Neural Plasticity 1: Experience-dependent

Do the number of synapses (neural connections) remain stable throughout a lifetime?

No, the number of synapses (neural connections) is not stable throughout a lifetime.

If

not, when do the number of synapses peak? Do they plateau at some point?

They grow extensively in early postnatal development and then peak.

They then decrease (decay) during subsequent years and adolescence.

How do the mechanisms of long-term potentiation and long-term depression relate to

the competitive interaction of synapses for neurotrophin?

The elimination of synapses later in development is thought to be due to an experience-dependent Hebbian mechanism related to synaptic plasticity and competition for neurotrophin.

Would synapses with

correlated activity be potentiated or depressed? Why?

Synapses with correlated activity (firing together with the postsynaptic neuron) are potentiated (strengthened).

What is a critical period?

is a time window during development when experience has a maximum effect on acquiring an ability or behavior. If normal experience does not occur during this period, the ability or behavior may never be acquired.

Where are binocular neurons first found in the visual pathway?

driven by either eye) are first found in the Primary Visual Cortex (V1), specifically in cortical layers other than Layer 4.

In this region, are all

neurons completely binocular, or are there some monocular neurons?

most V1 neurons are responsive to both eyes, but some neurons remain strictly monocular.

During early visual deprivation, does the retina degenerate? or the thalamus? ...or

the cortex?

it degenerates in the cortex and is normal in the retina and thalamus

In development of binocular neurons, how would the response types of neurons change

with monocular deprivation during the whole critical period?

Neurons become responsive only to the non-deprived eye, leading to "cortical blindness" in the deprived eye.

In development of binocular neurons, how would the response types of neurons change

with monocular deprivation during several days of the

critical period?

Even short periods (e.g., 6 days at peak) cause severe reduction in binocular neurons and can lead to cortical blindness

In development of binocular neurons, how would the response types of neurons change

with monocular deprivation during the rest of lifetime starting after the critical period?

If deprivation occurs after the critical period closes (e.g., after 12 months in cats), the neurons' response types are similar to normal, undeprived cats

Are deficiencies acquired during the critical period permanent, or can they be made

normal at a later time?

acquired during the critical period, such as those caused by temporary visual deprivation, can cause extreme, permanent changes to the cortex. Once the critical period closes, effects become permanent

What does the critical period have to do with the initial overproduction of synapses and

the competition between synapses?

is the time during which there is an initial overproduction of synapses, and subsequent elimination occurs through competition.

is driven by Hebbian plasticity and the resulting struggle for neurotrophin/survival signals. Deprivation (lack of correlated activity) causes the synapses of the deprived eye to lose this competition

Why does amblyopia during the critical period lead to an absence of binocular neurons

(i.e., all become monocular)?

leads to an absence of binocular neurons because the misalignment causes the inputs from the two eyes to be uncorrelated.

What does this have to do with the amount of correlation

between synaptic inputs, and competition between synapses?

Uncorrelated inputs cannot drive binocular neurons effectively, meaning they compete for dominance over the postsynaptic neuron, causing some neurons to become dominated by the left eye and others by the right eye, resulting in a shift toward monocular neurons.

Are critical periods only in the visual system?

No. Critical periods have been identified for many other systems beyond vision, including sensory and cognitive systems, such as language acquisition