Affiliations: [a] Department of Neurology, Veterans Affairs Medical Center, Case Western Reserve University, Cleveland, OH, USA | [b] Department of Neuroscience, Veterans Affairs Medical Center, Case Western Reserve University, Cleveland, OH, USA | [c] Department of Biomedical Engineering, Veterans Affairs Medical Center, Case Western Reserve University, Cleveland, OH, USA | [d] Department of Neurology (Dr. Kim), Dankook University Hospital, Cheonan, Korea
Note: [*] Correspondence to: R. John Leigh, M. D., Department of Neurology, University Hospitals, 11100 Euclid Avenue, Cleveland, Ohio, 44106-5040, USA. Tel.: +216 421 3224; Fax: +216 231 3461; E-mail: rjl4@po.cwru.edu
Abstract: We measured gaze stability in darkness of four normal humans using the search coil technique. Subjects were tested first with their heads erect, and then with their heads positioned 180 degrees upside-down. In each position, subjects held their head stationary for one minute, and then actively performed pitch rotations for 20 sec. All subjects showed sustained chin-beating nystagmus in the upside-down position. Each subject showed a significant increase of slow-phase velocity directed towards their brow after 40 sec in the inverted versus erect position. Pitch head rotation had little effect on subsequent nystagmus, except for transient reversal in one subject. The sustained changes of vertical eye drifts induced by 180 deg change of head position suggest that otolithic factors may contribute to vertical nystagmus in normals. The subjects were retested after wearing a nicotine patch for 2 hours. In three subjects, nicotine induced brow-beating nystagmus; adopting a head-hanging position increased this nystagmus in two subjects. In a third session, subjects were tested after wearing a scopolamine patch for 2 hours; results were generally similar to the control condition. We conclude that normal subjects may show chin-beating (“downbeating”) nystagmus in a head-hanging position in darkness, reflecting a normal, physiological change in otolithic inputs brought about by the head orientation.
