.

Sensory attenuation (i.e., the phenomenon whereby self-produced sensations are perceived as less intense compared to externally occurring ones) is among the neurocognitive processes that help distinguishing ourselves from others. It is thought to be rooted in the motor system (e.g., related to motor intention and prediction), while the role of body awareness, which necessarily accompanies any voluntary movement, in this phenomenon is largely unknown. To fill this gap, here we compared the perceived intensity, somatosensory evoked potentials, and alpha-band desynchronization for self-generated, other-generated, and embodied-fake-hand-generated somatosensory stimuli. We showed that sensory attenuation triggered by the own hand and by the embodied fake hand had the same behavioral and neurophysiological signatures (reduced subjective intensity, reduced of N140 and P200 SEP components and post-stimulus alpha-band desynchronization). Therefore, signals subserving body ownership influenced attenuation of somatosensory stimuli, possibly in a postdictive manner. This indicates that body ownership is crucial for distinguishing the source of the perceived sensations.

Unilateral Spatial Neglect After Stroke: Current Insights.

INTRODUCTION: Unilateral spatial neglect (USN) is a disorder of contralesional space awareness which often follows unilateral brain lesion. Since USN impairs awareness of contralesional space/body and often of concomitant motor disorders, its presence represents a negative prognostic factor of functional recovery. Thus, the disorder needs to be carefully diagnosed and treated. Here, we attempted to present a clear and concise picture of current insights in the comprehension and rehabilitation of USN. METHODS: We first provided an updated overview of USN clinical and neuroanatomical features and then highlighted recent progresses in the diagnosis and rehabilitation of the disease. In relation to USN rehabilitation, we conducted a MEDLINE literature research on three of the most promising interventions for USN rehabilitation: prismatic adaptation (PA), non-invasive brain stimulation (NIBS), and virtual reality (VR). The identified studies were classified according to the strength of their methods. RESULTS: The last years have witnessed a relative decrement of interest in the study of neuropsychological disorders of spatial awareness in USN, but a relative increase in the study of potential interventions for its rehabilitation. Although optimal protocols still need to be defined, high-quality studies have demonstrated the efficacy of PA, TMS and tDCS interventions for the treatment of USN. In addition, preliminary investigations are suggesting the potentials of GVS and VR approaches for USN rehabilitation. CONCLUSION: Advancing neuropsychological and neuroscience tools to investigate USN pathophysiology is a necessary step to identify effective rehabilitation treatments and to foster our understanding of neurofunctional bases of spatial cognition in the healthy brain.

Acute and cumulative effects of rTMS on behavioural and EMG parameters in Focal Hand Dystonia.

Previous studies suggest that low-frequency repetitive Transcranial Magnetic Stimulation (rTMS) over contralateral premotor cortex (PMC) might ameliorate Focal Hand Dystonia (FHD) symptoms. In the present study behavioral and muscle activity outcomes were explored in a patient with FHD following a single and multiple sessions of rTMS. The patient's behavior was assessed on handwriting tasks, while surface EMG signals were recorded. In Experiment 1 evaluations were performed before and after one session of active and sham 1Hz rTMS over contralateral PMC. In Experiment 2, evaluations were performed before and after six sessions of the same treatment. In Experiment 1 active rTMS improved the patient's performance, although the EMG amplitude did not change. In Experiment 2, the patient showed an improvement of performance along with a decrease of 20% in the EMG amplitude. These results demonstrated that a single session of rTMS ameliorated the patient's performance, while multiple sessions were necessary to reduce muscles activity.

Phantom touch: How to unmask sensory unawareness after stroke.

Comprehending the nature of tactile disorders following brain damage is crucial to understand how the brain constructs sensory awareness. Stroke patients may be unaware of being touched on the affected hand if, simultaneously, they are touched on the unaffected hand (i.e., tactile extinction). More rarely, they feel touches on the two hands, when they are solely touched on the unaffected hand (i.e., synchiria). Using a novel assessment tool, we investigated whether in stroke patients with apparent intact tactile awareness on standard evaluation, tactile extinction might be possibly masked by phantom (synchiric) sensations (i.e., elicited by ipsilesional stimulation) arising exclusively during Double Simultaneous Stimulation (DSS). Patients with right (n = 17) and left (n = 8) hemisphere lesions and age-matched healthy controls (n = 13) were tested with the Tactile Quadrant Stimulation test, consisting in delivering unilateral or bilateral touches to one of four quadrants, identified on the participants' hands. In DSS trials, stimuli were applied to asymmetric quadrants. Participants reported the side(s) and then pointed to the site(s) of stimulation. We found that, with the exception of one patient who showed tactile extinction, about 50% of patients with overall intact tactile perception on classical evaluation, although reporting two stimuli in DSS, failed in pointing to the correct contralesional stimulated site. They reported the felt sensation in positions that corresponded to the ipsilesional stimulated sites. Thus apparent detections of contralesional touches in DSS were accounted for by 'phantom' sensations of ipsilesional stimulation that masked unawareness of contralesional touches when classic assessment was applied. Preliminary lesion analyses indicate that the symptom was associated with damage to structures often affected in tactile extinction. These findings, while unveiling important underestimation of the patients' neurological condition, provide a framework for investigating bihemispheric contributions to altered tactile perception following stroke.

Transcranial Magnetic Stimulation of Posterior Parietal Cortex Modulates Line-Length Estimation but Not Illusory Depth Perception.

Transcranial Magnetic Stimulation (TMS) may affect attentional processing when applied to the right posterior parietal cortex (PPC) of healthy participants in line with neuropsychological and neuroimaging evidence on the neural bases of this cognitive function. Specifically, the application of TMS to right PPC induces a rightward attentional bias on line length estimation in healthy participants (i.e., neglect-like bias), mimicking the rightward bias shown by patients with unilateral spatial neglect after damage of the right PPC. With the present study, we investigated whether right PPC might play a crucial role in attentional processing of illusory depth perception, given the evidence that a rightward bias may be observed in patients with neglect during perception of the Necker Cube (NC). To this end, we investigated the effects of low-frequency rTMS applied to the right or left PPC on attentional disambiguation of the NC in two groups of healthy participants. To control for the effectiveness of TMS on visuospatial attention, rTMS effects were also assessed on a frequently used line length estimation (i.e., the Landmark Task or LT). Both groups also received sham stimulation. RTMS of the right or left PPC did not affect NC perception. On the other hand, rTMS of the right PPC (but not left PPC) induces neglect-like bias on the LT, in line with previous studies. These findings confirm that right PPC is involved in deployment of spatial attention on line length estimation. Interestingly, they suggest that this brain region does not critically contribute to deployment of visuospatial attention during attentional disambiguation of the Necker Cube. Future investigations, targeting different areas of fronto-parietal circuits, are necessary to further explore the neuro-functional bases of attentional contribution to illusory depth perception.

Selective Emotional Dysregulation in Splenium Agenesis. A Case Report of a Patient With Normal Cognitive Profile.

Objective: Patients with lesions of the corpus callosum are rare and may present different symptoms of the disconnection syndrome. However, to-date studies on callosotomized patients have not been conclusive, likely because of the non-uniform nature of clinical features, the extent of resection, and methods used to investigate specific and related deficits. Agenesis of the corpus callosum (AgCC) may be asymptomatic and discovered incidentally or associated with very slight deficits diagnosed during neurological examinations. In this study, we reported a case of an apparently completely asymptomatic 23-year-old woman with appreciable agenesis of the splenium of the corpus callosum. Methods: She underwent a neurological evaluation, a comprehensive battery of neuropsychological tests to identify any subclinical dysfunction that may affect the functionality of the subject in the daily life. Specifically, the possible presence of emotion dysregulation was examined by using a self-report questionnaire. Results: She showed normal neuropsychological and emotional functioning, performing efficiently on tests measuring acquired brain impairment. Discussion: The present case is discussed in terms of neuroplasticity - with a focus on putative compensatory mechanisms - emphasizing the variegated clinical feature patterns of brain defects present from birth.

Endogenous orientation of visual attention in auditory space.

Visuospatial attention is asymmetrically distributed with a leftward bias (i.e. pseudoneglect), while evidence for asymmetries in auditory spatial attention is still controversial. In the present study, we investigated putative asymmetries in the distribution of auditory spatial attention and the influence that visual information might have on its deployment. A modified version of the Posner task (i.e. the visuo-audio spatial task [VAST]) was used to investigate spatial processing of auditory targets when endogenous orientation of spatial attention was mediated by visual cues in healthy adults. A line bisection task (LBT) was also administered to assess the presence of a leftward bias in deployment of visuospatial attention. Overall, participants showed rightward and leftward biases in the VAST and the LBT, respectively. In the VAST, sound localization was enhanced by visual cues. Altogether, these findings support the existence of a facilitation effect for auditory targets originating from the right side of space and provide new evidence for crossmodal links in endogenous spatial attention between vision and audition.

Shared neurocognitive mechanisms of attenuating self-touch and illusory self-touch.

Despite the fact that any successful achievement of willed actions necessarily entails the sense of body ownership (the feeling of owning the moving body parts), it is still unclear how this happens. To address this issue at both behavioral and neural levels, we capitalized on sensory attenuation (SA) phenomenon (a self-generated stimulus is perceived as less intense than an identical externally generated stimulus). We compared the intensity of somatosensory stimuli produced by one's own intended movements and by movements of an embodied fake hand. Then, we investigated if in these two conditions SA was equally affected by interfering with the activity of the supplementary motor area (SMA; known to be related to motor intention and SA) using single-pulse transcranial magnetic stimulation. We showed that ownership of the fake hand triggered attenuation of somatosensory stimuli generated by its movements that were comparable to the attenuation of self-generated stimuli. Furthermore, disrupting the SMA eliminated the SA effect regardless of whether it was triggered by actual participant's movements or by illusory ownership. Our findings suggest that SA triggered by body ownership relies, at least in part, on the activation of the same brain structures as SA triggered by motor-related signals.