One of the challenges for any theory of consciousness is to explain how minute dosages of an anesthetic can produce such distorted experiences. Under the influence of the drug, a volunteer describes his greatly altered experience, highlighting how his visual and auditory senses interact and even meld. Normally, input from the senses impacts the brain. The drug ketamine weakens the signals coming from the senses and replaces them with a jumble of activity spontaneously generated in the brain. This activity produces the hallucinations. Volunteers have undergone brain scans while they are hallucinating. Over several minutes, the scans have indicated slight changes in activity in the front of the brain. However, consciousness is too fleeting for the underlying subtle and transient changes in brain cell activity to be detected by such an approach. Vollenweider suggests that ketamine directly interferes with communication between nerve cells. Sometimes communication is even blocked. The drug may lead to new assemblies between nerve cells so that a different neural network gets established.