This is an exclusive excerpt from my book, The Physiology of Yoga.
The cerebrum is the largest portion of the brain and contains the cerebral cortex. The cerebrum is made up of two hemispheres, while the cortex can be separated into four lobes: the frontal lobe, the parietal lobe, the temporal lobe, and the occipital lobe (see the diagram below). The frontal lobe is involved in motor function including facial expression, problem solving, spontaneity, memory, language, initiation, judgement, impulse control, and social and sexual behavior. The most anterior portion of the frontal lobe is the prefrontal cortex, a critical portion that mediates intellectual or executive functions. The other lobes are responsible for sensory functions. The parietal lobe processes information from the body surface and its interaction with the environment. This is referred to as somatosensation. The occipital lobe is where visual processing begins, and the temporal lobe contains the cortical area for auditory processing but also has regions crucial for memory formation.
Lobes of the cerebral cortex
Neuroplasticity describes the nervous system’s ability to change in response to experience. So essentially the brain can direct its own changes. The roles of different parts of the cortex that we have discussed are not completely predetermined. In his book, Livewired: The Inside Story of the Ever-Changing Brain, David Eagleman (2020) describes how it is the pattern of inputs that determine the fate of the cortex. Eagleman goes on to explain how regions of the brain maintain their territory with continuous activity: If activity slows or stops (e.g., because of blindness), the territory tends to be taken over by its neighbors, a change that is measurable within an hour. Eagleman also hypothesizes that the circuitry underlying dreaming serves to amplify the visual system’s activity periodically throughout the night, allowing it to defend its territory against takeover from other senses.
Although children, teenagers, and young adults have a greater capacity for neuroplasticity, we all have neuroplasticity throughout our lives. As adults, we can encourage neuroplasticity by seeking novel challenges and applying focused, deliberate effort. The neurotransmitter glutamate (not to be confused with the food additive monosodium glutamate or MSG) is the primary mediator of nervous system plasticity (Zhou and Danbolt 2014), and plenty of rest is required to lock in the changes that have been made. Perhaps this is what is meant when yogis say that Savasana (Corpse Pose) is a chance for the mind to imprint changes—but even better is sleep. A review by Walker and Stickgold (2004) provided evidence of sleep-dependent memory consolidation and sleep-dependent brain plasticity. Therefore, getting adequate amounts of sleep can help us retain new information, and inadequate sleep can slow memory formation.
In a randomized controlled trial, Tolahunase and colleagues (2018) looked at the effect that yoga and meditation can have on people with major depressive disorder. The authors concluded that a decrease in depression severity following yoga and meditation interventions is associated with improved systemic biomarkers of neuroplasticity. In a systematic review by Gothe and colleagues (2019) looking at the effect yoga can have on brain health, the authors concluded that yoga has a positive effect on the structure and function of various regions of the brain, including the amygdalae and prefrontal cortex. Gothe and colleagues suggested that these studies offer promising early evidence that behavioral interventions like yoga may mitigate age-related and neurodegenerative declines as many of the regions identified are known to demonstrate significant age-related atrophy.
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References:
Eagleman, D. 2020. Livewired: The Inside Story of the Ever-Changing Brain. New York: Pantheon.
Gothe, N., I. Khan, J. Hayes, E. Erlenbach, and J. Damoiseaux. 2019. “Yoga Effects on Brain Health: A Systematic Review of the Current Literature.” Brain Plasticity 5 (1): 105-122.
Tolahunase, M., R. Sagar, M. Faiq, and R. Dada. 2018. “Yoga- and Meditation-Based Lifestyle Intervention Increases Neuroplasticity and Reduces Severity of Major Depressive Disorder: A Randomized Controlled Trial.” Restorative Neurology and Neuroscience 36 (3): 423-442.
Walker, M., and R. Stickgold. 2004. “Sleep-Dependent Learning and Memory Consolidation.” Neuron 4 (1): 121-133.
Zhou, Y., and N. Danbolt. 2014. “Glutamate as a Neurotransmitter in the Healthy Brain.” Journal of Neural Transmission 121 (8): 799-817.