Figure 1. Brodmann areas. Image Courtesy of Flickr under Creative Commons license
Cytoarchitecture
Korbinian Brodmann was the first to map the cortex according to the cell types present, identifying 52 separate regions named Brodmann’s areas. Thanks to new scientific techniques like fMRI, it is now apparent what functions each area has. The areas are on the gyri and separated by the sulci. This website highlights the most significant of them.
Somatosensory
Brodmann’s areas 3, 1 and 2 are all situated on the post central gyrus of the parietal lobe, otherwise known as the primary somatosensory cortex. The neurons here have sensory functions in touch and kinaesthesia. Areas 5 and 7 are the somatosensory association areas, posterior to the post central gyrus. The primary somatosensory cortex can be represented as a sensory homunculus, with more neurons within this area of cortex relating to hands, lips and tongue as the neurons are more active; whilst relatively fewer neurons relate to legs and arms.
Motor
Brodmann area 4 on the precentral gyrus, is the primary motor cortex. This area is involved in controlling voluntary movements of the body and the neurons are arranged somatotopically, as illustrated by the motor homunculus first described by Wilder Penfield. The neurons in this area of cortex contralaterally innervate the motor nuclei of the cranial nerves and lower motor nuclei. Brodmann area 6 is the pre-motor cortex and is responsible for the control of movement of proximal and trunk muscles of the body, as well as storing memory of learned movements. Brodmann areas 44 and 45 are also known as Broca’s area. This region of cortex, located on the inferior frontal gyrus, is involved in motor aspects of speech including production.
Visual
Brodmann’s area 17 is the primary visual cortex, situated on the posterior edge of the occipital lobe. This area receives input from both eyes via the lateral geniculate nucleus, represented in a retinotopic map. Information from here is transmitted through two pathways: the dorsal stream goes from V1, the primary visual cortex, to the visual association area, V2, and then onto V5 and Brodmann’s areas 5 and 7. This pathway is necessary for understanding where objects are in relation to other objects and the body, also called the “Where Pathway”. The ventral stream goes from V1 to V2 and then to V4 and the inferior temporal cortex. This pathway is described as the “What Pathway”, important in recognition of objects.
Auditory
Brodmann’s area 41 is the primary auditory cortex and is situated in the posterior of the superior temporal gyrus. This area of cortex has functions in processing sound information, as different neurons within the cortex recognise different frequencies of sound. Area 42 is the secondary auditory area involved in the recognition of speech, whilst areas 21 and 22 are the auditory association areas.
Personality
The idea of a personality is an abstract concept; however there are areas of the cortex involved in making us the way we are. Anterior to the prefrontal cortex, Brodmann areas 9, 10 and 11 are concerned with biological intelligence. This area is therefore implicated in mediating intellect, cognition, reasoning, judgement, attention, planning and conscience. It also has links to the limbic system for control of emotion. Brodmann area 8, the prefrontal cortex, is involved uncertainty and expectation, thus hope may originate here.
Did You Know…
There are 538 million cells in the primary visual cortex, Brodmann area 17
Did You Know…
41% of the total cerebral cortex volume is found in the frontal lobe, whilst only 18% is found in the occipital lobe
Figure2. Sensory Homunculus. Image courtesy of Flickr under Creative Commons license