PSY4320 Research methods in cognitive neurosciencePreliminary resultsLars T. Westlye, PhD Research Fellow Center for the Study of Human CognitionDepartment of Psychology, University of Oslol.t.westlye@psykologi.uio.no

Decreased P3a amplitude in the old compared to the young groupDecreased cortical thickness and FA in the old compared to the young groupCortical thickness and FA positively correlated with amplitude in both groups Spatial distribution and strenght of the relationships between vary between groupsHypotheses

Channel posititionsF = frontalZ = centralP = parietalO = occipitalCz

P3a

P3a amplitudeP3ayoungold

P3a amplitudeAmplitude significantly stronger in the young than the old groupIndependent samples t-test

P3a amplitudeSpatiotemporal distribution of the differences between young and old group (p3a) Increased frontal activation in old compared to young groupFRONTAL SHIFT?

Female 25 yearsFemale 74 yearsYoung vs old

Cortical thicknessYoungOldGeneral Linear Model testing the effect of groupThickness (vertexn) = (young 1) + (old 2) + errorH0: 1 = 2 (no difference between group) Mean young groupMean old group

YoungOldYoung > OldGeneral Linear Model testing the effect of groupColored areas:p(1= 2)< 5%(here we reject H0)

FARed areas: reduced FA in old compared to young group

FA~ 60 % of the skeleton voxels show a significant effect of group (young > old)

FA~ 60 % of the skeleton voxels show a significant effect of group (young > old)Independent samples t-test

NB! Life-span changes in FA are not linearFA increases until ~30 yearsYO

General Linear Model testing the effect of P3a amplitude on thickness within and between groupsThickness (vertexn) = (young1) + (old2) + (ERPy 3) + (ERPo 4) + errorWithin groups:H01: 3 = 0 (no relation between amplitude and thickness in young group )H02: 4 = 0 (no relation between amplitude and thickness in old group )Between groupsH03: 3 = 4 (no difference between 3 and 4) Cortical thickness vs P3a amplitude

Cortical thickness vs P3a amplitudeH0: 3 = 0 (no relation between amplitude and thickness in young group )Colored areas: the probability (p) of H0 < 5 %Young

Cortical thickness vs P3a amplitudeH0: 4 = 0 (no relation between amplitude and thickness in old group )Colored areas: the probability (p) of H0 < 5 %Old

p(3)=0p(4)=0Between groupsH03: 3 = 4 (no difference between the amplitude thickness correlations between groups) Within groups youngold

p(3 = 4) < 5%Red areas: thickness stronger related to amplitude in young than in old group

p(3 = 4) < 5%Red areas: thickness stronger related to amplitude in young than in old groupp(3)=0p(4)=0

FA vs P3a amplitude in young groupGreen areas: negative correlation between amplitude and FA

FA vs P3a amplitude in young group= -.67, p < .01

FA vs P3a amplitude in old groupRed areas: negative correlation between amplitude and FA

FA vs P3a amplitude in old group= -.71 p < .01

Low FAHigh FAHigh FATract 1Tract 2Crossing fibres?How do we explain the negative correlations between amplitude and FA?

How do we explain the negative correlations between amplitude and FA?Radial diffusionRadial diffusionIncreased radial diffusion?

How do we explain the negative correlations between amplitude and FA?Radial diffusionRadial diffusionAlongPerpendicularPositive correlation between radial diffusion and P3a amplitudeIncreased axonal calibre/diameter?

SummaryFA/thickness: Young > oldP3a positively correlated with thicknessP3a negatively correlated with FAP3a positively correlated with radial diffusionYoungOldYoung vs oldOldYoung

Q: How could we improve the study?

The inverse problemTheoretical source 1Theoretical source 2Scalp electrodesScalp EEGQuestion: How do you separate signals from the various sources?

Task #2

Correlate MRI brain structural measures (cortical thickness, diffusion tensor imaging) with ERP parameters between and across groupsA) How do the different measures change with age?B) Are the relationships between MRI and ERP different between groups? Research questions

Inter-trial variability

Female 25 yearsFemale 74 yearsYoung vs old

Does the same pattern emerge when comparing groups of subjects?-- Young participants

-- Old participants

Task #1

Compare peak amplitude and latency between two groups: Group A: young (n=30, 20-25 years) Group B: old (n=30, 70-75 years)Course research assignments