Within the skull, the cerebrum, which is divided into two hemispheres, occupies the uppermost region. The hemispheres are demarcated by a deep groove referred to as the longitudinal cerebral fissure and are each further divided into an inner core of white matter and an outer layer known as the cerebral cortex. The location of most activity in the cerebrum, the cerebral cortex is itself organized into six layers, which interact with one another via vertical columns of neurons. Some types of brain activity are associated with a single layer in the cerebral cortex, but most functions are believed to be controlled interactively. However, each hemisphere of the cerebrum is commonly linked with specific actions. For instance, the left hemisphere is associated with logic, reasoning, language, and numbering, while the right side of the cerebrum is more heavily involved with creativity, facial recognition, and depth perception.