6. Physiology of Photoreceptors
Vertebrate photoreceptors hyperpolarize and produce graded potentials
Photoreceptors use glutamate as transmitter
Bipolar cells can both hyperpolarize and depolarize producing both ON and OFF responses
ON bipolar – glutamate is inhibitory
OFF bipolar – glutamate is excitatory

7. Receptive Fields Record from a single ganglion cell in the retina
Using small spots of light activate the portion of the visual field that activates the neuron

8. Schematic Retina Showing a Receptive Field
Orange are excitatory inputs into the receptive field.
Blue are inhibitory inputs into the receptive field.
Receptors
Horizontal
Cells +
Bipolar Cells - -
Amacrine Cells
Ganglion Cells

9. Number of Action Potentials:
The excitatory connection
stimulates and increase in
the firing rate in the
ganglion cell.
Light strikes a cone
with an excitatory
connection to the
ganglion cell
Number of Action Potentials: 1

10. Light now fills the excitatory region of the receptive field.
Number of
Action
Potentials: 12

11. If light falls
in the
inhibitory
region, the
firing rate of
cell is
reduced.
Number of
Action
Potentials: 8

12. Lateral Inhibition – Variations in the On/Off Structure
Lights on the edge of the field cause a reduction in the background activity of the cell
On and off neurons
Center-surround structure – need to examine in light of different channels of information direct to the cerebral cortex

14. Receptive Fields in the Retina
Two types of ganglion cells:
on and off dependent upon the bipolar neurons
Center Surround structure of the receptive field described by Kuffler
Best activated by central illumination
Best inhibited by annular illumination

15. Different View of Center-Surround Organization: Parallel Pathways
Transformation of visual information is evident in the ganglion cells of the retina
X cells – sustained linear responses
Y cells – transient, excitatory non-linear responses

16. P and M Projections to LGN: Different Physiologic Channels
P cells in the retina (also known as midget ganglion cells) project to the parvocellular layers (3-6) of LGN
M cells in the retina (also known as parasol cells) project to the magnocellular (ventral most) layers (1-2) of the LGN
Intercalated layers are termed koniocellular (dustlike or tiny cells)

20. Physiology of V1
Originally studied by Hubel and Wiesel who demonstrated two types of neurons
Simple cells – constructed from LGN on/off cells
Complex cells – constructed from simple cells

26. Cortical Simple Cell

27. Cortical Complex Cells: Example of Hierarchy of V1
Strong orientation selectivity in cells
Moving bars in a specific direction
NO on/off areas like in simple cells
Receptive fields were not elongated
Located in layers 2,3, and 5 which receive input from layer 4 (from ? simple cells)