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Neural substrate of body size: illusory feeling of shrinking of the waist.

Ehrsson HH, Kito T, Sadato N, Passingham RE, Naito E - PLoS Biol. (2005)

Bottom Line: We found that activity in the cortices lining the left postcentral sulcus and the anterior part of the intraparietal sulcus reflected the illusion of waist shrinking, and that this activity was correlated with the reported degree of shrinking.These results suggest that the perceived changes in the size and shape of body parts are mediated by hierarchically higher-order somatosensory areas in the parietal cortex.Based on this finding we suggest that relative size of body parts is computed by the integration of more elementary somatic signals from different body segments.

View Article: PubMed Central - PubMed

Affiliation: Wellcome Department of Imaging Neuroscience, Institute of Neurology, London, United Kingdom. h.ehrsson@fil.ion.ucl.ac.uk

ABSTRACT
The perception of the size and shape of one's body (body image) is a fundamental aspect of how we experience ourselves. We studied the neural correlates underlying perceived changes in the relative size of body parts by using a perceptual illusion in which participants felt that their waist was shrinking. We scanned the brains of the participants using functional magnetic resonance imaging. We found that activity in the cortices lining the left postcentral sulcus and the anterior part of the intraparietal sulcus reflected the illusion of waist shrinking, and that this activity was correlated with the reported degree of shrinking. These results suggest that the perceived changes in the size and shape of body parts are mediated by hierarchically higher-order somatosensory areas in the parietal cortex. Based on this finding we suggest that relative size of body parts is computed by the integration of more elementary somatic signals from different body segments.

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Related in: MedlinePlus

Linear Relationship between Parietal Activity and the Strength of the Shrinking-Waist IllusionEach dot represents the values for one individual subject. The data is fitted with a least-squares regression line. In (A) and (B) we plot the activity from the peaks in the intraparietal region that showed the most significant relation between illusion strength and neuronal activity ([A]: x = −39, y = −42, z = 72, t = 3.81; p < 0.001 uncorrected, R2 = 0.4916, Pearson's R = 0.70; [B]: x = −48, y = −33, z = 54; t = 2.69; p < 0.009 uncorrected, R2 = 0.32, Pearson's R = 0.57). These peaks were identified by using SPM2 to search for parietal voxels using a second-level linear regression model. (C) and (D) show the relationship between illusion and activity at exactly those peak voxels detected in the interaction analysis (see Figure 2). (C) shows the cortex at the junction between the postcentral sulcus and the intraparietal sulcus (p < 0.027, y = 0.0385x + 0.1424, R2 = 0.23, Pearson's R = 0.48), and (D) illustrates the anterior part of the intraparietal cortex (p < 0.016, y = 0.0552x + 0.0488, R2 = 0.27, Pearson's R = 0.52). In all plots the y-axis indicates the BOLD response (contrast estimates for interaction effect) in the parietal cortex, and the x-axis indicates the illusory displacement of the wrists when in contact with the body (which corresponds to the degree of waist shrinking). These regressions are not driven by outliers because all four remained significant (p < 0.05) when we used a least-square fitting procedure that minimizes the effects of outliers (Robustfit in MATLAB; see Results for details).
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pbio-0030412-g003: Linear Relationship between Parietal Activity and the Strength of the Shrinking-Waist IllusionEach dot represents the values for one individual subject. The data is fitted with a least-squares regression line. In (A) and (B) we plot the activity from the peaks in the intraparietal region that showed the most significant relation between illusion strength and neuronal activity ([A]: x = −39, y = −42, z = 72, t = 3.81; p < 0.001 uncorrected, R2 = 0.4916, Pearson's R = 0.70; [B]: x = −48, y = −33, z = 54; t = 2.69; p < 0.009 uncorrected, R2 = 0.32, Pearson's R = 0.57). These peaks were identified by using SPM2 to search for parietal voxels using a second-level linear regression model. (C) and (D) show the relationship between illusion and activity at exactly those peak voxels detected in the interaction analysis (see Figure 2). (C) shows the cortex at the junction between the postcentral sulcus and the intraparietal sulcus (p < 0.027, y = 0.0385x + 0.1424, R2 = 0.23, Pearson's R = 0.48), and (D) illustrates the anterior part of the intraparietal cortex (p < 0.016, y = 0.0552x + 0.0488, R2 = 0.27, Pearson's R = 0.52). In all plots the y-axis indicates the BOLD response (contrast estimates for interaction effect) in the parietal cortex, and the x-axis indicates the illusory displacement of the wrists when in contact with the body (which corresponds to the degree of waist shrinking). These regressions are not driven by outliers because all four remained significant (p < 0.05) when we used a least-square fitting procedure that minimizes the effects of outliers (Robustfit in MATLAB; see Results for details).

Mentions: Next, we investigated whether there was a relationship between the activity in the parietal cortex and the strength of the body-image illusion. Because we had quantified the strength of the illusion for each subject in the test sessions prior to the scans, we could examine how the blood oxygenation level-dependent (BOLD) signal in the parietal cortex related to these illusion ratings. First, we used a linear regression model to search for voxels in the left intraparietal cortex in which the activity was related to the degree of body shrinkage across subjects (Figure 3). We found a peak of activation in the most anterior part of the intraparietal sulcus (Figure 3B; x = −48, y = −33, z = 54; t = 2.69; p < 0.009 uncorrected, R2 = 0.32, Pearson's R = 0.57). This peak was located within the cluster of active voxels detected in the factorial design above, and therefore it probably corresponds to the same area. Also just adjacent, we found a peak in the border zone between the anterior part of the intraparietal sulcus and the left superior parietal gyrus (Figure 3A; x = −39, y = −42, z = 72, t = 3.81; p < 0.001 uncorrected, R2 = 0.4916, Pearson's R = 0.70). Second, we examined exactly those peak voxels that were detected in the interaction analysis. As shown in Figure 3C and 3D, there was a linear relationship between the degree of illusory waist shrinking and the BOLD activity at these sites (p < 0.05 uncorrected). Taken together, these findings demonstrate that the subjects who reported the strongest shrinking-waist illusion also showed the strongest BOLD signal in the left postcentral sulcus and in the anterior part of left the intraparietal cortex.


Neural substrate of body size: illusory feeling of shrinking of the waist.

Ehrsson HH, Kito T, Sadato N, Passingham RE, Naito E - PLoS Biol. (2005)

Linear Relationship between Parietal Activity and the Strength of the Shrinking-Waist IllusionEach dot represents the values for one individual subject. The data is fitted with a least-squares regression line. In (A) and (B) we plot the activity from the peaks in the intraparietal region that showed the most significant relation between illusion strength and neuronal activity ([A]: x = −39, y = −42, z = 72, t = 3.81; p < 0.001 uncorrected, R2 = 0.4916, Pearson's R = 0.70; [B]: x = −48, y = −33, z = 54; t = 2.69; p < 0.009 uncorrected, R2 = 0.32, Pearson's R = 0.57). These peaks were identified by using SPM2 to search for parietal voxels using a second-level linear regression model. (C) and (D) show the relationship between illusion and activity at exactly those peak voxels detected in the interaction analysis (see Figure 2). (C) shows the cortex at the junction between the postcentral sulcus and the intraparietal sulcus (p < 0.027, y = 0.0385x + 0.1424, R2 = 0.23, Pearson's R = 0.48), and (D) illustrates the anterior part of the intraparietal cortex (p < 0.016, y = 0.0552x + 0.0488, R2 = 0.27, Pearson's R = 0.52). In all plots the y-axis indicates the BOLD response (contrast estimates for interaction effect) in the parietal cortex, and the x-axis indicates the illusory displacement of the wrists when in contact with the body (which corresponds to the degree of waist shrinking). These regressions are not driven by outliers because all four remained significant (p < 0.05) when we used a least-square fitting procedure that minimizes the effects of outliers (Robustfit in MATLAB; see Results for details).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1287503&req=5

pbio-0030412-g003: Linear Relationship between Parietal Activity and the Strength of the Shrinking-Waist IllusionEach dot represents the values for one individual subject. The data is fitted with a least-squares regression line. In (A) and (B) we plot the activity from the peaks in the intraparietal region that showed the most significant relation between illusion strength and neuronal activity ([A]: x = −39, y = −42, z = 72, t = 3.81; p < 0.001 uncorrected, R2 = 0.4916, Pearson's R = 0.70; [B]: x = −48, y = −33, z = 54; t = 2.69; p < 0.009 uncorrected, R2 = 0.32, Pearson's R = 0.57). These peaks were identified by using SPM2 to search for parietal voxels using a second-level linear regression model. (C) and (D) show the relationship between illusion and activity at exactly those peak voxels detected in the interaction analysis (see Figure 2). (C) shows the cortex at the junction between the postcentral sulcus and the intraparietal sulcus (p < 0.027, y = 0.0385x + 0.1424, R2 = 0.23, Pearson's R = 0.48), and (D) illustrates the anterior part of the intraparietal cortex (p < 0.016, y = 0.0552x + 0.0488, R2 = 0.27, Pearson's R = 0.52). In all plots the y-axis indicates the BOLD response (contrast estimates for interaction effect) in the parietal cortex, and the x-axis indicates the illusory displacement of the wrists when in contact with the body (which corresponds to the degree of waist shrinking). These regressions are not driven by outliers because all four remained significant (p < 0.05) when we used a least-square fitting procedure that minimizes the effects of outliers (Robustfit in MATLAB; see Results for details).
Mentions: Next, we investigated whether there was a relationship between the activity in the parietal cortex and the strength of the body-image illusion. Because we had quantified the strength of the illusion for each subject in the test sessions prior to the scans, we could examine how the blood oxygenation level-dependent (BOLD) signal in the parietal cortex related to these illusion ratings. First, we used a linear regression model to search for voxels in the left intraparietal cortex in which the activity was related to the degree of body shrinkage across subjects (Figure 3). We found a peak of activation in the most anterior part of the intraparietal sulcus (Figure 3B; x = −48, y = −33, z = 54; t = 2.69; p < 0.009 uncorrected, R2 = 0.32, Pearson's R = 0.57). This peak was located within the cluster of active voxels detected in the factorial design above, and therefore it probably corresponds to the same area. Also just adjacent, we found a peak in the border zone between the anterior part of the intraparietal sulcus and the left superior parietal gyrus (Figure 3A; x = −39, y = −42, z = 72, t = 3.81; p < 0.001 uncorrected, R2 = 0.4916, Pearson's R = 0.70). Second, we examined exactly those peak voxels that were detected in the interaction analysis. As shown in Figure 3C and 3D, there was a linear relationship between the degree of illusory waist shrinking and the BOLD activity at these sites (p < 0.05 uncorrected). Taken together, these findings demonstrate that the subjects who reported the strongest shrinking-waist illusion also showed the strongest BOLD signal in the left postcentral sulcus and in the anterior part of left the intraparietal cortex.

Bottom Line: We found that activity in the cortices lining the left postcentral sulcus and the anterior part of the intraparietal sulcus reflected the illusion of waist shrinking, and that this activity was correlated with the reported degree of shrinking.These results suggest that the perceived changes in the size and shape of body parts are mediated by hierarchically higher-order somatosensory areas in the parietal cortex.Based on this finding we suggest that relative size of body parts is computed by the integration of more elementary somatic signals from different body segments.

View Article: PubMed Central - PubMed

Affiliation: Wellcome Department of Imaging Neuroscience, Institute of Neurology, London, United Kingdom. h.ehrsson@fil.ion.ucl.ac.uk

ABSTRACT
The perception of the size and shape of one's body (body image) is a fundamental aspect of how we experience ourselves. We studied the neural correlates underlying perceived changes in the relative size of body parts by using a perceptual illusion in which participants felt that their waist was shrinking. We scanned the brains of the participants using functional magnetic resonance imaging. We found that activity in the cortices lining the left postcentral sulcus and the anterior part of the intraparietal sulcus reflected the illusion of waist shrinking, and that this activity was correlated with the reported degree of shrinking. These results suggest that the perceived changes in the size and shape of body parts are mediated by hierarchically higher-order somatosensory areas in the parietal cortex. Based on this finding we suggest that relative size of body parts is computed by the integration of more elementary somatic signals from different body segments.

Show MeSH
Related in: MedlinePlus