Microwave auditory responses

A vast amount of electrophysiological evidence has accumulated over the past several years demonstrating that auditory responses to microwave pulses are similar to those evoked by conventional acoustic pulses (6,7, U, 13,1 A, 15). Furthermore, they show that microwave acoustic effect is mediated by an electromechanical interaction which is initiated outside or at the cochlea. An alternative hypothesis involves direct stimulation of the cochlear nerve or neurons at higher levels along the auditory pathway. This latter mechanism is probably not at work as I shall presently demonstrate. 

Figure 3. Effects of brainstem lesions on the microwave pulse-evoked auditory responses from the vertex of a cat ( 1)...

There are three widely accepted routes by which bone-conducted sound stimulates the cochlea. These are the compres-sional, inertial and osseotympanic theories of bone conduction (12). Compressional bone conduction implies that the cochlear shell is compressed slightly in response of the pressure variation caused by a sound. Inertial bone conduction alludes to a relative motion between the ossicular chain and the temporal bone for low frequency vibrations. The osseotympanic theory denotes a mechanism by which relative movement of the skull, with respect to the mandible, sets up pressure variation in the air present in the auditory meatus. Since perception of microwave pulses are correlated with the capacity to hear high-frequency sound, it rules out inertial or osseotympanic bone conduction as potential mechanisms for microwave acoustic effect. 

This interpretation finds support in systematic studies of responses from brainstem nuclei following successive coagulative lesion production in the auditory loci (1 7). The effect of brainstem lesions on electrical potentials recorded from the superior olivary (SO) nucleus in response to microwave pulse stimulation is shown in Figure 3. Lesions in proximal nuclei (inferior colliculus, IC and lateral lemniscus, LL) had negligible influence on the response recorded from superior olivary nucleus. The response, however, disappeared after a lesion was made in its nucleus, thus, confirming the peripheral nature of the primary site of transduction. 

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