We can think of the brain as consisting of 3 main parts.

The brainstem, limbic system, and neocortex which developed in the following order:

The first is the brainstem which is the oldest part of the brain. It developed about 350 million years ago.
It’s responsible for basic survival functions such as breathing, heart rate, and blood pressure.
These functions are essential for life, but they are not dependent on higher-order functions such as thinking or consciousness.

Next is the limbic system which sits in the middle in both age and location in the brain.
It developed about 200 million years ago, and is responsible for our emotions, memory, and behaviour.
While these functions are important for survival, they are not as essential for life as the functions of the brainstem.

Finally, the neocortex. This is the newest part of the brain.
It developed about 100,000 years ago and is responsible for higher-order functions such as thought, language, and consciousness.
Now, whilst these functions are not essential for life or survival, they are what makes us human.

Of the 3 parts, because it is responsible for emotions, memory, and behaviour, the Limbic system is  a very powerful motivator in getting us to do things or avoid doing things. So it’s responsible for many of the mental health and wellbeing issues we have today such as anxiety/panic attacks, stress, depression, addictions, PTSD and phobias, even weight control. In understanding this we are better equipped to change the way we think and thereby change how we feel and in so doing we can climb out of the fog of depression or release ourselves from the grip of anxiety/panic attacks etc.