methodological issues for scanning geriatric populations
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Methodological issues for scanning geriatric populations. Andy James fMRI Journal Club October 12, 2004. Topics. Participant selection criteria Participants’ ability to perform task Our ability to measure functional data. Relevance of Aging Research. - PowerPoint PPT PresentationTRANSCRIPT
Methodological issues for scanning geriatric populations
Andy James
fMRI Journal Club
October 12, 2004
1) Participant selection criteria
2) Participants’ ability to perform task
3) Our ability to measure functional data
Topics
Relevance of Aging Research
Data from the US Bureau of the Census, 2000
Statistics for Participant Selection Criteria
Older Americans 2000: Key Indicators of Well-Being Federal Interagency Forum on Aging-Related Statistics (Forum)
Conditions Affecting Participant Selection Criteria
Neurological conditions• depression• strokes / infarcts• memory impairment
Physical conditions• cardiac pacemaker• artificial joints• dental fixtures• aneurysm clips• arthritis• spine curvature• tattoos
D’Esposito MD, Deouell L, and Gazzaley A. (2003). Nature Reviews, 4, 1-11
Participants’ Ability to Perform Functional Task
Performance influenced by:• Eyesight• Hearing• Arthritis• Memory• Attention and working
memory
Example: Serial Reaction Time task• Participants make motor responses
to viewed stimuli• Young RT: (sd) = 323 (17) ms• Older RT: (sd) = 524 (88) ms
Howard JH and Howard DV. (1997) Psychology and Aging, 12, 634-656
Introducing a sequence to stimulus location results in decreased RTs (learning).Should paradigm be adjusted to accommodate longer RTs?Is a 100 ms learning gain in RT equivalent across groups?
300-600 ms Rest of trialresponse
Total trial time: 1500 ms
300-600 ms Rest of trialresponse
Total trial time: 1500 ms
Ability to compare functional data
How do rigid / nonrigid transformations used to convert brains to Talairach or MNI space account for age-related morphology? (i.e. cortical shrinkage, ventricular enlargement)
How can we compare sizes/shapes of ROIs across age groups?
Head motion: stroke; age: mean 58 (range: 22-78) nonstroke; age: mean 59 (range 25-71) young; age: mean 28 (range 25-38)
Seto E, Sela G, McIlroy WE et al.. 2001. Neuroimage, 14, 284-297
Functional signal detection
Huettel SA, Singerman JD and McCarthy G. (2001). The effects of aging upon the hemodynamic response measured by functional MRI. Neuroimage, 13, 161-175.
Claim 1: The hemodynamic response function (HRF) changes with age:
Calcarine Fusiform
Functional signal detectionClaim 1: The hemodynamic response function (HRF) changes with age:
Functional signal detectionClaim 1: The hemodynamic response function (HRF) changes with age:
“Nonparametric comparison of relative standard deviation across all
epoch time points revealed that elderly subjects had a higher standard deviation than had the young in 15 of
19 time points (p<.01).”
Functional signal detectionClaim 2: Older participants have greater signal to noise ratios (SNRs) in
activated voxels than younger participants
CalcarineSD (ROI)
CalcarineSD (voxel)
Intersubject group variability
Functional signal detectionClaim 2: Older participants have greater signal to noise ratios (SNRs) in
activated voxels than younger participants
SNR not due to head motion
SNR differences largest when considering only single best voxel from ROI
Functional signal detectionClaim 2: Older participants have greater SNRs in activated voxels than young
Younger participants have significantly more active
voxels (p<.001, both ROIs)
Difference above is notan artifact from selected t-value (3.5)(note divergence at t=2.5)
Conclusions
Claim 1: The hemodynamic response function (HRF) changes with age.HRF appears to peak earlier and return to baseline faster for olderResults could be skewed by increased variability and a potential outlier in the older adult groupD’Esposito (1999) found no age difference for motor cortex.Aizenstein (2003, 2004) and Richter and Richter (2003) found no age difference in when HRFs peaked, but a delayed return to baseline among older adults (~12+ s for older vs ~10 for younger participants)
Aizenstein et al., 2004. The BOLD Hemodynamic response to aging. Journal of Cognitive Neuroscience, 16, 789-793.
Conclusions
Claim 2: SNR decreases with ageOlder brains exhibit greater HRF variabilityOlder brains are activated to a lesser spatial extent (smaller ROI areas) and to a lesser magnitude (t-value thresholds)SNR improves with the square root of trials performed
Possibly due to attenuated return to baseline? (Aizenstein)~1.5 SNR between groups means 2.25x as many trials for older adults
How feasible is this for paradigms?
Discussion: Your experiences with geriatric fMRI research.