Effect of noise in processing of visual information.
BACKGROUND
Information transmission and processing in the nervous system has stochastic nature. Multiple factors contribute to neuronal trial-to-trial variability. Noise and variations are introduced by the processes at the molecular and cellular level (thermal noise, channel current noise, membrane potential variations, biochemical and diffusion noise at synapses etc). The stochastic processes are affected by different physical (temperature, electromagnetic field) and chemical (drugs) factors. The aim of this study was experimental investigation of hypotheses that increase in the noise level in the brain affects processing of visual information. Change in the noise level was introduced by an external factor producing excess noise in the brain.


METHODS
An exposure to 450 MHz low-frequency modulated microwave radiation was applied to generate excess noise. Such exposure has been shown to increase diffusion, alter membrane resting potential, gating variables and intracellular Calcium efflux. Nine healthy volunteers passed the experimental protocol at the lower (without microwave) and the higher (with microwave) noise level. Two photos (visual stimuli) of unfamiliar, young male faces were presented to the subjects, one picture after another. The task was to identify later the photos from a group of six photos and to decide in which order they were presented. Each subject had a total of eight sessions at the lower and eight at the higher noise level. Each session consisted of 50 trials; altogether a subject made 800 trials, 400 at the lower and 400 at the higher noise level. Student t-test was applied for statistical evaluation of the results.


RESULTS
Correct recognition of both stimuli in the right order was better at the lower noise level. All the subjects under investigation showed higher numbers of right answers in trials at the lower noise level. Average number of correct answers from n=400 trials with microwave exposure was 50.3, without exposure 54.4, difference 7.5%, p<0.002. No difference between results at the lower and the higher noise level was revealed in the case of only partly correct or incorrect answers.


CONCLUSIONS
Our experimental results showed that introduced excess noise reduced significantly ability of the nervous system in correct processing of visual information.
Hinrikus
Hiie
H
Department of Biomedical Engineering, Technomedicum, Tallinn University of Technology, Ehitajate Rd 5, 19086 Tallinn, Estonia.
Karai
Deniss
D
Department of Biomedical Engineering, Technomedicum, Tallinn University of Technology, Ehitajate Rd 5, 19086 Tallinn, Estonia.
Lass
Jaanus
J
Department of Biomedical Engineering, Technomedicum, Tallinn University of Technology, Ehitajate Rd 5, 19086 Tallinn, Estonia.
Rodina
Anastassia
A
Department of Medical Physics, School of Medicine, University of Patras, University Campus, 265 04 Rio Patras, Greece.