Summary of Oral Evidence presented to IEGMP by Dr J Tattersall, Defence Evaluation and Research Agency (DERA), on Friday 21 January 2000

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There are three strands to DERA research at Porton Down in this area: radiofrequency (RF) modelling of unusual wave forms such as ultrawide band using computers and phantoms carried out by Simon Holden; effects on cultured human cells exposed to ultrawide band radiation carried out by Chris Lindsay; effects on nervous tissue carried out by John Tattersall. Dr Tattersall presented the results of his work, which is performed using simple RF fields. He wanted to know whether effects would occur below field intensities that would cause gross thermal changes and if so what frequencies or waveforms solicited these effects and what is the underlying mechanism.

The main approach is to use hippocampal slices from rat brain. This system is well established and widely studied. It has the advantage of a well-defined circuitry. Slices are exposed using a wave guide exposure system with the slice sitting in a 100-200 micrometre (µm) layer of saline in a moistened atmosphere. There are two apertures in the wave guide, one above to give access for electrodes, and one beneath for illumination. If the pathway is stimulated this produces an excitatory post-synaptic potential which generates a population spike that can be recorded on the other side of the synapse. When slices are exposed to 700 megahertz (MHz) RF, three responses are observed, nothing, increased amplitude and decreased amplitude; amplitude changes are defined as those that are greater than two standard deviations. Results are analysed by ANOVA (analysis of variance) and modulation is observed in around 60–70% of slices. The electric field strength used in these experiments is 71 volts per metre (V/m). The Group speculated that the results may be related to long-term potentiation and/or depression. Slices are stimulated once every thirty seconds in order to avoid tetanic induction. Dr Tattersall has also examined the effects of cumulative exposure and has observed a dose-response effect with potentiation at lower intensities and depression at higher intensities. As an alternative approach, he has used 4-amino pyridine to induce regular seizure-like spikes and has observed that RF exposure inhibited this epileptiform activity in around 30% of preparations. Dr Tattersall has also induced long-term potentiation in preparations and then tested the effects of exposure to 900 and 1800 MHz RF; significant effects were observed both before and after long-term potentiation with both frequencies. Effects are typically observed only on the population spike and not the excitatory post synaptic potential. Dr Tattersall believes that the effects he has observed are unlikely to be artifactual.

Dr Tattersall has also tested the effects of a 900 MHz Global System for Mobiles signal on spatial memory using a radial arm maze. However, he has observed no difference between the exposed and non-exposed subjects. Dr Tattersall accepts that these data exhibit a high degree of variability, but noted that the failure to find an effect might be due to the low specific energy absorption rates employed (maximum of 0.5 watts per kilogram). Although he had initially used groups of six animals he is now using groups of eight.

Dr Tattersall feels that the effect is unlikely to be thermal in origin and noted that it occurred at exposures that could be produced by mobile phones. The effect is observed with both continuous wave and pulsed signals, but has not been independently confirmed; there is a possibility that Dr Pakhomov at Brooks Airforce Base may replicate the study. The Group suggested that the observed effect could be a consequence of changes in calcium mobilisation; Dr Tattersall pointed out that he is currently using calcium imaging as a means of characterising activity and could easily use it to investigate changes in cellular calcium fluxes during RF exposure.

First issued 19 April 2000