Islands of Calleja

The islands of Calleja (kaˈʎexa; IC, ISC, or IClj) are a group of neural granule cells located within the ventral striatum in the brains of most animals. This region of the brain is part of the limbic system, where it aids in the reinforcing effects of reward-like activities. Within most species, the islands are specifically located within the olfactory tubercle; however, in primates, these islands are located within the nucleus accumbens, the reward center of the brain, since the olfactory tubercle has practically disappeared in the brains of primates. Both of these structures have been implicated in the processing of incentives as well as addictions to drugs. Projections to and from the islands supplement this knowledge with their involvement in the reward pathways for both cocaine and amphetamines. The islands of Calleja are specifically located within the ventral and medial lining of the ventral striatum in the brain, meaning that they lie towards the front and middle of this region within the temporal lobe. The insula magna, or the major island, of these complexes is located in the medial border of the nucleus accumbens. The ventral group of the islands lies along the pial border of the basal forebrain, a region of the frontal lobe that lies adjacent to the temporal lobe. Due to high concentrations of nitric oxide synthase, an enzyme that makes nitric oxide and includes another enzyme known as NADPH-diaphorase, the islands can be visualized via NADPH-diaphorase staining. Using this method, the islands have been suggested to be a single heterogeneous cell complex. The exact grouping of these structures is unique across species; however, the shaping of the structures is not the same across the hemispheres of the brain. The islands of Calleja are named after Julián Calleja y Sánchez, the Spanish anatomist, who studied the structure prior to publishing a paper in 1893 entitled "La región olfatoria del cerebro" ("The olfactory region of the brain"). Although the structure was named after him, Calleja was not the first to study it.