Schematic representation of the experimental set-up and protocol.

<p>A) In the left panel, a representation of the motor task is shown. On the PC monitor there was a starting line (black line), a target zone (colored lines) and a cursor (yellow and green dot). The lowest line of the target zone (green) represented the 60% of the subject’s MVF, while the highest line (light blue) represented the 120% of MVF, as measured for each participant in the calibration phase at the very beginning of the experiment. The task was to press a piston with the right index finger as strong as possible in order to reach the higher lines of the target zone. The pressures against the piston were recorded by a force transducer and converted in vertical displacements of the cursor. When the cursor entered the target zone, it changed from yellow to green. In the right panel, a representation of the TMS task is shown. The red line represents the 30% of MVF as measured in the calibration phase. Subjects had to maintain the cursor on the red line until the end of the trial. B) Timeline of the experimental protocol with a representation of the sessions sequence (baseline, manipulation and final) and TENS application. As schematically shown in the picture, the two groups of participants (control and experimental) received different verbal information about the effects of TENS. Moreover, in the manipulation session the two groups underwent different procedures: the experimental group performed the motor task with a surreptitious reduction of the cursor’s excursion range (conditioning procedure), while the control group performed the motor task without any reduction.</p

Additional parameters recorded during the TMS-task and at rest.

<p>A) Force level of the two groups of participants in the TMS-task, corresponding to the moment in which the TMS pulse was delivered. B) Index of fatigue (FI). The experimental (red line) and control group (green line) had similar FI values across the sessions, ruling out the effect of fatigue. C) EMG background activity recorded from the FDI muscle before the TMS pulse. D) EMG background activity recorded from the ADM muscle before the TMS pulse. E) MEP amplitude recorded at rest from the FDI muscle. F) MEP amplitude recorded at rest from the ADM muscle. All the data are represented as mean ± SE.</p

Neurophysiological data.

<p>A) MEP amplitude recorded from the FDI muscle was comparable in the experimental (red line) and the control (green line) and across sessions. B) MEP amplitude recorded from the ADM muscle was comparable in the experimental (red line) and the control (green line) and across sessions. C) Duration of the CSP was shorter in the final than in the baseline session in the experimental group (red line), whereas there was a slight increase, although not significant, in the control group (green line). Moreover, the two groups had different CSP duration in the final session. All the values are expressed as mean ± SE. **p < 0.010.</p

Behavioral and subjective data.

<p>A) Force profile (average of 50 trials) of the baseline (dashed lines) and final (solid lines) sessions in one subject of the experimental group (red lines) and one subject of the control group (green lines). B) Normalized force peak decreases in the experimental group (red line) from baseline to final session, whereas it remains stable in the control group (green line). Moreover, the two groups have nearly different values in the final session. C) Also the percentage of strong pressures decreases in the experimental group (red line) from baseline to final session, whereas it remains stable in the control group (green line). D) Scores of expectation of change in performance. The experimental group (red bar) expected a more negative change of performance than the control group (green bar). E) Judgments of treatment efficacy. The experimental group (red bar) has higher score than the control group (green bar). F) Subjective perception of force. In general, the experimental group (red line) felt weaker than the control group (green line). G) Sense of effort [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0125223#pone.0125223.ref022" target="_blank">22</a>] was overall higher in the final than in the baseline session. All the values are expressed as mean ± SE. **p < 0.010, *p < 0.050, ~ p = 0.056.</p

Individual Differences in the Rubber Hand Illusion are related to Sensory Suggestibility

Scores at the RHI task and Sensory Suggestibility Scale.<div><br></div

Demographic and clinical data of patients.

<p>a  =  Unified Parkinson’s Disease Rating Scale – III part (motor evaluation).</p><p>b  =  Hoehn & Yahr staging scale.</p

Additional control conditions in PD patients and healthy controls.

<p>The columns represent the mean percentage of correct response averaged across all the digit pairs for the affected and the less/unaffected hand. Control1 refers to the control condition with crossed fingers and one sphere on one fingertip, Control2 refers to the control condition with parallel fingers and two spheres simultaneously placed on the two fingertips. The bars represent the standard error. The two groups showed high and comparable number of correct responses in each additional control condition.</p

Mean scores for S3 related to an explicit feeling of ownership after synchronous and asynchronous stroking.

<p>The solid line shows a significant difference in scores between the two groups in the synchronous condition. The dashed lines indicate significant differences between synchronous and asynchronous conditions within each group. In both groups, the experience of illusion was rated higher after synchronous than after asynchronous stimulation. Error bars represent standard errors.</p

Correlation between S3 scores in the synchronous condition and the total SSS score.

<p>The graph shows Spearman’s correlation between the total SSS score (y-axis) and the explicit feeling of ownership (S3) after synchronous stimulation (x-axis) of the left and the right hand. The higher the degree of sensory suggestibility, the stronger the feeling of ownership of the rubber hand.</p

Experimental and control conditions.

<p>The experimenter set and maintained the correct position of the subject’s fingers during stimulation. A) Experimental condition: the digits were crossed and a sphere was placed in the contact point between them. This condition is usually associated with Aristotle’s illusion. B) Control condition: the digits were placed parallel and a sphere was placed in the contact point between them. This condition is usually associated with correct perception of an object. C) The additional control conditions for the crossed (<i>left</i>) and parallel (<i>right</i>) finger positions. In the first, the fingers were crossed and one sphere was placed on one finger, near the contact point. In this way it was possible to exclude an association between the crossed position and the “two-stimuli” response. In the second condition, the fingers were parallel and two spheres were simultaneously placed on them. This condition avoided the association between the parallel position and the “one-stimulus” response.</p