Effects of millimeter wave irradiation and equivalent thermal heating on the activity of individual neurons in the leech ganglion.

Sergii Romanenko,Daniel A Wagenaar,Peter H Siegel,Victor Pikov

doi:10.1152/jn.00357.2014

Abstract

Many of today's radiofrequency-emitting devices in telecommunication, telemedicine, transportation safety, and security/military applications use the millimeter wave (MMW) band (30–300 GHz). To evaluate the biological safety and possible applications of this radiofrequency band for neuroscience and neurology, we have investigated the physiological effects of low-intensity 60-GHz electromagnetic irradiation on individual neurons in the leech midbody ganglia. We applied incident power densities of 1, 2, and 4 mW/cm2 to the whole ganglion for a period of 1 min while recording the action potential with a standard sharp electrode electrophysiology setup. For comparison, the recognized U.S. safe exposure limit is 1 mW/cm2 for 6 min. During the exposure to MMWs and gradual bath heating at a rate of 0.04°C/s (2.4°C/min), the ganglionic neurons exhibited similar dose-dependent hyperpolarization of the plasma membrane and decrease in the action potential amplitude. However, narrowing of the action potential half-width during MMW irradiation at 4 mW/cm2 was 5 times more pronounced compared with that during equivalent bath heating of 0.6°C. Even more dramatic difference in the effects of MMW irradiation and bath heating was noted in the firing rate, which was suppressed at all applied MMW power densities and increased in a dose-dependent manner during gradual bath heating. The mechanism of enhanced narrowing of action potentials and suppressed firing by MMW irradiation, compared with that by gradual bath heating, is hypothesized to involve specific coupling of MMW energy with the neuronal plasma membrane.

Highlights

THE USE OF MILLIMETER WAVES (MMWs) has been rapidly increasing for a variety of over-the-airwaves applications, including high-speed wireless local area networks (Daniels et al 2010; Verma et al 2013), automotive driver assistance radars (Hasch et al 2012), nondestructive testing (Ahmed et al 2012), airport security screening (Luukanen et al 2013), and nonlethal crowd control weapons (LeVine 2009; Woods and Ketner 2012)
The existence of such transient effects on the nerve endings in fully dressed humans was demonstrated during the military testing of a nonlethal crowd control weapon that, according to a disclosed U.S Air Force protocol, “exceeds the pain threshold but does not exceed the threshold for tissue damage” upon transient skin exposure to MMWs at 95 GHz (Gross 2010)
The effects of low MMW power density levels (Ͻ0.5 mW/cm2) on activity of individual neurons were first evaluated in rodent cortical slices (Pikov et al 2010): we observed fully reversible neuronal hyperpolarization, action potential (AP) narrowing, and a bimodal effect on the firing rate, attributed to inherent heterogeneity of connectivity of sampled pyramidal neurons

Summary

Introduction

THE USE OF MILLIMETER WAVES (MMWs) has been rapidly increasing for a variety of over-the-airwaves applications, including high-speed wireless local area networks (Daniels et al 2010; Verma et al 2013), automotive driver assistance radars (Hasch et al 2012), nondestructive testing (Ahmed et al 2012), airport security screening (Luukanen et al 2013), and nonlethal crowd control weapons (LeVine 2009; Woods and Ketner 2012). Very few studies were performed in a living organism to evaluate the transient effects of MMWs on the nervous tissue. The existence of such transient effects on the nerve endings in fully dressed humans was demonstrated during the military testing of a nonlethal crowd control weapon that, according to a disclosed U.S Air Force protocol, “exceeds the pain threshold but does not exceed the threshold for tissue damage” upon transient skin exposure to MMWs at 95 GHz (Gross 2010). The effects of low MMW power density levels (Ͻ0.5 mW/cm2) on activity of individual neurons were first evaluated in rodent cortical slices (Pikov et al 2010): we observed fully reversible neuronal hyperpolarization, action potential (AP) narrowing, and a bimodal effect on the firing rate, attributed to inherent heterogeneity of connectivity of sampled pyramidal neurons. Preliminary results of this study have been reported in three conference proceedings (Pikov and Siegel 2011; Romanenko et al 2013a, 2013b)

Methods

Results

Conclusion