Auditory event related potentials (P300) in rubber factory workers--a preliminary study.

The production of rubber products involves a mixture of complex chemicals (about 500) grouped' into various functional categories (I). The workers are accordingly exposed to these chemicals besides noise exceeding 85 dB. The effect of this workplace environment on central nervous system particularly the sensory and cognitive functions has not been w-,<II documented. In this connection we conducted study on 40' rubber factory workers-where we recorded stimulus related evoked potentials i.e. brain stem auditory, visual and somatosensory evoked potentials. In some of these subjects, we also conducted event related potentials (P 300) studies which measure cognitive functions of the brain and found interesting results. These workers belonging to raw material handling section of the factory, were brought to the Neurophysiology laboratory and asked to relax. SMP-4100, Auditory Stimulator and MEB-5200 Evoked Potential Recorder (NIHONKOHDEN, JAPAN) were used for this study. P 300 was measured from vertex (CZ and PZ) in response to random application of two type of sound stimuli, presented binaurally through head phones, applied to subject's ears. Standard auditory 'odd ball' paradigm (2) was used in application of more frequent (non target) and the other less frequent (target) stimuli and asking the subject to respond by pressing a button whenever a target, infrequent stimulus was presented. A total of 32 event responses so obtained were analysed by the evoked potential averaging method. Ag/AgCI disc electrodes, anchored with collodion were used for recording P 300 • Active electrodes (-ve) were placed at CZ and PZ with reference electrodes at ear lobules (AI + A 2). The ground electrodes was placed at FZ. The input impedence was kept below 5K ohms. Alternating tone bursts with a starting condensation phase, of 10 msec riselfall time, 100 msec duration (plateau time), intensity 70 dB, nHL and rate one every 2 see were used as target stimuli. 80% of total (160) tones were 1 K HZ (frequent) and 20% were 2 K HZ (rare). Stimulus sequence was random. The signals were in phase at two ears. The MEB-5200 settings were properly selected and evoked responses to the frequent and rare stimuli were filtered with a band pass 5-30 HZ (filter slope == 12 dB/octave) and averaged simultaneously for 32 responses. Data from two trials were obtained consequently and stored, analysed and averaged by the computer. The latency and amplitude of P 300 for target stimulus (rare) was calculated. Table I shows the values …