The islands of Calleja (Spanish: [kaˈʎexa]; IC, ISC, or IClj) are a group of neural granule cells located within the ventral striatum in the brains of most animals.

The insula magna, or the major island, of these complexes is located in the medial border of the nucleus accumbens.

Most members of the FOX proteins are typically involved in the formation of certain structures of an embryo, where mutations in these genes are evident through the human developmental disorders that result.

Some of the islands contain a "core" of neuropil, or unmyelinated axons and dendrites, filled with a large cell in some cases.

The islands of Calleja receive inputs from the back of the amygdala, which processes emotional memory,[2] as well as the septum, nucleus accumbens, and piriform cortex.

[5] The islands also receive information in the form of dopamine from the substantia nigra and ventral tegmental area, located in the midbrain of the brainstem.

By receiving dopamine inputs from the substantia nigra and the ventral tegmental area, the islands become one of the many regions that process the rewarding feelings associated with this neurotransmitter.

Opioids and amphetamines take advantage of the reward pathways in that they influence greater releases of dopamine and other neurotransmitters that reinforce the feelings associated with the administration and effects of the drugs.

The islands of Calleja region is the preferential binding site for cariprazine withinin the mouse striatum, a drug known for its strong antipsychotic and antidepressant efficacy.

[20] In rodents, the islands play a role in reproduction due to the neurons' estrogen-binding capacity and the structure's ability to concentrate estradiol.