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You’re probably familiar with grey matter, it’s a popular term in pop culture, but its lesser-known sibling white matter is just as interesting—and may be just as important. (3) The left and the right side of the brain are different. We only use 10% of the brain. Alcohol kills brain cells. Too much TV will rot your brain.
Did you spot the brain myths in that first paragraph? We hear a lot about the brain, but how much do we really know about the mysterious organ that makes us who we are? There are a lot of myths about the brain, and the insidious “10%” is the worst of the lot, but we’ve learned a lot about how the brain works, especially in the last few decades. (1)(2)
Understanding The Basics
Before we can take a deep dive into white vs. grey matter, we first need to understand how our brain communicates. Our nervous system is governed by an estimated 10 billion neurons!
These small but mighty cells are responsible for receiving, integrating and transmitting information in our body and mind. In the brain there are many types of neurons with different functions, but generally speaking a neuron consists of four parts; a soma (cell body), an axon, dendrites, and a synapse. (4)
Think of the neuronal network as a connection between two cities:
Soma: Similar to how a metropolitan center is a bustling hub of jobs and innovation, the soma is a processing and production hub of chemicals called neurotransmitters (ex: serotonin, norepinephrine and dopamine). (4)
Axon: The axon is the highway that connects two cities. These are long pathways that extend from one soma to the other. It’s responsible for communicating electrical impulses to networks of neurons. It’s also wrapped in what is known as the myelin sheath, white coloured fatty cells which helps signal transmission. (4)
Dendrites: Dendrites are the roadways surrounding the city in close proximity that extend to surrounding neighbourhoods, and burrows. These short pathways extend from the soma, increasing the area available to receive signals from other neurons. (4)
Synapse: Like a shipping port that receives goods, the synapse receives neurotransmitters from neighbouring neurons. (4)
White Matter and Grey Matter: What’s the difference?
Grey matter is the “outer shell” of the brain and makes up most of the surface, or cortex, as well as the cerebellum, cerebrum, and brain stem. Grey matter is made up of mostly somas and dendrites, where the integration and initiation of local information takes place, in other words information is processed and passed in close proximity to other neurons.
Grey matter gets its name from the pinkish grey colour of the brain tissue in these areas—which comes from a dense collection of somas, dendrites, and non-myelinated axons. (5)(6)(7)(8)
White matter is what lies beneath the grey matter in the brain. White matter is mostly made up of axon tracts which transmit global electrical signals to other neurons, that is to say information is passed to further regions of the body.
It gets its name from the fatty tissue that wraps around the axon called myelin. Myelin is lighter in colour, hence “white matter” and is an excellent insulator that allows for faster delivery of electrical signals to other neurons. (9)
White Matter and Grey Matter: Where and Why?
White and grey matter extend all the way from the brain down into the spinal cord. Here, white matter takes up most of the outer layer, and the grey rests inside. Why? (6)
Think of it as efficiency. If the spinal cord is responsible for bringing motor information from our brain to our body, the short connections of grey matter in the spine would have to reach further to send signals to the body to move.
However, since long axon tracts are on the outside layer, it’s much faster for signals to get to your motor neurons. These longer pathways on the outside layer help create fast signal transmission so you can react and move quickly. (8) (10).
For all the attention on grey matter, it only makes up 40% of the brain. White matter actually dominates, at about 60%. Where grey matter gets the edge is in oxygen—95 percent of the oxygen that goes to the brain goes right to the grey matter.
This may be because the grey matter handles things like higher processing and other cognitive functions, whereas white matter is greatly responsible for carrying electrical signals—a computer compared to a power supply. (11)
How can we improve our white or grey matter?
The brain is not static. Just as a city’s power lines need maintenance, and your computer gets slower over time until you upgrade, there are things you can do to benefit your brain matter—both white and grey.
Repairing White Matter After Injury: A brain injury can be severely debilitating but, depending on the injury, it doesn’t have to be permanent. A common white matter injury is a spinal injury: if the white matter in the spinal cord is pinched or squashed, the information needed to move limbs doesn’t get where it needs to go, leading to paralysis. As long as the neurons are healthy, the axons (the brain’s power lines), can be repaired. Stimulating stem cells in the brain may be key in helping this repairing process. (12) (13) (14)
Repairing Grey Matter After Injury: Grey matter injury is more common than white, as it lies on the outside of the brain. The neurons that make up grey matter are also vulnerable to a lack of oxygen. Grey matter injuries can be repaired through therapeutic means: like patients with partial paralysis learning how to walk again. (12) (15)
Improving White Matter: A recent study found that physical activity in children improved the “microstructure” of the white matter in their brain. MRI scans have also found that teenagers who practice martial arts, judo in this case, have improved white matter connectivity. Even older adults benefit from exercise, as increased white matter can stave off cognitive diseases like Alzheimers. (16) (17) (18)
Improve your brain with meditation and exercise
Meditation has also been shown to improve white matter. Research participants who practiced mindfulness meditation were shown to have improved white matter in as little as 2-4 weeks! (19)
Improving Grey Matter: Much more research has been conducted on grey matter over white matter. Just like with white matter, exercise, specifically cardio exercise, improved their brain health especially when it came to memory. Learning a second language was found to be effective in combating grey matter decline as a result of MS. (20) (21)
Mindfulness meditation practice has been found to significantly alter the structure of the brain. MRI images of participants who had completed 8 weeks of 27-minute daily meditation practice revealed: “increased gray-matter density in the hippocampus, known to be important for learning and memory, and in structures associated with self-awareness, compassion, and introspection.” (22)
The brain may still be a mystery but more and more studies are released every year that shed more light on white and grey matter, and how they impact the way we think, move, and feel. While there is still lots to learn, it’s clear that exercise and meditation have a profound impact on your brain’s health, as if you needed another reason to take care of yourself!
Voss,M.W., et al., (2012) The influence of aerobic fitness on cerebral white matter integrity and cognitive function in older adults: Results of a one‐year exercise intervention. [online] Available at: https://onlinelibrary.wiley.com/doi/full/10.1002/hbm.22119 [Accessed March 29, 2020]
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