The midbrain, also known as the mesencephalon, activates in response to specific stimuli. It responds both to signals from within the body and to external events. Research on midbrain activation looks at which areas of the brain respond to given stimuli and how these play a role in learning and other activities that require more complex brain activity. People with a particular interest in this subject can apply to participate in brain studies, where researchers scan the brains of their subjects while they are exposed to various stimuli.
This section of the brain is part of the brainstem, located between this structure and the higher level cortexes responsible for critical thinking, language, and other complex activities. Signals from the higher and lower brain pass through the midbrain, activating it as they move through so the neurons can determine where to route the information. Midbrain activation can also directly control some processes, like eye movements and the physiological processes involved in arousal.
When stimuli occur inside the body, a cascade of neurotransmitters sends the signal through the brainstem to the midbrain, where it decides what to do with the information. It can pass it on to another area of the brain or take action to directly regulate a process like internal temperature control. The midbrain also activates in response to external stimuli like sights and sounds, processing the information and bundling it to an appropriate location elsewhere in the brain.
This structure plays a role in associative learning, and research suggests that subjects respond more strongly to certain kinds of stimuli than to others, exhibiting selective midbrain activation. This may reflect the history of the human race, which would have needed to be especially attuned to stimuli that might be dangerous. The ability to process and respond quickly to information like an approaching predator would have allowed early humans to survive, passing on their genes to the next generation.
Some mental illnesses, particularly schizophrenia, appear to interfere with midbrain activation. This can play a role in the development of hallucinations, delusions, and other phenomena experienced by people with mental illness. The provision of medications to such patients can help normalize their neurotransmitters to suppress such experiences by controlling the pathways involved in midbrain activation and other neurological processes. Variable success on medications among psychiatric patients occurs because each brain is slightly different, and the medications may affect patients in different ways as a result.