Comparison of the effects of millimeter wave irradiation, general bath heating, and localized heating on neuronal activity in the leech ganglion Sergii Romanenko ab , Peter H. Siegel a , Daniel A. Wagenaar a , Victor Pikov b* a California Institute of Technology, Pasadena, CA 91125 USA b Huntington Medical Research Institutes, Pasadena, CA 91105 USA ABSTRACT The use of electrically-induced neuromodulation has grown in importance in the treatment of multiple neurological disorders such as Parkinson’s disease, dystonia, epilepsy, chronic pain, cluster headaches and others. While electrical current can be applied locally, it requires placing stimulation electrodes in direct contact with the neural tissue. Our goal is to develop a method for localized application of electromagnetic energy to the brain without direct tissue contact. Toward this goal, we are experimenting with the wireless transmission of millimeter wave (MMW) energy in the 10-100 GHz frequency range, where penetration and focusing can be traded off to provide non-contact irradiation of the cerebral cortex. Initial experiments have been conducted on freshly-isolated leech ganglia to evaluate the real-time changes in the activity of individual neurons upon exposure to the MMW radiation. The initial results indicate that low-intensity MMWs can partially suppress the neuronal activity. This is in contrast to general bath heating, which had an excitatory effect on the neuronal activity. Further studies are underway to determine the changes in the state of the membrane channels that might be responsible for the observed neuromodulatory effects. Keywords: Neuron, action potential, leech, millimeter waves, non-invasive, brain, GHz, terahertz. INTRODUCTION Modulation of neuronal activity and excitability has been utilized for treating Parkinson’s disease, dystonia, epilepsy, chronic pain, cluster headache, and other neurological disorders [1]. Amongst the available neuromodulation approaches, electrical stimulation is presently the most common technique for inducing neuronal excitatory and inhibitory effects used in the treatment of these disorders [2]. Despite clinical availability of electrical stimulation devices, their adoption by neurosurgeons and patients has lagged, in part because of the considerable risks associated with the surgical procedures for their insertion, and the potential for tissue damage during long-term implantation [3]. In an effort to reduce the risks and inherent invasiveness of surgically implanted electrodes, we are exploring the potential application of non-contact focused electromagnetic energy on the nervous tissue. In an earlier study using rat-pup cortical slices, we demonstrated the feasibility of directly affecting neuronal activity using this approach [4]. To directly study the mechanisms of the observed neuromodulatory effects of the MMWs on neurons, we have begun working with freshly-dissected leech segmental ganglia, as they provide a simple biological preparation for the neurophysiological evaluation of specific identifiable neurons over an extended experimentation period. Previously, it has been reported [5] that focused microwaves (1-5 GHz) can inhibit the firing rate of individual ganglionic neurons in another invertebrate, Aplysia. In contrast, an equivalent amount of observed temperature rise by general bath heating produced an increase in the firing rate in a variety of poikilothermic animals, such as Aplysia [5], cockroach [6], and fly [7], as well as in homeothermic animals, such as the cat [8]. The heating-induced increase in the firing rate has been postulated to be due to faster opening dynamics of the voltage-gated K + and Na + channels in the cell membrane [9], as well as changes in the membrane capacitance [10]. Recently, the ability of localized infrared heating to induce neuronal Invited Paper Terahertz and Ultrashort Electromagnetic Pulses for Biomedical Applications, edited by Gerald J. Wilmink, Bennett L. Ibey, Proc. of SPIE Vol. 8585, 85850N · © 2013 SPIE · CCC code: 1605-7422/13/$18 · doi: 10.1117/12.2006504 Proc. of SPIE Vol. 8585 85850N-1 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 04/08/2013 Terms of Use: http://spiedl.org/terms