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 (CPT(SVR)) and the CPT of recognition visual reactions (CPT(RVR)) 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.
Dassanayake
T
T
Department of Physiology, Faculty of Medicine, Peradeniya, Sri Lanka. tlag23@yahoo.co.uk
Weerasinghe
V
V
Dangahadeniya
U
U
Kularatne
K
K
Dawson
A
A
Karalliedde
L
L
Senanayake
N
N
D000109:Acetylcholine / Q000378:metabolism; D000328:Adult; D001921:Brain / Q000187:drug effects / Q000378:metabolism / Q000503:physiopathology; D003072:Cognition Disorders / Q000139:chemically induced* / Q000503:physiopathology / Q000523:psychology; D004569:Electroencephalography / Q000187:drug effects; D019054:Evoked Potentials, Motor / Q000187:drug effects / Q000502:physiology; D005074:Evoked Potentials, Visual / Q000187:drug effects / Q000502:physiology; D005260:Female; D006801:Humans; D007306:Insecticides / Q000506:poisoning*; D008297:Male; D009483:Neuropsychological Tests; D062025:Organophosphate Poisoning; D010468:Perceptual Disorders / Q000139:chemically induced* / Q000503:physiopathology / Q000523:psychology; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D014796:Visual Perception / Q000187:drug effects / Q000502:physiology
D007306:Insecticides; D000109:Acetylcholine