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Chapter 6
reward condition (reward x task switching x accuracy: F(1,11) = 7.651, p = 0.018, η2 = 0.410;
figure 6.4
). In addition, sham surgeries did not affect overall accuracy (surgery x accuracy:
F(1,11) < 1; main effect of accuracy: F(1,11) = 4.997, p = 0.047, η2 = 0.312).
Surgeries in the group with lesions of the AcbC on the other hand, did affect rewarded task-
switching performance (surgery x reward x task switching x accuracy: F(1,11) = 6.782, p =
0.025, η2 = 0.381;
figure 6.4
), without affecting overall performance (surgery x accuracy:
F(1,11) < 1; main effect of accuracy: F(1,11) = 13.189, p = 0.004, η2 = 0.545). More specifically,
prior to surgery, the task-switching performance improved in the high compared with a low
reward context (reward x task switching x accuracy: F(1,11) = 4.850, p = 0.05, η2 = 0.306),
while this pattern was reversed after lesions of the core (reward x task switching x accuracy:
F(1,11) = 6.133, p = 0.031, η2 = 0.358). The reversal of the effect was characterized by improved
task-switching performance on low reward trials after surgery (F(1,11) = 6.788, p = 0.024, η2
= 0.382), in combination with a numerical impairment on task-switching performance during
high reward trials (F(1,11) = 3.229, p = 0.1, η2 = 0.227). This effect was confirmed by directly
comparing the groups, showing a difference between the sham and lesion group after surgery
(group x reward x switch x accuracy: F(1,22) = 8.099, p = 0.009, η2 = 0.269), which was not
present before surgery (group x reward x switch x accuracy: F(1,22) < 1; group x accuracy
(F(1,22) < 1). This difference was due to a relative task-switch improvement in the lesion
group in the low reward context (F(1,22) = 7.492, p = 0.012, η2 = 0.254), and a numerical
impairment in this group in task-switching performance in the high reward context (F(1,22)
= 1.188, p > 0.1), compared with the sham group.
In summary, prior to surgery, task-switching performance was overall better in the high,
compared with low reward context. Sham surgeries did not affect this beneficial effect of
a high reward context on task-switching performance, whereas lesions of the AcbC did.
Importantly, lesions of the AcbC did not affect overall accuracy on test, or performance
during discrimination training.
Discussion
The current study assessed whether the core of the nucleus accumbens plays a crucial role
in exerting motivational control over behaviour, thereby facilitating an agent to effectively
pursue goals. Using a paradigm in rodents that parallels a well-established paradigm in
human subjects (Aarts et al., 2010; van Holstein et al., 2011; Aarts et al., 2014a; Aarts et al.,
2015), (and see Etzel et al., 2015; Fuentes-Claramonte et al., 2015) we showed that animals
were able to use cues to prepare for an upcoming change in cognitive demands and that
this task-switching ability was improved in a high reward context. This ability to improve
cognitive control in a high-reward situation changed after excitotoxic lesions of the AcbC.
More specifically, animals with an intact AcbC exhibited better cognitive control in a high
relative to a low reward situation, whereas this effect was reversed after lesions of the AcbC.
The reversal of this effect was characterized in particular by improved task-switching