BISC 421 1st Edition Lecture 19 Outline of Current LectureI. Retinal Receptive FieldsCurrent LectureRetinal ReceptiveBipolar Cells (pool input from photoreceptors & contact ganglion cells. Photoreceptors(capture light)Retina - The retinal region occupied by visual sense cellswhose connections converge upon a given retinal ganglion cell shall be termed the receptivefield of that ganglion cell… Hartline, Harvey Lecture, 1942•Exit path from retina-‐ horizontal cells are amacrine cells •Photoreceptors capture lightbipolar cells pool input and contact ganglionsganglions send info to the brainStructure of the Receptive Field of a Ganglion Cell in the Cat’s RetinaOn OfKuffler J. Neurophys. 1953•Ganglion cell drawn as its receptive field•Central region + periphery (roughly circular, concentric)•Did light fash in the middle evoke a train of APs while it was fashed or afer it turned of?•Red: Excited at light on•Blue: excited at light off•White circle in middle: where response is most intense•Mutually antagonistic relationship-‐ a spot that covers whole refective field is not as much as an impact •If you fash the center and the surround at the same time-‐ way smaller responseSynopsis:•Pretend to hunt for the center by fashing a bright spot at various positions in visual space•Flash the bright spot in the to demonstrate the “on response”•Flash a big spot over the center and surround to show that stimulating both subregions in tandem yields weaker responses than stimulating the center alone•Flash a dark spot in the center and a bight annulus in the surround to demonstrate the “offresponse” •Flash bright spots again to measure “control” responsesResponses of On and Off center ganglion cells to a bright spot fashed in the center•+ on response, - ‐ responds when light off•on cell fires very hard•off cell: spontaneous firing suppressed when bright fashed, then when it is turned off then it APs a lotResponses of On and Off center ganglion cells to a dark spot fashed in the center•Opposite of last time•Neurons strongly inhibited by dark spots•Off responses do not have a delay as it seems hereInfuence of the Surround•Instead of switching spot of, we make it bigger to also stimulate the surround•Firing rate reduces•Subfield antagonism-‐ very robust in center alone and far less robust when you include surrounding•When you switch it of, it stops firingResponses of different ganglion cells to an edge•How we string them together•Dashed red line-‐ spontaneous rate, when APs fire but not much is happening•B: inhibition•C: return to spontaneous rate or a bit higher because inhibition is taken away•D: strong response because off center is excited, too; whole center is sitng in light; part of how we are able to see edges•E: elevated off spontaneous because center is a little strongerResponses of a photoreceptor and downstream bipolar and ganglion cells•All photoreceptors hyper polarize to cells-‐ have 2 diferent kinds of bipolar cells•Darkness: excites on bipolar cells by Glu-‐depolarization•Off center bipolar cells hyperpolarize•Both synapses are glutamertergic•Of:
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