A Napse is a neuron-like enemy inside Bowser's Body in Mario & Luigi: Bowser's Inside Story. They are located in the Energy Hold. It appears to be a cell covered by a ring of dendrites that moves freely around its red rounded body. It will attack Mario or Luigi using electrical discharges that are colored either red, or green. One of its attacks includes summoning two energy balls colored red and green. It will then spin around turning both the red and green balls into blue ones. The energy balls will then hit the respective brother, depending on its former color, so the player needs to keep an eye on the order the Napse has the energy balls. This attack is avoided by jumping. Another one of its attack includes getting red and green energy balls from other Napses around it. Once it has obtained enough, it will shoot the energy balls at the bros. This attack is avoided by jumping. This enemy can also multiply, but not as often as the Airnapse. However, when it multiplies, the Napse loses 1/2 of its remaining health and its duplicate gets the other 1/2 of its remaining health. Napses take extra damage from fire. There is also a special Pixelated Napse that appears in the Memory Banks, organizing and guarding Bowser's memories.
Their name comes from synapse, gaps between neurons in the brain where information is passed through.