I believe that many creative modalities can be usefully included in a therapeutic relationship. There are times when spoken dialog can be more difficult, unwelcome, inhibited, or even frankly unhelpful. Other types of activities can be part of a therapeutic milieu, and work on non-verbal forms of communication, as well as other forms of positive experience in the therapeutic frame.
The use of music in therapy is well-established. Music therapy is a recognized profession, with a substantial academic literature behind it. I believe that music is under-utilized in therapy generally, perhaps considered outside the scope of experience or training of most therapists. Even therapists with a background interest in music may not share this with patients, for a variety of reasons. The predominantly oral tradition of psychotherapy can be so dominant sometimes as to view non-verbal activities as eccentricity.
Music -- listening, performing, learning, and coordinating -- can touch upon the following therapeutic themes:
1) emotional expression
2) performance anxiety / communicative inhibition
4) assumptions about capacity or incapacity to learn something new
5) focusing on an activity which is sufficiently engaging as to calm anxiety or agitation, or at least distract attention away from negative emotions or unwelcome thoughts
7) a sense of achievement
8) patterning the same learning schedule which leads to psychological change or skill acquisition of any sort -- some immediate progress in the moment--which needs to be enjoyable in itself-- but part of a process which can include thousands of hours of experience to grow substantially
9) a sense of trust and "harmony" with the therapist; possibility a modality which makes the therapeutic relationship stronger
10) on a sort of psychodynamic or developmental level, music could be understood as one of the individual's first experiences of emotional soothing (from the mother humming or singing to her infant), a modality which precedes verbal language. There might be deprivations or problems associated with this dynamic for some individuals, which could become a therapeutic theme if music was part of the frame of activities and discussion.
11) music preferences and interests are, of course, an element of identity expression. I believe that questions about music preference and experience are a useful part of a psychiatric history; often an understanding about this part of a person immediately deepens understanding, and offers a chance to connect in different ways, to build rapport and interested collaboration.
Many types of music therapy involve having the patient improvise on a simple instrument, etc., or perhaps listen to music. I think that doing cooperative musical exercises can be a valuable element, in which the therapist can act partly as collaborator or music teacher. The technical skill level is not relevant, in my opinion, and in fact could be considered a type of neutral transferential theme to be worked with in the therapy. Simply practicing a simple technical exercise on an instrument--even during a conversation--could be a tactic to help attain calm and relaxation, in the same way that many other physical skills can be relaxing (e.g. knitting, swimming, yoga).
Here is a review of some of the research literature on music therapy:
2009 meta-analytic review showing music therapy robustly effective for a wide range of problems in severe mental illness, including overall function, well-being, and symptom control. More sessions are more effective; 16-51 sessions associated with large effect sizes.
a 2011 article from the British Journal of Psychiatry, showing robust effects of music therapy in the treatment of depression. There was a "control group", but in this case the control group received "standard care" (medications + a few sessions of psychotherapy), while the active group received this same standard care plus up to 20 sessions of music therapy. So, in my opinion, the study did not control for the effect of simply spending time with the patients for 20 extra sessions. There should have been a control group which had 20 sessions of the same length of time as the music therapy group, but doing a "placebo" activity. Nevertheless, this does show that, at the very least, doing music activities with patients during therapy sessions is a supportable practice.
2005 Cochrane review showing that music therapy is an effective component of therapy for schizophrenia, leading to improved global state, as well as probable positive changes in various symptom clusters.
2008 Cochrane review showing that music therapy may be effective in the treatment of depression. 4 of 5 studies showed greater improvements in depressive symptoms in the music therapy group compared to standard care.
music therapy shown to be helpful to improve the rate of rehabilitation in brain injury or stroke
this is quite a cute study, showing that listening to Mozart's K.448 (sonata for 2 pianos) once nightly for 6 months leads to substantial reductions in seizures in children with refractory epilepsy. It's a weak study, of course, since there is no control group.
a similar study, but a bit stronger, since it shows that Mozart's K. 448 leads to an immediate change in EEG patterns, as long as the recording does not have prominent higher harmonics. I've noticed this myself, that tones with very strong higher-order harmonics above the fundamental tone can prevent focus on music performance, particularly for those with very strong ear skills, or could even be strident and unpleasant. Mozart himself was apparently very sensitive to this as a child. This leads to another issue, about sound level: the modern habit of listening to music at very high sound levels could sabotage not only one's hearing, but also the psychological benefits of the music.
a discussion of the role of music in non-suicidal self-injury.
I think some music may itself be self-injurious, or at least a consistent cue associated with self-injury; but clearly there is therapeutic potential, for music to be helpful in affect regulation or as a healthy substitute behaviour instead of self-injuring.
I'm curious as to the manner in which musical lyrics or the emotional tone in music affects "self-talk" or inner emotional tone. In a "Rogersian" sense, music with very depressive or hostile lyrical or tonal content may help a person to feel less alone--a type of empathic bond with the music--which may be therapeutic. But I believe that such a bond is much more therapeutic if it leads to a sense of resolution of the underlying problems, or offers a consistent message of hope or joy despite whatever empathic connections are made with sadness, anger, emptiness, etc. I think the greatest songs (present in all genres and eras) are those which suggest a resolution for problems of suffering or emotional pain, rather than simply evoking the negative emotion.