Prorocentroic acid (PA) was isolated from the dinoflagellate Prorocentrum hoffmannianum. Relative configurations for its 35 asymmetric centers were determined by analysis of NMR data including heteronuclear couplings and quantum mechanical calculations. PA was tested by using murine cortical neurons grown on microelectrode arrays. Long-term exposure to subtoxic concentrations induced a significant reorganization of neuronal signaling, mainly by changes in the bursting activity. The observed effects could be due to the activation of a plasticity process.