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This Article Full Text Full Text (PDF) Supplemental data All Versions of this Article: 583/2/555    most recent jphysiol.2007.137711v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Deans, J. K. Articles by Jefferys, J. G. R. Search for Related Content PubMed PubMed Citation Articles by Deans, J. K. Articles by Jefferys, J. G. R. Related Collections Neuroscience

¹ Department of Neurophysiology, Division of Neuroscience, Medical School, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK

The sensitivity of brain tissue to weak extracellular electric fields is important in assessing potential public health risks of extremely low frequency (ELF) fields, and potential roles of endogenous fields in brain function. Here we determine the effect of applied electric fields on membrane potentials and coherent network oscillations. Applied DC electric fields change transmembrane potentials in CA3 pyramidal cell somata by 0.18 mV per V m^–1 applied. AC sinusoidal electric fields have smaller effects on transmembrane potentials: sensitivity drops as an exponential decay function of frequency. At 50 and 60 Hz it is 0.4 that for DC fields. Effects of fields of 16 V m^–1 peak-to-peak (p-p) did not outlast application. Kainic acid (100 nM) induced coherent network oscillations in the beta and gamma bands (15–100 Hz). Applied fields of 6 V m^–1 p-p (2.1 V m^–1 r.m.s.) shifted the gamma peak in the power spectrum to centre on the applied field frequency or a subharmonic. Statistically significant effects on the timing of pyramidal cell firing within the oscillation appeared at distinct thresholds: at 50 Hz, 1 V m^–1 p-p (354 mV m^–1 r.m.s.) had statistically significant effects in 71% of slices, and 0.5 V m^–1 p-p (177 mV m^–1 r.m.s.) in 20%. These threshold fields are consistent with current environmental guidelines. They correspond to changes in somatic potential of 70 µV, below membrane potential noise levels for neurons, demonstrating the emergent properties of neuronal networks can be more sensitive than measurable effects in single neurons.

(Received 31 May 2007; accepted after revision 21 June 2007; first published online 28 June 2007)
Corresponding author J. G. R. Jefferys: Department of Neurophysiology, Division of Neuroscience, Medical School, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK. Email: j.g.r.jefferys{at}bham.ac.uk

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