Affiliations: [a] Department of Physiology, Aeromedical Center, Chungbuk, Korea | [b] Department of Preventive Medicine, Aeromedical Center, Chungbuk, Korea | [c] Department of Otolaryngology, Aeromedical Center, Chungbuk, Korea
Note: [*] Correspondence to: Moo Hoon Lee, Department of Otolaryngology, Aeromedical Center, P.O. Box 18, Ssangsu-Ri, Namil-Myun CheongWon-Kun, Chungbuk Korea 363-849. Tel.: +82 431 229 5481; Fax: +82 431 221 8951; E-mail: aeromc@netsgo.com
Abstract: To investigate the short-term vestibular habituation, we performed the 4 successive velocity step tests on 28 volunteers, the peak velocity of which was 100 deg/sec with acceleration and deceleration of 100deg/sec2. As the repeated rotations might alter the vestibulo-ocular reflex (VOR), sinusoidal rotations at a frequency of 0.16 Hz were also given before and after the 4 successive velocity step tests to investigate the changes of gain and phase of VOR. The 28 volunteers were divided into two groups, group I and II, according to their responses to repeated rotations. In group I (25 subjects, mean age 23.7 year), the mean values of the slow cumulative eye position (SCEP), the time integral of eye velocity during nystagmus, was reduced after each trial of the 4-successive velocity step tests as follows; 403.4±29 degree (1st trial), 346.2±37 degree (2nd trial), 278.3±33 degree (3rd trial) and 256.6±36 degree (4th trial). The time constant of the nystagmus was also reduced as follows; 12.9±0.78 second (1st trial), 12±0.63 second (2nd trial), 9.7±0.78 second (3rd trial) and 9.9±0.54 second (4th trial). In group II (3 subjects, mean age 28.3 year), the mean values of SCEP gradually increased; 774.3±135 degree (1st trial), 1127±178 degree (2nd trial), 1096.3±123.4 degree (3rd trial) and 1225.7±199.7 degree (4th trial). The time constant of the nystagmus increased; 15.7±2.7 second (1st trial), 22±4.5 second (2nd trial), 22.3±3.3 second (3rd trial) and 23.3±5.7 second (4th trial). The gain of vestibulo-ocular reflex (VOR) induced by sinusoidal rotations at a frequency 0.16 Hz increased in both groups: 0.59±0.03 to 0.78±0.06 (group I) and 0.65±0.07 to 1.15±0.06 (group II). Phase changes were also observed. In group I, the phase was shifted from 0.6±0.6 degree to −0.40±0.6 degree. In group II, the phase was shifted from 3.67±1.86 degree to −0.33±0.33 degree. The repeated rotation did not induce a common nystagmic response in all subjects. Thus, person to person variations should be considered in short term vestibular habituation.
Keywords: vestibular habituation, slow cumulative eye position (SCEP), gain, phase
