Researchers who study the functions of the cortex divide it into three functional categories of regions, or areas. One consists of the primary sensory areas, which receive signals from the sensory nerves and tracts by way of relay nuclei in the thalamus. Primary sensory areas include the visual area of the occipital lobe, the auditory area in parts of the temporal lobe and insular cortex, and the somatosensory area in the parietal lobe. A second category is the primary motor area, which sends axons down to motor neurons in the brainstem and spinal cord. This area occupies the rear portion of the frontal lobe, directly in front of the somatosensory area. The third category consists of the remaining parts of the cortex, which are called the association areas. These areas receive input from the sensory areas and lower parts of the brain and are involved in the complex process that we call perception, thought, and decision making.