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Mapping Muscles Activation to Force Perception during Unloading.

Toma S, Lacquaniti F - PLoS ONE (2016)

Bottom Line: In fact a global measure of the muscles considered was able to predict approximately 60% of the perceptual decisions total variance.Moreover the inter-subjects differences in psychophysical sensitivity showed high correlation with both participants' muscles sensitivity and participants' joint torques.Overall, our findings gave insights into both the role played by the corticospinal motor commands while performing a force detection task and the influence of the gravitational muscular torque on the estimation of vertical forces.

View Article: PubMed Central - PubMed

Affiliation: Centre of Space Bio-medicine, University of Rome Tor Vergata, Rome, Italy.

ABSTRACT
It has been largely proved that while judging a force humans mainly rely on the motor commands produced to interact with that force (i.e., sense of effort). Despite of a large bulk of previous investigations interested in understanding the contributions of the descending and ascending signals in force perception, very few attempts have been made to link a measure of neural output (i.e., EMG) to the psychophysical performance. Indeed, the amount of correlation between EMG activity and perceptual decisions can be interpreted as an estimate of the contribution of central signals involved in the sensation of force. In this study we investigated this correlation by measuring the muscular activity of eight arm muscles while participants performed a quasi-isometric force detection task. Here we showed a method to quantitatively describe muscular activity ("muscle-metric function") that was directly comparable to the description of the participants' psychophysical decisions about the stimulus force. We observed that under our experimental conditions, muscle-metric absolute thresholds and the shape of the muscle-metric curves were closely related to those provided by the psychophysics. In fact a global measure of the muscles considered was able to predict approximately 60% of the perceptual decisions total variance. Moreover the inter-subjects differences in psychophysical sensitivity showed high correlation with both participants' muscles sensitivity and participants' joint torques. Overall, our findings gave insights into both the role played by the corticospinal motor commands while performing a force detection task and the influence of the gravitational muscular torque on the estimation of vertical forces.

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Individual psychometric thresholds as function of individual elbow joint torques, overall muscular activity and muscle-metric PSE.A) Individual median (± S.E.) of net (black) and residual (gray) elbow flexion torques as function of individual psychophysical PSE (± S.E.) of those subjects that respected goodness of fit criteria and joint torques were extracted. Residual torque values were obtained by removing the gravitational component from the total net torque. Negative torques indicate downward resultant joint torque. Positive values represent resultant upward joint torques. Continuous lines and r values are the best fitting regression line and the resultant Pearson correlation through the data points, respectively. B) PSE values as function of individual overall muscular activity calculated by extracting the median of the sum of the normalized MAV value among muscles at each trial for all subjects showing R² merged > 0.5. Negative values indicate main flexor overall muscular activity, while positive represent overall extensor activity. Pearson correlation and best fitting regression line were extracted excluding subject 12 and 13. C) Correlation among individual psychophysical PSE (± S.E.) and PSE (± S.E.) extracted from muscle-metric curve (same data as in Fig 4). In all plots, r values represent statistically significant Pearson correlation (p< 0.05).
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pone.0152552.g006: Individual psychometric thresholds as function of individual elbow joint torques, overall muscular activity and muscle-metric PSE.A) Individual median (± S.E.) of net (black) and residual (gray) elbow flexion torques as function of individual psychophysical PSE (± S.E.) of those subjects that respected goodness of fit criteria and joint torques were extracted. Residual torque values were obtained by removing the gravitational component from the total net torque. Negative torques indicate downward resultant joint torque. Positive values represent resultant upward joint torques. Continuous lines and r values are the best fitting regression line and the resultant Pearson correlation through the data points, respectively. B) PSE values as function of individual overall muscular activity calculated by extracting the median of the sum of the normalized MAV value among muscles at each trial for all subjects showing R² merged > 0.5. Negative values indicate main flexor overall muscular activity, while positive represent overall extensor activity. Pearson correlation and best fitting regression line were extracted excluding subject 12 and 13. C) Correlation among individual psychophysical PSE (± S.E.) and PSE (± S.E.) extracted from muscle-metric curve (same data as in Fig 4). In all plots, r values represent statistically significant Pearson correlation (p< 0.05).

Mentions: As it can be noticed from Table 1, the psychophysical PSE values we considered (values reported in bold in the first and last rows of the table) cover a wide range of values across subjects, from 0.1 N to 18.8 N. In practice, subjects perceived the lowest detectable upward force on their arm (i.e., PSE) at widely different stimulus intensities. This finding suggests that participants may have used different strategies to judge the external forces and make a perceptual decision. The three plots depicted in Fig 6 describe the outcome of our analysis aimed to investigate the variables that mainly correlated with the inter-individual differences in psychophysical sensitivity. In general, we found a highly significant correlation between the inter-subjects variability in the PSEs and the variability of the total (net) and residual elbow flexion torques, r: -0.77 (n = 7, p = 0.04) and r: -0.99 (n = 7, p = 0.00), respectively. Correlation values measured between individual PSEs and participants’ shoulder flexion residual torques (not illustrated) were similar to those observed with elbow torques (n = 7, r: -0.98, p = 0.00), however the differences among subjects’ PSEs poorly correlated with their net shoulder torques (n = 7, r: -0.43, p = 0.37) and resulted not statistically significant.


Mapping Muscles Activation to Force Perception during Unloading.

Toma S, Lacquaniti F - PLoS ONE (2016)

Individual psychometric thresholds as function of individual elbow joint torques, overall muscular activity and muscle-metric PSE.A) Individual median (± S.E.) of net (black) and residual (gray) elbow flexion torques as function of individual psychophysical PSE (± S.E.) of those subjects that respected goodness of fit criteria and joint torques were extracted. Residual torque values were obtained by removing the gravitational component from the total net torque. Negative torques indicate downward resultant joint torque. Positive values represent resultant upward joint torques. Continuous lines and r values are the best fitting regression line and the resultant Pearson correlation through the data points, respectively. B) PSE values as function of individual overall muscular activity calculated by extracting the median of the sum of the normalized MAV value among muscles at each trial for all subjects showing R² merged > 0.5. Negative values indicate main flexor overall muscular activity, while positive represent overall extensor activity. Pearson correlation and best fitting regression line were extracted excluding subject 12 and 13. C) Correlation among individual psychophysical PSE (± S.E.) and PSE (± S.E.) extracted from muscle-metric curve (same data as in Fig 4). In all plots, r values represent statistically significant Pearson correlation (p< 0.05).
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4816335&req=5

pone.0152552.g006: Individual psychometric thresholds as function of individual elbow joint torques, overall muscular activity and muscle-metric PSE.A) Individual median (± S.E.) of net (black) and residual (gray) elbow flexion torques as function of individual psychophysical PSE (± S.E.) of those subjects that respected goodness of fit criteria and joint torques were extracted. Residual torque values were obtained by removing the gravitational component from the total net torque. Negative torques indicate downward resultant joint torque. Positive values represent resultant upward joint torques. Continuous lines and r values are the best fitting regression line and the resultant Pearson correlation through the data points, respectively. B) PSE values as function of individual overall muscular activity calculated by extracting the median of the sum of the normalized MAV value among muscles at each trial for all subjects showing R² merged > 0.5. Negative values indicate main flexor overall muscular activity, while positive represent overall extensor activity. Pearson correlation and best fitting regression line were extracted excluding subject 12 and 13. C) Correlation among individual psychophysical PSE (± S.E.) and PSE (± S.E.) extracted from muscle-metric curve (same data as in Fig 4). In all plots, r values represent statistically significant Pearson correlation (p< 0.05).
Mentions: As it can be noticed from Table 1, the psychophysical PSE values we considered (values reported in bold in the first and last rows of the table) cover a wide range of values across subjects, from 0.1 N to 18.8 N. In practice, subjects perceived the lowest detectable upward force on their arm (i.e., PSE) at widely different stimulus intensities. This finding suggests that participants may have used different strategies to judge the external forces and make a perceptual decision. The three plots depicted in Fig 6 describe the outcome of our analysis aimed to investigate the variables that mainly correlated with the inter-individual differences in psychophysical sensitivity. In general, we found a highly significant correlation between the inter-subjects variability in the PSEs and the variability of the total (net) and residual elbow flexion torques, r: -0.77 (n = 7, p = 0.04) and r: -0.99 (n = 7, p = 0.00), respectively. Correlation values measured between individual PSEs and participants’ shoulder flexion residual torques (not illustrated) were similar to those observed with elbow torques (n = 7, r: -0.98, p = 0.00), however the differences among subjects’ PSEs poorly correlated with their net shoulder torques (n = 7, r: -0.43, p = 0.37) and resulted not statistically significant.

Bottom Line: In fact a global measure of the muscles considered was able to predict approximately 60% of the perceptual decisions total variance.Moreover the inter-subjects differences in psychophysical sensitivity showed high correlation with both participants' muscles sensitivity and participants' joint torques.Overall, our findings gave insights into both the role played by the corticospinal motor commands while performing a force detection task and the influence of the gravitational muscular torque on the estimation of vertical forces.

View Article: PubMed Central - PubMed

Affiliation: Centre of Space Bio-medicine, University of Rome Tor Vergata, Rome, Italy.

ABSTRACT
It has been largely proved that while judging a force humans mainly rely on the motor commands produced to interact with that force (i.e., sense of effort). Despite of a large bulk of previous investigations interested in understanding the contributions of the descending and ascending signals in force perception, very few attempts have been made to link a measure of neural output (i.e., EMG) to the psychophysical performance. Indeed, the amount of correlation between EMG activity and perceptual decisions can be interpreted as an estimate of the contribution of central signals involved in the sensation of force. In this study we investigated this correlation by measuring the muscular activity of eight arm muscles while participants performed a quasi-isometric force detection task. Here we showed a method to quantitatively describe muscular activity ("muscle-metric function") that was directly comparable to the description of the participants' psychophysical decisions about the stimulus force. We observed that under our experimental conditions, muscle-metric absolute thresholds and the shape of the muscle-metric curves were closely related to those provided by the psychophysics. In fact a global measure of the muscles considered was able to predict approximately 60% of the perceptual decisions total variance. Moreover the inter-subjects differences in psychophysical sensitivity showed high correlation with both participants' muscles sensitivity and participants' joint torques. Overall, our findings gave insights into both the role played by the corticospinal motor commands while performing a force detection task and the influence of the gravitational muscular torque on the estimation of vertical forces.

Show MeSH
Related in: MedlinePlus