How Does the Nervous System Develop and Change?

From developmental assembly and sensitive periods to learning, adult plasticity, and the limits of recovery.

Level: Intermediate
Reading load: 10 core readings in 5 units
Prerequisites: The Biological Psychology foundation, with the Neural Circuits syllabus recommended, or comparable familiarity with neurons, synapses, circuits, and causal comparisons. Willingness to work through cellular diagrams, longitudinal comparisons, and technical methods. The guides introduce essential terms; reproducing every calculation is not required.
Last reviewed: September 2026

Introduction

A nervous system has a history. Its cells acquire their places and connections during development, and experience continues to alter what has been formed. Yet the familiar claim that experience changes the brain tells us little until we ask what changed: a connection, a synaptic response, an imaging signal, or a person's performance. Each observation opens a different part of the history.

This path begins with the assembly of a nervous system, then asks how the timing of experience matters. It moves from a synaptic model of memory to observations of individual structures during learning, and from those microscopic observations to human imaging and an intervention in later adulthood. The final unit asks whether change restores a movement, supports a different strategy, or even makes another function harder to recover.

The readings combine conceptual reviews with empirical comparisons. Keep a record of the organism, timescale, biological measure, and behavioral outcome in each. By the end, you should be able to explain how genes, cells, activity, and surroundings interact in development; evaluate a claim that the timing of experience changes its effects on development; and distinguish evidence of neural change from evidence of its mechanism or benefit. Several papers are technically demanding, and the path is best approached over multiple sittings.

Unit 1 of 5

How is a nervous system assembled?

Before asking how experience modifies a circuit, establish how there comes to be a circuit at all. Stiles and Jernigan connect cell production, migration, specialization, and communication with the organization of a developing brain. The question is how these processes interact, not which percentage of an individual brain belongs to genes or environment.

Reading
1 of 10
The Basics of Brain Development
Stiles, J., & Jernigan, T. L. (2010). The basics of brain development. Neuropsychology Review, 20(4), 327–348. https://doi.org/10.1007/s11065-010-9148-4
Major synthesis · Moderate · Full work: 22 pages
Trace one developmental process from cellular conditions through connections to a possible functional consequence.
Why you’re reading it. This supplies the assembly framework that later examples of timing and plasticity need.
A question to consider. Choose a developing neural pathway and explain how the history of its cells and a signal from their surroundings could jointly affect its organization.

Unit 2 of 5

When does timing matter?

Experience acts on a system with a history. Knudsen provides a framework for changing susceptibility and for constraints that remain after early development. Hubel and Wiesel then make timing experimentally concrete by varying deprivation and recovery in the cat visual system. Keep an age-dependent effect distinct from a universal deadline or a claim that adult change is impossible.

Reading
2 of 10
Sensitive Periods in the Development of the Brain and Behavior
Knudsen, E. I. (2004). Sensitive periods in the development of the brain and behavior. Journal of Cognitive Neuroscience, 16(8), 1412–1425. https://doi.org/10.1162/0898929042304796
Foundational argument · Major synthesis · Moderate · Full work: 14 pages
Follow how the circuit's current state affects what a particular experience can change.
Why you’re reading it. This turns the developmental overview into a question about susceptibility, persistence, and the conditions for later change.
A question to consider. What observations at several ages would distinguish a gradual decline in sensitivity from a sharply bounded critical period?
Reading
3 of 10
The Period of Susceptibility to the Physiological Effects of Unilateral Eye Closure in Kittens
Hubel, D. H., & Wiesel, T. N. (1970). The period of susceptibility to the physiological effects of unilateral eye closure in kittens. The Journal of Physiology, 206(2), 419–436. https://doi.org/10.1113/jphysiol.1970.sp009022
Landmark empirical study · Moderate · Full work: 18 pages
Track the age, duration, recovery interval, and measured response in each comparison.
Why you’re reading it. This applies the timing framework to an intervention whose neural and behavioral outcomes need not recover together.
A question to consider. Which additional comparison would best separate the effect of deprivation duration from the age at which ordinary visual input returns?

Unit 3 of 5

What changes with learning and experience?

A learning-related change can concern how strongly cells communicate or the structures through which they communicate. Bliss and Collingridge explain why persistent synaptic changes might support memory; Xu and colleagues track the appearance and survival of spines during motor learning. Compare functional and structural evidence while keeping the inference to memory open to further tests.

Reading
4 of 10
A Synaptic Model of Memory: Long-Term Potentiation in the Hippocampus
Bliss, T. V. P., & Collingridge, G. L. (1993). A synaptic model of memory: Long-term potentiation in the hippocampus. Nature, 361(6407), 31–39. https://doi.org/10.1038/361031a0
Foundational argument · Major synthesis · Challenging · Full work: 9 pages
Connect the properties of potentiation with the requirements of a memory mechanism, keeping induction and maintenance distinct.
Why you’re reading it. This supplies a mechanistic proposal against which observations of learning-related structure can be evaluated.
A question to consider. What feature of a memory task would you use to test the importance of input-specific rather than indiscriminate synaptic strengthening?
Reading
5 of 10
Rapid Formation and Selective Stabilization of Synapses for Enduring Motor Memories
Xu, T., Yu, X., Perlik, A. J., Tobin, W. F., Zweig, J. A., Tennant, K., Jones, T., & Zuo, Y. (2009). Rapid formation and selective stabilization of synapses for enduring motor memories. Nature, 462(7275), 915–919. https://doi.org/10.1038/nature08389
Landmark empirical study · Methodological contribution · Moderate · Full work: 5 pages
Compare the changing identities of spines with their total number and the animal's learning history.
Why you’re reading it. This adds longitudinal structural evidence without equating a persistent structure with a demonstrated memory trace.
A question to consider. What would you need to add to Xu's design to distinguish structures needed for further improvement from structures needed to retain an already learned skill?

Unit 4 of 5

How does change extend across life?

Microscopic observations make mechanisms visible, but they cannot simply be read off a human scan. Zatorre and colleagues explain that measurement gap. Draganski's brief juggling study and Erickson's older-adult trial then provide contrasting designs for studying adult change. Separate evidence that an intervention changes an anatomical measure from evidence that this change causes a behavioral benefit.

Reading
6 of 10
Plasticity in Gray and White: Neuroimaging Changes in Brain Structure During Learning
Zatorre, R. J., Fields, R. D., & Johansen-Berg, H. (2012). Plasticity in gray and white: Neuroimaging changes in brain structure during learning. Nature Neuroscience, 15(4), 528–536. https://doi.org/10.1038/nn.3045
Methodological contribution · Major synthesis · Moderate · Full work: 9 pages
Build a short list of biological processes that could influence each structural imaging measure.
Why you’re reading it. This prepares the move from identified spines to aggregate human tissue measurements.
A question to consider. If a scan changed after training, which additional observation would help distinguish a synaptic account from a vascular or myelin-related account?
Reading
7 of 10
Changes in Grey Matter Induced by Training
Draganski, B., Gaser, C., Busch, V., Schuierer, G., Bogdahn, U., & May, A. (2004). Changes in grey matter induced by training. Nature, 427(6972), 311–312. https://doi.org/10.1038/427311a
Landmark empirical study · Accessible · Full work: 2 pages
Use the imaging framework to interpret the three-scan comparison and the relation between measured structure and skill.
Why you’re reading it. This provides a compact adult-learning example with a design different from the randomized trial that follows.
A question to consider. Which alternative explanation would an active, randomly allocated comparison group address, and which cellular ambiguity would remain?
Reading
8 of 10
Exercise Training Increases Size of Hippocampus and Improves Memory
Erickson, K. I., Voss, M. W., Prakash, R. S., Basak, C., Szabo, A., Chaddock, L., Kim, J. S., Heo, S., Alves, H., White, S. M., Wojcicki, T. R., Mailey, E., Vieira, V. J., Martin, S. A., Pence, B. D., Woods, J. A., McAuley, E., & Kramer, A. F. (2011). Exercise training increases size of hippocampus and improves memory. Proceedings of the National Academy of Sciences, 108(7), 3017–3022. https://doi.org/10.1073/pnas.1015950108
Landmark empirical study · Moderate · Full work: 6 pages
Compare the between-group findings for hippocampal volume and memory, then examine what the correlations add.
Why you’re reading it. This extends the question to later adulthood while testing how far an anatomical intervention effect supports a behavioral explanation.
A question to consider. What conclusion remains justified when the groups differ in anatomical change but improve comparably on the memory task?

Unit 5 of 5

What limits adaptation and recovery?

The value of neural change depends on what it enables and what it constrains. Jones distinguishes returning toward an earlier movement pattern from learning another way to achieve an outcome. Kim and colleagues then examine a case in which training accompanies more synapses but poorer performance of the affected limb. End by specifying the function, strategy, and mechanism before deciding whether a change counts as recovery.

Reading
9 of 10
Motor Compensation and Its Effects on Neural Reorganization After Stroke
Jones, T. A. (2017). Motor compensation and its effects on neural reorganization after stroke. Nature Reviews Neuroscience, 18(5), 267–280. https://doi.org/10.1038/nrn.2017.26
Major synthesis · Critical reappraisal · Moderate · Full work: 14 pages
Separate task success, movement pattern, and neural reorganization in the review's examples.
Why you’re reading it. This gives the final unit a precise way to distinguish recovery from compensation while recognizing the usefulness of both.
A question to consider. For a reaching task, what observation would distinguish restoration of the original movement from success through a newly learned strategy?
Reading
10 of 10
Experience with the “Good” Limb Induces Aberrant Synaptic Plasticity in the Perilesion Cortex After Stroke
Kim, S. Y., Allred, R. P., Adkins, D. L., Tennant, K. A., Donlan, N. A., Kleim, J. A., & Jones, T. A. (2015). Experience with the “good” limb induces aberrant synaptic plasticity in the perilesion cortex after stroke. The Journal of Neuroscience, 35(22), 8604–8610. https://doi.org/10.1523/JNEUROSCI.0829-15.2015
Contemporary update · Challenging · Full work: 7 pages
Keep the manipulated experience, measured synapses, motor map, and reaching outcome separate as you assess the proposed mechanism.
Why you’re reading it. This tests the assumption that more structural plasticity must mean better function and brings the earlier measurement distinctions together.
A question to consider. Design one follow-up that would test whether the additional connections cause the poorer outcome, while also checking whether the animal changed its movement strategy.

Scope and omissions

This path concerns neural assembly and mechanisms of change across development, experience, adulthood, and focal injury. It is not a complete account of embryology, molecular genetics, every form of memory, or every neural system. Visual and motor preparations provide tractable comparisons, while human imaging introduces a different scale and level of inference. The selection does not establish universal age cutoffs, quantify genetic and environmental shares of an individual outcome, evaluate brain-training products, or recommend clinical rehabilitation. Lifespan behavioral trajectories, social settings, and population heritability have complementary treatments in other areas. Animal procedures, selected human samples, and specific tasks set limits on generalization.

Synthesis

Development and experience work upon what came before. Cells acquire identities and locations, connections form and change, and activity unfolds within conditions shaped by earlier growth. Change remains possible beyond early sensitive periods, but its character depends on the system, its history, and the demands placed upon it. Plasticity names a capacity for change; whether that change helps must be established separately.

The evidence also changes with the level of observation. A synaptic response, a persistent spine, an MRI estimate, and a successful movement are different outcomes. Connecting them requires comparisons that distinguish proposed mechanisms, establish the relevant timescale, and show what the change contributes. A larger neural measure does not by itself demonstrate better functioning, and renewed task success may reflect compensation as well as restoration.

To examine how neural activity interacts with bodily signals, hormones, and immune processes, continue with How Do Brain and Body Regulate Each Other?.

Evaluate one claim that an experience has changed the brain. Specify the organism and developmental state, the experience and comparison, the biological measure, the behavioral outcome, and a plausible alternative mechanism. Propose a follow-up that could separate these accounts. For a complementary account of learning and retention at the behavioral level, continue with How Does Practice Build Skill?; for development within changing social settings, follow How Do Contexts Shape Developmental Pathways?.