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9.01 Introduction to Neuroscience Fall 2007
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The optic nerve carries theoutput of the eye
Figure by MIT OpenCourseWare. 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, 2001. ISBN: 9780683305968.
E ye
Optic Nerve
Optic Chiasm
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Finding the “receptive field”
• Record the action potentials of an axon in the optic nerve
• Present visual stimuli at various locations
• Find the location at which a stimulus can cause changes in the firing rate.
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ON-center cell
• There is a background firing rate.
• The rate increases when the stimulus is in the receptive field (drawn circle).
Image removed due to copyright restrictions.
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The cornea is more refractivethan the lens of the eye
Figure by MIT OpenCourseWare. After figure 9.7 in Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, MD: Lippincott Williams & Wilkins, 2001. ISBN: 9780683305968.
Focal Dal Dal Dal Distancistancistancistancistancistance
Refrefrefracactivtivtive Pe Pe Power (Der (Der (Der (Der (Dioptioptioptiopters) = ers) = ers) = ers) = ers) = ers) = ers) = 1
Focal Dal Dal Dal Distancistancistancistancistancistance (m)e (m)e (m)e (m)
e (m)
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Five classes of cells
• Vertical elements – photoreceptors – bipolar cells – ganglion cells
• Horizontal elements – horizontal cells – amacrine cells
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The retinahas layers
Image removed due to copyright restrictions.Cross section electron microscope image of the human retina.Figure 1 (Plate 32) in Boycott B. B. and J. E. Dowling. "Organizationof the Primate Retina: Light Microscopy." Phil Trans R Soc B 255, no. 799 (March 27, 1969): 109-184. doi: 10.1098/rstb.1969.0004.
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Retinal circuitry
Figure by MIT OpenCourseWare. After figure 9.11 in Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, MD: Lippincott Williams & Wilkins, 2001. ISBN: 9780683305968.
Ganglion cells
Direct pathway
Output
Input
Photoreceptors
Ganglion cell axonsprojecting to forebrain
Amacrinecell
Bipolarcell
Horizontalcell
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Opthalmoscopic view
Image removed due to copyright restrictions.The retina, as viewed through an opthalmoscope.Figure 9.5 in Bear, Mark F., Barry W. Connors, and Michael A. Paradiso.Neuroscience: Exploring the Brain. 3rd ed. Baltimore, MD: Lippincott Williams& Wilkins, 2007. ISBN: 9780781760034.
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Variation in acuity with retinal
Anstis, 1974
position
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The density of photoreceptorsdecreases in the periphery
90o70o50o30o10o10o30o 050o70o
Distance across retina
Rods
Cones
FoveaBlind spot
Num
ber/m
m2 Rods
Figure by MIT OpenCourseWare.
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Rods and cones
Figure by MIT OpenCourseWare. After figure 9.13 in Bear, Mark F., Barry W. Connors, and Michael A. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, MD: Lippincott Williams & Wilkins, 2001. ISBN: 9780683305968.
Conephoto-receptor
Scotopic/night vision 1000 x more light sensitive
Photopic/day visionColor vision
Outersegments
Innersegments
Synapticterminals
Cell bodies
Membranous diskscontaining photopigment
Rodphotoreceptor
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Light causes photoreceptors tohyperpolarize
• Dark current due to open sodium channels
• Light depletes cGMP, closing sodium channels
Figure by MIT OpenCourseWare. After figure 9.17 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, 2001. ISBN: 9780683305968.
0 mV
0 mV
Vm
}Na
+
Inner Segment
Outer Segment
LightDark
MembraneDepdarization
MembraneHyperpdarization
GMP
cGMPcGMP }
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ON and OFF bipolar cells
• Light has different effects on bipolar cells
• ON cells depolarize • OFF cells hyperpolarize
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Transient vs. sustainedresponses
• Stimulus
• Response
time
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Temporal antagonism
• Stimulating the center causes a transient increase.
• Removal of the stimulus causes a transient decrease (relative to background).
Image removed due to copyright restrictions.
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Center-surround antagonism
• OFF-center prefers: • ON-center prefers:– dark spot in center – light spot in center – light annulus – dark annulus
Ganglion cellreceptive field
OFF-center ganglioncell output:
Center
Dark spot
Patch ofretina Surround
Figure by MIT OCW. After figures 9.23 a, b, and c in: Bear, Mark F., Barry W. Connors, and MichaelA. Paradiso. Neuroscience: Exploring the Brain. 2nd ed. Baltimore, MD: Lippincott Williams &Wilkins, 2001. ISBN: 9780683305968.
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Horizontal cells are coupled bygap junctions
Xin and Bloomfield
Photo removed due to copyright restrictions.
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Resistive network model
Figure 3 in Carver A. Mead and Misha Mahowald. "A Silicon Model of EarlyVisual Processing." In Computational Neuroscience. Cambridge, MA: MIT Press, 1993. Courtesy of Carver A. Mead and Misha Mahowald, authors,and Eric L. Schwartz, editor. Used with permission.
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Silicon retinaNeuromorphic VLSI K. Zaghloul and K. Boahen, 2004f
Kareem Zaghloul. Used with permission.
Source: Zaghloul, Kareem A., and Kwabena Boahen. "A Silicon Retina that
• •
Courtesy o
Reproduces Signals in the Optic Nerve." J Neural Eng 3 (2006) 257–267.Courtesy of IOP Publishing, Inc. Used with permission.
f
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Chevreul’s illusion
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Light: reality vs. perception
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Receptive field model