Cognitive deficits that can follow TBI include impaired attention; disrupted insight, judgement, and thought; reduced processing speed; distractibility; and deficits in executive functions such as abstract reasoning, planning, problem-solving, and multitasking. Memory loss, the most common cognitive impairment among head-injured people, occurs in 20–79% of people with closed head trauma, depending on severity. People who have suffered TBI may also have difficulty with understanding or producing spoken or written language, or with more subtle aspects of communication such as body language. Post-concussion syndrome, a set of lasting symptoms experienced after mild TBI, can include physical, cognitive, emotional and behavioral problems such as headaches, dizziness, difficulty concentrating, and depression. Multiple TBIs may have a cumulative effect. A young person who receives a second concussion before symptoms from another one have healed may be at risk for developing a very rare but deadly condition called second-impact syndrome, in which the brain swells catastrophically after even a mild blow, with debilitating or deadly results. About one in five career boxers is affected by chronic traumatic brain injury (CTBI), which causes cognitive, behavioral, and physical impairments. Dementia pugilistica, the severe form of CTBI, affects primarily career boxers years after a boxing career. It commonly manifests as dementia, memory problems, and parkinsonism (tremors and lack of coordination).