you have two types of cells in your brain, neurons and glia. neurons transmit nerve impulses using neurotransmitters. glial cells are support cells. they provide nutrition and produce myelin for the neurons. you have about ten times as many glial cells as neurons.
glioma is a cancer caused by a mutation in glial cells. THC has been shown to inhibit growth of these cancer cells. THC has never been shown to cause damage to any healthy brain cells.