Cannabis slows down the speed of neurotransmission, exposing the cerebral cortex to fewer slower moving neural stimuli. This allows the higher centres of the brain to more rationally assess relative danger or the negativity and put a more rational point of view on that sensory input, often taking the edge off anxiety or preventing a panic attack.
In medical school, doctors are taught 70% of the brain exists to turn off the other 30%. Dopamine is one of the “off switches” that helps modulate sensory input. One suggestion is that Cannabis and cannabinoids increase the amount of free dopamine in the brain by preventing the dopamine from binding to another neurochemical dopamine transporter. The transporter and dopamine form an electrochemical bond that ties up the dopamine so that it is not free to act as an “off switch”. These cannabinoids replace the dopamine and the amount of free dopamine available to depolarise the presynaptic neuron also increases.