Referred to: The author is referring to the complexity of the human brain and its functioning.

Why does the author say so?
The author says so because the human brain is an incredibly complex organ that controls all bodily functions, thoughts, emotions, and behaviors. The brain is composed of billions of neurons that communicate with each other through chemical and electrical signals. The brain also has different regions that are responsible for specific functions, such as memory, language, and vision. The way the brain processes information and controls behavior is not fully understood, and there is still much to learn about this complex organ.

Details:
The complexity of the human brain can be understood from the following points:

- The brain is composed of billions of neurons that communicate with each other through chemical and electrical signals.
- The brain has different regions that are responsible for specific functions, such as memory, language, and vision.
- The way the brain processes information and controls behavior is not fully understood.
- The functioning of the brain is influenced by various factors such as genetics, environment, and experience.
- The brain is capable of learning, adapting, and changing throughout life.
- The brain is also responsible for regulating bodily functions such as heart rate, breathing, and digestion.
- Neurological disorders such as Alzheimer's disease, Parkinson's disease, and schizophrenia are a result of dysfunction in the brain.
- Studying the brain and its functioning is a challenging task that requires interdisciplinary fields such as neuroscience, psychology, and biology.

In conclusion, the complexity of the human brain and its functioning can be mind-boggling. Despite years of research, there is still much to learn about the brain. Studying the brain is crucial for understanding neurological disorders and developing treatments for them.