Hippocalcin is a neuron-specific calcium-binding protein found primarily in the plasma membrane of brain and retinal tissue, with increased expression observed in hippocampal pyramidal cells. Through its calcium-dependent signal regulation, hippocalcin can both inhibit rhodopsin kinase and increase phospholipase D2 expression. In order to regulate kinase and phospholipase activity, hippocalcin must bind to the plasma membrane where it can then bind two calcium ions for use in signal regulation. The hippocalcin protein is highly conserved in mouse, rat and human tissue and has a suggested role in neural plasticity and associative memory by contributing to the survival of neurons during aging. The loss of hippocalcin expression is thought to contribute to age-related impairment of post-synaptic functions related to neuronal degradation.