when discussing his relationship with his wife amber, travis says, "i have this very strong sense of commitment and tranquility." researchers have suggested that the neurophysiological basis of this feeling may be due to brain chemicals related to

Morphine

Explanation: Morphine is a medicational drug that is used for the relieving the pain of the body under the prescription.It is prescribed to be taken in limited amount otherwise overdose cause cause serious damage to the body.

According to the neurophysiology, morphine can affect the brain by inducing plasticity.Thus, the Travis is stating about his calmness and commitment feeling in his mind.