Discoveries at the turn of the 19th century were the beginning of conceptual compartmentalization of cerebral functioning, starting with the 2 lobes of the cerebrum. This set the stage for the era of brain localization: identifying which parts of the brain handled different processes.
In the mid-19th century, French physiologist Pierre Flourens lobotomized pigeons and rabbits to investigate localization. He concluded that the cerebrum was responsible for higher mental functioning, the cerebellum handled balance and motor coordination, and the medulla nominally managed autonomic systems, including circulation and respiration.
Flourens also found that destroying the brainstem (medulla oblongata) resulted in certain death. He also showed that the brain could reorganize itself. In doing so, Flourens proved that strict localization could not be the correct impression of mental processing. Flourens failed to pinpoint specific regions for cognition and memory, leading him to believe that this processing was diffused.
Also in the mid-19th century, French anatomist Paul Broca was an early proponent of brain mapping, and a firm believer in strict localization. His mistaken belief arose after studying the brain of a man who lost the ability to speak after suffering from a brain lesion but could still understand speech.
With rare exception, in the 19th century, and for more than half of the 20th century, scientists believed that brain areas were so specialized that one area dedicated to sensory input processing could never do the work of another.
Extending the concept of the central and peripheral nervous systems being not only structurally but also functionally different, the senses were considered localized receptors, with each sense sending its signals to a specific part of the brain for processing.