Brain Activation for Effort in Human Learning: A Critical and Systematic Review of fMRI Studies

This paper aims to review studies concerned on registering the activation of brain areas during the performance of tasks based on effort, as well as on determining specifically the role of the amygdala in such situations. The search was carried out in three databases: PubMed database, Neuroscience Information Framework, and PsycARTICLES section of the APA PsycNET database; 48 studies presented a methodological arrangement clearly oriented to analyze the effort during the performance of learning tasks. The studies reviewed employed tasks like memorization, decision-making, calculation, motor sequences, and spatial discrimination. Though some variability is found, the main key areas activated for such tasks were: a) Prefrontal cortex, insula, and anterior cingulate cortex in memorization tasks; (b) Cerebellum, basal ganglia, motor and pre-motor areas in specific motor tasks; (c) Nucleus accumbens and striatum when explicit reinforcing consequences and high effort were involved; (d) Cingulate cortex for effort requirements and persistent behavior; and (e) Hypothalamus, hippocampus, and related regions for the initial consolidation of memory, as well as for spatial discrimination. The amygdala was activated only under very specific conditions: in unpredictable contingencies (i.e., for superstitious behavior), and when the effort was far above the average. Thus, since the amygdala is the main area activated in aversive conditioning, we conclude that the performance of tasks based on effort, in general, cannot be considered equivalent to the aversive conditioning in neurological terms, accordingly to the review performed.