Galen of Pergamon ( 129 AD - 210 AD) was one of the most important figures in classical medical science. Galen's achievements in neuroscience were great and long lasting.
For Galen , the main point of brain anatomy was the ventricles. He stated that the central function of them was to produce and distribute psychic pneuma , the vital force throughout the nervous system. Except for that , he also gave an explanation for all the functions of the nervous system ( both intellectual, motor and sensory) . Hence, he emphasized that all these functions were due to psychic pneuma, which is a prerequisite for life and enters when the inspired air from the lungs goes to the left ventricle of the heart where it is changed to vital pneuma. This is then distributed through the arterial system to enter all parts of the body including the brain through two vascular structures. These two structures are: rete mirabile = network of fine arteries lying at the base of the brain and choroid plexuses.
Galen felt that the vital spirits were converted in the rete mirabile into animal spirits that were stored in the cerebral ventricles and then went into the hollow nerves to produce movement and sensation. He developed a concept of localization of mental activity. His concept was that imagination, reason and memory were the three intellectual functions that could be affected separately.
In the field of neuroanatomy Galen described cranial nerves, such as corpus callosum, the tectum, the formix, the epiphysis of pineal body, the sympathetic chain and posterior roots of the spinal nerves. He also defined the recurrent laryngeal nerve characterizing it as vocal nerve. Not only he described the ventricular system of the brain as the seat of the psychic spirit, but also he studied extensively the function of spinal cord, focusing its importance on the movement of the body.
Brain plays an important role in the homeostatic equilibrium of the soul.The psychic spirit ( pneuma) according to Galen resides in the ventricles of the brain. It is the psychic pneuma which accounts for sensation and voluntary motion. Responsible for the cognition, the perception and the memory is the brain. The mental and psychical health of the human being is based on the equilibrium and the harmonious relationship between the three parts of the soul, which are the brain, the heart and the liver.
Galen characterized motor nerves coming from the posterior part of the brain as hard and sensory nerves from the the anterior part as soft. He thought that the anterior part of the brain is the seat of perception and reason, though the posterior plays a a major role in the life and vegetative function of the man. According to him, the brain is the hegemonikon, the principal organ which rules and controls all the functions and activities of the human body.