Landscape architecture students use virtual reality goggles to view their “photospheres.” Virtual reality provides a sense of place. The cardboard goggles cost

How long does it take for neuroplasticity to significantly change the structure of the brain and the ways we think?

I think there are two separate questions here:

  1. How long does it take for neuroplasticity to significantly change the structure of the brain?
  2. How long does it take for neuroplasticity to significantly change the way we think?

Question 2 is much harder to address, because the phrase “the way we think” is highly ambiguous and open to interpretation. Also, the word “significantly” means one thing in experimental research (statistical significance) [1], and another in everyday parlance (importance).

Neuroplasticity is a broad term covering the following concepts:

  • Synaptic plasticity: changes in the connections between neurons. This can take place very rapidly — in milliseconds. Consolidation of these changes can take much longer.
  • Nonsynaptic plasticity: changes to gene expression, ion channels, axons, dendrites, and other structural and physiological factors linked to neuronal networks. Since this covers a broad range of phenomena, the time scales range from milliseconds to minutes, hours and days. For instance, one study showed that administering prolonged unavoidable stress to rats over the course of ten days can lead to a decrease in dendritic branching in the hippocampus, and an increase in dendritic branching in the amygdala. [2] Another interesting nonsynaptic plasticity mechanism is experience-guided changes in white matter.[3]

Effectively, your brain is always changing slightly, adjusting itself based on your experience. And almost every part of the brain shows some degree of plasticity. Cognitive abilities are typically associated with the prefrontal cortex, but other areas including the hippocampus, amygdala, and the basal ganglia are also important. (And we mustn’t forget the thalamus, which sends inputs to all of cortex, plus most of the key subcortical areas!) Presumably plasticity in areas that send signals to these areas can also contribute to cognitive abilities. This means virtually every part of the brain can in principle influence cognition. The idea that “higher” functions or cognition can be localized in the same way as sensory and motor functions is still somewhat controversial, and there are neuroscientists who dispute it [4].

How much change counts as significant change? That depends on your notion of significance. And whether a structural change counts as a change in the way you think is a completely different matter — more philosophy and psychology than neuroscience at this point.

For argument’s sake let’s assume that learning something new is a small change in the way you think. You can learn very rapidly indeed. Fear conditioning experiments in animals show that we are capable of “one-shot learning“.  If a sound is played shortly before a mild electric shock is delivered  to a rodent, the animal will learn that the sound predicts the shock,  and will respond fearfully to it the next time it is played. Synaptic plasticity takes place on the milliseconds to seconds time  scale. When you learn something new — a person’s name, an email  address, a phone number — we assume there are synaptic changes taking place in your brain.

But perhaps it is more reasonable to suppose that learning a single fact leaves your “way” of thinking unchanged. In order to guesstimate the time-scale for major changes in your mental habits, the best place to look is probably real life stories of change and conversion. A “Damascene conversion” can lead you to do an about-face, suddenly changing the way you think and behave. More common is the slow accretion of small changes that add up, so that after a year or two you realize that if you could talk to your younger self, you would probably have a major argument!

Notes & References:

[1] Statistical significance is a measure experimentalists use to judge the probability that the  results they obtained arose purely by chance. This is very different  from the colloquial meaning of the word “significance”. For example, a  change of 0.1% in some connection strength might be considered an insignificant effect size, but it can be established to be statistically significant.

[2] Chronic Stress Induces Contrasting Patterns of Dendritic Remodeling in Hippocampal and Amygdaloid Neurons

[3] EDIT: Marc Ettlinger pointed this example out: A study showed that six weeks of juggling induced measurable changes in human white matter structure.(Training induces changes in white matter architecture.) This may happen because of adaptive changes in myelination. Myelin is a sheath that forms around the axons of neurons that project a long(ish) distance. The more myelination there is, the faster the conduction of signals along the axon. Adaptive myelination is an exciting direction for modeling with spikes. A quick search came up with a handful of papers, including this one: Role of myelin plasticity in oscillations and synchrony of neuronal activity

[4] William Uttal’s book The New Phrenology (which I have only read  a chapter or so of) describes how the “localization of function” thread  that runs through fMRI and other neuroscientific approaches may be a  misguided return to the notorious Victorian pseudoscience of phrenology. Here is a precis of the book.