Impulse control is managed by the brain's inhibition pathway, primarily located in the right inferior frontal gyrus of the prefrontal cortex. When a neurotypical person feels the urge to speak out of turn, this region sends an inhibitory signal that blocks the motor action of speaking. In ADHD, dopamine deficiency means this inhibitory signal arrives late—often a fraction of a second *after* the words have already left your mouth.
Secondly, the ADHD working memory (the 'mental scratchpad' managed by the dorsolateral prefrontal cortex) is severely bottlenecked. It can usually hold only a few chunks of information at once. When listening to someone speak, the buffer is full. If an original thought arises, the brain faces a crisis: overwrite the original thought (forget it) or stop listening to hold onto it. The brain chooses to dump the thought out loud to clear the buffer.
Finally, sensory hyper-reactivity plays a role. An ADHD brain processes the speaker's tone, the end of their sentence, and their body language much faster. The ADHD person often predicts the end of the sentence before the speaker gets there. The brain, craving stimulation, becomes bored waiting for the inevitable conclusion and "jumps the gun" to move the conversation to the next hit of dopamine.
