Don’t stop me now! The brain-basis of movement
We are constantly on the move - walking, running, dancing, scrolling on our phones! Most of the time, we move without even thinking about it! But have you ever stopped to consider how we move? It may surprise you to know that the simplest of movements require quite a lot of brainpower!
How do we move?
In our ‘Introducing: Your Brain’ blog, we learned how messages are sent to and from the brain by neurons. We also learned that the peripheral nervous system receives sensory input, sends it to your central nervous system for processing, then awakens muscles in response to instructions from the brain. Unsurprisingly, the most important brain region for goal-directed movement is the motor cortex! In order to move, your motor cortex needs to attain certain information from other brain regions. The parietal lobe must figure out the position of your body in space, while the frontal lobe must set a goal and devise strategies to attain it. Basically, your motor cortex needs to work out where you are, what you want to do, and how you are going to do it! Say you want to take a sip from your cup of tea. Seems like a fairly simple task, right? Wrong! Deciding to pick up the cup initially activates your frontal cortex, which in turn sends a message to your motor cortex. Using the information supplied by the visual cortex, the motor cortex must plan a path for your hand to follow to reach the cup. The message to move is sent from the motor cortex, down the spinal cord, eventually reaching your muscles. Your muscles then execute the movement (contract) that enables you to pick up your cup. To ensure this movement is effective and fast - so you do not miss the cup or knock it over - your brain constantly receives feedback from your senses to accurately adjust your hand as it moves.
There are two types of neurons that carry information to and from the CNS. Afferent neurons carry information from sensory stimuli to the CNS. Efferent neurons carry motor information back from the CNS to relevant muscles, causing movement. However not all movement is voluntary, like picking up a cup of tea. Involuntary movements, otherwise known as reflexes, are automatic muscle responses to particular stimuli. Have you ever touched a boiling hot pot? How did you respond? When your body comes in contact with something that could cause you harm, it withdraws immediately, before your brain gets a chance to process the threat. When you touch something extremely hot, receptors in your skin quickly send a signal to your spinal cord. This message is processed in the spinal cord and a response is sent back to your hand immediately - move! This process, illustrated below, is known as a ‘reflex arc’.
Image Credit: Edmund Custers, Owlcation
Mapping Movement
In our second blog, we explained how a number of different brain regions are required to ride a bike. For example, visual processing and attention-related areas are needed to navigate, while the brainstem increases heart rate and breathing during the exercise. The cerebellum is also required to coordinate pedalling and maintain balance. And, of course, motor areas are called upon to move pedals and steer! But did you know that very specific parts of the motor cortex control specific parts of the body?
In 1870, Hitzig and Fritsch (1) electrically stimulated different parts of a dog’s motor cortex to investigate the brain-basis of movement. Depending on which part of the motor cortex they activated, a different part of the dog’s body would move! They even lesioned specific parts of the motor cortex, and found that it resulted in paralysis of specific body parts! This is how the motor homunculus - a motor map within the precentral gyrus of the primary motor cortex - was discovered. Researchers have since realised that we also have a similar sensory homunculus - a sensory map within the postcentral gyrus of the somatosensory cortex. Interestingly, smaller body parts take up more space within the cortex than bigger parts. If you look closely at the image below you will notice that your toes take up much more space than your shoulders or even your entire arm!
Image Credit: ScienceSource
Your brain: The original GPS
How do you know how to get to school? Or work? Or home? There are three different types of neurons that enable us to navigate the world around us: head direction cells, place cells, and grid cells. Head direction cells, as the name suggests, are activated - or fire - when you point your head in a specific compass direction. Place cells, on the other hand, fire when you enter a specific location. Place cells, collectively, act as a cognitive representation of a specific location in space. That is, place cells make independent maps for each environment in which you find yourself. These cells recognise where exactly you are in the world you are!
Grid cells fire in a repeating hexagonal shape of locations that span your whole environment. Grid cells integrate information concerning location, distance, and direction. These cells track where you are in space. Now, you may be wondering: How do we know about these cells? Well, much of our current understanding of the link between neuronal activity and movement stems from studies of rats! Researchers like nobel-prize winner John O’Keefe used miniaturized equipment to record individual brain cells activity within freely moving rodents.
Image Credit: John Smart, Brain Preservation Foundation
The above image depicts neuronal activity within the entorhinal cortex (temporal lobe) of a rat when moving around inside a box (2). The black lines trace the movement of the rat and the red dots signify a spike in neuronal activity. Notice that place cells (left) only fire in one location, whereas grid cells fire at regular intervals.
The many reasons to move!
Did you know that moving can make your brain work more efficiently? Non-human studies strongly suggest that physical activity promotes the development of new neuronal architecture. For example, providing mice with running wheels has been shown to increase their neuronal growth and synapse formation (3) ! In humans, short bursts of physical activity (10 - 20 minutes) have been associated with improved performance on a variety of attention, memory and executive control tasks (4). Physical activity has even been linked to better academic achievement (5) ! So if you want to boost your brainpower, all you need to do is move!
Come back next week when Jen will be talking about language and our brains! In the meantime, check out our Twitter and Facebook pages for all the latest news from our lab!
References
Hagner, M. (2012). The electrical excitability of the brain: toward the emergence of an experiment. Journal of the History of the Neurosciences, 21(3), 237-249. https://www.ncbi.nlm.nih.gov/pubmed/22724486
Moser, M. B., Rowland, D. C., & Moser, E. I. (2015). Place cells, grid cells, and memory. Cold Spring Harbor Perspectives in Biology, 7(2), a021808. https://www.ncbi.nlm.nih.gov/pubmed/25646382
Hillman, C. H., Erickson, K. I., & Kramer, A. F. (2008). Be smart, exercise your heart: exercise effects on brain and cognition. Nature reviews neuroscience, 9(1), 58-65. https://www-nature-com.ucd.idm.oclc.org/articles/nrn2298
Chang, Y. K., Labban, J. D., Gapin, J. I., & Etnier, J. L. (2012). The effects of acute exercise on cognitive performance: a meta-analysis. Brain research, 1453, 87-101. https://www-sciencedirect-com.ucd.idm.oclc.org/science/article/pii/S0006899312004003?via%3Dihub
Deslandes, A., Moraes, H., Ferreira, C., Veiga, H., Silveira, H., Mouta, R., ... & Laks, J. (2009). Exercise and mental health: many reasons to move. Neuropsychobiology, 59(4), 191-198. https://www.karger.com/Article/Pdf/223730
Further reading
Castiello, U., & Begliomini, C. (2008). The cortical control of visually guided grasping. The Neuroscientist, 14(2), 157-170.
Crossman, A. R., & Neary, D. (2015). Neuroanatomy: an illustrated colour text (5th ed.). Edinburgh: Churchill Livingstone Elsevier.
Diedrichsen, J., Shadmehr, R. & Ivry, R. B. (2010) The coordination of movement: optimal feedback control and beyond. Trends in Cognitive Science, 14, 31-9.
O'Keefe, J. (1976). Place units in the hippocampus of the freely moving rat. Experimental Neurology, 51(1), 78-109.