Brain stem evoked responses associated with low-intensity pulsed UHF energy med./bio.

The study was designed to be a parametric study of the effect of low-intensity pulse modulated ultra high frequency (UHF) energy on the functioning of the central nervous system. In this report, it is demonstrated that pulse modulated UHF energy at low power densities evokes potentials in the brain stem. The required experimental conditions are defined.

• animal
• cat
• whole body
• partial body: head; body

Evoked potentials in the brain stem were induced by illumination with pulse modulated UHF energy. The threshold power density necessary to evoke the responses was approximately 30 µW/cm² average and 60 mW/cm² peak. The results indicate that the potentials were neural rather than an artifact of the situation. Using an echosorb shield to cover the entire cat, or head, or body, it was found that the head must be exposed to the UHF energy in order to have an effect occur. Within the carrier-frequency range used (1.2-1.525 GHz), there seemed to be a reduction of effect at the highest frequency. Variation in power density has a distinct effect on the evoked potentials. Polarization of the energy, whether perpendicular or parallel to the spine, does not seem to have much effect though this is not unequivocal. As pulse-repetition frequency is changed, the evoked response does not change significantly until the pulse-repetition frequency is greater than approximately 50 pulses/sec. When greater than this, there is often an overlap of activity evoked by the series of stimuli.