Cevette, Michael J.

AbstractBackgroundThe need exists for a device that can rapidly and accurately assess mild cognitive impairment (MCI). Because the link between oculometrics and cognition is well‐documented, the Oculo‐Cognitive Addition Test (OCAT) was developed which tracks users’ eye movements as they complete a simple mental addition test.MethodOCAT consisted of 12 trials of summing three consecutive single‐digit numbers, shown separately on three consecutive screens (Figure 1). The first, second, and third screen in each trial corresponded to low, medium, and high cognitive workload. Using an infinity‐loop pattern of 24 symmetrical positions, eye movements were captured systematically in horizontal, vertical, and diagonal directions (Figure 2).MCI was simulated by exposing subjects to 5 minutes of hypoxic gas mixture (8% O2 + balance N2). 20 subjects completed OCAT in baseline (i.e. normal room air), hypoxic, and post‐baseline (i.e. 20 minutes of room air) conditions. Raw scan‐paths were collected with an eye‐tracking device. Oculometrics pertaining to fixations and saccades were extracted. Statistical significance was assessed using repeated measures ANOVA. Effect size and clinical significance was evaluated using computed Cohen’s d.ResultOCAT completion time significantly increased from baseline to hypoxia, which corresponded to a significant decrease in cerebral oxygenation from baseline to hypoxia (Figure 3). From baseline to hypoxia, saccadic latency significantly increased while saccadic velocity significantly decreased in the diagonal direction, however, results in the horizontal and vertical directions were not significant (Figure 4). Fixation time significantly increased from baseline to hypoxia in medium and high cognitive workload, but did not significantly change in low cognitive workload (Figure 5). From baseline to hypoxia, fixation size did not significantly change in any cognitive workload, however, the fluctuation in fixation size significantly increased in medium cognitive workload. From baseline to hypoxia, fixation area significantly increased in low and high cognitive workload, but did not significantly change in medium cognitive workload.ConclusionOCAT can detect subtle changes in oculometrics that correlate with MCI. This study provides rationale for providing varying degrees of cognitive load to elucidate subtle changes in oculometrics that may otherwise go undetected in neurocognitive tests that do not increase cognitive load.

Galvanic stimulation has long been used as a nonmechanical means of activating the vestibular apparatus through direct action on the vestibular nerve endings. This stimulation has been reported to be safe, but no studies have examined the potential changes in the corresponding cochlear receptors. The aim of the present study was to evaluate the effect of galvanic vestibular stimulation (GVS) on distortion product otoacoustic emissions (DPOAEs). Fourteen subjects underwent DPOAEs during several conditions of GVS. The DPOAEs ranged from ∼ 1 kHz to ∼ 8 kHz at 65/55 dB for f1/f2 and with an f2/f1 ratio of 1.2. The subjects were evaluated at 10 stimulation conditions that ranged from −2.0 mA to +2.0 mA for each frequency. Statistical analysis showed no significant differences in DPOAE amplitudes for all conditions with and without GVS. Results also showed no significant differences between DPOAE amplitudes before and after GVS. Multivariate analysis found subject variability in DPOAE amplitude, which was not thought to be GVS related. Results indicated that GVS produced neither temporary nor permanent changes in DPOAEs.

Thirty‐six weanling guinea pigs were fed either a low (600 ppm) or normal (3000 ppm) diet of magnesium for 8 weeks. One half of each diet group received intramuscular injections of magnesium‐depleting drugs, furosemide and gentamicin. The other half were controls and received equal intramuscular injections of saline. Auditory brainstem responses were obtained from all animals before and after 8 weeks of treatment of diet and drugs to examine the effects of treatment upon hearing and auditory brainstem function. A three‐way analysis of variance of dietary magnesium, by drug and by sex, showed no significant differences in auditory brainstem wave V thresholds, wave V latencies, or interpeak wave I‐V latencies between the control and experimental groups. The low magnesium diet group, which received drugs, had significantly greater wave V auditory brainstem response amplitudes. Results can be explained on the basis of magnesium influencing the uptake of calcium into both the hair cells and associated brainstem pathways.