Probing the mechanism of saccade-associated head movements through observations of head movement propensity and cognition in the elderly.
Humans may accomplish gaze shifts by eye-only saccades or combined eye-head saccades. The mechanisms that determine whether the head moves remain poorly understood. Many observations can be explained if phylogenetically ancient circuits generate eye-head saccades by default and frontal cerebral structures interrupt this synergy when eye-only saccades are preferable. Saccade-associated head movements have been reported to increase in the elderly. To test the hypothesis of frontal inhibition of head movements, we investigated whether the increase is associated with a decline in frontal cognitive function. We measured head movement tendencies and cognition in volunteers aged 61-80. Measures of head movement tendency included the customary range of eye eccentricity, customary range of head eccentricity, range of target eccentricities evoking predominantly eye-only saccades, and two measures of head amplitude variation as a function of target eccentricity. Cognitive measures encompassed verbal fluency, verbal memory, non-verbal memory, and executive function. There was no correlation between cognition and any measure of head movement tendency. We combined these elderly data with measurements of head movements in a group aged 21-67 and found mildly reduced, not increased, head movement tendencies with age. However, when confronted with a task that could be accomplished without moving the head, young subjects were more likely to cease all head movements. While inconclusive regarding the hypothesis of inhibition of saccade-associated head movements by cerebral structures, the results indicate the need to distinguish between mechanisms that define head movement tendencies and mechanisms that adapt head motion to the geometry of a specific task.
Thumser
Zachary C
ZC
Louis Stokes Cleveland Department of Veterans Affairs Medical Center, Cleveland, OH, USA.
Adams
Nancy L
NL
Lerner
Alan J
AJ
Stahl
John S
JS
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology; D003071:Cognition / Q000502:physiology; D053483:Eye Movement Measurements; D005133:Eye Movements; D005260:Female; D005625:Frontal Lobe / Q000502:physiology; D019416:Head Movements / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D008959:Models, Neurological; D009483:Neuropsychological Tests; D012438:Saccades / Q000502:physiology; D055815:Young Adult