Until recently, the transient ischemic attack (TIA) was defined as a picture of a focal neurological impairment lasting less than 24 hours.  In other words, it was basically a case of stroke, whose symptoms disappeared spontaneously after a few minutes or hours.
The current definition is slightly different. According to the American Heart Association and the American Stroke Association (AHA/ASA), the transient ischemic attack, popularly called mini-stroke, is a transient occurrence of neurological abnormality caused by ischemic foci in the spinal cord, brain, or retina, without acute cerebral infarction. 
Explaining in a simpler way, TIA arises when a region of the nervous system, usually these of brain, suffers a relevant, but temporary, reduction in blood flow, which is sufficient to cause ischemia (restriction of blood and oxygen supply), but insufficient to cause cerebral infarction (death of brain tissue). The patient with TIA has symptoms of stroke only for a short period of time, usually not more than an hour. When the blood flow is restored, the symptoms disappear spontaneously.
Symptoms of TIA
The signs and symptoms of TIA depend on the affected artery, the size of the vascularized territory, and the pathophysiological mechanism behind the ischemia. Some features help to direct the investigation:
- TIAs of embolic origin are those whose symptoms take the longest to reverse. More than 80% of TIAs lasting more than 1 hour are of embolic origin.
- TIAs that occur under a low flow of the carotid artery usually last a few minutes but can occur repeatedly (once a week or even several times a day).
- Lacunar TIAs usually take less than 1 hour and can also appear repeatedly. Lacunar strokes are usually preceded by repeated episodes of lacunar TIA.
The symptoms of a transient ischemic attack may be slightly different from person to person, but they are always short-lived. In most cases, symptoms last less than an hour, but can last up to 24 hours.
Possible warning signs of TIA are below.
Difficulty Speaking or Articulating Words (Aphasia)
The aphasia is defined as a language disorder affecting a person’s ability to communicate.  It usually happens due to an injury or stroke, but it can also develop gradually, in the care of TIA.
People who have mild stroke (TIA) often find it difficult to talk properly or articulate words. This type of injury can affect the left cerebral hemisphere, responsible for the ability to speak, read, write and understand. But each of these aspects of language is located in a different part so all of this cognitive ability may not be affected.