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Figure by MIT OCW. After figure 9.20 in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore,

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Presentation on theme: "Figure by MIT OCW. After figure 9.20 in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore,"— Presentation transcript:

1 Figure by MIT OCW. After figure 9.20 in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins, ISBN: Spectral sensitivity of cones ˙ Three types of opsins ˙ Color blindness is caused by lack of one or more cone types Wavelength (nm) Relateive response Blue cones Green cones Red cones

2 Image removed due to copyright reasons. Please see figure 9-21 in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins, ISBN: Color space is 3d ˙ Any color can be synthesized by mixing three primary colors. ˙ Young-Helmholtz trichromacy theory

3 Retinal ganglion cells Output cells of the retina Send a million axons in the optic nerve Background rate of spiking Rate of spiking is modulated up or down by visual stimulation

4 Visual neurophysiology Anesthetized cat Video: visual stimulus seen by cat Audio: extracellular recording

5 Receptive field The area of retina (or of visual space) in which a stimulus can cause changes in the activity of a neuron. The preferred stimulus is that which causes the most increase in rate of action potential firing.

6 Center-surround antagonism Figure by MIT OCW. After figures 9.23 a, b, and c in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins, ISBN: Ganglion cell Receptive field Patch of retina Center Surround Dark spot OFF-center ganglion Cell output:

7 Visual stimuli Moving spot Flashed spot Annulus Spot with changing ciameter Moving bar

8 Figure by MIT OCW. A fter figure 9.27 in: B ear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins, ISBN: Transient vs. sustained Light in receptive field center Action potentials per second ON OFF M-type Ganglion cell (ON center) P-type Ganglion cell (ON center) note: offset of visual stimulus can lead to suppression of spiking below background rate (not shown here)

9 P and M ganglion cells Figure by MIT OCW. After figure 9.26 in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins, ISBN: ˙ Smaller P-type (90%) ˙ Sustained ˙ Stimulus form ˙ Color-opponent ˙ Larger M-type (5%) ˙ Transient ˙ Stimulus movement

10 Color aftereffect ˙ Psychological evidence of red-green and blue-yellow opponency ˙ Herings opponent process theory Figure by MIT OCW. After figure 9.29 in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins, ISBN:

11 Images removed due to copyright reasons. Please see figure 9.28 in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins, ISBN: Neural basis of color opponency

12 Dual process theory Resolution of the debate with a hybrid theory Photoreceptors - Young-Helmholtz trichromacy Ganglion cells - Hering color opponency Further reading: S.E. Palmer, Vision Science, MIT Press (1999).

13 Sensitivity to spatial differences Four categories of OFF-center ganglion cells responding to an edge Ganglion cell Receptive field Patch of retina Center Surround Dark spot OFF-center ganglion Cell output: Responses of cells near the edge a exaggerated contrast-enhancement Figure by MIT OCW. After figure 9.24 in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins, ISBN:

14 Simultaneous contrast illusion Figure by MIT OCW. After figure 9.25 in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins, ISBN:

15 Mach and Chevreul

16 Images removed due to copyright reasons. Please see figures 9.22 a, b, and c in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins, ISBN: Lateral inhibition Horizontal cells Amacrine cells

17 Convolution Mathematical idealization of retinal computation Image removed due to copyright reasons.

18 Engineering applications Silicon retinas - Kwabena Boahen (U penn) Retinal prosthetics - John Wyatt (MIT)

19 Central visual system

20 Figure by MIT OCW. After figure 10.2 in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins, ISBN: Retinofugal projection Eye Optic Nerve Optic Chiasm Stalk of Pituitary Gland Optic Tract Cut Surface of Brain Stem

21 Figure by MIT OCW. After figure 10.3 in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins, ISBN: Right and left visual hemifields ˙ The left visual hemifield is viewed by the right hemisphere, and vice versa. Binocular Visual Field Fixation Point Left Visual Hemifield Right Visual Hemifield Left Eye Left Optic Nerve Left Optic Tract Right Eye Right Optic Nerve Right Optic Tract Optic Chiasm

22 Retinogeniculocortical pathway Retina LGN V1 pathway for conscious visual perception Images removed due to copyright reasons. Please see figures 10.4 a and b in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins, ISBN:

23 Images removed due to copyright reasons. Please see figure 10.8 in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins, ISBN: Lateral geniculate nucleus ˙ dorsal thalamus ˙ major targets of optic tracts

24 Retinotopy Neighboring retinal cells project to neighboring LGN cells. There are maps of visual space in the LGN. Magnification of map for central vision.

25 LGN input is segregated Figure by MIT OCW. After figure 10.9 in: Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, Md.: Lippincott Williams & Wilkins, ISBN: ˙ contra: layers 1,4,6 ˙ ipsi: layers 2,3,5 ˙ retinotopic map in each layer ˙ maps are aligned Right LGN Left LGN Left Temporal Retina Left Nasal Retina Right Nasal Retina Right Temporal Retina

26 LGN function?? Receptive fields like retinal ganglion cells 80% of excitatory synapses from conrtex Neuromodulatory input - alertness - attention - sleep


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