GABA‐ergic control of visual perception in healthy volunteers: effects of midazolam, a benzodiazepine, on spatio‐temporal contrast sensitivity.

Abstract

1. We studied the effects of midazolam (MDZ), a benzodiazepine, on spatio‐temporal contrast sensitivity, choice reaction time, and mood visual analogue scales in healthy volunteers. 2. Eight extensively trained, healthy volunteers were included in a placebo‐controlled cross‐ over double‐blind trial of MDZ (0.15 mg kg‐1). Treatments were injected intramuscularly and evaluations were performed before and 0.5, 1, 2, 3 and 4 h after drug administration. Spatio‐temporal contrast sensitivity was measured using a micro‐computer with appropriate software. Stimuli were vertical gratings with adjustable contrast, with spatial frequencies of 0.25, 1 and 4 cpd. Four conditions of temporal modulation were used: the grating was either static or drifting laterally with temporal frequencies of 1, 3 and 9 Hz. 3. An analysis of variance was performed on the data. As compared with placebo, MDZ induced an increase in choice reaction time and sedation (as assessed on visual analogue scales). From 0.5‐4 h after the injection, MDZ produced an overall decrease in visual sensitivity, as compared with placebo. More specifically, MDZ preferentially affected medium to high spatial frequencies and low temporal frequencies. Several non‐exclusive hypotheses may account for the results: 1) an increase in the size of the receptive fields, 2) a preferential effect on the visual parvocellular pathways which mediate the sensitivity to high spatial and low temporal frequencies.

Impairment of contrast sensitivity in long-term lorazepam users

“…Moreover, sedation effects did not differ between the two groups either. Our results do not (Blin et al 1993;Harris and Phillipson 1995) of a specific effect of lorazepam on either the parvo-or magno-cellular pathway. They are consistent with results obtained in lorazepam-and triazolam-treated subjects (Maddock et al 1993).…”

“…The possibility that benzodiazepines impair one or another system in a selective way is not clear from the literature. What all studies show, however, is a global loss in contrast sensitivity (Blin et al 1993;Harris and Phillipson 1995). As far as we know, an exploration of contrast sensitivity had not yet been carried out in chronic users of lorazepam.…”

Psychophysical assessment of magno- and parvocellular function in schizophrenia

“…This is difficult to assess directly because, on the one hand, it would be unethical to withhold medication but, on the other hand, unreasonable to test patients when in an acute phase, just prior to receiving medication. Benzodiazepines have been reported to produce overall losses of sensitivity (Blin, et al, 1993 ;Giersch, et al, 1997). Long term use of benzodiazepines, however, seems to produce little effect on retinal function (Stafanous et al, 1999).…”

Weakened Center-Surround Interactions in Visual Motion Processing in Schizophrenia

“…Indeed, GABAergic effects on visual perception (Blin et al, 1993) and motion integration and segmentation (Giersch and Lorenceau, 1999) have been reported. Thus, use of medication that has considerable effects on the GABAergic system might lead to unwanted confounds.…”