HTR6 and psychiatric disorder: Unlike other serotonin receptors found throughout the body, the 5-HT6R expression is restricted to the central nervous system where it shows the highest densities in brain regions involved in higher-level cognitive functions, such as the striatum, hippocampus, and prefrontal cortex, making it an attractive target for the treatment of cognitive deficits associated with several psychiatric disorders of neurodevelopmental origin, as well as of neurodegenerative diseases.