Reduced dimension stimulus decoding and column-based modeling reveal architectural differences of primary somatosensory finger maps between younger and older adults.

The primary somatosensory cortex (SI) contains fine-grained tactile representations of the body, arranged in an orderly fashion. The use of ultra-high resolution fMRI data to detect group differences, for example between younger and older adults' SI maps, is challenging, because group alignment often does not preserve the high spatial detail of the data. Here, we use robust-shared response modeling (rSRM) that allows group analyses by mapping individual stimulus-driven responses to a lower dimensional shared feature space, to detect age-related differences in tactile representations between younger and older adults using 7T-fMRI data. Using this method, we show that finger representations are more precise in Brodmann-Area (BA) 3b and BA1 compared to BA2 and motor areas, and that this hierarchical processing is preserved across age groups. By combining rSRM with column-based decoding (C-SRM), we further show that the number of columns that optimally describes finger maps in SI is higher in younger compared to older adults in BA1, indicating a greater columnar size in older adults' SI. Taken together, we conclude that rSRM is suitable for finding fine-grained group differences in ultra-high resolution fMRI data, and we provide first evidence that the columnar architecture in SI changes with increasing age.

Perceptual aftereffects of adiposity transfer from hands to whole bodies.

Adaptation aftereffects for features such as identity and gender have been shown to transfer between faces and bodies, and faces and body parts, i.e. hands. However, no studies have investigated transfer of adaptation aftereffects between whole bodies and body parts. The present study investigated whether visual adaptation aftereffects transfer between hands and whole bodies in the context of adiposity judgements (i.e. how thin or fat a body is). On each trial, participants had to decide whether the body they saw was thinner or fatter than average. Participants performed the task before and after exposure to a thin/fat hand. Consistent with body adaptation studies, after exposure to a slim hand participants judged subsequently presented bodies to be fatter than after adaptation to a fat hand. These results suggest that there may be links between visual representations of body adiposity for whole bodies and body parts.

Aphantasia within the framework of neurodivergence: Some preliminary data and the curse of the confidence gap.

Aphantasia is a neurocognitive phenomenon affecting voluntary visual imagery, such that it is either entirely absent, or markedly impaired. Using both the social and medical models of disability, this article discusses the extent to which aphantasia can be understood as a disorder or just a form of neutral neurodivergence, given that imagery plays a central role in thinking and memory for most other people. Preliminary school performance data are presented, showing that low imagery does not necessarily complicate life, especially given compensatory strategies and low societal barriers. In addition, we discuss the consequences of labelling aphantasia a disorder with regard to self- and public stigma, and we provide further data regarding a confidence gap, by which aphantasics perceive themselves as performing worse than they objectively do. We conclude that aphantasia should be understood as neutral neurodivergence and that labelling it a disorder is not only wrong, but potentially harmful.

A gaze-contingent saccadic re-referencing training with simulated central vision loss.

Patients with central vision loss (CVL) adopt an eccentric retinal location for fixation, a preferred retinal location (PRL), to compensate for vision loss at the fovea. Although most patients with CVL are able to rapidly use a PRL instead of the fovea, saccadic re-referencing to a PRL develops slowly. Without re-referencing, saccades land the saccade target in the scotoma. This results in corrective saccades and leads to inefficient visual exploration. Here, we tested a new method to train saccadic re-referencing. Healthy participants performed gaze-contingent visual search tasks with simulated central scotoma in which participants had to fixate targets with an experimenter-defined forced retinal location (FRL). In experiment 1, we compared single-target search and foraging search tasks in the course of five training sessions. Results showed that both tasks improved the efficiency of gaze sequences and led to saccadic re-referencing to the FRL. In experiment 2, we trained participants extensively for 25 sessions, both with and without a gaze-contingent FRL-marker visible during training. After extensive training, observers' performance approached that of foveal vision. Thus, gaze-contingent FRL-fixation may become an efficient tool for saccadic re-referencing training in patients with central vision loss.

Non-invasive recording of high-frequency signals from the human spinal cord.

Throughout the somatosensory system, neuronal ensembles generate high-frequency signals in the range of several hundred Hertz in response to sensory input. High-frequency signals have been related to neuronal spiking, and could thus help clarify the functional architecture of sensory processing. Recording high-frequency signals from subcortical regions, however, has been limited to clinical pathology whose treatment allows for invasive recordings. Here, we demonstrate the feasibility to record 200-1200 Hz signals from the human spinal cord non-invasively, and in healthy individuals. Using standard electroencephalography equipment in a cervical electrode montage, we observed high-frequency signals between 200 and 1200 Hz in a time window between 8 and 16 ms after electric median nerve stimulation (n = 15). These signals overlapped in latency, and, partly, in frequency, with signals obtained via invasive, epidural recordings from the spinal cord in a patient with neuropathic pain. Importantly, the observed high-frequency signals were dissociable from classic spinal evoked responses. A spatial filter that optimized the signal-to-noise ratio of high-frequency signals led to submaximal amplitudes of the evoked response, and vice versa, ruling out the possibility that high-frequency signals are merely a spectral representation of the evoked response. Furthermore, we observed spontaneous fluctuations in the amplitude of high-frequency signals over time, in the absence of any concurrent, systematic change to the evoked response. High-frequency, "spike-like" signals from the human spinal cord thus carry information that is complementary to the evoked response. The possibility to assess these signals non-invasively provides a novel window onto the neurophysiology of the human spinal cord, both in a context of top-down control over perception, as well as in pathology.

Autosuggestion: a cognitive process that empowers your brain?

Autosuggestion is a cognitive process that is believed to enable control over one's own cognitive and physiological states. Despite its potential importance for basic science and clinical applications, such as in rehabilitation, stress reduction, or pain therapy, the neurocognitive mechanisms and psychological concepts that underlie autosuggestion are poorly defined. Here, by reviewing empirical data on autosuggestion and related phenomena such as mental imagery, mental simulation, and suggestion, we offer a neurocognitive concept of autosuggestion. We argue that autosuggestion is characterized by three major factors: reinstantiation, reiteration, and volitional, active control over one's own physiological states. We also propose that autosuggestion might involve the 'overwriting' of existing predictions or brain states that expect the most common (but not desired) outcome. We discuss potential experimental paradigms that could be used to study autosuggestion in the future, and discuss the strengths and weaknesses of current evidence. This review provides a first overview on how to define, experimentally induce, and study autosuggestion, which may facilitate its use in basic science and clinical practice.

Discriminating Free Hand Movements Using Support Vector Machine and Recurrent Neural Network Algorithms.

Decoding natural hand movements is of interest for human-computer interaction and may constitute a helpful tool in the diagnosis of motor diseases and rehabilitation monitoring. However, the accurate measurement of complex hand movements and the decoding of dynamic movement data remains challenging. Here, we introduce two algorithms, one based on support vector machine (SVM) classification combined with dynamic time warping, and the other based on a long short-term memory (LSTM) neural network, which were designed to discriminate small differences in defined sequences of hand movements. We recorded hand movement data from 17 younger and 17 older adults using an exoskeletal data glove while they were performing six different movement tasks. Accuracy rates in decoding the different movement types were similarly high for SVM and LSTM in across-subject classification, but, for within-subject classification, SVM outperformed LSTM. The SVM-based approach, therefore, appears particularly promising for the development of movement decoding tools, in particular if the goal is to generalize across age groups, for example for detecting specific motor disorders or tracking their progress over time.

Intact Organization of Tactile Space Perception in Isolated Focal Dystonia.

BACKGROUND: Systematic perceptual distortions of tactile space have been documented in healthy adults. In isolated focal dystonia impaired spatial somatosensory processing is suggested to be a central pathophysiological finding, but the structure of tactile space for different body parts has not been previously explored. OBJECTIVES: The objective of this study was to assess tactile space organization with a novel behavioral paradigm of tactile distance perception in patients with isolated focal dystonia and controls. METHODS: Three groups of isolated focal dystonia patients (cervical dystonia, blepharospasm/Meige syndrome, focal hand dystonia) and controls estimated perceived distances between 2 touches across 8 orientations on the back of both hands and the forehead. RESULTS: Stimulus size judgments differed significantly across orientations in all groups replicating distortions of tactile space known for healthy individuals. There were no differences between groups in the behavioral parameters we assessed on the hands and forehead. CONCLUSIONS: Tactile space organization is comparable between patients with isolated focal dystonia and healthy controls in dystonic and unaffected body parts. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Spatial Filtering of Electroencephalography Reduces Artifacts and Enhances Signals Related to Spinal Cord Stimulation (SCS).

OBJECTIVES: How spinal cord stimulation (SCS) in its different modes suppresses pain is poorly understood. Mechanisms of action may reside locally in the spinal cord, but also involve a larger network including subcortical and cortical brain structures. Tonic, burst, and high-frequency modes of SCS can, in principle, entrain distinct temporal activity patterns in this network, but finally have to yield specific effects on pain suppression. Here, we employ high-density electroencephalography (EEG) and recently developed spatial filtering techniques to reduce SCS artifacts and to enhance EEG signals specifically related to neuromodulation by SCS. MATERIALS AND METHODS: We recorded high-density resting-state EEGs in patients suffering from pain of various etiologies under different modes of SCS. We established a pipeline for the robust spectral analysis of oscillatory brain activity during SCS, which includes spatial filtering for attenuation of pulse artifacts and enhancement of brain activity potentially modulated by SCS. RESULTS: In sensor regions responsive to SCS, neuromodulation strongly reduced activity in the theta and low alpha range (6-10 Hz) in all SCS modes. Results were consistent in all patients, and in accordance with thalamocortical dysrhythmia hypothesis of pain. Only in the tonic mode showing paresthesia as side effect, SCS also consistently and strongly reduced high-gamma activity (>84 Hz). CONCLUSIONS: EEG spectral analysis combined with spatial filtering allows for a spatially and temporally specific assessment of SCS-related, neuromodulatory EEG activity, and may help to disentangle therapeutic and side effects of SCS.

Adaptation aftereffects reveal that tactile distance is a basic somatosensory feature.

The stage at which processing of tactile distance occurs is still debated. We addressed this issue by implementing an adaptation-aftereffect paradigm with passive touch. We demonstrated the presence of a strong aftereffect, induced by the simultaneous presentation of pairs of tactile stimuli. After adaptation to two different distances, one on each hand, participants systematically perceived a subsequent stimulus delivered to the hand adapted to the smaller distance as being larger. We further investigated the nature of the aftereffects, demonstrating that they are orientation- and skin-region-specific, occur even when just one hand is adapted, do not transfer either contralaterally or across the palm and dorsum, and are defined in a skin-centered, rather than an external, reference frame. These characteristics of tactile distance aftereffects are similar to those of low-level visual aftereffects, supporting the idea that distance perception arises at early stages of tactile processing.

The Sensitive Period for Tactile Remapping Does Not Include Early Infancy.

Visual input during development seems crucial in tactile spatial perception, given that late, but not congenitally, blind people are impaired when skin-based and tactile external representations are in conflict (when crossing the limbs). To test whether there is a sensitive period during which visual input is necessary, 14 children (age = 7.95) and a teenager (LM; age = 17.38) deprived of early vision by cataracts, and whose sight was restored during the first 5 months and at age 7, respectively, were tested. Tactile localization with arms crossed and uncrossed was measured. Children showed a crossing effect indistinguishable from a control group (Ns = 28, age = 8.24), whereas LM showed no crossing effect (Ns controls = 14, age = 20.78). This demonstrates a sensitive period which, critically, does not include early infancy.

Eating and body image: Does food insecurity make us feel thinner?

Body image distortions are common in healthy individuals and a central aspect of serious clinical conditions, such as eating disorders. This commentary explores the potential implications of body image and its distortions for the insurance hypothesis. In particular, we speculate that body image may be an intervening variable mediating the relationship between perceived food scarcity and eating behavior.

Using temporal order judgments to investigate attention bias toward pain and threat-related information. Methodological and theoretical issues.

Recently, Vanden Bulcke, Crombez, Durnez, and Van Damme (2015) investigated whether the attentional prioritization of a specific location due to the anticipation of pain is modality specific or multisensory. They used a temporal order judgment task in which participants judged the order of either two tactile or two visual stimuli, one presented on each hand. Additionally, participants either expected the occurrence of a painful stimulus on one hand or the absence of any pain. Results showed that participants' judgments were biased to the advantage of the stimuli, tactile or visual, presented at the location where pain was expected. The authors concluded that the anticipation of pain leads to a multisensory prioritization of information presented at the threatened spatial location. Here, we would like to question their conclusion in terms of a genuine attentional modulation of multisensory nature, based on methodological and theoretical grounds.

How the inner repetition of a desired perception changes actual tactile perception.

Autosuggestion is a cognitive process where the inner repetition of a thought actively influences one's own perceptual state. In spite of its potential benefits for medical interventions, this technique has gained little scientific attention so far. Here, we took advantage of the known link between intensity and frequency perception in touch ('Békésy effect'). In three separate experiments, participants were asked to modulate the perceived intensity of vibrotactile stimuli at the fingertip through the inner reiteration of the thought that this perception feels very strong (Experiment 1, n = 19) or very weak (Experiments 2, n = 38, and 3, n = 20), while they were asked to report the perceived frequency. We show that the task to change the perceived intensity of a tactile stimulus via the inner reiteration of a thought modulates tactile frequency perception. This constitutes the first experimental demonstration that an experimental design that triggers autosuggestion alters participants' tactile perception using a response orthogonal to the suggested variable. We discuss whether this cognitive process could be used to influence the perception of pain in a clinical context.

Age-related differences in finger interdependence during complex hand movements.

The well-known decrease in finger dexterity during healthy aging leads to a significant reduction in quality of life. Still, the exact patterns of altered finger kinematics of older adults in daily life are fairly unexplored. Finger interdependence is the unintentional comovement of fingers that are not intended to move, and it is known to vary across the lifespan. Nevertheless, the magnitude and direction of age-related differences in finger interdependence are ambiguous across studies and tasks and have not been explored in the context of daily life finger movements. We investigated five different free and daily-life-inspired finger movements of the right, dominant hand as well as a sequential finger tapping task of the thumb against the other fingers, in 17 younger (22-37 yr) and 17 older (62-80 yr) adults using an exoskeleton data glove for data recording. Using inferential statistics, we found that the unintentional comovement of fingers generally decreases with age in all performed daily-life-inspired movements. Finger tapping, however, showed a trend towards higher finger interdependence for older compared with younger adults. Using machine learning, we predicted the age group of a person from finger interdependence features of single movement trials significantly better than chance level for the daily-life-inspired movements, but not for finger tapping. Taken together, we show that for specific tasks, decreased finger interdependence (i.e., less comovement) could potentially act as a marker of human aging that specifically characterizes older adults' complex finger movements in daily life.NEW & NOTEWORTHY Kinematic finger movement data were analyzed with regard to age-related differences. Extensive analyses of complex and daily-life-inspired movements reveal that the direction of age effects is not uniform but task-dependent: Although older adults generally show more finger interdependence than younger adults in a simple finger tapping task, this effect is reversed for daily-life-inspired movement tasks. For these tasks, finger interdependence indices offer potential new markers to predict the age group of an individual using machine learning approaches.

Non-visual spatial strategies are effective for maintaining precise information in visual working memory.

Visual working memory content is commonly thought to be composed of a precise visual representation of stimulus information (e.g., color, shape). Nevertheless, previous research has shown that individuals represent this visual information in different formats, historically dichotomized into "verbal" and "visual" formats. With growing popular knowledge of aphantasia, or the absence of sensory mental imagery, recent studies have demonstrated that individuals with aphantasia perform similarly to individuals with typical imagery on visual working memory tasks. This suggest that the use of non-visual strategies may be sufficient to perform visual working memory tasks, which were previously thought to be strictly visual. To investigate the effects of different strategies on performance in a visual working memory task, we recruited individuals across the visual imagery spectrum and tested their ability to identify relatively small (3°), medium (6°), or large (10°) changes in the degree of orientation of gratings held in working memory. Subsequently, participants indicated the extent to which they used five different strategies: visual, spatial, verbal, semantic, and sensorimotor. Results revealed that individuals with aphantasia and typical imagery performed similarly to each other across all task difficulty levels. Individuals with typical imagery dominantly used visuospatial strategies, but surprisingly, individuals with aphantasia overwhelmingly preferred the use of non-visual spatial and sensorimotor strategies over verbal strategies. These results suggest that non-visual spatial and sensorimotor strategies can be adopted in visual working memory tasks and these strategies are equally effective as visuospatial strategies. This calls for a rethinking of the "visual" versus "verbal" dichotomy, and provides evidence for the use of other non-visual mental representations in working memory tasks.

Gravitational and retinal reference frames shape spatial memory.

When reproducing the remembered location of dots within a circle, judgments are biased toward the center of imaginary quadrants formed by imaginary vertical and horizontal axes. This effect may result from the heightened precision in the visual system for these orientations in a retinotopic reference frame, or alternately on the internal representation of gravity. We dissociated reference frames defined by the retina and by gravity by having participants locate dots from memory in a circle when their head was upright (aligned with gravity) versus tilted 30° to the left (misaligned with gravity). We mapped the structure of spatial prototypes in a data-driven way using a novel "imaging" procedure. We calculated the rotation of the prototype maps which maximized the similarity between postures, letting us quantify the contribution of each reference frame. Spatial categories are determined by a combination of reference frames, with clear contributions from both gravitational and retinal factors. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Tilt adaptation aftereffects reveal fundamental perceptual characteristics of tactile orientation processing on the hand.

Orientation information contributes substantially to our tactile perception, such as feeling an object's shape on the skin. For vision, a perceptual adaptation aftereffect (tilt aftereffect; TAE), which is well explained by neural orientation selectivity, has been used to reveal fundamental perceptual properties of orientation processing. Neural orientation selectivity has been reported in somatosensory cortices. However, little research has investigated the perceptual characteristics of the tactile TAE. The aim of the current study was to provide the first demonstration of a tactile TAE on the hand and investigate the perceptual nature of tactile TAE on the hand surface. We used a 2-point stimulation with minimal input for orientation. We found clear TAEs on the hand surface: Adaptation induced shifts in subjective vertical sensation toward the orientation opposite to the adapted orientation. Further, adaptation aftereffects were purely based on orientation processing given that the effects transferred between different lengths across adaptor and test stimuli and type of stimuli. Finally, adaptation aftereffects were anchored to the hand: tactile TAE occurred independently of hand rotation and transferred from palm to dorsum sides of the hand, while the effects did not transfer between hands. Our findings demonstrate the existence of hand-centered perceptual processing for basic tactile orientation information. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Changing reference frames during the encoding of tactile events.

The mindless act of swatting a mosquito on the hand poses a remarkable challenge for the brain. Given that the primary somatosensory cortex maps skin location independently of arm posture [1, 2], the brain must realign tactile coordinates in order to locate the origin of the stimuli in extrapersonal space. Previous studies have highlighted the behavioral relevance of such an external mapping of touch, which results from combining somatosensory input with proprioceptive and visual cues about body posture [3-7]. However, despite the widely held assumption about the existence of this remapping process from somatotopic to external space and various findings indirectly suggesting its consequences [8-11], a demonstration of its changing time course and nature was lacking. We examined the temporal course of this multisensory interaction and its implications for tactile awareness in humans using a crossmodal cueing paradigm [12, 13]. What we show is that before tactile events are referred to external locations [12-15], a fleeting, unconscious image of the tactile sensation abiding to a somatotopic frame of reference rules performance. We propose that this early somatotopic "glimpse" arises from the initial feed-forward sweep of neural activity to the primary somatosensory cortex, whereas the later externally-based, conscious experience reflects the activity of a somatosensory network involving recurrent connections from association areas.