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This Article Full Text Full Text (PDF) All Versions of this Article: 567/1/95    most recent jphysiol.2005.088468v1 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 Kenkre, J. S Articles by Mahroo, O. A. R Search for Related Content PubMed PubMed Citation Articles by Kenkre, J. S Articles by Mahroo, O. A. R

¹ Physiological Laboratory, University of Cambridge, Downing Street, Cambridge CB2 3EG, UK
² Division of Neuroscience, John Curtin School of Medical Research, The Australian National University, Canberra, ACT 0200, Australia

We used a conductive fibre electrode placed in the lower conjunctival sac to record the a-wave of the human photopic electroretinogram elicited by bright white flashes, delivered during, or at different times after, exposure of the eye to bright white illumination that bleached a large fraction (90%) of the cone photopigment. During steady-state exposures of this intensity, the amplitude of the bright-flash response declined to 50% of its dark-adapted level. After the intense background was turned off, the amplitude of the bright-flash response recovered substantially, for flashes presented within 20 ms of background extinction, and fully, for flashes presented 100 ms after extinction. In addition, a prominent ‘background-off a-wave’ was observed, beginning within 5–10 ms of background extinction. We interpret these results to show, firstly, that human cones are able to preserve around half of their circulating current during steady-state illumination that bleaches 90% of their pigment and, secondly, that following extinction of such illumination, the cone circulating current is restored within a few tens of milliseconds. This behaviour is in stark contrast to that in human rods, where the circulating current is obliterated by a background that bleaches only a few percent of the pigment, and where full recovery following a large bleach takes at least 20 min, some 50 000 times more slowly than shown here for human cones.

(Received 13 April 2005; accepted after revision 27 May 2005; first published online 2 June 2005)
Corresponding authors O. A. R. Mahroo and T. D. Lamb: Division of Neuroscience, John Curtin School of Medical Research, The Australian National University, Canberra, ACT 0200, Australia. Email: omar.mahroo{at}cantab.net and trevor.lamb{at}anu.edu.au

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