Humans, but not zebra finches, produce spontaneously isochronous song through the lifespan.

The global prevalence of hypothyroidism is considered to be 1–2% (). It is most frequently caused by autoimmune disease, , Hashimoto thyroiditis (), and affects more women than men (). Hyperthyroidism has a similar female preponderance, with prevalences of 2–3% and 0.2–0.3% among women and men, respectively (; ). It is also primarily the result of autoimmunity, in this case, Graves’ disease (). Anxiety disorders have a prevalence of 14% and are thus the most common psychiatric conditions (). Both anxiety disorders and thyroid dysfunction, particularly hyperthyroidism, may present with similar symptoms, such as nervousness, insomnia, and impaired concentration (; ). Further, physical signs, , palpitations, sweating and diarrhea are found in both diseases (; ; ). There is also evidence that thyroid hormones affect brain monoamine metabolism (; ; ; ) which is thought to be altered in anxiety disorders, too (). Symptom overlap and similar brain metabolism pathways suggest a relationship between both groups of disorders and beg the question of whether people diagnosed with thyroid disorders are at a higher risk of developing anxiety disorders.