title: Reduced Haemodynamic Response in the Ageing Visual Cortex Measured by Absolute fNIRS.
abstract: The effect of healthy ageing on visual cortical activation is still to be fully explored. This study aimed to elucidate whether the haemodynamic response (HDR) of the visual cortex altered as a result of ageing. Visually normal (healthy) participants were presented with a simple visual stimulus (reversing checkerboard). Full optometric screening was implemented to identify two age groups: younger adults (n = 12, mean age 21) and older adults (n = 13, mean age 71). Frequency-domain Multi-distance (FD-MD) functional Near-Infrared Spectroscopy (fNIRS) was used to measure absolute changes in oxygenated [HbO] and deoxygenated [HbR] haemoglobin concentrations in the occipital cortices. Utilising a slow event-related design, subjects viewed a full field reversing checkerboard with contrast and check size manipulations (15 and 30 minutes of arc, 50% and 100% contrast). Both groups showed the characteristic response of increased [HbO] and decreased [HbR] during stimulus presentation. However, older adults produced a more varied HDR and often had comparable levels of [HbO] and [HbR] during both stimulus presentation and baseline resting state. Younger adults had significantly greater concentrations of both [HbO] and [HbR] in every investigation regardless of the type of stimulus displayed (p<0.05). The average variance associated with this age-related effect for [HbO] was 88% and [HbR] 91%. Passive viewing of a visual stimulus, without any cognitive input, showed a marked age-related decline in the cortical HDR. Moreover, regardless of stimulus parameters such as check size, the HDR was characterised by age. In concurrence with present neuroimaging literature, we conclude that the visual HDR decreases as healthy ageing proceeds.
authors.affiliation: Department of Vision Sciences, Glasgow Caledonian University, Glasgow, United Kingdom.
authors.forename: Laura McKernan
authors.initials: LM
authors.lastname: Ward
authors.affiliation: Department of Vision Sciences, Glasgow Caledonian University, Glasgow, United Kingdom.
authors.forename: Ross Thomas
authors.initials: RT
authors.lastname: Aitchison
authors.affiliation: Department of Vision Sciences, Glasgow Caledonian University, Glasgow, United Kingdom.
authors.forename: Melisa
authors.initials: M
authors.lastname: Tawse
authors.affiliation: Department of Vision Sciences, Glasgow Caledonian University, Glasgow, United Kingdom.
authors.forename: Anita Jane
authors.initials: AJ
authors.lastname: Simmers
authors.affiliation: Department of Vision Sciences, Glasgow Caledonian University, Glasgow, United Kingdom.
authors.forename: Uma
authors.initials: U
authors.lastname: Shahani
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000097:blood / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology; D005260:Female; D006439:Hemodynamics / Q000502:physiology*; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D008297:Male; D008875:Middle Aged; D010108:Oxyhemoglobins / Q000378:metabolism; D010775:Photic Stimulation; D012146:Rest; D019265:Spectroscopy, Near-Infrared; D014793:Visual Cortex / Q000098:blood supply* / Q000502:physiology*; D055815:Young Adult
chemical_list: D006454:Hemoglobins; D010108:Oxyhemoglobins; C100003:deoxyhemoglobin