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. 2018 May 8;7:e32740.
doi: 10.7554/eLife.32740.

The Causal Role of the Somatosensory Cortex in Prosocial Behaviour

Free PMC article

The Causal Role of the Somatosensory Cortex in Prosocial Behaviour

Selene Gallo et al. Elife. .
Free PMC article


Witnessing another person's suffering elicits vicarious brain activity in areas that are active when we ourselves are in pain. Whether this activity influences prosocial behavior remains the subject of debate. Here participants witnessed a confederate express pain through a reaction of the swatted hand or through a facial expression, and could decide to reduce that pain by donating money. Participants donate more money on trials in which the confederate expressed more pain. Electroencephalography shows that activity of the somatosensory cortex I (SI) hand region explains variance in donation. Transcranial magnetic stimulation (TMS) shows that altering this activity interferes with the pain-donation coupling only when pain is expressed by the hand. High-definition transcranial direct current stimulation (HD-tDCS) shows that altering SI activity also interferes with pain perception. These experiments show that vicarious somatosensory activations contribute to prosocial decision-making and suggest that they do so by helping to transform observed reactions of affected body-parts into accurate perceptions of pain that are necessary for decision-making.

Keywords: EEG; SI; TMS; empathy for pain; helping; human; neuroscience.

Conflict of interest statement

SG, RP, LM, MS, LB, CF, AH, BL, TM, JS, AA, CK, VG No competing interests declared


Figure 1.
Figure 1.. Paradigm.
(A) Top: a snapshot from the Hand and Face videos (examples of each condition are presented in Videos 1–4). Middle: trial structure. The red arrow indicates the timing of the shock delivery, belt touching the hand or beginning of the color saturation changes. The gray gradient graphically illustrates the dynamic of the face reaction and color saturation changes, with stronger gray corresponding to stronger facial expression or stronger saturation. The intensity of the OutputMovie is equal to the intensity of InputMovie minus the donation. Bottom: run structure. The same structure was used in the EEG and TMS experiments. Gray lightning symbols indicate when TMS was applied in the TMS version of the experiment. (B) A snapshot from the Color videos (see Videos 5, 6) and the trial structure for the rating task.
Figure 1—figure supplement 1.
Figure 1—figure supplement 1.. Histograms of participants’ responses for the credibility and movie repetition detection for the experiment with the Costly Helping paradigm.
The dotted grey line indicates the cut-off used as exclusion criteria.
Figure 2.
Figure 2.. ROIs and TMS results.
(A) The relationship between InputMovie intensity, as assigned by an independent pool of participants during the movies validation procedure, and given donation for hand and face videos. Each point is the group average donation for the specific intensity. Error bars represent S.E.M. (B) Pain Localizer ROIs. Left: results of the pain localizer within the primary somatosensory cortices (see 'Supplementary information') shown on the Colin brain together with contours of regions associated with hand (blue) and face (red) movements. These contours were generated using the meta-analyses tool Neurosynth (Yarkoni et al., 2011). Specifically, we generated reverse inference maps using the search terms ‘grasping’ and ‘speech production’ to probe movements of the hand and of the face, respectively, and intersected each with an anatomical map of the left SI from the anatomy toolbox (as the union of BA1, 2, 3a and 3b). Right: schematic visualization of the dorsal and ventral ROIs within the EEG template space, and approximate site of the TMS stimulation. (C) Interaction Condition x TMS results. *p<0.05. Error bars represent S.E.M. (D) The left render shows the location of the five HD-tDCS electrodes on the scalp and where the central anode is positioned relative to our d-SIL ROI (red). The image was created by inserting fish oil omega three pills in place of the HD-tDCS electrodes inside the electrodes holders. A participant was wearing the montage while a T1-weighted anatomical image was acquired (TR = 8.2 ms, TE = 3.8 ms, flip angle = 8°, FOV = 240 mm × 240 mm, 1 × 1 × 1 mm isotropic voxels). The right render shows the 3D simulation of current density changes expected from our tDCS montage, obtained using the electrostatic finite element method (FEM) offered by the Matlab toolbox COMETS 2 (Jung et al., 2013).
Figure 3.
Figure 3.. Regression between SI activity and donation.
(A) Left: relationship between brain activity of one example participant at a given time-point and the Z-donation for all the trials of that participant. The linear trend represents the slope of the robust regression performed on these values. Right: time-course of the robust regression slopes (betas) for the same example participant. (B) Time-course of the Hotelling's t-squared (Ht2) test on the slopes for the significant ROI and condition. Because the two significant Hand clusters are very close in time, for illustrative purposes only, they have been evidenced by a single yellow band. (C) Grand averages for high (darker lines) and low (lighter lines) donation for each dipole, SI-ROI and condition. (D) Right hemisphere results. Significant clusters based on Ht2 are shown in yellow.
Author response image 1.
Author response image 1.
Author response image 2.
Author response image 2.

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