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SUMMARY:Dark adaptation of human retinal rod bipolar cells - Trevor Lamb\,
  Division of Neuroscience JCSMR\, and ARC Centre of Excellence in Vision S
 cience\, Australian National University\, Canberra
DTSTART:20060816T120000Z
DTEND:20060816T130000Z
UID:TALK5150@talks.cam.ac.uk
CONTACT:Cordula Becker
DESCRIPTION:Following exposure of the eye to very intense illumination\, o
 ne’s visual threshold is initially greatly elevated\, and the recovery o
 f sensitivity proceeds slowly\, over a period of tens of minutes. How earl
 y in the visual system is the desensitization present?  I will describe ex
 periments undertaken in collaboration with Allison Cameron and Omar Mahroo
  that have examined desensitization at the level of the rod bipolar cell i
 n the living human eye\, using recordings of the ERG b-wave response under
  scotopic conditions.  We first measured light-adaptation of the dim-flash
  response (using steady backgrounds)\, and then measured dark-adaptation a
 fter bleaches at a range of levels.  Following a large bleach\, the rod bi
 polar cell response was almost eliminated for ~10 min\, and had half-recov
 ered after ~20 min.  We applied a “Crawford transformation” to map des
 ensitization into equivalent background intensity\, and found that the sco
 topic dark-light decayed with a characteristic slope of 0.24 decade/min\, 
 as found psychophysically.  We conclude that much of the dark adaptation b
 ehaviour of the overall visual system is present at the level of the first
  synapse.
LOCATION:Seminar Room (ground floor)\, Craik-Marshall Building
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