Ketamine acts on a wide range of brain receptors. At low doses, it is most likely to affect a family of glutamate receptors called NMDA receptors (located in your limbic system, which is responsible for learning, memory, and emotional regulation). After glutamate has activated the NMDA receptor, it opens a channel for the flow of positively-charged ions. Ketamine blocks the channel, preventing the neuron from being excited. Now, instead of exciting a neuron, a neurotransmitter may be inhibitory. It opens channels for negatively-charged ions, making the neuron less likely to spike. NMDA receptors are found on a lot of neurons that release inhibitory neurotransmitters. By interfering with the excitement of these neurons, ketamine has the counterintuitive effect of increasing neuronal activity.