Dopamine, Motor Imagery, and Proprioception: A Neurochemical Probe into the Perception-Imagery Debate

The relationship between mental imagery and perception is a key debate in cognitive neuroscience. This study experimentally investigated how acute dopaminergic modulation influences motor imagery and proprioceptive perception. We conducted a double-blind, placebo-controlled, pre-post study with 42 healthy young adults, using branched-chain amino acids (BCAAs) to indirectly manipulate dopaminergic tone. We assessed serum prolactin levels, motor imagery ability (MIQ-3), and passive limb positioning performance. Results confirmed successful dopaminergic modulation: the BCAA group's prolactin levels remained stable, while controls showed a typical diurnal decrease. This modulation selectively impaired internal visual motor imagery, suppressing the natural improvement observed in the placebo group. For proprioception, overall mean Constant Error (CE) and Absolute Error (AE) were unaffected; however, motor consistency (Variable Error, VE) significantly worsened in the BCAA group and improved in controls. Exploratory analyses also revealed complex, angle-dependent changes in CE and AE. This nuanced dissociation suggests dopamine differentially affects motor simulation and perception. Findings challenge strong perceptualist theories, supporting partial functional dissociation and highlighting the sensitivity of specific motor imagery and angle-specific proprioceptive processing to neurochemical fluctuations.