Part 4A: Real Neurons
9/30/08
A Very Brief Tour of
Real Neurons
IV. Neural Network Learning
(and Real Brains)
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Left Hemisphere
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(fig. from internet)
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Typical Neuron
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Animation of Neuron
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An animated film about nicotine addiction
A good visualization of a single neuron
©2006, Hurd Studios
Winner of NSF/AAAS Visualization
Challenge
• View flash video
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Part 4A: Real Neurons
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Grey Matter vs. White Matter
Neural Density in Cortex
• 148 000 neurons / sq. mm
• Hence, about 15 million / sq. cm
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(fig. from Carter 1998)
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Cortical Areas
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Intercortical Connections
(1) Short arcuate bundles, (2) Superior longitudinal
fasciculus, (3) External capsule, (4) Inferior occipitofrontal
fasciculus, (5) Uncinate fasciculus, (6) Sagittal stratum, (7)
Inferior longitudinal fasciculus
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Brodman’s Areas
Neural Representations
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Part 4A: Real Neurons
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Macaque Visual System
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(fig. from Van Essen & al. 1992)
Hierarchy
of
Macaque
Visual
Areas
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(fig. from Van Essen & al. 1992)
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Bat Auditory
Cortex
Neurons
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(figs. from Suga, 1985)
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Dendritic Trees of Some Neurons
Typical Neuron
A.
B.
C.
D.
E.
F.
G.
H.
I.
J.
K.
L.
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inferior olivary nucleus
granule cell of cerebellar cortex
small cell of reticular formation
small gelatinosa cell of spinal
trigeminal nucleus
ovoid cell, nucleus of tractus solitarius
large cell of reticular formation
spindle-shaped cell, substantia
gelatinosa of spinal chord
large cell of spinal trigeminal nucleus
putamen of lenticular nucleus
double pyramidal cell, Ammon’s horn
of hippocampal cortex
thalamic nucleus
globus pallidus of lenticular nucleus
(fig. from Trues & Carpenter, 1964)
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Part 4A: Real Neurons
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Axonal Net
Axonal
Terminations
(Tectum of Turtle)
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(fig. from Sereno & Ulinski 1987)
Minicolumn
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(fig. from Arbib 1995)
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Layers and Minicolumns
• Up to 100 neurons
– 75–80% pyramidal
– 20–25% interneurons
• 20–50µ diameter
• Length: 0.8 (mouse) to
3mm (human)
• 6105 synapses
• 75–90% synapses outside
minicolumn
• Interacts with 1.2105
other minicolumns
• Mutually excitable
• Also called micro-column
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(fig. from Arbib 1995, p. 270)
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Macrocolumns
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70 inhibitorally-coupled minicolumns in humans
70% of minicol. connections are within macrocol.
Winner-takes-all networks
Basket neurons provide shunting inhibition between minicolumns
Represent microfeatures
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(fig. from Arbib 1995, p. 270)
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Part 4A: Real Neurons
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Intracortical Connections
Neural
Networks in
Visual
System of
Frog
• Dendrites extend 2–4
minicol. diameters
• Axons extend 5 (or
even 30–40) minicol.
diameter
• Periodic spacing of
axon terminal clusters
causes entrainment
• 2107 connections to
macrocolumn
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Reorganization of Cortex
(fig. from Arbib 1995, p. 1039)
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Orientation Columns
• Median nerve
sectioned to show
fluidity of cortical
organization
• (C) before
• (D) immediately
after
• (E) several months
later
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(fig. < McClelland & al, Par. Distr. Proc. II)
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(fig. < Nicholls & al., Neur. to Brain)
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Slow Potential Neuron
Orientation Columns
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(fig. < Nicholls & al., Neur. to Brain)
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(fig. < Anderson, Intr. Neur. Nets)
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Part 4A: Real Neurons
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Variations in Spiking Behavior
Frequency
Coding
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(fig. from Anderson, Intr. Neur. Nets)
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Chemical Synapse
Synapses
1.
2.
3.
4.
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video by Hybrid Medical Animation
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Action potential
arrives at synapse
Ca ions enter cell
Vesicles move to
membrane, release
neurotransmitter
Transmitter
crosses cleft,
causes
postsynaptic
voltage change
(fig. from Anderson, Intr. Neur. Nets)
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Typical Receptor
Axon Hillock
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(fig. from Anderson, Intr. Neur. Nets)
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(fig. from Peters, Palay & Webster)
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Part 4A: Real Neurons
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Dendrite &
Dendritic
Branches
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(fig. from Peters, Palay & Webster)
Dendrite &
Dendritic Spine
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Excitatory
Synapse
Between
Axon
Terminal and
Dendritic
Thorn
(fig. from Peters, Palay & Webster)
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axon
terminal
rite
dend
(fig. from Peters, Palay & Webster)
Various
Synapses
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(fig. from Peters, Palay & Webster)
Myelinated
Axon Making
Synapse on
Dendrite
Neuropil
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axon
(fig. from Peters, Palay & Webster)
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axon
terminal
dendritic
thorn
synapse
(fig. from Peters, Palay & Webster)
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Part 4A: Real Neurons
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Dendro-dendritic Synapses
Electrotonic Synapse
Type II
(symmetric)
Type I
(asymmetric)
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(fig. from Peters, Palay & Webster)
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(fig. from Peters, Palay & Webster)
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5B
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