Lorazepam: A New Tool to Study the Processing of Discontinuities

The involvement of GABA_A in the computation of visual information has been suggested in numerous electrophysiological studies. It might play a role, in particular, in the generation of the responses of hypercomplex cells involved in the processing of discontinuities. Benzodiazepines like lorazepam enhance the fixation of GABA on the GABA_A receptor. We tested the hypothesis that lorazepam enhances the detection of discontinuities, with static stimuli composed of horizontal line-segments. There were four types of stimuli, with (1) collinear and discontinuous, (2) collinear and continuous, (3) parallel and discontinuous, and (4) parallel and continuous elements. A stimulus was presented on each trial in the centre of a computer screen for 160 ms. The task was to decide whether the stimulus was continuous or discontinuous. Response was given on two response keys. The results showed that lorazepam-treated subjects were faster at detecting a discontinuity when the stimulus included two aligned line-segments (− −) as compared to two parallel line-segments (=). Placebo-treated subjects displayed equivalent performance in the two conditions. These results support the hypothesis that lorazepam enhances responses to line-ends. They are consistent with previous results, obtained with static drawings, letters, fragmented squares, and dynamic stimuli. Lorazepam might be a useful tool to investigate visuo-perceptual integration processes and to link experimental psychology and electrophysiology.