The purpose of this research is to understand how a neurostimulation technique, transcranial electrical stimulation (tES), affects brain function in adults with chronic subjective tinnitus measured with functional magnetic resonance imaging (fMRI). This study targets a specific kind of tES called transcranial direct current stimulation (tDCS), where a mild, constant current is passed between electrodes placed on the scalp.

This is an investigator-initiated MRI study of High Definition (HD) transcranial electrical stimulation (tES) in adults with chronic subjective tinnitus. HDtES is a mild, noninvasive form of brain stimulation using small electrodes to target a small part of the brain/cortex. Primary outcomes are changes in brain function and connectivity measured with MRI before and after a single 20-minute session of HDtES. Secondary outcomes are changes in tinnitus symptoms after 20-minutes of HDtES on 5 consecutive days.

Inclusion Criteria:

1. Ages between 18 and 75

2. Race/ethnicity: all races and ethnic groups

3. Sex/Gender: all

4. Capacity to provide informed consent

5. Subjective tinnitus symptoms confirmed by patient self report meeting the following criteria:

   1. Present for at least one year prior to start of study
   2. Present (can be heard when consciously attended to) >50% of awake time
   3. Intrudes (is heard even when attempting to ignore/mask) >10% of awake time

6. Has discussed tinnitus symptoms with clinician (i.e., physician, audiologist) to confirm low/no likelihood of physical or neurological origin of tinnitus symptoms (e.g., acoustic neuroma, Meniere's Disease, etc.), confirmed by patient self-report

7. Stable standard or no pharmacological treatment regimen for tinnitus with no change in treatment 6 weeks prior to study start

Exclusion Criteria:

1. Ages below 18 (neurobiology is quite different in children vs. adults)

2. Ages above 75 (cortical excitability changes with age)

3. Tinnitus symptoms with known medial origin, including:

   1. Meniere's disease
   2. Pulsatile tinnitus
   3. Acoustic neuroma
   4. Spontaneous optoacoustic emissions
   5. Any other known medical origin

4. Severe mood disorder (major depression or anxiety)

5. Diagnosis of any medical condition potentially affecting brain function, including:

   1. neuropsychiatric or mental disorders (bipolar, post-traumatic stress disorder, etc.)
   2. severe mood disorders (major depression or anxiety)
   3. psychotic states or disorders
   4. developmental disorders
   5. neurological disorders, including mild cognitive impairment
   6. significant head injury
   7. significant history of alcohol/substance abuse or dependence
   8. active chronic pain condition (>1 year duration)
   9. other major medical conditions (e.g., cancer, stroke).

6. MRI contraindications:

   1. metal or other implants that are not MR-safe
   2. claustrophobia
   3. pregnancy or suspected pregnancy

7. tDCS contraindications*:

   1. skin conditions or injuries on the scalp
   2. hair extensions, wigs, braids, etc. that cannot be removed prior to the study
   3. metal implants or pacemakers (also contraindicated for MRI)

8. Non-English speakers (due to written consent and questionnaires administered)

9. Significant history of alcohol/substance abuse or dependence within last 12 months

10. Neurostimulation or neuromodulation treatment longer than 20 minutes within the past 3 months

11. Current medication use potentially affecting brain function, including decongestants, antihistamines, benzodiazepines or other anticonvulsants, or anti-psychotics.