Behavioral performance
Figure 1B and 1C show the accuracy rate and reaction time (RT) of dollar, cent, and nil trials. For both men and women, the accuracy rates were close to 67%, suggesting the success of the staircase procedure. There were no significant sex differences in the accuracy rate of dollar (t56=-0.76; p=0.45), cent (t61=-0.37; p=0.70), or nil (t61=-0.73; p=0.47) trials or in the RT of dollar (t56=0.05; p=0.96), cent (t61=-0.04; p=0.97), or nil (t58=0.04; p=0.97) trials.
Men showed higher sensitivity to reward (SR) score than women, and, in contrast, women showed higher sensitivity to punishment (SP) score than men (Table 1). We examined the relationship between behavioral performance and SR and SP for men and women together and separately. In linear regressions, SR score was positively correlated with the accuracy rate of dollar trials in men + women (r61=0.28, p=0.02) and in women (r25=0.52, p=0.006). SR score was also positively correlated with the accuracy rate of cent trials in men + women (r61=0.33, p=0.008) and in women (r25=0.51, p=0.007). SR score was negatively correlated with the RT of cent trials in women (r25=-0.44, p=0.02), SP score was positively correlated with the RT of dollar trials in women (r25=0.50, p=0.007), and SP was positively correlated with the RT of cent trials in men + women (r61=0.28, p=0.03) (Figure 2). The r and p values of all correlations are shown in Table 2. However, although women appeared to show more significant correlations between SR/SP scores and performance measures, relative to men, the slope tests did not reveal significant sex differences in any of these correlations (all p’s ≥ 0.47).
Table 2. Linear regressions between performance measures and SR/SP.
|
AR Dollar (%)
|
AR Cent (%)
|
RT Dollar (ms)
|
RT Cent (ms)
|
|
r
|
p
|
r
|
p
|
r
|
p
|
r
|
p
|
SR (M + F)
|
0.28
|
0.02*
|
0.33
|
0.008*
|
-0.19
|
0.12
|
-0.22
|
0.08
|
SR (M)
|
0.24
|
0.17
|
0.27
|
0.12
|
-0.17
|
0.33
|
-0.14
|
0.42
|
SR (F)
|
0.52
|
0.006*
|
0.51
|
0.007*
|
-0.31
|
0.11
|
-0.44
|
0.02*
|
|
|
|
|
|
|
|
|
|
SP (M+F)
|
0.04
|
0.74
|
0.01
|
0.92
|
0.21
|
0.09
|
0.28
|
0.03*
|
SP (M)
|
0.08
|
0.65
|
-8.47e-4
|
0.99
|
0.10
|
0.53
|
0.24
|
0.15
|
SP (F)
|
-0.10
|
0.62
|
0.001
|
0.99
|
0.50
|
0.007*
|
0.37
|
0.06
|
Accuracy rate (AR, %) and reaction time (RT, ms) and sensitivity to reward (SR) and sensitivity to punishment (SP) scores for men and women combined (M+F), men (M), and women (F). *p<0.05. Degrees of freedom for M + F: 61; M: 34; F: 25.
Sex differences in regional responses to reward anticipation (“bet”)
In a one-sample t test, we evaluated regional activations to anticipation to win dollar vs. nil, cent vs. nil and dollar vs. cent in men and women combined (Figure 3). Anticipation of reward involved activation of the ventral striatum (VS), dorsal striatum, thalamus, midbrain, as well as primary and supplementary motor and visual cortical areas. In a covariance analysis with age as a covariate, men and women did not show significant differences in activation to reward anticipation during dollar vs. nil, cent vs. nil, or dollar vs. cent trials.
[Figure 3 about here]
Sex differences in regional activations to feedback (win or loss)
In a one-sample t-test, we evaluated regional activations to dollar win vs. nil, cent win vs. nil, dollar vs. cent win, dollar loss vs. nil, cent loss vs. nil, and dollar vs. cent loss in men and women combined. These results are shown in Figure 4.
[Figure 4 and Figure 5 about here]
In covariance analyses to compare men and women with age as a covariate for each of these contrasts, we observed sex differences in activation (men > women) in the right orbitofrontal cortex, left cerebellum, right occipital cortex and supplementary motor area (SMA), for dollar win > nil (Figure 5A), and in the left temporal cortex and SMA for cent win > nil (Figure 5B). Clusters meeting cluster p < 0.05 FWE are summarized in Table 3. None of the other contrasts, including dollar win vs. dollar loss and cent win vs. cent loss (not shown in the figure), showed significant sex differences.
Table 3. Sex differences (men > women) in regional activations to reward feedback.
Cluster
|
Voxel
|
MNI coordinates (mm)
|
Side
|
Brain region
|
size (k)
|
(peak Z)
|
x
|
y
|
z
|
|
|
Dollar Win > Nil
|
136
|
4.31
|
27
|
44
|
-8
|
R
|
Orbitofrontal cortex
|
347
|
3.99
|
-18
|
-40
|
-23
|
L
|
Cerebellum
|
267
|
3.97
|
12
|
-1
|
58
|
R/L
|
SMA
|
269
|
3.79
|
6
|
-85
|
28
|
R
|
Occipital cortex
|
Cent Win > Nil
|
353
|
5.40
|
-48
|
-4
|
10
|
L
|
Premotor area
|
336
|
4.30
|
-6
|
-1
|
58
|
L
|
SMA
|
Note: voxel p<0.001 uncorrected; cluster p<0.05 FWE; R: right; L: left. The sign of Z
value indicates the direction of correlation. SMA: supplementary motor area.
Whole brain regression with SP and SR scores
For each of the six contrasts, we performed a linear regression with both SR and SP scores as regressors and years of age as a covariate for men and women combined as well as separately. A cluster in the right caudate head (x = 9, y = 14, z = 4, voxel Z = 3.81, volume = 3978 mm3) met the threshold of voxel p<0.001, uncorrected and cluster p<0.05 FWE-corrected, and showed activity during cent loss vs. nil in positive correlation with the SR score in men and women combined. We extracted the β contrast (cent loss – nil) for all subjects and compared men and women in the correlation with a slope test (49). The results showed that the β contrast was positively correlated with SR score for men (r34 = 0.59, p = 0.00016) but not for women (r25 = 0.14, p = 0.48), suggesting that the correlation was driven primarily by men. Further, a slope test confirmed the sex difference (z = 2.004, p = 0.046) (Figure 6).
[Figure 6 about here]