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Abstract:
The dorsolateral prefrontal cortex (DLPFC) is suggested to be
involved in the generation of internally triggered behavior, called
self-determined actions. However, this assumption is questioned by
studies relating DLPFC activation in the self-determined action
task to task-specific working memory (WM) load. To assess these
assumptions we compared regional blood flow in a self-determined
action task and a WM task with fMRI. Using parametric designs we
manipulated difficulty in both tasks and asked whether
difficulty-related activity changes are localized in similar
regions in these separate tasks. Generation of self-determined
actions was investigated by asking subjects to generate random
finger sequences. Difficulty was manipulated by increasing movement
frequency (1 movement per 2 seconds versus 2 per second). WM load
was investigated with an n-back task with 3 load-steps (0back -
2back). The results showed: 1) Commonly in both tasks, the left
DLPFC, a region in the vicinity of left and right frontal
eyefields, SMA, left and right intraparietal sulcus were activated.
2) In these regions increased generation difficulty and WM load led
to increased regional blood flow. 3) For the random generation task
difficulty-sensitive DLPFC regions could be predicted if we
transferred the localization of WM load-sensitive regions from the
n-back to the random generation task. These results indicate
fMRI-activation during self-determined actions to be related to WM
load in the random generation paradigm.
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