A neurophysiological approach to radiation-induced ‘phosphene’ phenomenon: Studies in awake and anaesthetized mice.

This experiment was designed to study mechanisms of ‘phosphene vision’. In human physiology ‘phosphenes’ refer to luminous sensations produced by stimuli other than light. Experiments performed to reproduce the phenomenon, refer to phosphenes induced by electrical stimulation of retina and by accelerated particles during space flights. In order to study these mechanisms we programmed a series of experiments: in a preliminary experiment, visual evoked responses (VEPs), electroretinograms (ERGs) and oscillatory potentials (OPs) to flash stimulations were recorded in unanaesthetized and anaesthetized mice bearing chronically implanted electrodes. In the unanaesthetized animals, the responses displayed stimulus-depended increase in amplitude and decrease in latency, up to a plateau at about 2.082–2.383 phy. In particular, OPs at 1 Hz stimulus showed a maximal amplitude effect starting at about 2.684 phy intensity. In the anaesthetized animals, urethane produced a latency increase and an amplitude decrease of all evoked responses. Finally, to study the ‘phosphene phenomenon’ a beam of accelerated carbon particles (energy 100 and 300 MeV/n) was delivered into the retina and sensorimotor cortex of anaesthetized mice. Cycles of light flashes were also administered. Following accelerated particles stimulation cycles to the retina, 500 to 5000 per stimulus, 30 stimuli per cycle, stimulus time-related waveforms in mice cortex were recorded. Their amplitude and latency appeared to be related to energy delivered. The short waveform latency, and the lack of retinal potentials and oscillatory potentials following particles stimuli suggest that the impact of accelerated particles does not produce activation of retinal chemical structures. This appears as the first objective demonstration of radiation-induced ‘phosphenes’.