Attention deficit hyperactivity disorder (ADHD) is a cognitive and behavioral condition that is thought to arise due to biochemical differences and/or connection problems in the so-called "executive functioning" center(s) in the brain. These areas are not yet fully structurally defined or localized, but most recent studies using functional MRI scans and other new modalities suggest that one key area in the prefrontal cortex. Symptoms vary among children but can include: poor concentration, difficulty focusing on tasks, fidgeting or increased movement, poor sleep, and difficulty organizing and prioritizing tasks. Coexistent learning "disabilities" and vision, hearing, and/or speech conditions must be tested for and excluded. Treatment consists of individualized therapy that includes behavioral strategies, strengthening communication between parents and teachers and pediatricians, addressing possible coexistent mental health issues and learning challenges, and sometimes the use of medication.