Nausea and vomiting are common upper gut complaints in patients. Nausea is defined as an unpleasant painless sensation frequently before vomiting but not always. It is associated with changes in gut nervous system which can cause associated sensations of sweating, rapid heart rate, and fainting. Nausea may serve as an early gut warning system. It is not pain but can be associated with pain. Nausea is also associated with motion sickness.

Nausea and vomiting are different. Nausea requires conscious perception in the higher brain while vomiting can occur even if unconscious due to hard wired reflexes in the brain stem. There are animal models for vomiting which are well studied but no great animal models for nausea because it is a subjective conscious perception so only humans can accurately report it to other humans. As a result, much less is known about nausea. There are multiple medications which are effective for vomiting prevention but many of those medications are far less effective for nausea.

Nausea and Vomiting inputs come from various parts of the body such as the gut, inner ear for balance, heart which feed into the brain stem and a place called the nucleus tractus solitarius and then into the upper brain- the cortex and parts of that within the brain.

Some of Dr. Kuo’s important research was to study brain activation changes with magnetic resonance imaging in human when they were induced to have nausea with a visual stimulus of moving black and white stripes. The areas of the brain that were activated included the amygdala, dorsal pons and locus ceruleus when the nausea sensation started to happen. As nausea got worse, areas such as the anterior cingulate cortex and insula began to activate in patterns similar to pain even though the subjects were not experiencing pain. This suggested that nausea can activate the same areas in the brain as pain and maybe can be treated in the same manner.

Nausea is a combination of sensations feedback from the gut and other places such as the heart and lungs which are all controlled but the visceral autonomic nervous system which are further interpretated and modulated by the brain. This requires a threshold of stimulation for mental awareness of the sensation of nausea which can be variable between people as well as being variable within a person depending on the situation and condition of that patient.

Evaluation of nausea requires a careful history regarding timing and triggers. Many medications can also cause nausea. Neurology and gut evaluations can be helpful to rule out causes but most of the time these evaluations are normal.  There is a definition for Functional Idiopathic Nausea in which the bothersome nausea occurring several times a week in the absence of other causes. Treatments can include medications which decrease vomiting (anti-emetics), medications to increase gut emptying and medications to change the nerve ending sensitivity of the gut and brain towards nausea. Alternatives may include the use of acupuncture, hypnosis and cognitive behavioral therapy or cannabis.