Focal transcranial direct current stimulation of auditory cortex in chronic tinnitus: A randomized controlled mechanistic trial.

Objective: The goal of this pilot MRI study was to understand how focal transcranial direct current stimulation (tDCS) targeting auditory cortex changes brain function in chronic tinnitus. Methods: People with chronic tinnitus were randomized to active or sham tDCS on five consecutive days in this pilot mechanistic trial (n=10/group). Focal 4×1 tDCS (central anode, surround cathodes) targeted left auditory cortex, with single-blind 2mA current during twenty-minute sessions. Arterial spin-labeled and blood oxygenation level dependent MRI occurred immediately before and after the first tDCS session, and tinnitus symptoms were measured starting one week before the first tDCS session and through four weeks after the final session. Results: Acute increases in cerebral blood flow and functional connectivity were noted in auditory cortex after the first active tDCS session. Reduced tinnitus loudness ratings after the final tDCS session correlated with acute change in functional connectivity between an auditory network and mediodorsal thalamus and prefrontal cortex. Reduced tinnitus intrusiveness also correlated with acute change in connectivity between precuneus and an auditory network. Conclusions: Focal auditory-cortex tDCS can influence function in thalamus, auditory, and prefrontal cortex, which may associate with improved tinnitus. Significance: With future refinement, noninvasive brain stimulation targeting auditory cortex could become a viable intervention for tinnitus.