Cognitive Function

Awareness and thinking are dependent on integrated and organized thoughts, subjective experiences, emotions, and mental processes, each of which resides, to a certain extent, in anatomically defined regions of the brain. Self-awareness requires that the organism senses this personal stream of thoughts and emotional experiences. The inability to maintain a coherent sequence of thoughts, accompanied usually by inattention and disorientation, is the best definition of confusion, a disorder of the content of consciousness.(1)

Alertness is a measure of a patient's awareness of his or her environment and situation. Abnormal states range from confusion to lethargy, delirium, stupor, and at the end of the spectrum, coma. Similarly, orientation is a person's ability to describe knowledge of person, place, and time. Simple questions may be asked, such as the patient's name, where they live, the current date or day of the week, or season of the year to evaluate orientation. Disorientation is frequently associated with organic brain syndromes (e.g., dementia).(2)

Confusion is a behavioral state of reduced mental clarity, coherence, comprehension, and reasoning.(1) Inattention and disorientation are the main early signs; however, as an acute confusional state worsens, there is deterioration of memory, perception, comprehension, problem solving, language, praxis, visuospatial function, and various aspects of emotional behavior, each identified with particular regions of the brain.

Changes in a person's state of consciousness such as confusion, lethargy, and delirium may be caused by many medical conditions including fever, ischemia, trauma, or brain diseases. It may also be caused by suppression of cerebral function from extrinsic factors such as drugs or toxins. Additional potential causes include internal metabolic derangements such as hypoglycemia, azotemia, hepatic failure, or hypercalcemia; and any brainstem lesion that can cause damage to the reticular activating system (RAS). However, if confusion is a feature of a dementing illness, it will become chronic in nature and will manifest as having an effect primarily on memory as opposed to acute confusion. Sometimes what was thought to be a confused state may be more clearly defined as a single cortical deficit in higher mental function such as impaired language comprehension, loss of memory, appreciation of space, in which case each is defined by the dominant behavioral change rather than characterizing the state as confusion.

The confused patient is usually subdued, and not inclined to speak, and is inactive physically. Psychiatrists will sometimes interchange the terms of confusion and delirium, while neurologists tend to keep the two separate, generally using the term delirium to describe a patient who is in an agitated, hypersympathotonic, hallucinatory state, most frequently caused by drug or alcohol withdrawal, or hallucinogenic drugs.

Memory helps to test a patient's ability to recall both past and present information. Memory is generally considered the most common and the most important cognitive ability that is lost. Clinicians may test a patient's memory by asking questions about the history of their present illness or a recent meal. Additionally, they may ask a patient to remember three unassociated words, such as a color, a person's address, and an object, then, later in the interview, ask if the patient can recall what they were asked to remember. These are tests of present or short-term m