Fairness, the notion that people deserve or have rights to certain resources or kinds of treatment, is a fundamental dimension of moral cognition. Drawing on recent evidence from economics, psychology, and neuroscience, we ask whether self-interest is always intuitive, requiring self-control to override with reasoning-based fairness concerns, or whether fairness itself can be intuitive. While we find strong support for rejecting the notion that self-interest is always intuitive, the literature has reached conflicting conclusions about the neurocognitive systems underpinning fairness. We (...) propose that this disagreement can largely be resolved in light of an extended Social Heuristics Hypothesis. Divergent findings may be attributed to the interpretation of behavioral effects of ego depletion or neurostimulation, reverse inference from brain activity to the underlying psychological process, and insensitivity to social context and inter-individual differences. To better dissect the neurobiological basis of fairness, we outline how future research should embrace cross-disciplinary methods that combine psychological manipulations with neuroimaging, and that can probe inter-individual, and cultural heterogeneities. (shrink)

BackgroundTranscranial direct current stimulation targeting the primary motor hand area may induce lasting shifts in corticospinal excitability, but after-effects show substantial inter-individual variability. Functional magnetic resonance imaging can probe after-effects of TDCS on regional neural activity on a whole-brain level.ObjectiveUsing a double-blinded cross-over design, we investigated whether the individual change in corticospinal excitability after TDCS of M1-HAND is associated with changes in task-related regional activity in cortical motor areas.MethodsSeventeen healthy volunteers received 20 min of real or sham TDCS on separate (...) days in randomized order. Real and sham TDCS used the classic bipolar set-up with the anode placed over right M1-HAND. Before and after each TDCS session, we recorded motor evoked potentials from the relaxed left first dorsal interosseus muscle after single-pulse transcranial magnetic stimulation of left M1-HAND and performed whole-brain fMRI at 3 Tesla while participants completed a visuomotor tracking task with their left hand. We also assessed the difference in MEP latency when applying anterior-posterior and latero-medial TMS pulses to the precentral hand knob.ResultsReal TDCS had no consistent aftereffects on mean MEP amplitude, task-related activity or motor performance. Individual changes in MEP amplitude, measured directly after real TDCS showed a positive linear relationship with individual changes in task-related activity in the supplementary motor area and AP-LM MEP latency.ConclusionFunctional aftereffects of classical bipolar anodal TDCS of M1-HAND on the motor system vary substantially across individuals. Physiological features upstream from the primary motor cortex may determine how anodal TDCS changes corticospinal excitability. (shrink)