Beyond the session: delayed effects of prefrontal theta-burst stimulation onthe liking of newly learned melodies

Reward operates as a cycle in which a stimulus produces a pleasure response, and the degree of pleasure experienced reinforces the behaviours that lead back to it. Music provides a useful model for examining this cycle because it is intrinsically pleasurable, can be learned, and engages reward-related frontostriatal circuitry that overlaps with circuitry involved in primary and secondary rewards, such as food, sex, and money. Transcranial magnetic stimulation (TMS), a non-invasive stimulation method, has been shown to produce bidirectional effects on music-evoked pleasure by increasing or decreasing activity in cortical regions, such as the left dorsolateral prefrontal cortex (DLPFC), that are functionally connected to subcortical regions, including the striatum. Here, we further characterize the reward cycle by incorporating TMS into a paradigm that combines musical pleasure ratings with an early musical skill acquisition task. In a within-subjects, counterbalanced crossover design, 23 participants with 2-10 years of musical experience received intermittent TBS (iTBS; excitatory) and continuous TBS (cTBS; inhibitory) over the left DLPFC in separate sessions. Participants rated the pleasantness of short piano melodies before stimulation (T0), immediately afterwards (T1), and 24 hours later (T2). After stimulation, they learned to play the melodies, and pitch and rhythm accuracy were assessed during three performance phases, namely acquisition, immediately after acquisition, and 24 hours later. Liking did not differ between conditions at T1; however, the increase in liking from baseline (T0) to T2 was significantly larger following iTBS than cTBS, a divergence that emerged across the 24-hour interval spanning both learning and sleep. Pitch and rhythm accuracy did not differ between conditions at any phase, despite improvement across trials in both. These results indicate that TMS to the left DLPFC can produce delayed, condition-dependent shifts in musical liking without a parallel change in early skill acquisition.