Exercising Your Brain

Lesley Stein

Exercise Affects on the Brain

Most people exercise to improve their physique, however, physical exercise is also a workout for your brain.  Exercise has been shown to reduce anxiety, stress, and most fascinating, increase neurogenesis.  I would like to share with you how new neurons are created in this process and how they relate to endorphins, Parkinson’s, and Alzheimer’s disease. 

How Does Neurogenesis Occur in the Brain?

Neurogenesis in the brain is currently not completely understood.  Based on current studies, neurogenesis occurs in the hippocampus, which is responsible for learning and memory.  One main theory is that the mild stress generated by exercise increases the influx of calcium; in turn activating transcription factors in the hippocampus.  These transcription factors allow the Brain-Dervied Neurotrophic Factor (BDNF) gene to be expressed, which produces BDNF proteins (a member of the neurotrophin family in growth factors) that stimulate neurogenesis.  BDNF are produced as a protective measure against stress to protect existing neurons by increasing the efficiency of signal transmissions across the synaptic cleft between neurons.  This signal plasticity is believed to be the foundation of learning and memory.  

BDNF have also shown capabilities of repairing neurons.  An interesting study was conducted analyzing BDNF contribution to repairing injured neurons.  Scientist compared inactive mice to active mice after an injury and saw active mice had regenerated more sciatic axons (neurons in the distal spinal cord of the hind limb) than the inactive mice.  To ensure neurons were being repaired through neurotrophin signals (through exercise), active mice were injected with a neurotrophin-blocking agent.  As predicted, the active mice with the neurotrophin-blocking agent did not regenerate axons in neurons.  This proved that exercise activates damaged neurons to regenerate axons through neurotrophin signals.  The video below shows how the BDNF proteins influence neurogenesis.

Start time: 1:50; End time: 2:50

Alzheimer’s and Parkinson’s Disease Relevancy

Parkinson’s and Alzheimer’s disease are a result in reduced amounts of neurons.  Therefore, based on studies like the one found above, exercise can potentially be an aspect of a patient’s treatment plan.  Exercise increases neuronal connections by increasing dendrite connections between neurons.  This generates a denser network of neurons that allows for improved processing and storage of information.  Exercise has even been shown to decrease the loss of dopaminergic neurons in Parkinson’s mice.  To read more on this topic click here.

Exercise Affecting Your Mood?

Have you ever noticed that after a hard work out you feel happier, less stressed, or more alert?  There have been several studies that show even 30 minutes of working out can improve mental health.  Any type of exercise, whether it be running, sports, dancing, swimming, cycling, or even gardening, can decrease anxiety and depression.  There are several hypothesis scientists have studied to explain the effects of exercise on one’s mood and emotion.  A well-supported hypothesis is that exercise increases blood circulation to the brain and interacts with the hypothalamic-pituitary-adrenal (HPA) axis.  The HPA axis controls reactions to stress and regulates mood and emotion.  It is believed that through these interaction (?) feedback loops are formed (see the figure below).  The regions of the brain that interact with the HPA axis are the amygdala, which responds to stress, the limbic system, which regulates mood, and the hippocampus, which is involved in creating memories as well as mood.  Exercise affects this pathway by increasing the amounts of melatonin and serotonin, while decreasing the amount of cortisol.  The diagram below shows the pathway of the HPA axis and the negative feedbacks involved. 

The  hypothalamic-pituitary-adrenal (HPA) axis

Endorphins Make You Happy

Even our infamous blonde Elle (Reese Witherspoon) from Legally Blonde knows the role of endorphins when she states, “Exercise gives you endorphins.  Endorphins make you happy.  Happy people just don't shoot their husbands, they just don't.”  Most people understand that these peptides are released during exercise and make you feel happy, but let’s take a deeper look at the brain to see how and why this occurs.  First off, endorphins act as neurotransmitters that are produced in the pituitary gland of the brain and released at the onset of stress or pain.  The endorphins follow the pain pathway, where a painful stimulus is transmitted through neurons into the dorsal horn (in the spinal cord).  Neurons receive the neurotransmitters carrying the pain signal and continue through the spinal cord, to the brain where we perceive pain.  Endorphins intercept this pathway when they are released into the dorsal horn the same way as the pain neurotransmitters.  Endorphins inhibit the pain neurotransmitters from being released by binding to opioid receptors in neurons.  This creates fewer impulses to the brain, and thus the brain registers less pain. 

The pain pathway

Endorphins have also been described as a feeling of euphoria.  This makes sense because endorphins attach to the same neurons as opiates such as morphine and heroin.  But why isn’t exercise as addictive as opiates, especially when exercise is much better for you?  While exercise can be addictive, the reward for exercise is more delayed that opiates.  The initial pain of exercise exceeds that of an instant drug that gives you the sense of euphoria.  Furthermore, the brain uses the feeling of fatigue, which is an inhibiting response to exercise, to keep our bodies at homeostasis.   This could discourage people from exercising before they reach the threshold of the addictive euphoric sensation.  Addictive or not, exercising increases neurogenesis, can help with diseases that decrease neurons, and brighten your mood.  Basic message: keep on exercising or get started, it will help you get through grad school!

References:

Stranahan, A.M., K. Lee, and M.P. Mattson. 2008. Central Mechanisms of HPA axis Regulation by Voluntary Exercise. Neuromolecular Med. 10 (2):118-127.

Pesce, C., C. Crova., L. Cereatti, R. Casella, M. Bellucci. 2009. Physical activity and mental performance in preadolescents: Effects of acute exercise on free-recall memory. Mental Health and Physical Activity. Vol 2:16-22.

Byrne, A. and Byrne, D.G. 1993. The Effect of Exercise on Depression, Anxiety and Other Mood States: A Review. Journal of Psychosematic Research Vol 37: 565-574.

Sharma, A., V. Madaan, and F.D. Petty. 2006. Exercise for Mental Health. Prim Care Companion J Clin Psychiatry. 8 (2): 106.

Sibley, B.A. and S.L. Beilock. 2007. Exercise and working memory:

An individual differences investigation. Journal of Sport & Exercise Psychology 29: 783-791.

Wu, S.H., T.F. Wang, L. Yu, C.J. Jen, J.I. Chuang, F.S. Wu, C.W. Wu, Y.M. Kuo.  2011. Running exercise protects the substantia nigra dopaminergic neurons against inflammation-induced degeneration via the activation of BDNF signaling pathway. Brain, Behavior, and Immunity Vol 25: 135-146.

Martin Duclos and Antoine Tabarin. 2011. Exercise, Training, and the Hypothalamo– Pituitary–Adrenal Axis. Hormone Use and Abuse by Athletes Ch 2.

Images, Videos, and Links:

Srivastava, Anoop Kumar. 2010. Pain: physiological consideration. Momeopathis Journal Vol 3 Issue 9.

Abitama, Edra. 2013. Workout benefit for brain health. Health and Nutrition. 

Lepeley, Lucy. Exercise and the brain.  27 May 2011. <http://www.youtube.com/watch?v=SiLMzFo9TO4>.