Development N17 Flashcards
NS deals with a ________ environment
predictable
Genetic determinants
most of the NS circuitry is established prenatally
To deal with variations in habits, social environment, and physical attributes
the CNS maintains the ability to modify its connections, called adaptive adjustments
Sensitive (critical) period
a period during which the capacity to adjust the NS circuitry in response to environment becomes limited
A range of functional properties exist that a circuit could adopt, but if the appropriate experiences are not gained
circuits never attain the ability to process information in a typical fashion (impaired perception and behavior my be permanent)
Experience shapes the visual cortex
depriving visual stimuli, results in cortical blindness, meaning the visual cortex no longer responds to visual input
Hubel and Wiesel experiment proves the sensitive period
sutured monkey’s eye closed from 0-6 mo, animal was blind in that eye (cortical blindness)
Congenital cataracts prove the sensitive period
Congenital cataracts removed during infancy results in full vision
Cataracts removed between 10-20 resulted in the inability to perceive shape and form
Primary visual cortex
where information from two eyes first comes together; located in occipital lobe
Visual experience early in life determines
how much visual cortex is devoted to processing input (via neurons in the LGN) and degree to which inputs are combined
Layer 4 of the primary visual cortex
inputs from each eye cluster separately here, cells activated by each eye send input to common target cells above and below layer 4
target cells above and below layer 4 of the primary visual cortex receive input from
BOTH the right and left eye (SMALL proportion respond exclusively to 1 eye)
Binocular interaction
represented by the anatomical convergence on the same target
Visual experience during the sensitive period
results in competition among afferents from the LGN to layer 4; normally the eyes are used equally resulting in equal ocular dominance columns
Unequal balance between LGN afferents, due to vision impairments (monocular lid closure or cataracts) causes
impaired eye to lose the ability to drive layer 4 neurons in a large region of the cortex, LGN afferents from the normal eye GAIN ability to drive layer 4 neurons in a larger portion on the cortex
Result from impaired eye on functional properties
activity in the visual cortex becomes driven largely by LGN afferents from the normal eye
Axonal Architecture also changes if visual experience is withdrawn
axonal arbors of the LGN to layer 4 shrink in the impaired eye and expand in the normal eye
In cats, 1 week deprivation of visual stimuli before 6 mo of age results in
complete loss of vision; whereas deprivation in an adult has no effect
Critical period
period of maturation of cortical connections that is reliant on experience and stimuli
Closure of sensitive periods
once adequate experience is perceived, the circuit IRREVERSIBLY commits to a pattern of connectivity
Experience-driven sharpening of functional tuning
Major factor that decreases the plasticity of circuits; experience selects for anatomical connections and synaptic efficacy that refine excitatory and inhibitory connections, once this refining takes place it is difficult to alter via different experiences
Deprivation of appropriate experiences causes the sensitive period to be ________
prolonged
Raising cats in complete darkness would
prolong the critical period for ocular representation in the visual cortex
What event triggers sensitive period adjustments?
powerful and repeated activation of neurons at the site where change takes place
