The key issue underlying the symptoms of inattention and hyperactivity is an underlying deficit in inhibitory control.

Some people describe the experience of ADHD as being akin to trying to watch four different TV channels all at the one time. Your brain is receiving a whole bunch of information all at once and instead of being able to effectively concentrate on one channel, it ineffectively attempts to concentrate on multiple channels at the one time. Not only is this ineffective, it can become exhausting and unsettling.

ADHD: What Is It