The social cognitive basis of music processing has long been noted, and recent research has shown that trait empathy is linked to musical preferences and listening style. Does empathy modulate neural responses to musical sounds? We designed two functional magnetic resonance imaging (fMRI) experiments to address this question. In Experiment 1, subjects listened to brief isolated musical timbres while being scanned. In Experiment 2, subjects listened to excerpts of music in four conditions (familiar liked (FL)/disliked and unfamiliar liked (UL)/disliked). For both types of musical stimuli, emotional and cognitive forms of trait empathy modulated activity in sensorimotor and cognitive areas: in the first experiment, empathy was primarily correlated with activity in supplementary motor area (SMA), inferior frontal gyrus (IFG) and insula; in Experiment 2, empathy was mainly correlated with activity in prefrontal, temporo-parietal and reward areas. Taken together, these findings reveal the interactions between bottom-up and top-down mechanisms of empathy in response to musical sounds, in line with recent findings from other cognitive domains.

Background

Motion sensitive cells within macaque V5, but not V1, exhibit motion opponency whereby their firing is suppressed by motion in their anti-preferred direction. fMRI studies indicate the presence of motion opponent mechanisms in human V5.

Objective/hypothesis

We tested two hypotheses. 1) Performance of a motion discrimination task would be poorer when stimuli were constructed from pairs of dots that moved in counter-phase vs. in-phase, because counter-phase dots would activate motion opponent mechanisms in V5. 2) Offline 1 Hz rTMS of V5 would impair discrimination performance for in-phase stimuli but not counter-phase stimuli, and the opposite effect would be found for rTMS of V1.

Methods

Stimuli were constructed from 100 dot pairs. Paired dots moved along a fixed motion axis either in counter-phase (motion opponent stimulus) or in-phase (non-opponent motion stimulus). Motion axis orientation discrimination thresholds were measured for each stimulus. Blocks of 300 trials were then presented at 85% correct threshold and discrimination accuracy was measured before and after 1 Hz offline rTMS of either V1 or V5. Subjects were 8 healthy adults.

Results

Discrimination thresholds were significantly larger (worse) for counter-phase than in-phase stimuli (p = 0.02). V5 rTMS mildly impaired discrimination accuracy for the in-phase dot stimuli (p = 0.02) but not the counter-phase dot stimuli. The opposite effect occurred for V1 rTMS (p = 0.05).

Conclusions

Opponent motion mechanisms are present within human V5 and activation of these mechanisms impairs motion discrimination. In addition, perception of the motion axis within opponent motion stimuli involves processing within V1.

Theta burst stimulation (TBS) is thought to affect reward processing mechanisms, which may increase and decrease reward sensitivity. To test the ability of TBS to modulate response to strong primary rewards, participants hypersensitive to primary rewards were recruited. Twenty men and women with at least two opposite-sex, sexual partners in the last year received two forms of TBS. Stimulations were randomized to avoid order effects and separated by 2 hours to reduce carryover. The two TBS forms have been demonstrated to inhibit (continuous) or excite (intermittent) the left dorsolateral prefrontal cortex using different pulse patterns, which links to brain areas associated with reward conditioning. After each TBS, participants completed tasks assessing their reward responsiveness to monetary and sexual rewards. Electroencephalography (EEG) was recorded. They also reported their number of orgasms in the weekend following stimulation. This signal was malleable by TBS, where excitatory TBS resulted in lower EEG alpha relative to inhibitory TBS to primary rewards. EEG responses to sexual rewards in the lab (following both forms of TBS) predicted the number of orgasms experienced over the forthcoming weekend. TBS may be useful in modifying hypersensitivity or hyposensitivity to primary rewards that predict sexual behaviors. Since TBS altered the anticipation of a sexual reward, TBS may offer a novel treatment for sexual desire problems.

Paired associative stimulation (PAS) is a widely used noninvasive brain stimulation protocol to assess neural plasticity. Its reproducibility, however, has been rarely tested and with mixed results. With two consecutive studies, we aimed to provide further tests and a more systematic assessment of PAS reproducibility. We measured intraclass correlation coefficients (ICCs)-a widely used tool to assess whether groups of measurements resemble each other-in two PAS studies on healthy volunteers. The first study included five PAS sessions recording 10 MEPS every 10 min for an hour post-PAS. The second study included two PAS sessions recording 50 MEPS at 20 and 50 min post-PAS, based on analyses from the first study. In both studies PAS sessions were spaced one week apart. Within sessions ICC was fair to excellent for both studies, yet between sessions ICC was poor for both studies. We suggest that long term meta-plasticity effects (longer than one week) may interfere with between sessions reproducibility.