PATTERN SHIFT VISUAL EVOKED RESPONSE APPLICATION IN NEUROLOGY

An evoked response (ER) or evoked potential ( E P) is an electrical response of the brain to a visual, auditory or somatosensory stimulus. The transient electrical event recorded at the scalp in response to a visual stimulus of shifting pattern of squares is named pattern shift visual evoked response (PSVER). The PSVER has been studied in a large group or normal controls and patients with neurologic diseases. With the development of more stable stimulation techniques, powerful amplifiers and computers able to sum and average the evoked potentials and exclude the background noise ( E E C, muscle artifacts) the ER became clinically useful. The long latency components of the ER, appearing more than 75 milliseconds (msec) after stimulation has a relatively large amplitude (5-50 microvolts) and varies with many psychological parameters, such as attention and state of consciousness. However, the PSVER is the long latency response with the highest degree of wave form consistency and stability. We discuss the PSVER, a non-invasive clinical test, emphasizing the basic procedure, the normal responses, the pathophysiology, the abnormal findings, the indications and the value of the test. TECHNICAL CONSIDERATIONS The patient sits one meter from a TV monitor and fixates on a small dot in the center of the screen where an alternating checkerboard pattern of black and white squares is seen. The patient wears his usual glasses. Each eye is tested separately, with a patch placed over the opposite eye. Scalp electrodes are placed in the occipital region at 0, 0 and 0 (international 10-20 system) with a vertex reference (CZ). Linked ears are used as an alternative reference. Electrodes are attached to the scalp with collodion and electrolytic paste is used to maintain impedances below 6000 ohms