Eye movements and the electroencephalogram (EEG) were recorded in intact rabbits during an optokinetic test when the animals were exposed to pure-tone sound (85 dB at 4,000 Hz), impulse noise (159 dB), and vibration directed to the abdomen (at an amplitude of 0.9 mm at frequencies of 40 to 140 Hz). The frequency and velocity of optokinetic nystagmus significantly increased in response to these stimuli. The increase seen with vibration was greater than that resulting from sound, and the response was strongest when sound and vibration were combined. The increase of optokinetic nystagmus seen with induced vibration was progressive and dependent on the frequency. The increase was weakest during vibration at 40 Hz and strongest during vibration at 140 Hz. Electroencephalograms (EEGs) of the amygdaloid complex, dorsal hippocampus, midbrain reticular formation, and frontal motor cortex all were activated during exposure to sound and vibration, but activation of the hippocampal EEG was most closely related to the increase of optokinetic nystagmus. During optokinetic tests, impulse noise regularly triggered nystagmic beats. When the rabbits were not in the test apparatus, nystagmus was produced in response to about 18 per cent of the presentations of impulse noise, while activation of the EEG was constant. Thus, vibration and noise, when excessive, may interfere with visual orientation and hence disturb equilibrium. These findings can be related to the nonspecific dizziness that occurs in aerospace or industrial workers exposed to excessive noise and vibration.

Acoustic Stimulation↗

PubMedDate not supplied

Enhancement of eye motor response and electrical brain activity during noise and vibration in rabbits.

The relationship between electroencephalogram (EEG) and eye movements was studied in rabbits during optokinetic, vestibular, and optovestibular tests. EEG was recorded through permanently implanted electrodes. Exposure to noise and vibration increased the frequency and the velocity of optokinetic nystagmus (OKN). The increase was greater during vibration but greatest during combined noise and vibration. EEG activity was closely linked to changes in OKN and was particularly evident with the appearance of theta waves in the dorsal hippocampus. Also, rotation of the rabbit produced considerable activation in the EEG.

Animals↗

PubMedDate not supplied

Modulation of the visuo-ocular reflex by the vestibulo-ocular reflex in peripheral vision.

Peripheral OKN was produced by stimulating the visual field with a special device, designed by Miyoshi et al. Stimuli to induce peripheral OKN and rotatory nystagmus (RN) were applied to the same subject simultaneously. The results obtained were as follows. 1) In the case of the whole visual field, with a target velocity of 30 degrees/sec the combined slow-phase velocity of OKN and RN was also a constant 30 degrees/s in any phase of rotation of the subject and with any combinations of the rotationary directions of subject and target. 2) In the case of the peripheral visual field; when both OKN and RN were in the same direction, the slow-phase velocity of the combined OKN was 10-20% greater than that of the peripheral OKN alone. However, the combined OKN never exceeded the velocity of the target. In contrast, when OKN and RN directions were opposed, combined OKN was correspondingly decreased by about the same 10-20% amount.

Adult↗