A traumatic brain injury (TBI) refers to a brain injury that is caused by an outside force. TBI can be caused by a forceful bump, blow, or jolt to the head or body, or from an object entering the brain. Not all blows or jolts to the head result in TBI.
Head injuries have the capacity to alter behavior, and those changes depend on the severity and number of injuries. Short-term changes include feeling dizzy, confused, and exhausted. An injured person could have a headache, nausea, blurred vision, ringing in the ears, and sensitivity to light and sound.
People who suffer a TBI may lose the ability to concentrate as intently as they did previously, which may manifest at work, in conversations, or in household tasks. They may struggle to remember events or facts. Personality may shift as well: One may become more irritable, angry, or impulsive, or less able to exercise self-control. TBI sufferers may struggle with depression and anxiety, as well as sleep disturbances.
Repeated concussions can lead to Chronic Traumatic Encephalopathy (CTE).
A 2013 study that followed 1.4 million Danish citizens found that individuals with TBI were four times more likely to develop a mental illness. People who received a TBI were 65 percent more likely to develop schizophrenia, 59 percent more likely to develop depression, and 28 percent more likely to develop bipolar disorder.
Another study found that experiencing depressive symptoms after a head injury is more common than not; the prevalence of depression after TBI was greater than 50 percent. Yet another found that people who received a concussion in the past were three times more likely to die by suicide.
https://www.psychologytoday.com/us/basics/traumatic-brain-injury