Event-related potentials (ERPs) are an objective measure of brain response to a specific sensory, cognitive, or motor event. This test is useful in evaluating persons with dementia or decreased mental functioning. It is also helpful in differentiating persons with real organic brain defects affecting cognitive function from those who are unable to interact with the examiner because of motor or language defects or those unwilling to cooperate because of problems such as depression or schizophrenia.

These measurements use an EEG and the method of auditory EP testing in which sound stimuli are transmitted through earphones. A rare tone is associated with a prominent endogenous P₃ component that reflects the differential cognitive processing of that tone. Although a systematic neurologic increase in P₃ component latency occurs as a function of increasing age in normal persons, in many instances of neurologic diseases associated with dementia, the latency of the P₃ component has been reported to exceed substantially the normal age-matched value.

1. This procedure is the same as that for BAEP.

2. Ask patients to count the occurrences of audible rare tones they hear through the earphones.

3. Follow guidelines in Chapter 1 for safe, effective, informed intratest care.

An increased or abnormal P₃ latency is associated with neurologic diseases producing dementia, such as the following:

1. Alzheimer disease

2. Metabolic encephalopathy such as that associated with hypothyroidism or alcoholism with severe electrolyte disturbances

3. Brain tumor

4. Hydrocephalus

Pretest Patient Care

1. Explain the purpose and procedure of the test.

2. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Latency of P₃ component normally increases with age.

Normal

• No shift of P₃ components to longer latencies

• ERP: Absolute latency of P₃ waveform

• P₃ wave mean and SD 294 ± 21 msec