ess - modification of neural circuits

psychologist D.O Hebb

Psychologist D.O. Hebb (1949): hypothesized that the
coordinated activity of a presynaptic terminal and a
postsynaptic neuron strengthens the synaptic connection
between them
• Originally formulated to explain the cellular process of learning
and memory
• Widely applied to situations involving long-term modifications of
in synaptic strength (development)
• Synaptic terminals strengthened by correlated activity will be
retained or sprout new branches
• Terminals weakened by uncorrelated activity will lose their
connection with the post synaptic cell

synaptic pruning

Synaptic pruning is the process by which the brain eliminates excess or weaker synaptic connections between neurons during development.

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🔹 In simple terms:

It's like the brain's way of "spring cleaning"—keeping the important connections and removing the ones that aren't used much.

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🔹 Why it happens:

• Early in development, the brain forms far more synapses than it needs.

• Through experience and activity, the brain identifies which synapses are useful and which are unnecessary.

• Synapses that are used frequently are strengthened.

• Synapses that are rarely used are pruned away.

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🔹 When it happens:

• Begins in early childhood, especially in the first few years.

• Continues through adolescence and even into early adulthood.

• Peaks in areas like the visual cortex around age 2, and in the prefrontal cortex (decision-making, reasoning) during the teen years.

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🔹 Why it's important:

• Makes neural networks more efficient.

• Supports learning, memory, and cognitive development.

• Helps shape the final architecture of the brain based on experience.

environmental factors influence life

Critical Periods: time when experience and neural activity that reflects that experience have maximal effect on the acquisition or skilled execution of a particular behavior
• Parental Imprinting in hatchling birds: hatchling recognizes its parent
• expressed only if animals have specific experiences during a particular time (hours or days) in early postnatal development.
• Critical periods for sensorimotor skills and complex behaviors last much longer
• Language acquisition in humans
• Song birds: male birds acquire the capacity to produce species-specific song by mimicking tutor birds

critical period

Basic Properties of Critical Periods
• Time during which a given behavior requires specific
environmental influences in order to develop normally
• Once a critical period ends, the core features of a
behavior are largely unaffected by subsequent
experience
• If not exposed to appropriate stimuli during the critical
period it is difficult or impossible to remedy
• In most mammals, including humans, critical periods rely
particularly on changes in organization and function of
circuits in the cerebral cortex

How does experience change neural circuits
during critical periods? How do patterns of
activity modify connections?

Must rely on signals generated by synaptic activity
associated with sensory experience, perceptual and
cognitive processing, or motor performance
• NMDA receptors – excitatory neurotransmission
• Regulation of the number and placement of local
inhibitory synapses and the expression of GABA
receptors on post synaptic sites are sensitive to
changes in levels of electrical activity during early
postnatal life
• Neurotransmitters and neurotrophins that influence
critical periods are thought to modulate intracellular
calcium levels