Testosterone and Neural Function

Inclusion Criteria: * Male * Hypogonadal (Serum Total T \<300 ng/dL, Free T \<46 pg/mL, or bioavailable T \<110 ng/dL) with signs/symptoms of hypogonadism * Age 18-80 years * Traumatic or non-traumatic spinal cord injury (SCI) * Time since injury (TSI) more than 12 months * American Spinal Injury Association (ASIA) Injury classification Scale (AIS) A, B, C, or D * Stable prescription medication regimen for at least 30 days * Not currently receiving pharmacological treatment for hypogonadism * Must be able to commit to study requirements of 3 visits within a 30-day period * Provide informed consent Exclusion Criteria: * Extensive history of seizures * Ventilator dependence or patent tracheostomy site * History of neurologic disorder other than SCI * History of moderate or severe head trauma * Currently receiving treatment for hypogonadism * History of allergy, hypersensitivity, or other significant adverse reaction to testosterone replacement therapy * Significant cardiovascular disease or cardiac conduction disease * Active psychological disorder * Moderate or severe brain injury, stroke, tumor, multiple sclerosis, or abscess * Recent history (within 3 months) of substance abuse * Pressures sores stage 3 or greater * Active infection * Frequent severe migraines * Recent history (within past 6 months) of recurrent autonomic dysreflexia, defined as a syndrome of sudden rise in systolic pressure greater than 20 mm Hg or diastolic pressure greater than 10 mm Hg, without rise in heart rate, accompanied by symptoms such as headache, facial flushing, sweating, nasal congestion, and blurry vision (this will be closely monitored during all screening and testing procedures) * History of implanted devices with electromagnetic properties: brain/spine/nerve stimulators, aneurysm clips, ferromagnetic metallic implants in the head (except for inside mouth); cochlear implants; cardiac pacemaker/defibrillator; intracardiac lines; currently increased intracranial pressure; or other contraindications to brain or spine stimulation * Use of medications that significantly lower seizure threshold, such as amphetamines, neuroleptics, dalfampridine, and bupropion.