1. Activity-dependent Development
Nature vs. Nurture
Development of ocular dominance in mammalian visual cortex
Critical period

2. Roger Sperry David Hubel Torsten Wiesel
Nobel Prize in Physiology or Medicine 1981
Roger Sperry
David Hubel
Torsten Wiesel

3. Roger Sperry
Regenerating retinal ganglion neurons project to their appropriate position
normal frog frog with rotated eye
Axons know where to go; this process is NOT experience dependent. However, the details of the connection patterns between retina and tectum can be affected by experience (and electrical activity)
There is also some difference between regeneration (more specificity) and development (more “trial and error”)

4. Ocular dominance (OD) in mammalian visual cortex
left eye
right eye
ocular dominance column R L R L Rl Lr Rl Lr
layer 4 R L R L Rl Lr Rl Lr
~ 0.5mm

5. Afferent pathways from the two eyes
right eye
nasal
temporal
left V1
left eye
LGN 6 5 4 3 2 1 C I
right eye
left eye
Layer 4 R L

6. Categories of cells in terms of ocular dominance
Definition of ocular dominance index:
Response ipsi
Response ipsi + Response contra
od =
od = 1, ipsilateral only
od = 0, contralateral only
od = 0~1, binocular
Eyes
Cortical
cells 1 2 3 4 5 6 7
groups
contra-
equal
ipsi-

7. OD distribution in normal adult V1 (monkey)
Normal V1
Number of cells
Equal
contralateral
ipsilateral
OD groups
Normal adult V1 --
(above & below layer 4) binocular cells are common, with each eye well represented roughly equally

8. OD distribution in V1 after monocular deprivation
monocular deprivation (MD) -- suture one eye of the newborn animal (monkey) for several months, reopen.
V1 after monocularly depriving the contralateral eye
Number of cells
Equal
contralateral
ipsilateral
OD groups
MD V1 --
Ocular dominance shifts to the non-deprived eye.
Animal blind in the sutured eye.

9. Effect of monocular deprivation on OD was observed in multiple mammalian species

10. Transneuronal dye to study the structure of OD columns
left
right
radioactive
amino acid
eye 6
LGN C 5 I 2 4 C 3 I I 2 C 1 V1 L R L R L
layer 4
Areas which get inputs from the injected eye are labeled

11. Compare OD columns in newborns, adults and MD animals
normal adults - labeled and unlabeled alternate
layer 4
new borns - no OD column, all areas are labeled
layer 4
MD animals - deprived eye columns shrink, non-deprived eye columns expand
layer 4
deprived eye
non-deprived eye

12. Segregation of LGN afferents
- new borns
1. single LGN afferent has lots of branches, covers a big area
2. axon terminals from the two eyes overlap extensively
layer 4 L R
- normal adults
1. selective elimination of axon branches
2. local outgrowth of new axon branches
layer 4 L R
- MD animals
1. axon terminals from the closed eye retract more
2. axon terminals from the open eye take over more areas
layer 4
open eye
deprived eye

13. OD column formation is an activity-dependent, competitive process
Experiments:
1. Binocular injection of TTX, blocks segregation of OD columns
- segregation is activity dependent
2. If both eyes are deprived (binocular deprivation), OD columns are normal!
- segregation also depends NOT on the absolute level of activity, but on the balance between the input from the two eyes, thus seems to be competitive
Mechanism:
1. Normal development
- initially the axon terminals from the two eyes overlap
- at local region, inputs from one eye happen to be stronger
2. Monocular deprivation
- open eye more active, take over more territory
- deprived eye less active, lose most of the territory

14. Critical period
1. Monocular deprivation (MD) causes a shift of OD toward the non-deprived eye. This is effective only before certain age. MD has no effect on adult animals.
critical period: a period in early life that the neural circuit is susceptible to external sensory inputs (e.g. MD). This period depends on the species and the neural circuit.
For OD in V1:
cat: 3rd week -- 3 months
monkey: first 6 months
human: 1st year most important, but extends to 5-10 years
2. MD within the critical period, the effect is permanent and irreversible.
This finding has profound implications in treatment of congenital cataracts in children
3. MD within the most sensitive part of the critical period (e.g., first 6 wk for monkey), a few day’s MD results in a complete loss of vision in the sutured eye.

15. Critical periods of other neural functions
visual system
- OD
cat: rd week ~ 3 months
monkey: first 6 months
human: st year, also extends to 5-10 year
more complex visual functions (e.g., contour integration) often have longer critical period
other aspects of brain function
- Bird imprinting behavior
Konrad Lorenz ( )
- Monkey social interaction
newborn monkeys reared in isolation for 6-12 months, behaviorally abnormal
- Human
- language: 2-7 years of age
- early social interaction:
no social interaction
foundling home
withdrawn
babies
with social interaction
nursing home
normal