A lack of dopamine in the brain is sometimes caused by either diseases such as Parkinson's Disease or even depression.
Other medical conditions can also cause a lack of dopamine in the brain due to the body not producing the amount of dopamine due to the medical conditions.
Not only that but a lack of dopamine can be caused by problems with the receptors in a persons brain.
If you're having a lack of dopamine in your brain you can increase the levels of dopamine in your brain by adding tyrosine and phenylalanine to your diet.
Tyrosine is an amino acid that has a critical role in the production of dopamine that your brain needs.