The reproducibility of binocular pattern reversal visual evoked potentials: a single subject design.

This study aimed to investigate the within-participant variability over time of both amplitude and peak latency measures of pattern reversal visual evoked potentials (pVEPs). As a large number of factors are known to contribute to the variability of the pVEPs (such as fixation instability and drowsiness), testing was conducted in controlled conditions with two co-operative participants. PVEPs were recorded during 24 sessions, over an eight-week period using the same equipment and recording settings. The participants viewed a plasma monitor binocularly from a distance of 1 meter. High contrast (97%), black and white checks of side subtense 50', 25', and 12.5' pattern reversed 3/s in a 28 degree test field. The different sized checks were presented in a pseudo-random order. Three runs, each of 100 trials, were acquired to each stimulus from an active electrode placed at Oz referred to aFz. The amplitude of N80-P100 and the latency of P100 were measured. P100 amplitude and latency were stable across sessions and did not depend upon the order of check size presentation. As expected, variation in amplitude was greater than peak latency. The coefficients of variation for different check sizes and participants were 9-14% for pVEP amplitude, but only 1-2% for P100 latency.

When do asymmetrical full-field pattern reversal visual evoked potentials indicate visual pathway dysfunction in children?

Our study aimed to find out the association between full-field pattern reversal visual evoked potential (pVEP) transoccipital asymmetries and half-field pVEP transoccipital distributions in children. Over a six-month period, 46 patients (mean age: 9 years 9 months) had both monocular full-field and half-field pVEPs to test checks subtending 50 min of arc in a 35 degree full-field and 0-17.5 degree lateral half-field. Silver-silver chloride electrodes placed at Oz, O1 and O2 were referred to Fz. Monocular full-field data were categorised according to the degree of transoccipital asymmetry. Half-field data were measured and summated to see whether they explained any full-field asymmetry. In this cohort of 46 patients, eight (17%) patients had symmetrically distributed monocular full-field pVEPs for each eye. Four of these patients had normal half-field pVEP distributions for each eye, but the other four showed a half-field deficit in one or both eyes. Of the 38 patients with asymmetrically distributed full-field pVEPs in at least one eye, 17 (44%) patients showed a half-field deficit, 20 (53%) showed responsive, but symmetrically distributed half-field responses, and one patient (3%) showed typical half-field distributions. Half-field pVEPs can help explain full-field asymmetries and should be attempted in any child able to co-operate with testing and in whom visual pathway dysfunction is suspected.

A study of intensity dependence of the auditory evoked potential (IDAEP) in medicated melancholic and non-melancholic depression.

BACKGROUND: Major Depressive Disorder is widely recognised to be a heterogeneous syndrome with numerous depressive phenotypes, one of which is melancholic depression. Patients with melancholic depression exhibit treatment responses and outcomes that differ from patients with non-melancholic depression. The current study aimed to assess whether differences existed between melancholic and non-melancholic subtypes of depression, as measured by the event related potential, intensity dependence of the auditory evoked potential (IDAEP). METHODS: IDAEP was assessed in 14 melancholic and 13 non-melancholic depressed subjects and 14 controls. RESULTS: The melancholic patients had a significantly shallower IDAEP slope than the non-melancholic patients not explained by depression severity or age. LIMITATIONS: Antidepressants were taken by all patients in this study and the effect of continual use of these drugs on the IDAEP slopes has yet to be confirmed. CONCLUSIONS: These results provide support for neurobiological differences between melancholic and non-melancholic depressive subtypes. Melancholic depression may be characterized by ongoing over function of the serotonin system in spite of medication treatment.