midbrain
noun
mid·brain
ˈmid-ˌbrān 
: the middle of the three primary divisions of the developing vertebrate brain or the corresponding part of the adult brain between the forebrain and hindbrain that includes the tectum, tegmentum, and substantia nigra
called also mesencephalon
see brain illustrationExamples of midbrain in a Sentence
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For example, the brainstem’s midbrain reticular nucleus, which is involved in initiating movement, is a fairly underexplored region, Abbasi-Asl said.
—
Amber Dance, Quanta Magazine, 9 Feb. 2026
Heatstroke in particular has been associated with specific types of long-term cognitive impairment, including aphasia, and damage to neurons in the cerebellum, hippocampus and midbrain.
—Nora Bradford, Scientific American, 29 July 2025
The progressive neurodegenerative disorder impacts the area of the brain called the midbrain, which produces the chemical dopamine.
—Angelica Stabile, FOXNews.com, 25 July 2025
Rigid thinkers tend to have lower levels of dopamine in their prefrontal cortex and higher levels of dopamine in their striatum, a key midbrain structure in our reward system that controls our rapid instincts.
—Matt Richtel, New York Times, 8 Apr. 2025
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Amber Dance, Quanta Magazine, 9 Feb. 2026
Heatstroke in particular has been associated with specific types of long-term cognitive impairment, including aphasia, and damage to neurons in the cerebellum, hippocampus and midbrain.
—Nora Bradford, Scientific American, 29 July 2025
The progressive neurodegenerative disorder impacts the area of the brain called the midbrain, which produces the chemical dopamine.
—Angelica Stabile, FOXNews.com, 25 July 2025
Rigid thinkers tend to have lower levels of dopamine in their prefrontal cortex and higher levels of dopamine in their striatum, a key midbrain structure in our reward system that controls our rapid instincts.
—Matt Richtel, New York Times, 8 Apr. 2025
See All Example Sentences for midbrain
Cite this Entry
“Midbrain.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/midbrain. Accessed 15 Feb. 2026.
Copy CitationKids Definition
midbrain
noun
mid·brain
ˈmid-ˌbrān
: the middle division of the three primary divisions of the developing brain of a vertebrate animal or the parts of the adult brain that develop from it that contains the optic lobes and is situated between the forebrain and the hindbrain
Medical Definition
midbrain
noun
mid·brain
ˈmid-ˌbrān
: the middle division of the three primary divisions of the developing vertebrate brain or the corresponding part of the adult brain that includes a ventral part containing the cerebral peduncles and a dorsal tectum containing the corpora quadrigemina and that surrounds the aqueduct of Sylvius connecting the third and fourth ventricles
called also mesencephalon
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