Can the Brain Change? Neuroplasticity, Brain-Training Apps and the Gut-Brain Axis Through the Research

This article is general information for understanding scientific concepts. If you are worried about low mood or memory decline, talk to a doctor before turning to diets or apps.

Why brain claims inflate so easily

Neuroscience really is advancing quickly. That makes it easy for animal studies or small results to be turned into promises that “this will change your brain.” Let’s sort three popular topics into what is confirmed and what we don’t yet know.

Neuroplasticity: the brain changes for life — slowly

Neuroplasticity is the brain’s capacity to change its connections and structure with experience. Hebb (1949) proposed that “neurons that fire together strengthen their connections,” and later research supported the idea.

• The longer London taxi drivers had memorised the city’s complex streets, the larger the back of their hippocampus was (Maguire et al., 2000).
• People who learned to juggle for three months gained grey matter in visual-motion areas, which shrank again once they stopped practising (Draganski et al., 2004).

The limits are clear too. These changes come from long repetition and can reverse when practice stops. Whether new neurons form in the adult hippocampus is still debated: in 2018, one study reported “almost none” (Sorrells et al., 2018) and another “throughout old age” (Boldrini et al., 2018). The idea that “you can quickly rewire your brain if you set your mind to it” is an exaggeration.

Ten minutes of brain training a day: only the practised task improves

Brain-training apps advertise better memory and focus. The research broadly says this:

• In an experiment where over 11,000 people did six weeks of online brain training, scores on the trained tasks rose but did not transfer to other cognitive abilities (Owen et al., 2010).
• Reviewing the field, Simons et al. (2016) concluded that training improves the practised task and closely similar ones, with little evidence that it boosts everyday cognition.

Some approaches have firmer evidence. Older adults who did a year of aerobic exercise increased hippocampal volume by about 2% and improved memory slightly (Erickson et al., 2011). Play brain games for fun, and look after exercise, sleep and learning new things too. Why attention leaks is covered further in the article on the limits of attention and memory.

The gut-brain axis: the gut and brain talk, but it’s not the “basis of intuition”

The gut and brain influence each other through the vagus nerve, hormones, immune signals and substances produced by gut microbes. Cryan et al. (2019) reviewed this gut-brain axis research in depth.

• In a large Belgian cohort, people with depression had fewer of certain gut bacteria, such as Coprococcus (Valles-Colomer et al., 2019). This is a correlation, though; whether it is cause or effect is still unknown.
• In a small randomised trial, people with depression who received 12 weeks of Mediterranean-style dietary support improved more (Jacka et al., 2017). It was small, so larger studies are needed.

Some points are often exaggerated. It is true that “90% of serotonin is made in the gut,” but gut serotonin does not cross the blood-brain barrier into the brain. And “gut feeling” is a figure of speech; there is no evidence that gut microbes produce intuition.

The idling brain: the default mode network

Raichle et al. (2001) identified a set of brain regions that become active together precisely when people are resting rather than doing a task, and called it the default mode network (DMN). It is mainly used when we recall the past, imagine the future or guess what others are thinking.

• Links to creativity: research suggests creative ideas emerge best when the DMN and the executive control network, which handles focus, work together (Beaty et al., 2016). Zoning out alone does not produce creativity.
• The benefit of stepping away: people who did an easy, unrelated task while leaving a hard problem aside came up with more ideas when they returned to it (Baird et al., 2012).
• A caution: minds wander for nearly half of waking hours, and people generally report being less happy while it happens (Killingsworth & Gilbert, 2010). Restful idling and drifting into worry are worth telling apart.

Summary at a glance

Topic	What research has confirmed	What’s exaggerated
Neuroplasticity	Long repetition changes structure	”You can rewire it quickly”
Brain training	Only practised tasks improve	”Ten minutes a day makes you smarter”
Exercise	Small effects on hippocampal volume and memory	—
Gut-brain axis	Gut and brain exchange signals	”Gut serotonin makes your mood,” “the gut makes intuition”
Default mode network	Network active at rest; creativity comes from cooperation with the control network	”Zoning out makes creativity explode”

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References

• Hebb, D. O. (1949). The Organization of Behavior. Wiley.
• Maguire, E. A., et al. (2000). Navigation-related structural change in the hippocampi of taxi drivers. PNAS, 97(8), 4398–4403.
• Draganski, B., et al. (2004). Neuroplasticity: Changes in grey matter induced by training. Nature, 427(6972), 311–312.
• Sorrells, S. F., et al. (2018). Human hippocampal neurogenesis drops sharply in children to undetectable levels in adults. Nature, 555(7696), 377–381.
• Boldrini, M., et al. (2018). Human hippocampal neurogenesis persists throughout aging. Cell Stem Cell, 22(4), 589–599.
• Owen, A. M., et al. (2010). Putting brain training to the test. Nature, 465(7299), 775–778.
• Simons, D. J., et al. (2016). Do “brain-training” programs work? Psychological Science in the Public Interest, 17(3), 103–186.
• Erickson, K. I., et al. (2011). Exercise training increases size of hippocampus and improves memory. PNAS, 108(7), 3017–3022.
• Cryan, J. F., et al. (2019). The microbiota-gut-brain axis. Physiological Reviews, 99(4), 1877–2013.
• Valles-Colomer, M., et al. (2019). The neuroactive potential of the human gut microbiota in quality of life and depression. Nature Microbiology, 4(4), 623–632.
• Jacka, F. N., et al. (2017). A randomised controlled trial of dietary improvement for adults with major depression (the ‘SMILES’ trial). BMC Medicine, 15(1), 23.
• Raichle, M. E., et al. (2001). A default mode of brain function. PNAS, 98(2), 676–682.
• Beaty, R. E., Benedek, M., Silvia, P. J., & Schacter, D. L. (2016). Creative cognition and brain network dynamics. Trends in Cognitive Sciences, 20(2), 87–95.
• Baird, B., et al. (2012). Inspired by distraction: Mind wandering facilitates creative incubation. Psychological Science, 23(10), 1117–1122.
• Killingsworth, M. A., & Gilbert, D. T. (2010). A wandering mind is an unhappy mind. Science, 330(6006), 932.