Musical stimuli stimulate neural networks associated with various functional domains, such as movement, cognition, communication, emotion, and social responses
[100][67]. Studies clearly demonstrate that instrumental music without lyrics, Chinese and Western music can evoke changes in emotion and stimulate the brain structures involved with motivation, reward, and emotion
[101,102,103,104,105][68][69][70][71][72]. There is evidence that music can provoke changes in individual emotions, hormone arousal, emotional motor expression, and action movements
[102][69]. The studies included in this analysis used various experimental approaches, such as investigating music-evoked experiences of intense pleasure, emotional responses to consonant or dissonant music, happy or sad music, joy- or fear-evoking music, musical expectancy violations and music-evoked tension. Listening to joyful dance-tunes has been shown to reduce stress and enhance emotional responses, such as joy and peace
[105,106][72][73]. In particular, music is observed to stimulate increase in blood–oxygen level dependent (BOLD) signals in the amygdala, and the hippocampus
[105][72]. A meta-analysis of functional neuroimaging studies
[103][70] found that the amygdalae, hypothalamus, and hippocampus, which are vital parts of the brain in producing emotion and in experiencing PTSD symptoms, are stimulated by music. None of the included studies used music with lyrics. The ventral tegmental area (VTA), involved in dopamine production and release within the reward system, is also significantly activated by both unfamiliar musical pieces and the participant’s favorite music, in contrast, PFC activity was positively correlated with pleasure scores associated with music
[107,108][74][75]. However, favorite versus neutral music listening contrasts showed a greater activation in healthy participants than depressed patients
[107][74].
PTSD is characterized by hypervigilance associated with altered connectivity between the amygdalae and the hippocampus
[41][76]. Communication between these brain areas is vital in the symptomatology of PTSD. There is evidence that participant’s own favorite music to which they usually had a chill experience, can enhance the connection between the amygdalae, PFC, and the hippocampus
[110][77]. Moreover, contrast analysis of joy, fear and neutral musical stimuli revealed strongest BOLD signals in the superficial amygdala during joyful music, such as classical music, Irish jigs, jazz, reggae, South American and Balkan music
[111][78]. Thus, music could potentially play a role in balancing the processing of stimuli and in reducing the amygdala’s startle response so they can revert to the premorbid state. Moreover, attentive listening to musical clips played with the piano or violin can also stimulate PFC
[112][79], and therefore, can possibly recruit PFC to exert inhibitory control over amygdalic stress responses. Initiating communication between the amygdalae, PFC and hippocampus through music can, therefore, not only mitigate the hypervigilance of PTSD, but can also enhance cognitive processing of emotions.
Attentive listening to or playing music can stimulate neurogenesis and neuroplasticity in the brain
[100,106,113][67][73][80] which is relevant for individuals with PTSD who experience neuronal loss and impaired neurogenesis in parts of the limbic system. The increased hippocampal communication with the hypothalamus can also help balance the HPA axis
[113][80]. There is evidence suggesting that musical training in healthy participants can stimulate the hippocampus, induce neurogenesis, and produce a larger hippocampus
[114,115,116][81][82][83]. Altering the hippocampal volume can consequently increase positive emotions and regulate negative affect. Koelsch and Skouras (2014) reported increased functional connectivity between the hippocampus and hypothalamus, and amygdalae and nucleus accumbens during exposure to joyful music in healthy adults
[117][84]. The study used non-vocal joyful instrumental music from various epochs and styles. In addition, several studies on music-evoked emotions have reported activity changes in the hippocampus associated with a reduction of emotional stress associated with a lowering of the cortisol level
[106,118,119,120][73][85][86][87]. Overall, 75% of these studies involved experimenter-selected music (classical, new age or easy listening, and world), while the other 25% involved self-selected music, either “entirely self-selected” or “quasi-self-selected”. Clinical studies, which included a majority of the ICU population, demonstrated a stress-reducing effect of music listening irrespective of genre, self-selection of the music, or duration of listening
[118][85]. Classical music demonstrated a significant reduction in cortisol levels among mechanically ventilated ICU survivors
[119][86].
Evidence suggests that active vs. passive music therapy may have differential effects on patient engagement and receptivity. According to fMRI and PET scan studies, active music participation engages more parts of the brain than just listening to music
[121][88]. In a qualitative study, passive music therapy participants reported an immediate therapeutic effect, such as a reduction in anxiety
[122][89]. Active music therapy participants, on the other hand, described interactive session elements as stimulating, alleviating anxiety through pleasant social interaction. Music improvisation (drum based) has been found to be effective in expressing and managing emotions among veterans with PTSD
[95][62]. Moreover, a systematic review showed that passive listening to relaxing music didn’t seem to have any significant effects on PTSD symptoms, suggesting the importance of active music therapy to evoke change in PTSD patients
[89][56]. The researchers posited that specialist skills and an ongoing therapeutic relationship is vital in reducing symptoms of PTSD.
However, music selection needs careful consideration. Music that the participant does not enjoy may result in a stress rather than a relaxation response. Moreover, music can trigger strong memories, which influence the affective response to music and can, therefore, modulate the therapeutic effects of music
[123][90]. In the acute phase of critical illness, despite some controversy around the role of patients’ music preferences, it appears that patient-directed music selection associates with better outcomes
[124][91].
In our rSev
iew, seveeral studies allowed participants to choose music from a variety of musical genres. However, participants’ choices were restricted within the range of selections offered by the researchers.
A systematic review on mMusic interventions for mechanically ventilated patients reported participant dropout rates to be higher in researcher-selected music compared to patient-selected
[125][92]. Instead, studies involving a music therapist to assess patient music preferences have reported no dropouts and a high degree of participant satisfaction
[70,98,99][35][65][66]. Therefore, self-selected music appears to be associated with both the effectiveness of music interventions and participant retention.
Basic psychoacoustic properties of music, such as pitch (high or low tone of sounds), rate (fast or slow speed of sounds), loudness (loud or soft intensity of sounds), mode (major or minor key), timbre, and rhythm have been shown to be important factors in the perception and induction of positive as well as negative emotional states. The music therapy research supports music containing a slower tempo, low pitch, containing primarily string composition, regular rhythmic patterns, no extreme changes in dynamics, and no lyrics are associated with relaxation, joy, or peace
[126][93]. The tempo of 60–80 beats per minutes can help induce a state of relaxation and regulate emotions
[127][94]. A study by Beck et al., 2021, used predictable slow-tempo music to decrease arousal and induce relaxation in PTSD patients
[99][66]. In addition, the harmonic complexity of relaxing music should be consonant and remain within the diatonic key with a clear tonal center
[126,127][93][94]. Predictable music leads to positive responses, such as reward, appraisal, and pleasantness, thus it may support the relaxation response, while dissonant and unexpected harmonies with frequent chord changes activate the amygdala and defeat the purpose of emotion regulation
[128][95]. Research has stated that music with less sharp timbres has been proven to induce relaxation
[126][93]. Possible instrumental arrangements include piano, cello, flute and marimba
[127][94]. In addition, the use of instrumental music over nature sounds can effectively induce relaxation.