A 34-year-old man from urban Delhi presents with a 3-month history of palpitations, tremor, heat intolerance, and weight loss of 6 kg despite good appetite. On examination, he is tachycardic (HR 112 bpm), has a fine tremor, warm moist skin, and a diffuse tender thyroid enlargement. Laboratory tests reveal TSH 0.02 mIU/L (normal 0.4–4.0), free T4 4.2 ng/dL (normal 0.8–1.8), free T3 8.9 pg/mL (normal 2.3–4.2), and thyroid peroxidase (TPO) antibodies negative. Thyroid uptake scan shows diffusely increased tracer uptake. Which of the following best explains the mechanism of excessive thyroid hormone secretion in this patient?