Effect of low-level, low-frequency electric fields on EEG and behavior in Macaca nemestrina.

Summary A series of experiments has been done to assess the effects of low-level, low-frequency electric fields on the behavior and EEG of monkeys. Three monkeys were implanted with subcortical and cortical EEG electrodes and trained to press a panel on a fixed interval-limited hold schedule. The monkeys were rewarded for pressing the panel once every 5 sec within a 2.5 sec enable period. After the animals were performing well, they were tested under low-level electric fields (2.8 V p-p); the voltage was applied to 2 large metal plates 40 cm apart so that the monkey's head was completely within the field. Fields frequency was set at 7 or 10 c/sec within the range of typical EEG recording (0-33 c/sec). Four hour daily tests of fields-on were randomly interspersed with 4 h runs with field-off. Under the 7 c/sec fields, the monkeys showed a significantly faster interresponse time in 5 of 6 experiments. Mean differences between fields-on and fields-off were 0.4 sec or greater. The 10 c/sec fields did not produce a reliable effect on behavior. Analysis of the EEG data showed a relative peak in power at the frequency of the fields (10 c/sec and 7 c/sec) for the hippocampus in all 3 monkeys. Similar peaks were seen less consistently in the amygdala and the centre median.

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