Evoked responses. Overused, underused, or misused?

Evolution of Visual Evoked Potentials in Optic Neuritis

The visual evoked potential (VEP) latency was either abnormally prolonged or absent in the involved eye of 47 patients with optic neuritis. Twenty-two of these patients with known multiple sclerosis (MS), had similar abnormalities to 25 patients with no clinical evidence of MS. Follow-up clinical assessment and VEP were done 10 to 42 (mean 22) months later in 34 patients. In 15 of 34 patients with no VEP from the involved eye during initial examination, 6 returned to normal, 8 had prolonged latencies and 1 still had no response at follow up. Of 19 patients who initially had prolonged latencies in the involved eye, 6 returned to normal, 11 had prolonged latencies and 2 had no response at follow up. The VEP is helpful in confirming the diagnosis of ON. The examination must be performed when the patient is symptomatic or soon thereafter as 35% of our patients with an abnormal initial VEP had a normal VEP at follow up. This normalization was not related to the severity of the initial VEP abnormality.

Electroencephalography (EEG) in the differential diagnosis of dementia

Recent technical advances in neurodiagnostic procedures have improved significantly our knowledge of the pathophysiology of a number of disease processes and how they relate to behavioral manifestation. This paper focuses on advances in electroencephalography (EEG) and the implications that this growing body of research has for the diagnosis of suspected brain disorders in older patients.

Amplitude and phase characteristics of the steady-state visual evoked potential

The amplitude and phase characteristics of the steady-state visual evoked potential (VEP) and grating perception were studied for an unbiased group of fifteen healthy female subjects. The variability of VEP data, as obtained by using a digital sweep technique, was high between subjects but relatively low within them. Earlier claims that psychophysical detection thresholds can be predicted from VEP amplitude values were confirmed, whereas no correlation could be established between amplitude values and the perception of suprathreshold contrast. By using a principle of minimum phase difference the importance of VEP phase as an indicator of data reliability and of perceptual encoding processes could also be established.

The influence of height, age and gender on the interpretation of median nerve SEPs

Median nerve SEPs were studied in 120 normal subjects. Highly significant correlations with height and age were found for all SEP peak latencies, but not for the interpeak latency N19-N13. A significant gender difference was found for N13 and N19 peak latencies, the males having longer latencies. No sex-related correlations in central conduction time could be shown. It is emphasized that reliable SEP interpretation should include simultaneous height, age and gender corrections.