methodological issues for scanning geriatric populations

15
Methodological issues for scanning geriatric populations Andy James fMRI Journal Club October 12, 2004

Upload: dustin-moon

Post on 31-Dec-2015

24 views

Category:

Documents


1 download

DESCRIPTION

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 Presentation

TRANSCRIPT

Page 1: Methodological issues for scanning geriatric populations

Methodological issues for scanning geriatric populations

Andy James

fMRI Journal Club

October 12, 2004

Page 2: Methodological issues for scanning geriatric populations

1) Participant selection criteria

2) Participants’ ability to perform task

3) Our ability to measure functional data

Topics

Page 3: Methodological issues for scanning geriatric populations

Relevance of Aging Research

Data from the US Bureau of the Census, 2000

Page 4: Methodological issues for scanning geriatric populations

Statistics for Participant Selection Criteria

Older Americans 2000: Key Indicators of Well-Being Federal Interagency Forum on Aging-Related Statistics (Forum)

Page 5: Methodological issues for scanning geriatric populations

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

Page 6: Methodological issues for scanning geriatric populations

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

Page 7: Methodological issues for scanning geriatric populations

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

Page 8: Methodological issues for scanning geriatric populations

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

Page 9: Methodological issues for scanning geriatric populations

Functional signal detectionClaim 1: The hemodynamic response function (HRF) changes with age:

Page 10: Methodological issues for scanning geriatric populations

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).”

Page 11: Methodological issues for scanning geriatric populations

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

Page 12: Methodological issues for scanning geriatric populations

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

Page 13: Methodological issues for scanning geriatric populations

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)

Page 14: Methodological issues for scanning geriatric populations

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.

Page 15: Methodological issues for scanning geriatric populations

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.