Chihiro Harada

Recording Eye Movement During Stepping in Place With a CCD (Charge-Coupled Device) Imagesensor

A new system for recording eye movements using a charge-coupled device (CCD) imagesensor in a video camera, in which less than 0.5 degree of horizontal and vertical eye movements can be recorded, was applied in 7 subjects. Eye movements were recorded while they stepped in place. We observed 5 normal subjects, a patient with horizontal and vertical oscillopsia during walking, and one with a chronic limp. In the normal adults, the amplitude of vertical eye movement was less than 0.5 degree, and the horizontal eye movement was less than 2 degrees. The mean amplitude of horizontal and vertical eye movements in the subject who limped was larger than that of normal subjects. The patient who complained of vertical oscillopsia during walking showed the largest amplitude of vertical eye movement among any subject tested. The vertical oscillopsia in the patient was due to the largest amplitude of vertical eye movement. This system for recording eye movements will be useful in analyzing the mechanism of gaze fixation during walking.

Neural Responses to Electrical Stimulation of the Cochlea in Guinea Pigs

A special bridge circuit was constructed to compensate stimulus artifact to determine the effects of an alternating current (AC) in the range of 3 to 20 kHz and direct current (DC) stimulation on the activity of cochlear nerve fibers. When AC and DC stimulation of the same fiber were compared, a greater current intensity was required to change the spike rate with AC stimulation than DC stimulation. While positive DC stimulation reduced activity, negative DC stimulation increased the spike rate. AC stimuli excited fibers in a manner similar to that observed with negative DC stimulation. Thresholds increased with stimulus frequency, suggesting that the effects of AC stimulation on the discharge rate are independent of the CF (characteristic frequency) of a fiber. The effects of short-time AC and DC stimulation on cochlear fiber activity lasted only during the stimulation, and the spontaneous activity did not significantly differ before and after electrical stimulation.

A cace of Bilateral Medial Longitudinal Fasciculus (MLF) Syndrome with Exotropia

A case of bilateral MLF syndrome with exotropia due to brain stem infarction is reported. A 77-year-oldwoman developed sudden diplopia with dizziness. Ocular motor findings on admission were : On forward gaze, she used only the right eye, and the left eye was in the full abduction position;she could adduct the left eye to the midposition when using it for fixation ; leftward gaze evoked left-beating nystagmus of the left eye, but the right eye did not adduct ; righward gaze evoked right-beating nystagmus of the right eye but the left eye did not adduct; on upward gaze, right eye movement was in-sufficient ; downward gaze was possible ; convergence was insufficient.MRI (T2 weight spin echo image) displayed a high signal intensity area in the midbrain teg-mentum, but the pons was intact. On the basis of these findings, the diagnosis was intact. On the basis of these findings, the diagnosis was bilateral MLF syndrome with non-paralytic exotropia.The lesion in this case may be bilateral MLF and right oculomoter nucleus disorder. The exotropia of this patient may have been due to bilatreral dysfunction of the MLF and hyper-function of the left paramedian pontine reticular formation (PPRF).The difference between paralytic pontine exotropia (PPE) and non-paralytic pontione exotropia (NPPE) is also discussed in this paper.