= Electrical stimulation
<Electrical stimulation> applies a controlled electrical perturbation to influence a biological preparation. <Electrodes> couple an imposed <electric current> or <electric potential difference> to the surrounding tissue; the resulting <electric field> can change <membrane potential> and the probability of an <action potential>. The effect depends on waveform, geometry, tissue and cell state, not just one amplitude number.
For an illustrative rectangular current pulse, transported <electric charge> is $Q=I\Delta t$. A $20\,\mathrm{\mu A}$ pulse lasting $100\,\mathrm{\mu s}$ carries $2\,\mathrm{nC}$. Two pulses can have the same charge but different amplitudes and durations, so charge equality does not establish an identical neural effect. This is a dimensional example, not a stimulation protocol or a biological threshold.
A 2007 experiment used weak <electrical stimulation> of the <lateral habenula> and measured inhibition of <dopaminergic neurons>.<Lateral habenula as a source of negative reward signals in dopamine neurons by Masayuki Matsumoto and Okihide Hikosaka>[Abstract; stimulation intervention and recorded dopamine-neuron inhibition]{ref} Combining intervention with recordings addresses causation more directly than noting that two populations vary together. Nevertheless, a response does not establish that only one cell type was activated or that the intervening connection is direct. Spatial spread and the stimulated elements remain experimental questions.
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