Musical training increases functional connectivity, but does not enhance mu suppression

Experimental suppression of transcranial magnetic stimulation-electroencephalography sensory potentials

The sensory experience of transcranial magnetic stimulation (TMS) evokes cortical responses measured in electroencephalography (EEG) that confound interpretation of TMS-evoked potentials (TEPs). Methods for sensory masking have been proposed to minimize sensory contributions to the TEP, but the most effective combination for suprathreshold TMS to dorsolateral prefrontal cortex (dlPFC) is unknown. We applied sensory suppression techniques and quantified electrophysiology and perception from suprathreshold dlPFC TMS to identify the best combination to minimize the sensory TEP. In 21 healthy adults, we applied single pulse TMS at 120% resting motor threshold (rMT) to the left dlPFC and compared EEG vertex N100-P200 and perception. Conditions included three protocols: No masking (no auditory masking, no foam, and jittered interstimulus interval [ISI]), Standard masking (auditory noise, foam, and jittered ISI), and our ATTENUATE protocol (auditory noise, foam, over-the-ear protection, and unjittered ISI). ATTENUATE reduced vertex N100-P200 by 56%, "click" loudness perception by 50%, and scalp sensation by 36%. We show that sensory prediction, induced with predictable ISI, has a suppressive effect on vertex N100-P200, and that combining standard suppression protocols with sensory prediction provides the best N100-P200 suppression. ATTENUATE was more effective than Standard masking, which only reduced vertex N100-P200 by 22%, loudness by 27%, and scalp sensation by 24%. We introduce a sensory suppression protocol superior to Standard masking and demonstrate that using an unjittered ISI can contribute to minimizing sensory confounds. ATTENUATE provides superior sensory suppression to increase TEP signal-to-noise and contributes to a growing understanding of TMS-EEG sensory neuroscience.

Cortical mu rhythms during action and passive music listening

Brain systems supporting body movement are active during music listening in the absence of overt movement. This covert motor activity is not well understood, but some theories propose a role in auditory timing prediction facilitated by motor simulation. One question is how music-related covert motor activity relates to motor activity during overt movement. We address this question using scalp electroencephalogram by measuring mu rhythms-cortical field phenomena associated with the somatomotor system that appear over sensorimotor cortex. Lateralized mu enhancement over hand sensorimotor cortex during/just before foot movement in foot versus hand movement paradigms is thought to reflect hand movement inhibition during current/prospective movement of another effector. Behavior of mu during music listening with movement suppressed has yet to be determined. We recorded 32-channel EEG (n = 17) during silence without movement, overt movement (foot/hand), and music listening without movement. Using an independent component analysis-based source equivalent dipole clustering technique, we identified three mu-related clusters, localized to left primary motor and right and midline premotor cortices. Right foot tapping was accompanied by mu enhancement in the left lateral source cluster, replicating previous work. Music listening was accompanied by similar mu enhancement in the left, as well as midline, clusters. We are the first, to our knowledge, to report, and also to source-resolve, music-related mu modulation in the absence of overt movements. Covert music-related motor activity has been shown to play a role in beat perception (Ross JM, Iversen JR, Balasubramaniam R. Neurocase 22: 558-565, 2016). Our current results show enhancement in somatotopically organized mu, supporting overt motor inhibition during beat perception.NEW & NOTEWORTHY We are the first to report music-related mu enhancement in the absence of overt movements and the first to source-resolve mu activity during music listening. We suggest that music-related mu modulation reflects overt motor inhibition during passive music listening. This work is relevant for the development of theories relating to the involvement of covert motor system activity for predictive beat perception.

Differential Activation and Functional Plasticity of Multimodal Areas Associated with Acquired Musical Skill

Training of a musical skill is known to produce a distributed neural representation of the ability to perceive music and perform musical tasks. In the present study we tested the hypothesis that the audiovisual perception of music involves a wider activation of multimodal sensory and sensorimotor structures in the brain, including those containing mirror neurons. We mapped the activation of brain areas during passive listening and viewing of the first 40 s of "Ode to Joy" being played on the piano by an expert pianist. To do this we performed brain functional magnetic resonance imaging during the presentation of 6 different stimulus contrasts pertaining to that musical melody in a pseudo-randomized order. Group data analysis in musically trained and untrained adults showed robust activation in broadly distributed occipitotemporal, parietal and frontal areas in trained subjects and much restricted activation in untrained subjects. A visual stimulus contrast focusing on the visual motion percept of moving fingers on piano keys revealed selective bilateral activation of a locus corresponding to the V5/MT area, which was significantly more pronounced in trained subjects and showed partial linear dependence on the duration of training on the left side. Quantitative analysis of individual brain volumes confirmed a significantly greater and wider spread of activation in trained compared to untrained subjects. These findings support the view that audiovisual perception of music and musical gestures in trained musicians involves an expanded and widely distributed neural representation formed due to experience-dependent plasticity.