Los efectos de la contaminación para las Comunidades

In this section we present the main neural activations from the Moral Dilemma task. IV.4.1. Difference between Allocations

We looked for brain areas that were correlated with the absolute difference in meals between the two allocations (ΔM ). Unlike the difference measures in Section IV.3.2., this measure is independent of the subject’s choice. ΔM was added as a parametric regressor with 3 values (0, 1, and 3) at the display of the scenario. We found a negative correlation in bilateral insula for both Take and Give scenarios (Fig. 55 and Table 6). The activation in the right hemisphere for the Give trials has only a very small overlap with the insula.

Fig. 55: Difference between allocations. Negative parametric activation in bilateral insula for both Take and Give trials with respect to ΔM when the scenario is displayed to subjects. A statistical map is shown alongside a pseudo-color legend with t- scores (p≤0.005, minimum cluster size: 5).

Scenario

Area

X

Y

Z

T

#Voxels

Left Insula -42 0 3 3.41 33 Take Right Insula 42 -3 6 3.26 15 Left Insula -39 6 6 4.40 42 Give Right Insula 48 6 3 3.65 38 Table 6: Activations in the insula for |ΔM|. X, Y, X = MNI location coordinates of peak voxel (mm); T = T-statistic of peak voxel; #Voxels = number of activated voxels in the cluster (p≤0.005, minimum cluster size: 5)

Since ΔM is negatively correlated with the brain activity in the insula, this implies that the larger the difference in meals, the smaller the activation in the insula. To verify this, we extracted the time-courses from the activated voxels in the insula, and segregated them according to the difference in meals between allocations. At about 6 seconds after the onset of the display screen the time-courses separate, indicating the insula is differentially activated with respect toΔM . Fig. 56 shows this for Take trials (the time-courses are similar for Give trials, although more noisy).

IV.4.2. Correlates of Efficiency, Equity and Utility in Take Trials

We next investigated whether there are any neural correlates of the welfare measures described in Section IV.3.2 in the Take scenarios. We were not able to use those measures directly as there is a correlation between the chosen and unchosen allocation. Instead, we used the difference measures (i.e., ΔM, ΔG, and ΔU), which measure the actual spread in efficiency, equity, and utility between the chosen and unchosen allocations. We hypothesize that various brain structures might track these measures.

Fig. 57: Delta equity in Take trials. Negative parametric activation in bilateral insula with respect to ΔG when subjects switch the lever and when the feedback screen is displayed. A statistical map is shown alongside a pseudo-color legend with t-scores (p≤0.005 for switch lever, and p≤0.002 for feedback, minimum cluster size: 5).

Screen

Area

X

Y

Z

T

#Voxels

Left Insula -36 -3 12 4.16 27 Switch Lever Right Insula 39 3 9 3.72 64 Left Insula -45 -6 12 4.89 18 Feedback Right Insula 45 -9 12 4.74 26 Table 7: Activations in the insula for ΔG during Take trials. X, Y, X = MNI location coordinates of peak voxel (mm); T = T- statistic of peak voxel; #Voxels = number of activated voxels (p≤0.005 for switch lever, and p≤0.002 for feedback, minimum cluster size: 5). Note that only the voxels that actually are in the insula were considered in #Voxels.

We used the difference measures to construct parametric regressors at various moments in the experiment, and looked for brain areas whose activation was correlated with those regressors. We found that the bilateral insula was negatively correlated with delta equity (ΔG) when subjects switched the lever, as well as when the feedback screen was presented (Fig. 57 & Table 7). There was also a weak correlation in the right insula when the projectile hit the lever. We also found that delta utility (ΔU) was positively correlated with brain activity in the caudate at the moment where the projectile hits the kids (Fig. 58).

Fig. 58: Delta utility in Take trials. Positive parametric activation in the caudate with respect to ΔU when the projectile hits the kids. The left figure panel shows a statistical map alongside a pseudo- color legend with t-scores (p≤0.005, minimum cluster size: 5). The right panel is a glass brain of the same activation, showing that the only activated brain structure is the caudate (84 voxels).

IV.4.3. Correlates of Efficiency, Equity and Utility in Give Trials

We also looked for similar activations with respect to the difference measures in Give trials, and found a positive correlation between delta equity (ΔG) and brain activity in the bilateral caudate. This correlation was present at several instances during scenarios: when the scenario was first displayed, when the subject switched the lever, when the projectile hit

the lever, and when the projectile hit the kids (see Table 8 for a summary). Although the peaks of activation were slightly different for each instance, there was quite a lot of overlap between voxels. Activation in the caudate when the projectile hits the kids is shown in Fig. 59.

Fig. 59: Delta equity in Give trials. Positive parametric activation in the caudate with respect to ΔG when the projectile hits the kids. Statistical map shown alongside a pseudo-color legend with t-scores (p≤0.005, minimum cluster size: 5)

Screen

Area

X

Y

Z

T

#Voxels

Display scenario Right caudate 18 18 12 3.74 37 Left caudate -6 12 9 3.25 9 Switch lever Right caudate 9 15 6 4.67 19 Left caudate -3 6 6 4.14 48 Hit lever Right caudate 6 6 6 4.48 35 Left caudate -12 6 12 4.27 39 Hit kids Right caudate 12 9 15 5.41 85 Table 8: Activations in the caudate for ΔG during Give trials. X, Y, X = MNI location coordinates of peak voxel (mm); T = T- statistic of peak voxel; #Voxels = number of activated voxels (p≤0.005, minimum cluster size: 5). Note that only the voxels that actually are in the caudate were considered in #Voxels.

Parametric correlations with respect to delta efficiency (ΔM) were found in the left thalamus (MNI coordinates of the peak: [-9 -9 9], 40 voxels, p<0.001) when the feedback screen was presented to subjects (Fig. 60), a region implicated in the evaluation of reward.

Fig. 60: Delta efficiency in Give trials. Positive parametric activation in the caudate with respect to ΔM during the feedback screen. Statistical map shown alongside a pseudo-color legend with t-scores (p≤0.001, minimum cluster size: 5)

In document Buscando voces indígenas en las obras de José María Arguedas (página 93-98)