Neural mechanisms of vibrotactile categorization.

The grouping of sensory stimuli into categories is fundamental to cognition. Previous research in the visual and auditory systems supports a two-stage processing hierarchy that underlies perceptual categorization: (a) a "bottom-up" perceptual stage in sensory cortices where neurons show selectivity for stimulus features and (b) a "top-down" second stage in higher level cortical areas that categorizes the stimulus-selective input from the first stage. In order to test the hypothesis that the two-stage model applies to the somatosensory system, 14 human participants were trained to categorize vibrotactile stimuli presented to their right forearm. Then, during an fMRI scan, participants actively categorized the stimuli. Representational similarity analysis revealed stimulus selectivity in areas including the left precentral and postcentral gyri, the supramarginal gyrus, and the posterior middle temporal gyrus. Crucially, we identified a single category-selective region in the left ventral precentral gyrus. Furthermore, an estimation of directed functional connectivity delivered evidence for robust top-down connectivity from the second to first stage. These results support the validity of the two-stage model of perceptual categorization for the somatosensory system, suggesting common computational principles and a unified theory of perceptual categorization across the visual, auditory, and somatosensory systems.

Clinical Outcomes of 1 kHz Subperception Spinal Cord Stimulation in Implanted Patients With Failed Paresthesia-Based Stimulation: Results of a Prospective Randomized Controlled Trial.

BACKGROUND: Pain relief via spinal cord stimulation (SCS) has historically revolved around producing paresthesia to replace pain, with success measured by the extent of paresthesia-pain overlap. In a recent murine study, by Shechter et al., showed the superior efficacy of high frequency SCS (1 kHz and 10 kHz) at inhibiting the effects of mechanical hypersensitivity compared to sham or 50 Hz stimulation. In the same study, authors report there were no differences in efficacy between 1 kHz and 10 kHz delivered at subperception stimulation strength (80% of motor threshold). Therefore, we designed a randomized, 2 × 2 crossover study of low frequency supra-perception SCS vs. subperception SCS at 1 kHz frequency in order to test whether subperception stimulation at 1 kHz was sufficient to provide effective pain relief in human subjects. METHODS: Twenty-two subjects with SCS, and inadequate pain relief based on numeric pain rating scale (NPRS) scores (>5) were enrolled, and observed for total of seven weeks (three weeks of treatment, one week wash off, and another three weeks of treatment). Subjects were asked to rate their pain on NPRS as a primary efficacy variable, and complete the Oswestry Disability Index (ODI) and Patient's Global Impression of Change (PGIC) as secondary outcome measures. RESULTS: Out of 22 subjects that completed the study, 21 subjects (95%) reported improvements in average, best, and worst pain NPRS scores. All NPRS scores were significantly lower with subperception stimulation compared to paresthesia-based stimulation (p < 0.01, p < 0.05, and p < 0.05, respectively). As with NPRS scores, the treatment effect of subperception stimulation was significantly greater than that of paresthesia based stimulation on ODI scores (p = 3.9737 × 10-5 ) and PGIC scores (p = 3.0396 × 10-5 ).

Beyond physical entrainment: competitive and cooperative mental stances during identical joint-action tasks differently affect inter-subjective neural synchrony and judgments of agency.

Little work has examined how mental stance alone, apart from physical entrainment, affects between-participant neural synchrony during joint social interaction. We report the first findings on how cooperative and competitive mental stances, even during identical visuomotor joint-action tasks, result in distinct neural oscillatory signatures in low beta and theta band between-participant phase synchrony. Two participants jointly controlled a cursor and were instructed to either compete or cooperate to move it to one of three targets. The visuomotor output was identical for both the compete and cooperate conditions because participants were privately given the same target for experimental trials. Cooperation enhanced theta band between-participant phase-locking value (PLV) midtrial at 1-2 seconds, reflecting activation of systems for social coordination to move the cursor in a shared direction. Competition enhanced low beta between-participant PLV, shifting from temporal to frontal regions, indicating that participants focused only on their target and later evaluated self-agency as winner or loser. This interpretation of the neural signature was corroborated by participants' greater post-trial ratings of the degree of control over the cursor during competition. Top-down cooperative and competitive mental stances shape perceptions of social context and affect interpersonal neural synchrony important for representation of self and others' actions.

A Feel for Numbers: The Changing Role of Gesture in Manipulating the Mental Representation of an Abacus Among Children at Different Skill Levels.

Abacus mental arithmetic involves the skilled acquisition of a set of gestures representing mathematical algorithms to properly manipulate an imaginary abacus. The present study examined how the beneficial effect of abacus co-thought gestures varied at different skill and problem difficulty levels. We compared the mental arithmetic performance of 6- to 8-year-old beginning (N = 57), intermediate (N = 65), and advanced (N = 54) learners under three conditions: a physical abacus, hands-free (spontaneous gesture) mental arithmetic, and hands-restricted mental arithmetic. We adopted a mixed-subject design, with level of difficulty and skill level as the within-subject independent variables and condition as the between-subject independent variable. Our results showed a clear contrast in calculation performance and gesture accuracy among learners at different skill levels. Learners first mastered how to calculate using a physical abacus and later benefitted from using abacus gestures to aid mental arithmetic. Hand movement and gesture accuracy indicated that the beneficial effect of gestures may be related to motor learning. Beginners were proficient with a physical abacus, but performed poorly and had low gesture accuracy during mental arithmetic. Intermediates relied on gestures to do mental arithmetic and had accurate hand movements, but performed more poorly when restricted from gesturing. Advanced learners could perform mental arithmetic with accurate gestures and scored just as well without gesturing. These findings suggest that for intermediate and advanced learners, motor-spatial representation through abacus co-thought gestures may complement visual-spatial representation of a mental abacus to reduce working memory load.

Groups and Emotional Arousal Mediate Neural Synchrony and Perceived Ritual Efficacy.

We present the first neurophysiological signatures showing distinctive effects of group social context and emotional arousal on cultural perceptions, such as the efficacy of religious rituals. Using a novel protocol, EEG data were simultaneously recorded from ethnic Chinese religious believers in group and individual settings as they rated the perceived efficacy of low, medium, and high arousal spirit-medium rituals presented as video clips. Neural oscillatory patterns were then analyzed for these perceptual judgements, categorized as low, medium, and high efficacy. The results revealed distinct neural signatures and behavioral patterns between the experimental conditions. Arousal levels predicted ratings of ritual efficacy. Increased efficacy was marked by suppressed alpha and beta power, regardless of group or individual setting. In groups, efficacy ratings converged. Individual setting showed increased within-participant phase synchronization in alpha and beta bands, while group setting enhanced between-participant theta phase synchronization. This reflected group participants' orientation toward a common perspective and social coordination. These findings suggest that co-presence in groups leads to a social-tuning effect supported by between-participant theta phase synchrony. Together these neural synchrony patterns reveal how collective rituals have both individual and communal dimensions. The emotionality of spirit-medium rituals drives individual perceptions of efficacy, while co-presence in groups signals the significance of an event and socially tunes enhanced agreement in perceptual ratings. In other words, mass gatherings may foster social cohesion without necessarily requiring group-size scaling limitations of direct face-to-face interaction. This could have implications for the scaling computability of synchrony in large groups as well as for humanistic studies in areas such as symbolic interactionism.

Cleavage of disulfide-linked fetuin-bisphosphonate conjugates with three physiological thiols.

An effective therapeutic agent for treatment of bone diseases is expected to exhibit a high affinity to bone. Conjugating proteins to bisphosphonates (BPs), a class of molecules with an exceptional affinity to bone mineral hydroxyapatite (HA), is a feasible means to impart such a bone affinity. Protein-BP conjugates with cleavable linkages, which allow protein release from the mineral, are preferable over conjugates with stable linkages. To this end, 2-(3-mercaptopropylsulfanyl)-ethyl-1,1-bisphosphonic acid (thiolBP) was conjugated onto fetuin, a model protein, using N-succinimidyl-3-(2-pyridyldithio)propionate to create disulfide-linked conjugates. Although the fetuin-thiolBP conjugates were stable under aqueous conditions, the disulfide linkage was readily cleaved in the presence of the physiological thiols l-cysteine, dl-homocysteine, and l-glutathione. dl-Homocysteine exhibited the highest cleavage of the disulfide linkage among these thiols. The imparted bone affinity as a result of thiolBP conjugation, as assessed by HA binding in vitro, was eliminated upon cleavage of the disulfide linkage. The cleavage of the conjugates bound to HA was as effective as the conjugate cleavage in solution, and even more so at high concentrations of l-glutathione. In conclusion, disulfide-linked fetuin-thiolBP conjugates exhibited a high affinity to HA, which was readily lost upon cleavage with thiols found in physiological milieu.