What Is Neuroplasticity?

For much of the twentieth century, science described the nervous system as an almost fixed structure once brain maturation was complete: rigid, unchangeable, with a stable architecture for life.

If that were entirely true, it would be very hard to explain something as everyday as a person learning to play an instrument at forty, or recovering, even partially, after a brain injury.

The evidence gathered since then points to a rather different reality, summed up in one concept: neuroplasticity, the nervous system’s capacity to modify itself in response to experience.

Learning is, literally, changing your brain

Biologist James Zull puts it directly: learning has to do with change and, at the same time, is change.

If you understand learning as a lasting change in behavior, it makes sense that it comes with real functional and structural changes in the brain. A common classification distinguishes three types:

• Morphological changes: growth of new terminals, synaptic boutons, and dendritic spines.
• Molecular changes: modifications in the proteins of neuronal membranes, which alter how each neuron responds to the activity of the others.
• Neurochemical changes: adjustments in the synthesis and release of neurotransmitters, which can increase or reduce the strength of a specific connection depending on how much it’s been used.

Hebb’s rule

In 1949, Canadian psychologist Donald Hebb proposed an idea that would become one of the most cited principles in neuroscience: memory must rest on a permanent structural change in the brain, achieved by modifying the efficiency of synapses that already existed, not necessarily by creating connections from scratch.

The more a specific connection between two neurons gets used, the more efficient that communication becomes. In 1992, in a popular-science article on brain development, neurobiologist Carla Shatz condensed this into a phrase that has become synonymous with neuroplasticity:

Cells that fire together wire together.

The first direct physiological evidence of such a mechanism came in 1973. Timothy Bliss and Terje Lømo stimulated a nerve pathway leading into the hippocampus of anesthetized rabbits with high-frequency trains of impulses and saw that the response of the receiving neurons stayed strengthened for hours. They called it long-term potentiation (LTP), and it remains the most studied cellular model of learning.

Neuroplasticity isn’t, then, a metaphor: it’s a verifiable physical change in the efficiency and structure of connections.

How actively you engage with what you’re studying, not just the time you put in, is what our deep vs. surface learning quiz sets out to distinguish.

Why some memories stick and others fade

Neuroplasticity also explains why not everything you learn gets etched in with the same firmness.

Short-term memory relies on circuits of neurons that stay active only for seconds; if that information doesn’t get transferred to more lasting storage, it disappears without leaving a permanent trace.

Long-term memory, by contrast, requires much deeper changes: synthesis of new proteins and permanent structural modifications in synaptic connections.

That consolidation process isn’t instant. It takes time (minutes to hours in its initial phase), a window during which it can be interrupted by events like a head injury, an electric shock, or alcohol. That explains why the memory of the minutes right before a hard knock or an intense scare is sometimes lost, while older, already-consolidated memories stay intact.

A change that doesn’t depend on creating new neurons

One point deserves clarifying: neuroplasticity mostly doesn’t consist of manufacturing brand-new neurons, but of modifying the connections between the ones that already exist.

The distinction matters because it separates two related but different phenomena. Neurogenesis is the appearance of new neurons; in the adult human brain it would be limited to very specific regions like the hippocampus, and its real extent is still under debate. Synaptic plasticity is the strengthening or weakening of connections between existing neurons, and it happens throughout the brain and throughout life.

Almost everything you learn day to day, from a new word to a manual skill, relies mainly on the second mechanism, far more widespread than the first.

Plasticity seen in adult brains

Two neuroimaging studies have become the classic examples showing that experience changes the structure of the adult brain, not just the child’s.

Eleanor Maguire and her team (2000) compared brain scans of London taxi drivers, who must memorize the city’s maze of streets to get their license, with those of people who didn’t drive taxis. The rear part of the hippocampus, involved in spatial memory, was larger in the taxi drivers, and its volume grew with years on the job; the front part, by contrast, was somewhat smaller. It’s a cross-sectional study, so on its own it doesn’t prove the causal direction, but the correlation with years of experience points to a change induced by use.

Draganski et al. (2004) took the experimental step: they taught juggling to adults who couldn’t do it and, after a few months of practice, saw an increase in gray matter in cortical areas involved in processing visual motion, which shrank again once they stopped practicing.

That’s why the idea of learning through practice, associated with the kinesthetic style, has a biological basis that holds for anyone, not for one “type” of learner: sustained practice leaves a physical trace, and that trace also fades with disuse.

Sources

• Bliss, T. V. P. & Lømo, T. (1973). Long-lasting potentiation of synaptic transmission in the dentate area of the anaesthetized rabbit following stimulation of the perforant path. The Journal of Physiology, 232(2), 331-356. doi:10.1113/jphysiol.1973.sp010273
• Draganski, B., Gaser, C., Busch, V., Schuierer, G., Bogdahn, U. & May, A. (2004). Neuroplasticity: Changes in grey matter induced by training. Nature, 427(6972), 311-312. doi:10.1038/427311a
• Hebb, D. O. (1949). The Organization of Behavior: A Neuropsychological Theory. Wiley.
• Maguire, E. A., Gadian, D. G., Johnsrude, I. S., Good, C. D., Ashburner, J., Frackowiak, R. S. J. & Frith, C. D. (2000). Navigation-related structural change in the hippocampi of taxi drivers. Proceedings of the National Academy of Sciences, 97(8), 4398-4403. doi:10.1073/pnas.070039597
• Shatz, C. J. (1992). The developing brain. Scientific American, 267(3), 60-67. doi:10.1038/scientificamerican0992-60
• Zull, J. E. (2002). The Art of Changing the Brain: Enriching Teaching by Exploring the Biology of Learning. Stylus.