Discharge Patterns and Functional Organization of Mammalian Retina

1. Discharge Patterns and Functional Organization of Mammalian Retina Stephen W. Kuffler 1951

2. Question • What is the functional organization of the mammalian retina? • How does it differ from that of the frog or the Limulus? • organization of connections, receptive fields

3. Theoretical Alternatives • The organization is different than that of the frog or limulus. • The organization is the same as that of the frog or the limulus • It is the same in some ways or different in others. -or more specifically . . .

4. Theoretical Alternatives • Alternatives for the organization of the retina: Direct Indirect Overlap No overlap

5. Logic • Stimulate specific areas of the retina and alter the parameters of the stimuli, while recording from that area with an electrode • The patterns of discharges from cells in response to varying stimuli will give clues as to the organization of the retina

6. Methods • Project light stimuli onto retinas of anesthetized cats using “Multibeam Ophthalmoscope”, while recording from one ganglion cell in that area with a microelectrode. • Eye was left intact • Manipulate Parameters of stimulus: location, size, intensity, duration, background illumination, number of points

7. Results • You can record from a single ganglion cell • Fig 1. Potentials recorded from retina by microelectrode. • 1A. And 1C. Show potential recorded from ganglion cells

8. Results • Receptive fields have a functional sub-structure • Concentric areas within RF in which light produces different responses: • “on” regions • “off” regions • “on-off” regions • RFs are more sensitive towards center.

9. Results • Fig. 4. Responses of specific regions within RF. (A) “on” region, (B) “off” region, (C) “on-off” region • Fig. 6. Distributions of discharge patterns within ganglion cell RF: crosses “on”, circles “off”, circles and crosses “on-off”

10. Results • Fig. 3. Extent of receptive field showing thresholds of stimulus intensity which trigger discharge • Fig. 5. Discharge activity caused by stimulation in different regions of center of receptive field

11. Results • When two areas within receptive field are stimulated, an interaction produces a different pattern of responses. • Interaction of stimulus parameters also causes variation of response

12. Results • Fig. 8. Interaction of 2 separate light spots in same RF.

13. Interpretation • Response patterns in RFs of cells reflect structural features of retina, i.e. “wiring” • There are more receptors in the center of a receptive field and less towards the edges. • Sideways connections in retina provide overlap of RFs and inhibition from other areas • Connections are indirect, fields are overlapping

14. Interpretation • Computation and processing of stimulus is already occurring at retinal level • At no point after light stimulates receptor do we have a “pure”, uninterpreted image of the world • Mammalian retina in some ways is more like invertebrate than frog.

15. Problems • Cats instead of monkeys • Effects of anesthesia • Problems with technique/technology • Really recording from only one cell? • Oversampling of large ganglion cells. • Scattering of light inside of eye