Letters to the Editor
In reply: We appreciate the opportunity to respond to comments on our manuscript "Feasibility of Auditory Cortical Stimulation for the Treatment of Tinnitus." De Ridder et al. correctly note that in this early report, we did not find acute alteration in tinnitus intensity despite all subjects showing reductions in subjective measures. With time, however, we have seen 50% of subjects note an intensity-suppressing effect of chronic stimulation (1). The points raised in the letter of De Ridder et al. letter may indeed play a role in this delayed response.
Our stimulation paradigm uses a 2-electrode extradural array and may therefore not deliver as high or as localized a current to the auditory cortex as the array and placement parameters used by De Ridder et al. (2) or the intraparenchymal placements of Seidman et al. (3). Therefore, changes in the cortex affecting the perception of tinnitus in our system may require longer periods of stimulation. It may be that each system works differently, and that intradural/intraparenchymal stimulation causes acute changes in neuronal excitability, whereas chronic extradural stimulation induces long-term plastic changes. Indeed, in some of our patients with battery depletion, the tinnitus has returned but at lower levels and in delayed fashion-indicating an underlying alteration in auditory cortical physiology.
Transcranial magnetic stimulation (TMS) may be important not only in screening patients for cortical stimulation but also in localizing stimulation sites. For example, the angular gyrus has recently been implicated in false auditory perceptions and may be a potential target for cortical stimulation (4,5). We will submit shortly our observations on TMS in subjects who have undergone cortical implantation. Interestingly, in our cohort, there does not appear to be a correlation between those that respond to TMS and those that responded to electrical stimulation.
We wholeheartedly agree with the sentiment that more clinical research in these areas is needed. Advances in electrode design, identification of stimulation sites, establishment of stimulation parameters, patient selection, and efficacy are important factors currently being determined by these continued investigations.
David R. Friedland, M.D., Ph.D.
Brian Harris Kopell, M.D.
Departments of *Otolaryngology and
Communication Sciences and †Neurosurgery
Medical College of Wisconsin and
Clement J Zablocki VA Medical Center
Milwaukee, Wisconsin, U.S.A.
1. Kopell BH, Friedland DR, Runge-Samuelson C, Ulmer JL, Gaggl W. Epidural cortical stimulation for the treatment of tinnitus. Abstract. International Neuromodulation Society Meeting; 2007; Acapulco, Mexico.
2. De Ridder D, De Mulder G, Verstraeten E, et al Primary and secondary auditory cortex stimulation for intractable tinnitus. ORL J Otorhinolaryngol Relat Spec
3. Seidman MD, De Ridder D, Elisevich K, et al Direct electrical stimulation of Heschl's gyrus for tinnitus treatment. Laryngoscope
4. De Ridder D, Van Laere K, Dupont P, Menovsky T, Van de Heyning P. Visualizing out-of-body experience in the brain. N Engl J Med
5. Plewnia C, Bischof F, Reimold M. Suppression of verbal hallucinations and changes in regional cerebral blood flow after intravenous lidocaine: a case report. Prog Neuropsychopharmacol Biol Psychiatry