Junctophilins contribute to the formation of junctional membrane complexes (JMCs) which link the plasma membrane with the endoplasmic or sarcoplasmic reticulum in excitable cells. Provides a structural foundation for functional cross-talk between the cell surface and intracellular calcium release channels. JPH4 is brain-specific and appears to have an active role in certain neurons involved in motor coordination and memory. Localized predominantly on the plasma membrane. The transmembrane domain is anchored in endoplasmic reticulum membrane, while the N-terminal part associates with the plasma membrane (By similarity). Specifically expressed in brain. Highest levels in the olfactory tubercle, caudate putamen, nucleus accumbens, hippocampal formation, piriform cortex and cerebellar cortex. Expressed in disctete neurons sites. In hippocampal formation, expressed in dendrites of hippocampal pyramidal and denate granule cells. In cerebellum, it is highly expressed in Purkinje cells, while it is weakly expressed in granular cells. The MORN (membrane occupation and recognition nexus) repeats contribute to the plasma membrane binding, possibly by interacting with phospholipids. Jph3 and Jph4 double null mutants exhibit atypical depolarizing responses, irregular cerebellar plasticity due to abolished crosstalk in Purkinje cells. There is hyperphosphorylation of PRKCG and mild impairment of synaptic maturation. Exploratory activity, hippocampal plasticity and memory are impaired and there is abnormal foot-clasping reflex. Due to intron retention. Belongs to the junctophilin family.