Cognitive processing of visual stimuli in patients with organophosphate insecticide poisoning

Objective: To determine the effect of organophosphate (OP) insecticide poisoning on cognitive processing time of visual stimuli. Methods: We compared 33 patients who recovered from the cholinergic phase (on average, 15 days after poisoning) with an age- and sex-matched control group. The tests used were simple visual reaction time (SVRT), recognition visual reaction time (RVRT), visual evoked potentials (VEP), and motor evoked potentials (MEP). The term cognitive processing time (CPT) was used to denote the time taken from the initial cortical perception of a stimulus to initiation of the descending motor impulse. CPT of each type of visual reaction was calculated by subtracting the sum of the visual impulse duration and the motor impulse duration from reaction time (CPT = reaction time - [P100 latency + total motor conduction time]). Results: Both the SVRT and RVRT were significantly prolonged in patients. There was no significant difference in P100 latency or total motor conduction time (TMCT) between patients and the controls. However, CPT of simple visual reactions (CPTSVR) and the CPT of recognition visual reactions (CPTRVR) were significantly prolonged in patients. Conclusions: Acute organophosphate poisoning may slow higher-order cognitive processing involved in visual stimulus detection and visual stimulus discrimination, even after clinical recovery from the cholinergic phase.