Download horizontal connections

MCB 105 Section 3
Announcements
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– DATE/TIME: Sundays, 5pm
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Avenue)
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How hardwired is the brain?
• Extrinsic vs intrinsic mechanisms
• William James: if we could splice the nerves so
that the excitation of the ear fed the brain
centre concerned with seeing, and vice versa,
we would “hear the lightning and see the
thunder”.
Auditory pathway
BRACHIUM of IC
Primary visual cortex (V1) organization
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Retinotopy
Ocular dominance columns
Orientation columns
“Blobs” – color-sensitive neurons
1) What was the important question the authors were trying to
address in this paper?
2) How are their experiments different/better than previous
attempts to address this question?
• What was the stimulus they used?
• What were the electrophysiological techniques used in this
paper? How do they work?
Fig 1A-D,G-J
Pinwheels vs ice cubes
What do they next try to quantify, and how?
Autocorrelation: How periodic is a signal?
Power spectrum (by Fourier Transform): How much of the power
of a signal is at a certain frequency?
Figure 1E,F,K,L
Fig 1M-O
Other similarities/differences between rewired A1 and V1?
Single unit recording
Figure 2A,B
Fig 2C,D
• What was the next question they asked?
• What technique did they use?
Columns of cells in the visual cortex with similar
function are linked through horizontal connections
Retrograde and anterograde tracing
• Retrograde tracing is used to trace neural connections from
their point of termination (the synapse) to their source (the
cell body).
• Anterograde tracing is the opposite.
• Also possible for some tracers to jump across synapses (e.g.
using modified rabies virus – retrograde; modified Herpes
virus –anterograde etc)
• What tracer do the authors use, and how does it work?
• Why only the B-subunit?
Fig 3A-C
Fig 3D-G
How about the number of patches?
Figure 4
Figure 5
Summary
A MODEL FOR A1 rewiring:
Thalamocortical
input
Horizontal
connections
Orientation
maps
Intrinsic constraints
What was the important question the authors were trying to address
in this paper?
Cross-modal cortical plasticity
What was different regarding how they lesioned the brain?
(compared to Sharma?)
Figure 1B
Describe the 1) Training phase 2) Lesions 3) Testing phases
Fig 2A-C
Fig 2D – what does this control for?
OTHER CONTROLS
• Location vs modality
• Right-left asymmetry? Is light on the “right”
perceived similarly to light on the “left”?
• Can rewired ferrets distinguish light from
sound?
LOW
CONTRAST
HIGH
LOW
SPATIAL FREQUENCY
HIGH
Fig 3A
Fig 3B
Fig 3C-D
Summary
• Cross-modal projection can mediate visual
behavior (therefore extrinsic inputs are
important!)
• But visual acuity is poorer in rewired animals
– What was their explanation for this?
• Alternative explanations?
How hardwired is the brain?
• Extrinsic vs intrinsic mechanisms
• William James: if we could splice the nerves so
that the excitation of the ear fed the brain
centre concerned with seeing, and vice versa,
we would “hear the lightning and see the
thunder”.
Extra slides
Example
Computing DSI and OSI with Fourier analysis
First fourier component
(same responses every 360
degrees)
2nd fourier component
(Same responses every 180
degrees)
Visual pathway