When the heart is the organ involved in a heart disease, brain is the organ involved in a mental illness. In the mental illness, certain parts of brain are damaged, resulting in symptoms involving cognitive function, content of thought, perception, emotion, behaviour and biological function (e.g. sleep and appetite), and impaired overall functioning of the person. Like many illnesses in other organs, there are effective evidence-based treatments for mental illness. With advent of neuroscience, the treatment of mental illness has been advancing over the past decades, particularly in pharmacological treatment.

You can refer to the following website.

What is a mental illness?

The source of information is provided by the Hospital Authority Castle Peak Hospital