By: Catherine Joachin
What is the brainstem?
The brainstem is the structure that connects the brain to the spinal cord. It houses important cranial nerve nuclei, monitors automatic bodily functions, promotes survival, and ensures cognitive functioning.
Functions of the brainstem
The brainstem is home to the cardiovascular, vasomotor, and respiratory control centers, which regulate heart rate, blood pressure, and breathing, among other activities (Thau, Reddy & Singh, 2022). 10 of the body’s 12 cranial nerves also reside in the area, allowing for the control of bodily functions pertaining to taste, sensations, and movement (Cleveland Clinic, n.d.).
The brainstem is divided into three main components: the midbrain, the pons, and the medulla oblongata (Cleveland Clinic, n.d.). These structures perform distinct regulatory functions but work together to serve as a bridge for neural pathways connecting the cerebrum, the cerebellum, and the spinal cord (American Association of Neurological Surgeons, n.d.).
In addition to its involvement in visual and auditory processing, the midbrain plays a significant role in the regulation of eye movements (Cleveland Clinic, n.d.). Through a dopamine-producing nucleus called the substantia nigra, it also controls movement and coordination (Johns Hopkins Medicine, n.d.)
The pons, which connects the midbrain to the medulla oblongata, contains the cranial nerve nuclei necessary for motor control of eyes, hearing, balance, attention, and facial movements (Johns Hopkins Medicine, n.d.).
The medulla oblongata is the bridge between the brainstem and the spinal cord. Its functions include the regulation of heart rhythm, blood flow, oxygen levels, carbon dioxide levels, and involuntary vasomotor actions such as vomiting, coughing, and swallowing (Johns Hopkins Medicine, n.d.).
The reticular activating system (RAS) also lies within the brainstem. It is a network of neurons that regulates sleep-wake cycles and attention (Cleveland Clinic, n.d.).
Brainstem-related conditions
Damage to the brainstem can lead to the development of several problems, including:
• Blood clots
• Brain tumors
• Encephalitis
• Heart attack (myocardial infarction)
• Stroke
• Sudden cardiac death
• Traumatic brain injury
(Cleveland Clinic, n.d.)
According to the American Stroke Association (2023), clinical features associated with brainstem strokes depend on the site of injury located within the area, meaning that symptoms can range from minor impairments such as vertigo and diminished consciousness to more severe afflictions like locked-in syndrome.
Symptoms associated with brainstem dysfunction include:
• Balance problems
• Loss of gag reflex
• Sleep disruptions
• Nausea or vomiting
• Slurred speech
• Stroke
• Difficulty swallowing, drinking, or eating
(Cleveland Clinic, n.d.)
The brainstem is crucial to the oversight of vital activities; therefore, severe injury can lead to an inability to regain consciousness, a condition also referred to as brain death (Cleveland Clinic, n.d.).
Brainstem and Epilepsy
Investigation into the role of the brainstem in epilepsy revealed an association between peri ictal brainstem posturing and generalized convulsive seizures (Vilella et al., 2021). In other words, this study suggests that decerebrate posturing may be an abnormal motor response to brainstem-related seizure activity.
Further evidence suggests that brainstem lesions may also be involved in the pathogenesis of seizures in patients with multiple sclerosis (Papathanasiou et al., 2010). Through the use of evoked potentials, research in this area revealed a significant relationship between multiple sclerosis, epilepsy, and somatosensory abnormalities in the brainstem (Papathanasiou et al., 2010)
Scientific literature promoting brainstem involvement in epilepsy notes that while a majority of cases focus on generalized seizures, research also revealed that brainstem injury can lead to focal epilepsy (Papathanasiou, 2010). Brainstem and cortical grey matter connectivity are particularly impaired in focal epilepsy (Mueller et al., 2019). This negatively affects cortical activation control.
Conclusion
The brainstem is essential for the regulation of vital processes. Breathing, heart rate, taste, head movements, and facial sensations are all controlled by the structures and nuclei contained in this brain region. Although the brainstem is often overlooked in studies on the genesis of seizures, research suggests that damage to this brain region may play an undervalued role in epilepsy.
References:
American Association of Neurological Surgeons. (n.d.). A Neurosurgeon’s Overview the Brain’s Anatomy. American Association of Neurological Surgeons. Retrieved from: https:// www.aans.org/en/Patients/Neurosurgical-Conditions-and-Treatments/Anatomy-of-the-Brain
American Stroke Association. (2023). Brain Stem Stroke. American Stroke Association. Retrieved from: www.stroke.org. https://www.stroke.org/en/about-stroke/types-of-stroke/brain stem-stroke
Cleveland Clinic. (n.d.). Brainstem. Cleveland Clinic. Retrieved from https:// my.clevelandclinic.org/health/body/21598-brainstem
Papathanasiou, E. S., Pantzaris, M., Myrianthopoulou, P., Kkolou, E., & Papacostas, S. S. (2010). Brainstem lesions may be important in the development of epilepsy in multiple sclerosis patients: An evoked potential study. Clinical Neurophysiology, 121(12), 2104–2110. https://doi.org/ 10.1016/j.clinph.2010.05.017
Vilella, L., Lacuey, N., Hampson, J. P., Zhu, L., Omidi, S., Ochoa-Urrea, M., Tao, S., Rani, M. R. S., Sainju, R. K., Friedman, D., Nei, M., Strohl, K., Scott, C., Allen, L., Gehlbach, B. K., Hupp, N. J., Hampson, J. S., Shafiabadi, N., Zhao, X., … Lhatoo, S. D. (2021). Association of peri-ictal brainstem posturing with seizure severity and breathing compromise in patients with generalized convulsive seizures. Neurology, 96(3), e352–e365. https://doi.org/10.1212/ WNL.0000000000011274
Mueller, S. G., Bateman, L. M., Nei, M., Goldman, A. M., & Laxer, K. D. (2019). Brainstem atrophy in focal epilepsy destabilizes brainstem-brain interactions: Preliminary findings. NeuroImage Clinical, 23, 101888–101888. https://doi.org/10.1016/j.nicl.2019.101888
Thau, L., Reddy, V., & Singh, P. (2012). Anatomy, Central Nervous System. Treasure Island (FL): StatPearls Publishing. Retried from https://www.ncbi.nlm.nih.gov/books/NBK542179/
