= Electroretinogram b-wave
The \b[electroretinogram b-wave] is a prominent positive-going component of many light-evoked <electroretinography> traces, associated strongly with the activity of <ON retinal bipolar cells>. It is an extracellular tissue-level signal, rather than the intracellular <membrane potential> of one <photoreceptor> or one bipolar cell. Its appearance and amplitude depend on the stimulus and recording conditions.<B-wave of the electroretinogram. A reflection of ON bipolar cell activity by Richard A. Stockton and Malcolm M. Slaughter>[Abstract: intraretinal fields, pharmacological isolation and ON bipolar contribution.]{ref}
The assignment was tested by perturbing retinal pathways. In amphibian preparations, APB suppressed ON bipolar responses and removed the b-wave; treatments suppressing OFF-related responses removed the light-offset d-wave while preserving the b-wave. Recording potassium changes along with field responses helped link the electrical component to a specific functional pathway.<B-wave of the electroretinogram. A reflection of ON bipolar cell activity by Richard A. Stockton and Malcolm M. Slaughter>[Selective pharmacological comparisons and extracellular potassium measurements.]{ref}
A later molecular perturbation supplied independent evidence. Mice lacking <TRPM1> retained a normal rod a-wave but lacked the b-wave, while direct bipolar-cell recordings supported disruption of postsynaptic ON signaling. A signal from the early photoreceptor stage can therefore persist when the later response is lost.<TRPM1 is required for the depolarizing light response in retinal ON-bipolar cells by Catherine W. Morgans and others>[Figures 3–4: ERG phenotype and direct bipolar recordings; residual responses in some cone ON cells qualify universality.]{ref}
For an illustrative trace, a preceding trough at $-80\,\mathrm{\mu V}$ and a positive peak at $120\,\mathrm{\mu V}$ are separated by $200\,\mathrm{\mu V}$. That trough-to-peak difference differs from the peak's $120\,\mathrm{\mu V}$ displacement above a zero baseline. Always state the amplitude convention; these invented values are not diagnostic limits or data from either study.
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