The contrast response functions (CRF) of pattern-appearance and motion-onset VEPs for periodic stimuli (gratings) were compared. The CRF for pattern-appearance is accelerative for the P100 component and compressive for the N200 component. Contrary to these results, the CRF for motion-onset shows an almost negligible slope for both components within the contrast range tested (0.5-64%). To better isolate the neural contributions to these different VEP components, we studied the effects of prior adaptation to stationary and moving gratings. Adaptation to stationary gratings has no effect on both VEP components for motion-onset and the P100 component for pattern-appearance, but did reduce the amplitude of the N200 for pattern-appearance. Adaptation to slow (1 deg/s) and fast (4 deg/s) gratings left the P100 amplitudes unaltered, while it significantly reduced the N200 amplitudes for both pattern-appearance and motion-onset. These results suggest that the N200 component of the motion-onset VEP is generated by motion-dependent neurons, whereas the same component for pattern-appearance arises from contrast-dependent neurons. The observed differences between P100 and N200 components appear to reflect the activity of both transient and sustained neural mechanisms.

Adaptation, Ocular↗

PubMedDate not supplied

Motion VEPs with simultaneous measurement of perceived velocity.

The dependency of the N200 amplitude of the motion-onset VEP evoked by a parafoveal grating of variable speed (0.25-13.5 deg/s, corresponding to 0.5-27 Hz) and constant contrast (4%) was studied. Additional measurements were made with parafoveally presented gratings of constant speed (2 deg/s, corresponding to 4 Hz) and a variable contrast (0.5-64%) before and after adaptation to a stationary or drifting grating. In this latter experiment, simultaneous psychophysical measurements were made of the perceived speed. The amplitude of the N200 wave increased with increasing stimulus speed within the slow speed range up to 1.5 deg/s (corresponding to 3 Hz). Adaptation to a stationary grating had no significant effect on the relationship between the N200 amplitude and stimulus contrast. Contrary to this, adaptation to a slowly drifting grating (1 deg/s, corresponding to 2 Hz) or to a rapidly drifting grating (4 deg/s, corresponding to 8 Hz) reduced the N200 amplitude significantly. Adaptation to a stationary grating slightly reduced the perceived speed of subsequently viewed gratings. Adaptation to a slowly drifting grating increased the perceived speed of the subsequently viewed gratings, whereas adaptation to a rapidly drifting grating decreased the perceived speed. The findings can be best explained by a two-channel model of speed perception. While the motion VEP reflects the sum of both channel activities, the psychophysical measures point to the antagonistic encoding of low and high velocities.

Adaptation, Ocular↗

PubMedDate not supplied

Polyunsaturated phosphatidyl-choline and interferon alpha for treatment of chronic hepatitis B and C: a multi-center, randomized, double-blind, placebo-controlled trial. Leich Study Group.

BACKGROUND/AIMS: Polyunsaturated phospatidyl-choline (PPC) has been shown to reduce serum aminotransferases in experimental hepatitis. This multi-center, randomized, double-blind, placebo-controlled trial evaluated the effects of PPC in patients with chronic hepatitis B and C in combination with interferon alpha 2a or 2b. The diagnosis of chronic viral hepatitis was based on an abnormal serum alanine aminotransferase (ALT) value (more than twice the upper value of normal), viral replication and chronic hepatitis found on liver biopsy. METHODOLOGY: Patients received 5 million I.U. (Hepatitis B) and 3 million I.U. (hepatitis C) interferon s.c. thrice weekly for 24 weeks, respectively, and were randomly assigned to additional oral medication with either 6 capsules of PPC (total daily dose: 1.8 g) or 6 capsules of placebo per day for 24 weeks. Biochemical response to therapy was defined as a reduction of ALT by more than 50% of pre-treatment values. The responders were treated for further 24 weeks after cessation of interferon therapy with either PPC or placebo. RESULTS: 176 patients completed the study protocol (per-protocol population: 92 in the PPC and 84 in the placebo group). A biochemical response (> 50% ALT reduction) was seen in 71% of patients who were treated with PPC, but only in 56% of patients who received placebo (p < 0.05). PPC increased the response rate in particular in patients with hepatitis C: 71% of those patients responded in the PPC group versus 51% in the placebo group (p < 0.05). Prolonged PPC therapy given to responders beyond the cessation of interferon therapy tended to increase the rate of sustained responders at week 48 in patients with hepatitis C (41% versus 15% in the control group; p = 0.064). In contrast, PPC did not alter the biochemical response to interferon in patients with hepatitis B. PPC did not accelerate elimination of HBV-DNA, HBeAg and HCV-RNA. CONCLUSIONS: In conclusion, PPC may be recommended in patients with chronic hepatitis C in combination with interferon and after termination of interferon in order to reduce the high relapse rate. PPC may not be recommended for patients with chronic hepatitis B. In contrast to IFN and other antiviral agents PPC does not carry major risks and is tolerated very well.

Adult↗