Figure 9. Effect of electric fields applied perpendicular to the soma—dendritic axis.

A, schematic diagram illustrating slice orientation at +90 deg and field sign convention. B, intracellular recording of transmembrane potential from a CA1 pyramidal cell during application of fields (bar). C, field recording from CA1 pyramidal cell layer during application of fields. A population spike was evoked by oriens stimulation 500 ms after field application. C1, expansion of field onset in trace C. C2, expansion of orthodromic population spikes during field application in trace C and orthodromic population spike in absence of fields (control). Note the orthodromic and non-synaptic ‘leading edge excitation’ at field onset (see Results), while field termination is associated with a capacitive artefact but no population spikes. D and E, summary of effect of electric fields applied at 90 deg on population spike amplitude and delay in response to CA1a oriens (D) and Ca1c LM (E) stimulation.