Individual Digits Research Articles

Neural Control of Individual Finger Movements Using Intracortical Recordings From a Person With Tetraplegia

Abstract INTRODUCTION Intracortical microelectrode arrays have allowed people to control robotic arm movements such as reaching and grasping. However, to restore dexterous movement, control of fingers will be required. We aimed to control individual finger movements of a virtual-reality hand on a person with tetraplegia. METHODS A 31-yr-old man with a C5/6 ASIA B spinal cord injury was implanted with two 88-channel intracortical microelectrode arrays (4 × 4 mm footprint, 1.5 mm shank-length) in the left motor cortex. Across 4 d, a 6-class linear discriminant classifier was used as an online decoder that output finger velocity commands every 20 ms. We quantified the number of channels and location significantly modulating each attempted finger movement using a Kolmogorov-Smirnov test. We also report the success rate to reach targets for flexing each of the five fingers and thumb abduction. RESULTS On average, there were 28 channels modulated by attempted finger movement on the lateral array as compared to 19 on the medial array. Attempted thumb flexion exhibited the highest (n = 18, P < .05) while ring finger had the fewest (n = 13, P < .05) modulated channels. The mean success rate was 61 ± 15% (chance: 17%). The participant was successful for 81% of the thumb flexion trials, while thumb abduction, index, middle, ring and pinky flexion achieved average accuracies of 75%, 63%, 49%, 38%, and 56% respectively. Of the failed trials, 93% failed due to co-activation of adjacent fingers, with middle and ring being the most interdependent. For example, the ring finger successfully flexed on 93% of the “ring finger” trials (high sensitivity), but middle was co-activated during 53% of the same trials (low specificity) resulting in trial failure. CONCLUSION A person with tetraplegia was able to use a brain-computer interface to control individual digits of a virtual robotic hand. Failed trials typically resulted from movement of adjacent fingers. This co-dependence should be accounted for in future control schemes.

Sex hormones and number processing. Progesterone and testosterone relate to hemispheric asymmetries during number comparison

Like many visual stimuli, multi-digit numbers are of a hierarchical nature, with whole number magnitudes depending on individual digit magnitudes. Accordingly, multi-digit numbers can be processed in a holistic (whole number magnitudes) or decomposed manner (digit magnitudes). The compatibility effect during number comparison serves as an indicator of decomposed processing. It is characterized by impaired performance for items where the larger number contains the smaller unit-digit. We were recently able to demonstrate, that the compatibility effect indeed depends on an individual's tendency to process visual hierarchical stimuli on a global or local level. Accordingly, factors affecting global-local processing, should also affect number magnitude processing, i.e. the compatibility effect. Among these factors are hemispheric asymmetries, sex differences and sex hormones (estradiol, progesterone, testosterone). In the present study 39 men and 37 naturally cycling women in their luteal cycle phase completed a number comparison task with stimuli randomly presented to the left and right hemifield. As in previous studies, we observed a larger compatibility effect in the right hemifield (left hemisphere) than in the left hemifield (right hemisphere) and in men than in women. However, this is the first study to evaluate the effects of sex hormones on hemispheric asymmetries during number comparison. We found progesterone to relate to increased hemispheric asymmetries in men, but decreased hemispheric asymmetries in women. Additionally, testosterone was negatively related to hemispheric asymmetries in women's compatibility effect in reaction times. These results add to the growing evidence that sex hormones relate to hemispheric asymmetries in cognitive functions.

Evidence against tetrapod-wide digit identities and for a limited frame shift in bird wings

In crown group tetrapods, individual digits are homologized in relation to a pentadactyl ground plan. However, testing hypotheses of digit homology is challenging because it is unclear whether digits represent distinct and conserved gene regulatory states. Here we show dramatic evolutionary dynamism in the gene expression profiles of digits, challenging the notion that five digits have conserved developmental identities across amniotes. Transcriptomics shows diversity in the patterns of gene expression differentiation of digits, although the anterior-most digit of the pentadactyl limb has a unique, conserved expression profile. Further, we identify a core set of transcription factors that are differentially expressed among the digits of amniote limbs; their spatial expression domains, however, vary between species. In light of these results, we reevaluate the frame shift hypothesis of avian wing evolution and conclude only the identity of the anterior-most digit has shifted position, suggesting a 1,3,4 digit identity in the bird wing.

The Sparthan Three-Dimensional Printed Exo-Glove: A Preliminary Evaluation of Performance Via Case Study

This paper describes the development and testing of a low-cost three-dimensional (3D) printed wearable hand exoskeleton to assist people with limited finger mobility and grip strength. The function of the presented orthosis is to support and enable light intensity activities of daily living and improve the ability to grasp and hold objects. The Sparthan Exoskeleton prototype utilizes a cable-driven design applied to individual digits with motors. The initial prototype is presented in this paper along with a preliminary evaluation of durability and performance efficacy.

Automated Rat Single-Pellet Reaching with 3-Dimensional Reconstruction of Paw and Digit Trajectories.

Rodent skilled reaching is commonly used to study dexterous skills, but requires significant time and effort to implement the task and analyze the behavior. Several automated versions of skilled reaching have been developed recently. Here, we describe a version that automatically presents pellets to rats while recording high-definition video from multiple angles at high frame rates (300 fps). The paw and individual digits are tracked with DeepLabCut, a machine learning algorithm for markerless pose estimation. This system can also be synchronized with physiological recordings, or be used to trigger physiologic interventions (e.g., electrical or optical stimulation).

A wearable neural interface for detecting and decoding attempted hand movements in a person with tetraplegia.

We are developing a wearable neural interface based on high-density surface electromyography (HDEMG) for detecting and decoding signals from spared motor units in the forearms of people with tetraplegia after spinal cord injury (SCI). A lightweight, form-fitting garment containing 150 disc electrodes and covering the entire forearm was used to map the myoelectric activity of forearm muscles during a wide range of voluntary tasks of a person with chronic tetraplegia after SCI (C5 motor and C6 sensory American Spinal Injury Association Impairment Scale B spinal cord injury). Despite exhibiting no overt finger motion, myoelectric signals were detectable for attempted movements of individual digits and were highly discriminable. Motor unit decomposition was used to identify the activity of >30 motor neurons, active specifically during rotation, pronation of the wrist (4 units), and flexion of the elbow joint (7 units), and during attempted movements of individual hand digits (1-5 units). In addition, we performed a neural connectivity analysis based on the power of the common oscillations of the identified motor neurons in the delta (~5Hz), alpha (~6-12 Hz), and beta bands (~15-30 Hz). This analysis showed clear common synaptic inputs to the identified motor neurons in all the analyzed frequency bands. This neural interface offers a new potential for the control of assistive technologies, whereby the motor neurons spared after SCI may serve as a direct readout of motor intent that allows proportional control over several distinct degrees of freedom. Moreover, this framework can be used to study the reorganization and recovery of spinal networks after injury and rehabilitation.

Context-dependent relationship in high-resolution micro-ECoG studies during finger movements.

The activation of the sensorimotor cortex as measured by electrocorticographic (ECoG) signals has been correlated with contralateral hand movements in humans, as precisely as the level of individual digits. However, the relationship between individual and multiple synergistic finger movements and the neural signal as detected by ECoG has not been fully explored. The authors used intraoperative high-resolution micro-ECoG (µECoG) on the sensorimotor cortex to link neural signals to finger movements across several context-specific motor tasks. Three neurosurgical patients with cortical lesions over eloquent regions participated. During awake craniotomy, a sensorimotor cortex area of hand movement was localized by high-frequency responses measured by an 8 × 8 µECoG grid of 3-mm interelectrode spacing. Patients performed a flexion movement of the thumb or index finger, or a pinch movement of both, based on a visual cue. High-gamma (HG; 70-230 Hz) filtered µECoG was used to identify dominant electrodes associated with thumb and index movement. Hand movements were recorded by a dataglove simultaneously with µECoG recording. In all 3 patients, the electrodes controlling thumb and index finger movements were identifiable approximately 3-6-mm apart by the HG-filtered µECoG signal. For HG power of cortical activation measured with µECoG, the thumb and index signals in the pinch movement were similar to those observed during thumb-only and index-only movement, respectively (all p > 0.05). Index finger movements, measured by the dataglove joint angles, were similar in both the index-only and pinch movements (p > 0.05). However, despite similar activation across the conditions, markedly decreased thumb movement was observed in pinch relative to independent thumb-only movement (all p < 0.05). HG-filtered µECoG signals effectively identify dominant regions associated with thumb and index finger movement. For pinch, the µECoG signal comprises a combination of the signals from individual thumb and index movements. However, while the relationship between the index finger joint angle and HG-filtered signal remains consistent between conditions, there is not a fixed relationship for thumb movement. Although the HG-filtered µECoG signal is similar in both thumb-only and pinch conditions, the actual thumb movement is markedly smaller in the pinch condition than in the thumb-only condition. This implies a nonlinear relationship between the cortical signal and the motor output for some, but importantly not all, movement types. This analysis provides insight into the tuning of the motor cortex toward specific types of motor behaviors.

Abstract 76: Motor and Sensory Control of Robotic Hands Through Fascicular Targeting

PURPOSE: 18-25,000 upper limb amputations occur in the US annually. We have developed fascicular targeting (FAST) as a surgical approach for implanting electrode interfaces within the individual component fascicular groups of the nerves in the residual limb of upper extremity amputees. Our hypothesis is that FAST, when combined with custom-developed technologies including longitudinal intrafascicular electrode (LIFE) interfaces, nerve stimulation and recording electronics, sensory stimulation patterns, and artificial intelligence (AI) motor decoding algorithms, will enable the restoration of naturalistic hand function in robotic hand protheses used by upper extremity amputees. METHODS: 5 upper extremity amputees were implanted with LIFE + cuff interfaces for durations ranging from 3 months up to 1 year. 3 subjects were partial-hand amputees with 2 FAST interfaces (2 ulnar nerve fascicles). 2 subjects were transradial amputees with 4 FAST interfaces (2 ulnar nerve and 2 median nerve fascicles). Weekly experimental sessions were performed: to assess stimulation parameters for sensory feedback, to record motor signals for robotic hand control, and to train and measure functional performance following restoration of naturalistic sensory feedback and motor control. Implants were removed at the completion of the trial. RESULTS: All implants were well-tolerated by subjects, with little to no functional morbidity caused by their participation in the trial. Sensory stimulation thresholds remained within a usable range for the duration of the trial. Stimulation patterns were used to elicit sensations perceived as either natural or non-natural, according to subjects’ preferences. Sensory discrimination and anatomic localization were also assessed. Motor signals were recorded using a novel microchip design with built-in artifact rejection circuitry. Acquisition of single-unit motor data permitted the use of AI-based signal decoding algorithms to establish independent, free-will control of all 5 digits of the robotic hand. Single-session decodes continued to work for over 3–4 weeks post-training. Functional performance using closed-loop sensorimotor control, with anatomically relevant sensory feedback and user controlled activation of individual digits of the robotic hand, will be discussed in detail. CONCLUSION: Fascicular targeting, when combined with specialized sensory stimulation and motor recording strategies, can enable true dexterity for upper extremity amputees using robotic hands. This holds promise for the development of full clinical systems to restore the hands of upper extremity amputees.

A method for assessing recovery of fine motor function of the hand in a rhesus monkey model of cortical injury: an adaptation of the Fugl–Meyer Scale and Eshkol–Wachman Movement Notation

Motor dysfunction of the upper extremity can result from stroke, cortical injury and neurological diseases and causes significant disruption of activities of daily living. While some spontaneous recovery in terms of compensatory movements does occur after injury to cortical motor areas, full recovery is rare. The distinction between complete recovery and compensatory recovery is important as the development of compensatory movements in the upper extremity may not translate into full functional use in human patients. However, current animal models of stroke do not distinguish full recovery from compensatory recovery. We have developed a Non-Human Primate Grasp Assessment Scale (GRAS) to quantify the precise recovery of composite movement, individual digit action, and finger-thumb pinch in our rhesus monkey model of cortical injury. To date, we have applied this GRAS scale to assess the recovery of fine motor function of the hand in young control and cell-therapy treated monkeys with cortical injury confined to the hand representation in the dominant primary motor cortex. We have demonstrated that with this scale we can detect and quantify significant impairments in fine motor function of the hand, the development of compensatory function during recovery and finally a return to full fine motor function of the hand in monkeys treated with a cell therapy.

Effects of muscle fatigue on directional coordination of fingertip forces during precision grip

Object manipulation requires well-coordinated force vectors involving both magnitudes and directions. Despite extensive studies about force magnitudes during manipulation, relatively little is known how the muscle fatigue could affect the directional coordination of fingertip forces. This study aims to examine the effects of muscle fatigue on inter-digit coordination of force directions during precision grip. Sixteen female subjects performed precision grip with their thumb and index finger before and after fatigue tasks, which required subjects to produce continuous submaximal pinch strength on the apparatus for a duration more than 200 s. Both their left and right hands were evaluated using the same testing protocol. The means and standard deviations of the coordination angle and the projection angle were applied to quantify the directional coordination across the digits and the force vector direction of each individual digit. Results showed that fatigue led to significant reduction in the mean values of coordination angle and that of projection angle of the index finger in the ipsilateral hand (p < 0.05). Meanwhile, fatigue induced increases in both the standard deviations of coordination angle and projection angle of both digits in the ipsilateral hand (p < 0.05). These results imply that the muscle fatigue could interfere with the grasping stability by altering the directional coordination of all the involved digits and the control of force directions for each individual digit. These findings provide insights into fatigue-related changes of force directional regulation and coordination in dexterous manipulation.

Comparison of fMRI Digit Representations of the Dominant and Non-dominant Hand in the Human Primary Somatosensory Cortex.

The tactile digit representations in the primary somatosensory cortex have so far been mapped for either the left or the right hand. This study localized all ten digit representations in right-handed subjects and compared them within and across the left and right hands to assess potential differences in the functional organization of the digit map between hands and in the structural organization between hemispheres. Functional magnetic resonance imaging of tactile stimulation of each fingertip in BA 3b confirmed the expected lateral-anterior-inferior to medial-posterior-superior succession from thumb to little-finger representation, located in the post-central gyrus opposite to the motor hand knob. While the more functionally related measures, such as the extent and strength of activation as well as the Euclidean distance between neighboring digit representations, showed significant differences between the digits, no side difference was detected: the layout of the functional digit-representation map did not consistently differ between the left, non-dominant, and the right, dominant hand. Comparing the absolute spatial coordinates also revealed a significant difference for the digits, but not between the left and right hand digits. Estimating the individual subject's digit coordinates of one hand by within-subject mirroring of the other-hand digit coordinates across hemispheres yielded a larger estimation error distance than using averaged across-subjects coordinates from within the same hemisphere. However, both methods should only be used with care for single-subject clinical evaluation, as an average estimation error of around 9 mm was observed, being slightly higher than the average distance between neighboring digits.

Tactile confusions of the fingers and toes.

Recent research has shown systematic patterns of confusions between digits of the hands and feet. The present study addressed whether such confusions arise from early somatosensory maps or higher level body representations. As the glabrous and hairy skin of the hands and feet have distinct representations in somatosensory cortex, an effect arising from early somatotopic maps may show distinct patterns on each skin surface. In contrast, if the effect arises from higher level body representations which represent the digits as volumetric units, similar patterns should be apparent regardless of which side of the digit is touched. We obtained confusion matrices showing the pattern of mislocalization on the glabrous and hairy skin surfaces of the toes (Experiment 1) and fingers (Experiment 2). Our results replicated the characteristic pattern of mislocalizations found on the glabrous skin reported in previous studies. Critically, these effects were highly similar on the hairy skin surface of both the toes and fingers. Despite the pattern of mislocalizations being highly stereotyped across participants, there were consistent individual differences in the pattern of confusions across the two skin surfaces. These results suggest that mislocalizations occur at the level of individual digits, consistent with their resulting from higher level body representations. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Dissociating parallel and serial processing of numerical value

Digits serve as useful tools for studying the interaction between low-level perceptual representations and higher-level semantic information, and also the degree to which processing these stimulus attributes relies on similar or different mechanisms. Following a body of literature that debates the influence of high-level, semantic information on perceptual processing, and work by Van Opstal and colleagues (2011) investigating whether subliminally presented digit arrays affect estimates of numerical averages, here we explored the temporal dynamics of extracting numerical values associated with each digit in an array. Specifically, we examined reaction times (RTs) for estimating the average of digit arrays of varying sizes to determine whether numerical meaning is extracted in parallel, or instead may require serial processing of individual digits. In Experiment 1, participants completed a numerical mean estimation task, along with visual search tasks designed to yield RT patterns across increasing display sizes thought to be characteristic of serial and parallel processes. In Experiment 2, we controlled for brightness cues that could have contributed to performance in Experiment 1. In both experiments, comparing RT patterns for the numerical averaging tasks to those of the search tasks suggested that semantic information from multiple digits may be extracted by a parallel processing mechanism. Unlike in either search task, RTs improved with increasing display size, indicating a potential benefit of larger displays as has been reported for extracting ensemble, or summary statistical representations of lower-level visual information.

An essential role for the nuclear protein Akirin2 in mouse limb interdigital tissue regression

The regulation of interdigital tissue regression requires the interplay of multiple spatiotemporally-controlled morphogen gradients to ensure proper limb formation and release of individual digits. Disruption to this process can lead to a number of limb abnormalities, including syndactyly. Akirins are highly conserved nuclear proteins that are known to interact with chromatin remodelling machinery at gene enhancers. In mammals, the analogue Akirin2 is essential for embryonic development and critical for a wide variety of roles in immune function, meiosis, myogenesis and brain development. Here we report a critical role for Akirin2 in the regulation of interdigital tissue regression in the mouse limb. Knockout of Akirin2 in limb epithelium leads to a loss of interdigital cell death and an increase in cell proliferation, resulting in retention of the interdigital web and soft-tissue syndactyly. This is associated with perdurance of Fgf8 expression in the ectoderm overlying the interdigital space. Our study supports a mechanism whereby Akirin2 is required for the downregulation of Fgf8 from the apical ectodermal ridge (AER) during limb development, and implies its requirement in signalling between interdigital mesenchymal cells and the AER.

Highly Integrated FPGA-Only Signal Digitization Method Using Single-Ended Memory Interface Input Receivers for Time-of-Flight PET Detectors.

We propose a new highly integrated field-programm-able gate array (FPGA) only signal digitization method for individual signal digitization of time-of-flight positron emission tomography (TOF PET). We configured I/O port of the FPGA with a single-ended memory interface (SeMI) input receiver. The SeMI is a single-ended voltage-referenced interface that has a common reference voltage per I/O Bank, such that each SeMI input receiver can serve as a voltage comparator. The FPGA-only digitizer that uses the single-ended input receivers does not require a separate digitizing integrated chip, and can obtain twice as many signals as that using LVDS input receivers. We implemented a highly integrated digitizer consisting of 82 energy and 82 timing channels using a 28-nm FPGA. The energy and arrival time were measured using a 625-ps binary counter, and a 10-ps time-to-digital converter (TDC), respectively. We first measured the intrinsic characteristics of the proposed FPGA-only digitizer. The SeMI input receiver functioned as the voltage comparator without undesirable offset voltage. The standard deviation value of the time difference measured using two SeMI input receivers with respective TDCs was less than 14.6 ps RMS. In addition, we fed signals from the TOF PET detectors to the SeMI input receivers directly and collected data. The TOF PET detector consisted of a 3 × 3 × 20mm3 LYSO crystal coupled with a silicon photomultiplier. The energy resolutions were 7.7% and 7.1% for two TOF PET detectors. The coincidence resolving time was 204 ps full width at half maximum. The SeMI digitizer with a high-performance signal digitizer, processor, and high-speed transceivers provides a compact all-in-one data acquisition system.

DIET: a multi-channel SiPM readout ASIC for TOF-PET with individual energy and timing digitizer

Monolithic scintillator detectors readout by silicon photomultiplier arrays can achieve favorable timing and spatial resolution in three dimensions and hence may significantly improve the sensitivity of PET and TOF-PET systems. This paper presents the development of a 64-channel SiPM readout ASIC, named DIET, with individual amplification and digitization of both energy and timing information. The chip performance such as input range and resolution were optimized for continuous LYSO crystal readout. The digitizer was implemented by a time-to-amplitude converter and a 10-bit Wilkinson type analog-to-digital converter. An automatic calibration method was proposed and implemented based on the timing distribution of SiPM dark counts. A prototype ASIC was fabricated in 0.18 μm CMOS process with the die area of 3 × 3 mm2. The chip was fully evaluated. For the energy measurement, the INL and noise was measured to be less than 0.6% and 0.88% respectively. For the timing measurement, the bin size of the time digitizer was measured to be 25 ps and the DNL of less than 0.45 LSB. The time resolution of 63.6 ps FWHM in single channel has been achieved for 20 p.e. signals at 0.5 p.e. threshold. The power consumption of the chip was less than 5 mW per channel. The chip was also tested with LYSO crystals (2 mm × 2 mm × 11 mm) coupled to SensL SiPMs after calibration with the dark counts. The energy resolution of 511 keV peak was measured to be 12.6% FWHM and the CRT of 334 ps FWHM was achieved.

Mapping the topological organisation of beta oscillations in motor cortex using MEG

The spatial topology of the human motor cortex has been well studied, particularly using functional Magnetic Resonance Imaging (fMRI) which allows spatial separation of haemodynamic responses arising from stimulation of different body parts, individual digits and even spatially separate areas of the same digit. However, the spatial organisation of electrophysiological responses, particularly neural oscillations (rhythmic changes in electrical potential across cellular assemblies) has been less well studied. Mapping the spatial signature of neural oscillations is possible using magnetoencephalography (MEG), however spatial differentiation of responses induced by movement of separate digits is a challenge, because the brain regions involved are separated by only a few millimetres. In this paper we first show, in simulation, how to optimise experimental design and beamformer spatial filtering techniques to increase the spatial specificity of MEG derived functional images. Combining this result with experimental data, we then capture the organisation of the post-movement beta band (13–30 Hz) oscillatory response to movement of digits 2 and 5 of the dominant hand, in individual subjects. By comparing these MEG results to ultra-high field (7T) fMRI, we also show significant spatial agreement between beta modulation and the blood oxygenation level dependent (BOLD) response. Our results show that, when using an optimised inverse solution and controlling subject movement (using custom fitted foam padding) the spatial resolution of MEG can be of order 3–5 mm. The method described offers exciting potential to understand better the cortical organisation of oscillations, and to probe such organisation in patient populations where those oscillations are known to be abnormal.

Somatotopy in the Human Somatosensory System.

Previous functional magnetic resonance imaging (fMRI) studies have demonstrated digit somatotopy in primary somatosensory cortex (SI), and even shown that at high spatial resolution it is possible to resolve within-digit somatotopy. However, fMRI studies have failed to resolve the spatial organisation of digit representations in secondary somatosensory cortex (SII). One of the major limitations of high spatial resolution fMRI studies of the somatosensory system has been the long acquisition time needed to acquire slices spanning both SI and SII. Here, we exploit the increased blood oxygenation level dependent contrast of ultra-high-field (7 Tesla) fMRI and the use of multiband imaging to study the topographic organisation in SI and SII with high spatial resolution at the individual subject level. A total of n = 6 subjects underwent vibrotactile stimulation of their face, hand digits and foot (body imaging) and their individual hand digits (digit mapping) for each left and right sides of the body. In addition, n = 2 subjects participated only in the body imaging experiment on both their left and right sides. We show an orderly representation of the face, hand digits and foot in contralateral primary cortex in each individual subject. In SII, there is clear separation of the body areas of the face, hand and foot but the spatial organisation varies across individual subjects. However, separate representation of the individual digits of the hand in SII could not be resolved, even at the spatial resolution of 1.5 mm due to largely overlapping representations.

A threshold model for polydactyly

We present a cellular automaton-based model for threshold behaviors in vertebrate digit patterning and polydactyly formation. The rules of the model follow classical reactor-diffusion algorithms. Yet it is not physical diffusion that is taken as the required natural agent but the propagation of cellular states, which can be represented by the same differential equations. The bistable cellular states in the model correspond to mesenchymal limb bud cells that can be either "on" or "off" for the cartilage differentiation pathway. Simulation runs demonstrate that reaction rate and cell number have the most decisive influence on the number of digit-like cell activation patterns. Threshold-based effects can generate supernumerary activation stripes via de novo condensation, stabilized bifurcation, and free floaters. All three behaviors are consistent with processes in natural polydactyly formation. It is argued that these effects are rooted in cell-based behaviors, not in gene regulation or globally diffusing morphogens. Our model suggests that the origin of discrete character states, such as individual digits, is a consequence of an additive cell state variable with a normal distribution that is transformed by a growth function with Turing behaviors into discontinuous phenotypic units. We discuss the application of this type of autopod patterning to the mutational, developmental, experimental, and evolutionary occurrences of polydactyly. The model provides a refinement of the previous Hemingway model for digit novelty and supports Turing type pattern formation in the vertebrate limb.

Effect of immobilization of the distal interphalangeal joint of fingers on grip strength.

Arthrodesis of the distal interphalangeal joint of the finger is an effective salvage treatment for end-stage arthropathy of the joint. This study aimed to evaluate the effect of simulated fusion of individual distal interphalangeal joints on the overall grip strength of the hand. Custom moulded thermoplastic splints were used to simulate fusion by immobilizing the index, middle, ring and little fingers' distal interphalangeal joints in turn in both hands of 56 healthy participants. Testing was performed with no immobilization and after immobilization of each of the individual digits. Grip strengths reduced significantly following immobilization of the distal interphalangeal joint. The degree of reduction became progressively more pronounced from the index to the little fingers (12%, 18%, 24% and 25%, respectively) and was similar for the dominant and non-dominant hands. This information may have clinical application when counselling patients regarding fusion of the distal interphalangeal joint of the fingers.