Methadone depression of visual signal detection performance.
In order to determine the origin of a previously reported slowing of simple visual reaction time in subjects receiving single doses of oral methadone, three well-trained subjects performed. a modified double flash detection task several times after single doses of 5 mg and 10 mg of oral methadone and a placebo. A Theory of Signal Detectability analysis allowed for a clear distinction between drug-induced changes in visual sensitivity and changes in response bias. It was found that methadone reduced visual sensitivity. The peak depression in detection as well as the duration of the depressed performance were dose-related. Depression in performance paralleled the subjective effect of the drug in each subject. Averaged visual evoked potentials showed significant changes at peak drug effect to the onset of each of the pair of stimuli. It was concluded that methadone depresses visual function by acting on the visual parts of the central nervous system. The retina, midbrain and thalamic visual nuclei were discussed as possible sites of action of methadone.