Affective dimensions of emotional memory shape corticospinal excitability in the upper and lower limbs in young males

Emotional memory influences motor control, potentially via the corticospinal tract, yet the factors causing this modulation remain poorly understood. This study investigated how recalling emotional memories modulates corticospinal excitability in upper- and lower-limb muscles and whether these effects are better captured by categorical (e.g., happiness) or dimensional (valence and arousal) models of emotion. In two experiments, transcranial magnetic stimulation was applied over the primary motor cortex while healthy male participants recalled memories associated with five emotional conditions: neutral, happiness, sadness, fear, and anger. Motor-evoked potentials (MEPs) were recorded from four upper-limb muscles (Experiment 1, N = 16) and five lower-limb muscles (Experiment 2, N = 21). Although there were some indications of emotion-related changes in MEP amplitudes in both the upper and lower limbs, there was no significant difference between emotion categories. Subsequent analyses using generalized additive mixed models revealed a negative linear relationship between arousal and MEP amplitudes, and a U-shaped relationship with valence, in the abductor pollicis brevis muscle (p = 0.017 and p = 0.005, respectively; adjusted R² = 0.919). Additionally, significant interactions between arousal and valence were observed in the first dorsal interosseous (p = 0.008, adjusted R² = 0.796) and extensor carpi radialis (p = 0.033, adjusted R² = 0.764) muscles. In lower-limb muscles, arousal showed a consistent positive association with MEP amplitudes (all:p < 0.05, adjusted R² = 0.623-0.891). These results suggest that affective dimensions, rather than categorical emotions, affect corticospinal excitability across muscles: individual muscles differ in their sensitivity to arousal and valence. These findings highlight the significance of affective dimensions in understanding the influence of emotional memory recall on corticospinal excitability.