The<unk>  was previously subdivided into primary (A1) and secondary (A2) projection areas and further association areas. The modern divisions of the<unk>  are the core (which includes primary<unk> , A1), the belt (secondary<unk> , A2), and the parabelt (tertiary<unk> , A3). The belt is the area immediately surrounding the core; the parabelt is adjacent to the lateral side of the belt. Besides receiving input from the ears via lower parts of the<unk>  system, it also transmits signals back to these areas and is interconnected with other parts of the cerebral cortex. Within the core (A1), its structure preserves tonotopy, the orderly representation of frequency, due to its ability to map low to high frequencies corresponding to the apex and base, respectively, of the cochlea. Data about the<unk>  has been obtained through studies in rodents, cats, macaques, and other animals. In humans, the structure and function of the<unk>  has been studied using functional magnetic resonance imaging (fMRI), electroencephalography (EEG), and electrocorticography. Development Like many areas in the neocortex, the functional properties of the adult primary<unk>  (A1) are highly dependent on the sounds encountered early in life. This has been best studied using animal models, especially cats and rats. In the rat, exposure to a single frequency during postnatal day (P) 11 to 13 can cause a 2-fold expansion in the representation of that frequency in A1. Importantly, the change is persistent, in that it lasts throughout the animal's life, and specific, in that the same exposure outside of that period causes no lasting change in the tonotopy of A1. Sexual dimorphism within the<unk>  can be seen in humans between males in females through the planum temporale, encompassing Wernicke's region, for the planum temporale within males has been observed to have a larger planum temporale volume on average, reflecting previous studies discussing interactions between sex hormones and asymmetrical brain development.
Auditory cortex
Barrel cortex
Postrhinal cortex
Language center
Olfactory tract
Brodmann area
Optic stalk
Olfactory trigone