Concept: Index finger
Cortical activity allotted to the tactile receptors on fingertips conforms to skilful use of the hand [1-3]. For instance, in string instrument players, the somatosensory cortical activity in response to touch on the little fingertip is larger than that in control subjects . Such plasticity of the fingertip sensory representation is not limited to extraordinary skills and occurs in monkeys trained to repetitively grasp and release a handle as well . Touchscreen phones also require repetitive finger movements, but whether and how the cortex conforms to this is unknown. By using electroencephalography (EEG), we measured the cortical potentials in response to mechanical touch on the thumb, index, and middle fingertips of touchscreen phone users and nonusers (owning only old-technology mobile phones). Although the thumb interacted predominantly with the screen, the potentials associated with the three fingertips were enhanced in touchscreen users compared to nonusers. Within the touchscreen users, the cortical potentials from the thumb and index fingertips were directly proportional to the intensity of use quantified with built-in battery logs. Remarkably, the thumb tip was sensitive to the day-to-day fluctuations in phone use: the shorter the time elapsed from an episode of intense phone use, the larger the cortical potential associated with it. Our results suggest that repetitive movements on the smooth touchscreen reshaped sensory processing from the hand and that the thumb representation was updated daily depending on its use. We propose that cortical sensory processing in the contemporary brain is continuously shaped by the use of personal digital technology.
The relation between pain perception and spatial representation of the body is poorly understood. In the thermal grill illusion (TGI), alternating non-noxious warm and cold temperatures cause a paradoxical, sometimes painful, sensation of burning heat . We combined thermal grill stimulation with crossing the fingers to investigate whether nociceptively mediated sensation depends on the somatotopic or spatiotopic configuration of thermal inputs. We stimulated the index, middle, and ring fingers when the middle finger either was or was not crossed over the index to generate “warm-cold-warm” patterns in either somatotopic or spatiotopic coordinates. Participants adjusted a temperature delivered to the other hand until it matched their perception of the cold target finger (index or middle). We found significant temperature overestimation when the target was central within the spatial configuration (warm-cold-warm) compared to when it was peripheral (cold-warm-warm). Crucially, this effect depended on the spatiotopic configuration of thermal inputs, but it was independent of the finger posture and present for both index and middle target fingers-the thermal grill effect for the middle finger was abolished when it was crossed over the index to adopt a spatiotopically peripheral position, while the same effect was newly generated for the index finger by the same postural change. Our results suggest that the locations of multiple stimuli are remapped into external space as a group; nociceptively mediated sensations depended not on the body posture, but rather on the external spatial configuration formed by the pattern of thermal stimuli in each posture.
Bodily training typically evokes behavioral and perceptual gains, enforcing neuroplastic processes and affecting neural representations. We investigated the effect on somatosensory perception of a three-day Zen meditation exercise, a purely mental intervention. Tactile spatial discrimination of the right index finger was persistently improved by only 6 hours of mental-sensory focusing on this finger, suggesting that intrinsic brain activity created by mental states can alter perception and behavior similarly to external stimulation.
- Journal of plastic, reconstructive & aesthetic surgery : JPRAS
- Published about 7 years ago
Calcifying aponeurotic fibroma is a rare benign soft tissue tumor that primarily occurs on the distal portion of the extremities of children and adolescents. It appears like a firm, painless and slowly growing mass with high local recurrence rates. The lesion has characteristic histological features with areas of proliferative plumps of fibroblasts, chondrocytes and foci of calcification. We present a case of calcifying aponeurotic fibroma of the sub-ungual area of the index finger distal phalanx with bone erosion, surgically treated. A 2 year follow up showed satisfactory functional result and no evidence of recurrence.
Abstract Although, the tremor of Parkinson’s disease (PD) usually, but not always, differs from essential tremor (ET), there is no simple bedside test to distinguish PD from ET. We believe we have made such an observation. We studied 50 consecutive tremor-dominant PD patients (mean age: 63.4 years; mean disease duration: 4.9 years) and 35 consecutive ET patients (mean age: 64.1 years; mean disease duration: 12.5 years). Among PD patients, 31 had a bilateral tremor and among ET patients, 29 patients had a bilateral tremor. Patients sat opposite the examiner and pointed both index fingers at the examiner’s index fingers. Then they closed their eyes. Within 15 seconds one or rarely both of the patient’s index fingers moved, was displaced, either upward and/or laterally. Finger displacement occurred only with bilateral simultaneous pointing with the patient’s eyes closed. All the tremor-dominant PD patients exhibited displacement of an index finger. In 46 patients it occurred on the side of dominant tremor, in 4 it occurred bilaterally. In 31 of 35 ET patients no displacement occurred. In 4 of 35 ET patients it occurred unilaterally on the side of dominant tremor. Odds ratio of distinguishing PD from ET: 89.62 at 95% confidence limits (5.31- 1513.4), p = 0. 0018. Sensitivity 100% (0.91 -1), specificity 89% (0.72- 0.96). Finger displacement can distinguish the tremor of PD from ET. The unilateral movement with eyes closed suggests the tremor of PD unlike ET may impact circuits involving the parietal and supplementary motor cortices.
In this review, an international group of senior hand surgeons was asked to provide their currently used methods, views, and advice on thumb and fingertip repair. The basic requirements and methods of thumb and fingertip repair are first outlined, followed by descriptions of the methods favored by individual units or surgeons. More recent innovative methods and modifications are described and challenging topics are discussed. This review ends by illustrating and discussing a few exploratory treatments that hold promise of greatly changing future perspectives of this common clinical problem.
This study was conducted to investigate relationships of self-identified cold tolerance and cold-induced vasodilatation (CIVD) in the finger. Nine males and 34 females participated in the following 2 tests: a CIVD test and a self-reported survey. The CIVD test was conducted 30-min cold-water immersion (3.8 ± 0.3 °C) of the middle finger at an air temperature of 27.9 ± 0.1 °C. The self-reported questionnaire consisted of 28 questions about whole and local body cold and heat tolerances. By a cluster analysis on the survey results, the participants were divided into two groups: high self-identified cold tolerance (HSCT, n = 25) and low self-identified cold tolerance (LSCT, n = 18). LSCT had lower self-identified cold tolerance (P < 0.001), preferred hot thermal stimulation (P = 0.006), and wore heavier clothing during daily life (P < 0.001) than HSCT. LSCT had significantly lower maximal finger temperatures (T max) (P = 0.040), smaller amplitude (P = 0.029), and delayed onset time of CIVD (P = 0.080) when compared to HSCT. Some questions examining the self-identified cold or heat tolerance had relationships with cold tolerance index, T max, and amplitude (P < 0.1). These results indicate that self-identified cold tolerance classified through a standardized survey could be a good index to predict physiological cold tolerance.
- Journal of experimental psychology. Human perception and performance
- Published over 4 years ago
Pointing gestures are a vital aspect of human communication. Nevertheless, observers consistently fail to determine the exact location to which another person points when that location lies in the distance. Here we explore the reasons for this misunderstanding. Humans usually point by extending the arm and finger. We show that observer’s interpret these gestures by nonlinear extrapolation of the pointer’s arm-finger line. The nonlinearity can be adequately described as the Bayesian-optimal integration of a linear extrapolation of the arm-finger line and observers' prior assumptions about likely referent positions. Surprisingly, the spatial rule describing the interpretation of pointing gestures differed from the rules describing the production of these gestures. In the latter case, the eye, index finger, and referent were aligned. We show that the differences in the production and interpretation of pointing gestures accounts for the systematic spatial misunderstanding of pointing gestures to distant referents. No evidence was found for the hypotheses that action-related processes are involved in the perception of pointing gestures. How participants interpreted pointing gestures was independent of how they produce these gestures and whether they had practiced pointing movements before. By contrast, both the production and interpretation seem to be primarily determined by salient visual cues. (PsycINFO Database Record
Recent physiological studies have showed that some visuotactile brain areas respond to other’s peripersonal spaces (PPS) as they would their own. This study investigates this PPS remapping phenomenon in terms of human behavior. Participants placed their left hands on a tabletop screen where visual stimuli were projected. A vibrotactile stimulator was attached to the tip of their index finger. While a white disk approached or receded from the hand in the participant’s near or far space, the participant was instructed to quickly detect a target (vibrotactile stimulation, change in the moving disk’s color or both). When performing this task alone, the participants exhibited shorter detection times when the disk approached the hand in their near space. In contrast, when performing the task with a partner across the table, the participants exhibited shorter detection times both when the disk approached their own hand in their near space and when it approached the partner’s hand in the partner’s near space but the participants' far space. This phenomenon was also observed when the body parts from which the visual stimuli approached/receded differed between the participant and partner. These results suggest that humans can share PPS representations and/or body-derived attention/arousal mechanisms with others.
- Proceedings of the National Academy of Sciences of the United States of America
- Published over 2 years ago
Self-perception depends on the brain’s abilities to differentiate our body from the environment and to distinguish between the sensations generated as a consequence of voluntary movement and those arising from events in the external world. The first process refers to the sense of ownership of our body and relies on the dynamic integration of multisensory (afferent) signals. The second process depends on internal forward models that use (efferent) information from our motor commands to predict and attenuate the sensory consequences of our movements. However, the relationship between body ownership and sensory attenuation driven by the forward models remains unknown. To address this issue, we combined the rubber hand illusion, which allows experimental manipulation of body ownership, and the force-matching paradigm, which allows psychophysical quantification of somatosensory attenuation. We found that a rubber right hand pressing on the left index finger produced somatosensory attenuation but only when the model hand felt like one’s own (illusory self-touch); reversely, the attenuation that was expected to occur during actual self-touch with the real hands was reduced when the participants simultaneously experienced ownership of a rubber right hand that was placed at a distance from their left hand. These results demonstrate that the sense of body ownership determines somatosensory attenuation. From a theoretical perspective, our results are important because they suggest that body ownership updates the internal representation of body state that provides the input to the forward model generating sensory predictions during voluntary action.