
So why do we talk about Right Brain and Left Brain? We do have only one brain, but it's got various 'bits'. The part of the brain that controls rational functions, the cerebral cortex, is made up of two halves. These are connected by masses of nerve fibers which allow 'messages' to pass between them. These halves are commonly called the right brain and left brain, but should more correctly be termed 'hemispheres'.

With the left part of our brain, we try to be objective and rational. We can focus on details and analytic facts, and we try to be both reasonable and practical. With the left part, we think things through, using our logic and make conscious decisions. We can relate experiences to both the past and the presence, and we like structures and patterns. We appreciate reality and like to recognize familiar things in the attempt to avoid change. The left part of our brain is responsible for processing numbers, and words, so that’s where we manage for example arithmetics, science, and languages.
Objective & rational. The left part of our brain makes sure we stay objective
Analytical. Objective thinking requires factual information. Anything analytical, like numbers and facts help in getting a clearer picture of a situation.
Conscious. When we think with the left part of our brain, we focus on details and logic.
Conservative. The left part of our brain causes that we are not particularly fond of new things and irregularities.
Structured. The left brain also responds to pattern and clean structures.

The right part of our brain is rather subjective. Instead of making rational and conscious decisions, this part relies on intuition. Our thinking in the right brain is spontaneous and influenced by emotions, such as our mood, or external emotion triggers. With this part of the brain, we use our imagination, fantasy, and personal beliefs to make up our mind. We are willing to take risks and focus on goals rather than the process it takes to get there. We appreciate images and emotional elements, rather than factual information.
Subjective. The right part of our brain is rather subjective and can be triggered with the look and feel of your artwork.
Intuitive. The right brain is intuitive.
Emotional. Our right brain can be activated by emotions, such as our mood or external triggers.
Experimental. The right brain doesn’t think much about consequences and is willing to try new things and engage in unfamiliar actions.
Goal focussed. Rather than thinking about processes, the right brain is concerned with the outcome and it doesn’t mind a complicated path to get there.
Though right-brain or non-verbal thinking is often regarded as more 'creative', there is no right or wrong here; it's merely two different ways of thinking. One is not better than the other, just as being right-handed is not 'superior' to being left-handed. What's important is to be aware that there are different ways of thinking, knowing what your natural preference is, and if it's strongly verbal (left brain) rather than visual (right brain) being open to trying new approaches which deliberately approach painting or drawing in a right-brain way.
With Art Therapy both hemispheres are triggered. On one side the client works from his right brain and on the other side the Art Therapist gives prompts to engage the left brain at the same time. This promotes balance in ways to approach challenges and it also stimulates the healing process of traumas which are stored in the right brain.