Finger Representations Research Articles

Cultural variability in finger representations / Variabilidad cultural en las representaciones con dedos

Finger representations are used to count or show quantities. How fingers are lifted to count and the type of representation that we use to communicate quantities have been the focus of studies that have aimed at providing evidence of dominant patterns across cultures. In the current study, we go beyond those studies and investigate intracultural variability. Specifically, whether finger counting habits and finger montring patterns are similar in children and adults. To this aim, a total of 3,210 Spaniard participants took part in this study (637 children and 2,573 adults). All of them were assessed regarding handedness, the way in which they counted with their fingers from 1 to 10 (finger counting) and how they show quantities with their fingers (finger montring). The results showed certain consistency; however, there was substantial variability within each group. Findings are interpreted within the context of current theories reinforcing the relevance of finger patterns to support the understanding of the meaning of numbers.

Finger-specific representations are sharpened during a fatiguing motor task

Introduction
 Motor fatigability is a limiting factor in any kind of setting, in which physical performance is required. Motor fatigability can be quantified through the decrease in movement speed, when low-force movements are performed repeatedly with maximal speed. In this study, we measure motor fatigability in healthy participants through fast finger tapping for 30s. Previous research has shown that the decrease in movement speed, also called motor slowing, is associated with a rise in brain activity, a reduction in surround inhibition in the primary sensorimotor cortex (SM1), and an increase in co-activation of antagonistic muscle groups involved in the movement (Bächinger et al., 2019). However, it remains an open question of whether motor slowing and the associated release of inhibition causes a reduction of signal-to-noise ratio for movement-specific information. Here, we aim to answer this question by assessing finger representations using representational similarity analysis (RSA) when participants perform fatiguing tapping with either the index or middle finger. We hypothesized that a reduction of movement-specific information would be associated with the index and middle finger representations in SM1 getting “blurred” over time due to a gradual break-down of surround inhibition. Thus, if the signal-to-noise ratio of movement-specific information decreases in parallel with motor slowing, we would expect finger representations to become more overlapping. Vice-versa, if the signal-to-noise ratio of movement-specific information increases despite motor slowing, we would expect sharper finger representation.
 Methods
 26 healthy young participants performed a motor slowing task during functional MRI. The participants performed 30s of maximal speed finger tapping with the index and the middle finger, alternating between trials. To quantify motor slowing from the behaviour, we performed a linear regression analysis. For the first-level general linear model of the fMRI data, the fingers were regressed separately and the 30s of tapping were further split into 3 x 10s regressors (time bin 1, bin 2, bin 3). We performed RSA separately on each 10s regressor for the anatomically defined regions of interest M1 and S1 hand area (Diedrichsen et al., 2013; Walther et al., 2016) and therefore obtained a dissimilarity measure for each time bin. A mixed effects model with the factor time was used to test whether dissimilarity changed across time bins.
 Results
 On the behavioural level, motor slowing could be observed, as tapping speed significantly decreased in each finger over time (F(1, 76) >= 5.78, p <=.05). Concerning the dissimilarity measure, we found an increase over time for S1 as well as M1 (F(2, 50) >= 17.41, p <=.001).
 Discussion/Conclusion
 We conclude that the finger representations in the sensorimotor cortex become more distinct with motor slowing. This suggests that the signal-to-noise ratio of movement-specific information is increased, potentially to compensate for supraspinal changes caused by fatigability.
 References
 Bächinger, M., Lehner, R., Thomas, F., Hanimann, S., Balsters, J., & Wenderoth, N. (2019). Human motor fatigability as evoked by repetitive movements results from a gradual breakdown of surround inhibition. eLife, 8, Article e46750. https://doi.org/10.7554/eLife.46750
 Diedrichsen, J., Wiestler, T., & Krakauer, J. W. (2013). Two distinct ipsilateral cortical representations for individuated finger movements. Cerebral Cortex, 23(6), 1362–1377. https://doi.org/10.1093/cercor/bhs120
 Walther, A., Nili, H., Ejaz, N., Alink, A., Kriegeskorte, N., & Diedrichsen, J. (2016). Reliability of dissimilarity measures for multi-voxel pattern analysis. NeuroImage, 137, 188–200. https://doi.org/10.1016/j.neuroimage.2015.12.012

The role of finger kinematics in the acquisition of number meaning in kindergarten: a pilot study

Several studies have shown that the acquisition of number meaning is related to finger motor representations. However, no study has tried to distinguish the respective roles of fingers representation and finger kinematics in this effect. Forty-three children (23 boys and 20 girls) enrolled in the middle class of kindergarten took part in the study. They were divided into two equivalent groups and compared on the acquisition of number meaning after a 2-week program designed to teach them a song about the numbers 1–9, scaffolded by visual supports. Each visual support included the symbolic representation of the number, the picture of an object mentioned in the song that rhymed with the number in French, and either a static image (static group) or an animated point-light display (animated group) of the finger representation. Results showed no difference between the two groups on the acquisition of numbers regarded as low (i.e., less than 5) but the animated group performed significantly better for numbers regarded as high (i.e., more than 5). Therefore, the present study shows the interest of using the observation of animated counting movement to teach number meaning in young children and suggests that finger kinematics may be more instrumental than static finger representation in the learning of number meaning. Future research is needed to confirm and specify this effect.

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.

Performing a vibrotactile discrimination task modulates finger representations in primary somatosensory cortex.

It is well established that vibrotactile stimuli are represented in somatotopic maps. However, less is known about whether these somatotopic representations are modulated by task demands and maybe even in the absence of tactile input. Here, we used a vibrotactile discrimination task as a tool to investigate these questions in further detail. Participants were required to actively perceive and process tactile stimuli in comparison to a no-task control condition where identical stimuli were passively perceived (no-memory condition). Importantly, both vibrotactile stimuli were either applied to the right index or little finger, allowing us to investigate whether cognitive task demands shape finger representations in primary somatosensory cortex (S1). Using multivoxel pattern analysis and representational similarity analysis, we found that S1 finger representations were more distinct during the memory than the no-memory condition. Interestingly, this effect was not only observed while tactile stimuli were presented but also during the delay period (i.e., in the absence of tactile stimulation). Our findings imply that when individuals are required to focus on tactile stimuli, retain them in their memory, and engage in active processing of distinctive stimulus features, this exerts a modulatory effect on the finger representations present in S1.NEW & NOTEWORTHY Using multivoxel pattern analysis, we found that discrimination task demands shape finger representations in the contralateral primary somatosensory cortex (S1), and that somatotopic representations are modulated by task demands not only during tactile stimulation but also to a certain extent in the absence of tactile input.

Multi-scale and cross-dimensional TMS mapping: A proof of principle in patients with Parkinson's disease and deep brain stimulation.

Transcranial magnetic stimulation (TMS) mapping has become a critical tool for exploratory studies of the human corticomotor (M1) organization. Here, we propose to gather existing cutting-edge TMS-EMG and TMS-EEG approaches into a combined multi-dimensional TMS mapping that considers local and whole-brain excitability changes as well as state and time-specific changes in cortical activity. We applied this multi-dimensional TMS mapping approach to patients with Parkinson's disease (PD) with Deep brain stimulation (DBS) of the sub-thalamic nucleus (STN) ON and OFF. Our goal was to identifying one or several TMS mapping-derived markers that could provide unprecedent new insights onto the mechanisms of DBS in movement disorders. Six PD patients (1 female, mean age: 62.5 yo [59-65]) implanted with DBS-STN for 1 year, underwent a robotized sulcus-shaped TMS motor mapping to measure changes in muscle-specific corticomotor representations and a movement initiation task to probe state-dependent modulations of corticospinal excitability in the ON (using clinically relevant DBS parameters) and OFF DBS states. Cortical excitability and evoked dynamics of three cortical areas involved in the neural control of voluntary movements (M1, pre-supplementary motor area - preSMA and inferior frontal gyrus - IFG) were then mapped using TMS-EEG coupling in the ON and OFF state. Lastly, we investigated the timing and nature of the STN-to-M1 inputs using a paired pulse DBS-TMS-EEG protocol. In our sample of patients, DBS appeared to induce fast within-area somatotopic re-arrangements of motor finger representations in M1, as revealed by mediolateral shifts of corticomuscle representations. STN-DBS improved reaction times while up-regulating corticospinal excitability, especially during endogenous motor preparation. Evoked dynamics revealed marked increases in inhibitory circuits in the IFG and M1 with DBS ON. Finally, inhibitory conditioning effects of STN single pulses on corticomotor activity were found at timings relevant for the activation of inhibitory GABAergic receptors (4 and 20 ms). Taken together, these results suggest a predominant role of some markers in explaining beneficial DBS effects, such as a context-dependent modulation of corticospinal excitability and the recruitment of distinct inhibitory circuits, involving long-range projections from higher level motor centers and local GABAergic neuronal populations. These combined measures might help to identify discriminative features of DBS mechanisms towards deep clinical phenotyping of DBS effects in Parkinson's Disease and in other pathological conditions.

Suppression of perceptual sensitivity to digital nerve stimulation induced by afferent volley from digital nerve of contralateral homologous finger.

The purpose of the present study is to investigate whether perceptual sensitivity to digital nerve stimulation is modulated by the afferent volley from the digital nerve of a contralateral finger. Fifteen healthy humans participated in this study. A test stimulus was given to the right-hand index finger, and a conditioning stimulus was given to one of the five fingers on the left hand 20, 30, or 40 ms before the test stimulus. The perceptual threshold of the finger stimulation was measured. The perceptual threshold of the test stimulus was significantly increased by a conditioning stimulus to the left-hand index finger given 40 ms before the test stimulus. In contrast, the threshold was not significantly changed by a conditioning stimulus to any finger other than the index finger. Perceptual sensitivity to digital nerve stimulation is suppressed by the afferent volley from the digital nerve of the contralateral homologous finger. This means that the afferent volley from the digital nerve suppresses the homologous finger representation in the ipsilateral somatosensory areas. These findings can be explained by the view that the afferent volley from the digital nerve of the index finger projects to the index finger representation in the contralateral primary sensory cortex and that the interhemispheric transcallosal inhibitory drive is provided from the secondary sensory cortex to the homologous finger representation in the contralateral secondary sensory cortex.

Hypnotic suggestions cognitively penetrate tactile perception through top-down modulation of semantic contents

Perception is subject to ongoing alterations by learning and top-down influences. Although abundant studies have shown modulation of perception by attention, motivation, content and context, there is an unresolved controversy whether these examples provide true evidence that perception is penetrable by cognition. Here we show that tactile perception assessed as spatial discrimination can be instantaneously and systematically altered merely by the semantic content during hypnotic suggestions. To study neurophysiological correlates, we recorded EEG and SEPs. We found that the suggestion “your index finger becomes bigger” led to improved tactile discrimination, while the suggestion “your index finger becomes smaller” led to impaired discrimination. A hypnosis without semantic suggestions had no effect but caused a reduction of phase-locking synchronization of the beta frequency band between medial frontal cortex and the finger representation in somatosensory cortex. Late SEP components (P80–N140 complex) implicated in attentional processes were altered by the semantic contents, but processing of afferent inputs in SI remained unaltered. These data provide evidence that the psychophysically observed modifiability of tactile perception by semantic contents is not simply due to altered perception-based judgments, but instead is a consequence of modified perceptual processes which change the perceptual experience.

The 3D Structural Architecture of the Human Hand Area Is Nontopographic.

The functional topography of the human primary somatosensory cortex hand area is a widely studied model system to understand sensory organization and plasticity. It is so far unclear whether the underlying 3D structural architecture also shows a topographic organization. We used 7 Tesla (7T) magnetic resonance imaging (MRI) data to quantify layer-specific myelin, iron, and mineralization in relation to population receptive field maps of individual finger representations in Brodman area 3b (BA 3b) of human S1 in female and male younger adults. This 3D description allowed us to identify a characteristic profile of layer-specific myelin and iron deposition in the BA 3b hand area, but revealed an absence of structural differences, an absence of low-myelin borders, and high similarity of 3D microstructure profiles between individual fingers. However, structural differences and borders were detected between the hand and face areas. We conclude that the 3D structural architecture of the human hand area is nontopographic, unlike in some monkey species, which suggests a high degree of flexibility for functional finger organization and a new perspective on human topographic plasticity.SIGNIFICANCE STATEMENT Using ultra-high-field MRI, we provide the first comprehensive in vivo description of the 3D structural architecture of the human BA 3b hand area in relation to functional population receptive field maps. High similarity of precise finger-specific 3D profiles, together with an absence of structural differences and an absence of low-myelin borders between individual fingers, reveals the 3D structural architecture of the human hand area to be nontopographic. This suggests reduced structural limitations to cortical plasticity and reorganization and allows for shared representational features across fingers.

Laminar VASO fMRI in focal hand dystonia patients.

Focal Hand Dystonia (FHD) is a disabling movement disorder characterized by involuntary movements, cramps and spasms. It is associated with pathological neural microcircuits in the cortical somatosensory system. While invasive preclinical modalities allow researchers to probe specific neural microcircuits of cortical layers and columns, conventional functional magnetic resonance imaging (fMRI) cannot resolve such small neural computational units. In this study, we take advantage of recent developments in ultra-high-field MRI hardware and MR-sequences to capture altered digit representations and laminar processing in FHD patients. We aim to characterize the capability and challenges of layer-specific imaging and analysis tools in resolving laminar and columnar structures in clinical research setups. We scanned N = 4 affected and N = 5 unaffected hemispheres at 7T and found consistent results of altered neural microcircuitry in FHD patients: 1) In affected hemispheres of FHD patients, we found a breakdown of ordered finger representation in the primary somatosensory cortex, as suggested from previous low-resolution fMRI. 2) In affected primary motor cortices of FHD patients, we furthermore found increased fMRI activity in superficial cortico-cortical neural input layers (II/III), compared to relatively weaker activity in the cortico-spinal output layers (Vb/VI). Overall, we show that layer-fMRI acquisition and analysis tools have the potential to address clinically-driven neuroscience research questions about altered computational mechanisms at the spatial scales that were previously only accessible in animal models. We believe that this study paves the way for easier translation of preclinical work into clinical research in focal hand dystonia and beyond.

Morphology, Connectivity, and Encoding Features of Tactile and Motor Representations of the Fingers in the Human Precentral and Postcentral Gyrus.

Despite the tight coupling between sensory and motor processing for fine manipulation in humans, it is not yet totally clear which specific properties of the fingers are mapped in the precentral and postcentral gyrus. We used fMRI to compare the morphology, connectivity, and encoding of the motor and tactile finger representations (FRs) in the precentral and postcentral gyrus of 25 5-fingered participants (8 females). Multivoxel pattern and structural and functional connectivity analyses demonstrated the existence of distinct motor and tactile FRs within both the precentral and postcentral gyrus, integrating finger-specific motor and tactile information. Using representational similarity analysis, we found that the motor and tactile FRs in the sensorimotor cortex were described by the perceived structure of the hand better than by the actual hand anatomy or other functional models (finger kinematics, muscles synergies). We then studied a polydactyly individual (i.e., with a congenital 6-fingered hand) showing superior manipulation abilities and divergent anatomic-functional hand properties. The perceived hand model was still the best model for tactile representations in the precentral and postcentral gyrus, while finger kinematics better described motor representations in the precentral gyrus. We suggest that, under normal conditions (i.e., in subjects with a standard hand anatomy), the sensorimotor representations of the 5 fingers in humans converge toward a model of perceived hand anatomy, deviating from the real hand structure, as the best synthesis between functional and structural features of the hand.SIGNIFICANCE STATEMENT Distinct motor and tactile finger representations exist in both the precentral and postcentral gyrus, supported by a finger-specific pattern of anatomic and functional connectivity across modalities. At the representational level, finger representations reflect the perceived structure of the hand, which might result from an adapting process harmonizing (i.e., uniformizing) the encoding of hand function and structure in the precentral and postcentral gyrus. The same analyses performed in an extremely rare polydactyly subject showed that the emergence of such representational geometry is also found in neuromechanical variants with different hand anatomy and function. However, the harmonization process across the precentral and postcentral gyrus might not be possible because of divergent functional-structural properties of the hand and associated superior manipulation abilities.

Intact finger representation within primary sensorimotor cortex of musician's dystonia.

Musician's dystonia presents with a persistent deterioration of motor control during musical performance. A predominant hypothesis has been that this is underpinned by maladaptive neural changes to the somatotopic organization of finger representations within primary somatosensory cortex. Here, we tested this hypothesis by investigating the finger-specific activity patterns in the primary somatosensory and motor cortex using functional MRI and multivariate pattern analysis in nine musicians with dystonia and nine healthy musicians. A purpose-built keyboard device allowed characterization of activity patterns elicited during passive extension and active finger presses of individual fingers. We analysed the data using both traditional spatial analysis and state-of-the art multivariate analyses. Our analysis reveals that digit representations in musicians were poorly captured by spatial analyses. An optimized spatial metric found clear somatotopy but no difference in the spatial geometry between fingers with dystonia. Representational similarity analysis was confirmed as a more reliable technique than all spatial metrics evaluated. Significantly, the dissimilarity architecture was equivalent for musicians with and without dystonia. No expansion or spatial shift of digit representation maps were found in the symptomatic group. Our results therefore indicate that the neural representation of generic finger maps in primary sensorimotor cortex is intact in musician's dystonia. These results speak against the idea that task-specific dystonia is associated with a distorted hand somatotopy and lend weight to an alternative hypothesis that task-specific dystonia is due to a higher-order disruption of skill encoding. Such a formulation can better explain the task-specific deficit and offers alternative inroads for therapeutic interventions.

Curved sixth fingers: Flexible representation of the shape of supernumerary body parts

A recent perceptual illusion induces the feeling of having a sixth finger on one's hand. It is unclear whether the representation of supernumerary fingers is flexible for shape. To test whether we can embody a sixth finger with a different shape from our own fingers, we induced a sixth finger which curved laterally though 180°. Participants reported feeling both curved and straight sixth fingers, depending on the stimulation pattern. Visual comparative judgements of the felt curvature of the supernumerary finger, showed means of 182° in the curved condition, and 35° in the straight condition. Our results show we can feel a supernumerary finger with different shape from our actual fingers, indicating that shape is represented flexibly in the perception of our hands. This study also adds evidence to the independence of the supernumerary finger from the actual fingers, showing we can represent the sixth finger with its own shape.

Finger-Based Numerical Training Increases Sensorimotor Activation for Arithmetic in Children-An fNIRS Study.

Most children use their fingers when learning to count and calculate. These sensorimotor experiences were argued to underlie reported behavioral associations of finger gnosis and counting with mathematical skills. On the neural level, associations were assumed to originate from overlapping neural representations of fingers and numbers. This study explored whether finger-based training in children would lead to specific neural activation in the sensorimotor cortex, associated with finger movements, as well as the parietal cortex, associated with number processing, during mental arithmetic. Following finger-based training during the first year of school, trained children showed finger-related arithmetic effects accompanied by activation in the sensorimotor cortex potentially associated with implicit finger movements. This indicates embodied finger-based numerical representations after training. Results for differences in neural activation between trained children and a control group in the IPS were less conclusive. This study provides the first evidence for training-induced sensorimotor plasticity in brain development potentially driven by the explicit use of fingers for initial arithmetic, supporting an embodied perspective on the representation of numbers.

Malleability of the cortical hand map following a finger nerve block.

Electrophysiological studies in monkeys show that finger amputation triggers local remapping within the deprived primary somatosensory cortex (S1). Human neuroimaging research, however, shows persistent S1 representation of the missing hand’s fingers, even decades after amputation. Here, we explore whether this apparent contradiction stems from underestimating the distributed peripheral and central representation of fingers in the hand map. Using pharmacological single-finger nerve block and 7-tesla neuroimaging, we first replicated previous accounts (electrophysiological and other) of local S1 remapping. Local blocking also triggered activity changes to nonblocked fingers across the entire hand area. Using methods exploiting interfinger representational overlap, however, we also show that the blocked finger representation remained persistent despite input loss. Computational modeling suggests that both local stability and global reorganization are driven by distributed processing underlying the topographic map, combined with homeostatic mechanisms. Our findings reveal complex interfinger representational features that play a key role in brain (re)organization, beyond (re)mapping.

Hasty sensorimotor decisions rely on an overlap of broad and selective changes in motor activity.

Humans and other animals are able to adjust their speed-accuracy trade-off (SAT) at will depending on the urge to act, favoring either cautious or hasty decision policies in different contexts. An emerging view is that SAT regulation relies on influences exerting broad changes on the motor system, tuning its activity up globally when hastiness is at premium. The present study aimed to test this hypothesis. A total of 50 participants performed a task involving choices between left and right index fingers, in which incorrect choices led either to a high or to a low penalty in 2 contexts, inciting them to emphasize either cautious or hasty policies. We applied transcranial magnetic stimulation (TMS) on multiple motor representations, eliciting motor-evoked potentials (MEPs) in 9 finger and leg muscles. MEP amplitudes allowed us to probe activity changes in the corresponding finger and leg representations, while participants were deliberating about which index to choose. Our data indicate that hastiness entails a broad amplification of motor activity, although this amplification was limited to the chosen side. On top of this effect, we identified a local suppression of motor activity, surrounding the chosen index representation. Hence, a decision policy favoring speed over accuracy appears to rely on overlapping processes producing a broad (but not global) amplification and a surround suppression of motor activity. The latter effect may help to increase the signal-to-noise ratio of the chosen representation, as supported by single-trial correlation analyses indicating a stronger differentiation of activity changes in finger representations in the hasty context.

HOS-FingerCode: Bispectral invariants based contactless multi-finger recognition system using ridge orientation and feature fusion

Fingerprints are a commonly used biometric for civil and forensic applications and the majority of them are captured by contact sensors. More recently, there is a trend toward the use of high resolution digital and video cameras to acquire contactless images. However, the processing of such images is challenging because of intra-class variations such as pose, rotation, translation and scaling due to hand orientation and deformation. They can, however, facilitate the use of full finger or multiple fingers or hand information rather than the fingertip alone. Although some recent research has investigated representation of full finger and hand information under relaxed conditions, current state-of-the-art methods are unable to address transformation issues without manual intervention. To overcome the issues of relaxed constrained nature, geometrical variations and invariant feature encoding regardless of finger orientation, we have used higher order spectral features (HOS-FingerCode) from ridge patterns. We employ an automated method to detect key points and constructs a graph of key-lines. Ridge orientation profiles along with the selected key-lines provide a 1D signal from which bispectral invariant features are extracted. In addition, two fusion schemes are proposed where fusion from multiple key lines combinations and feature fusion from multiple key line configurations are investigated to extract ridge pattern profile for a better performance. The features are pooled from multiple fingers by concatenation or compact bilinear pooling to yield the HOS-FingerCode for multi-finger biometrics. For a single-finger system using 3369 high resolution index and middle finger images, the algorithm better performs when different key lines configurations are fused. For geometrical variations of the images, the system is most impacted by pose than rotation and scale changes of the images, and is tolerant to such variations. For the multi-finger system using 3111 images from both fingers, the algorithm has achieved 93.8% TPR and 97.95% classification accuracy at a setting of 2% FPR. For the feature fusion scheme proposed for multi-finger system using concatenation and compact bilinear pooling, concatenation of features performs better than the compact bilinear pooling. Since multi-finger recognition system performed better than the single finger biometrics system, it can help to diminish the high traffic scenario in busy premises and will facilitate the soft identity verification.

Development of a Piezoelectric Actuated Tactile Stimulation Device for Population Receptive Field Mapping in Human Somatosensory Cortex With fMRI.

Multichannel tactile stimulation devices is need to investigate human finger population receptive field (pRF) characteristics in the primary somatosensory cortex during functional magnetic resonance imaging (fMRI). To accurately characterize right-hand somatosensory representation based on the Bayesian pRF model. Prospective. A water phantom and six healthy participants (four males, mean 23.8 years old). T1-weighted magnetization-prepared rapid gradient-echo, T2*-weighted echo planar imaging at 3T. The piezoelectric actuated tactile stimulation device consisted of execution unit and control unit. The output performance of the device was measured by a laser displacement sensor. The effect of the device on images' signal-to-noise ratio (SNR) was measured by phantom experiments. The activation representation arrangement order, relative volumes, and receptive field size of the right hand were assessed during the along-digits and cross-digits paradigms. The normality of the data was tested by the Shapiro-Wilk method. A paired-sample t test was performed to test pRF characteristics for all digit pairings. The significance level was set to P=0.05 (false discovery rate [FDR] correct). Percussive stimulation provided by the piezoelectric actuated tactile stimulator had a stable displacement (2.64 mm) over a wide range of vibration frequencies (0-30 Hz). The output delay of the device was 1millisecond. The device did not affect the image's SNR (without the device: SNR=138.24 ± 7.87, temporal SNR [TSNR]=440.03 ± 52.08. With the device: SNR=138.06 ± 8.44, TSNR=438.52 ± 56.38. PSNR =0.88, PTSNR =0.46). Representations of right-hand fingers showed the same arrangement order in both experiments (D1-D5 arranged along the central sulcus). However, the relative volumes of D3 showed significant differences in S1 (P=0.003). Among four subareas, the relative volumes of D3 were significantly different in area 1 (P=0.047). This developed stimulator, through experimental verification, could play a role in pRF mapping exploration. 2 TECHNICAL EFFICACY STAGE: 1.

“Hold infinity in the palm of your hand.” A functional description of time expressions through fingers based on Chinese Sign Language naturalistic data

AbstractThis paper investigates the relationship between fingers and time representations in naturalistic Chinese Sign Language (CSL). Based on a CSL Corpus (Shanghai Variant, 2016–), we offer a thorough description of finger configurations for time expressions from 63 deaf signers, including three main types: digital, numeral incorporation, and points-to-fingers. The former two were further divided into vertical and horizontal fingers according to the orientation of fingertips. The results showed that there were interconnections between finger representations, numbers, ordering, and time in CSL. Vertical fingers were mainly used to quantify time units, whereas horizontal fingers were mostly used for sequencing or ordering events, and their forms could be influenced by Chinese number characters and the vertical writing direction. Furthermore, the use of points-to-fingers (e.g., pointing to the thumb, index, or little finger) formed temporal connectives in CSL and could be patterned to put a conversation in order. Additionally, CSL adopted similar linguistic forms in sequential time and adverbs of reason (e.g., cause and effect: events that happened earlier and events that happen later). Such a cause-and-effect relationship was a special type of temporal sequence. In conclusion, fingers are essential for time representation in CSL and their forms are biologically and culturally shaped.

The long sixth finger illusion: The representation of the supernumerary finger is not a copy and can be felt with varying lengths

We can have a distorted perception of our body, instantly induced with multisensory illusions, anaesthesia or Virtual Reality, and recent studies show we can also feel extra body parts. Newport and colleagues (Newport et al., 2016) created an illusion that induces the feeling of having a sixth finger on one's hand, for a brief moment. By changing the paradigm with a double back and forth stroking, we were able to extend the duration of this illusion (Cadete & Longo, 2020), which can reflect an endured representation of a supernumerary finger. This innovation allowed us to test one specific distortion in the supernumerary finger: length. Patients with supernumerary phantom limb syndrome feel like they have an extra limb, as if one of their limbs was duplicated (Staub et al., 2006), resembling the same size and shape of the existing one. It is unclear from existing studies whether a supernumerary limb is represented as a copy of the existing limb, or if it is represented independently, with its own features. We therefore aimed to investigate whether the properties of the supernumerary sixth finger could be altered, independently of the actual little finger. Hence, we tested whether we can embody a sixth finger with double the size of the average little finger, and half its size. Participants reported feeling a long and a short sixth finger, and gave visual judgements on the felt length of the supernumerary finger, that matched the condition length. Overall, the results show that the supernumerary sixth finger is not a mere copy of the little finger but is represented independently, with distinct features from the existing finger. Moreover, the representation of the supernumerary finger is flexible, allowing the embodiment of a long or a short sixth finger.