PSY4320

Research methods in cognitive neuroscience

Preliminary resultsLars T. Westlye, PhD Research Fellow

Center for the Study of Human Cognition

Department of Psychology, University of Oslo

l.t.westlye@psykologi.uio.no

1. Decreased P3a amplitude in the old compared to the young group

2. Decreased cortical thickness and FA in the old compared to the young group

3. Cortical thickness and FA positively correlated with amplitude in both groups

4. Spatial distribution and strenght of the relationships between vary between groups

Hypotheses

Channel posititions

F = frontal

Z = central

P = parietal

O = occipital

Cz

P3a

P3a amplitude

P3ayoung

old

P3a amplitude

Young Old p

Cz 20.9 (8.7) 14.2 (7.7) .002

Amplitude significantly stronger in the young than the old group

Independent samples t-test

P3a amplitude

Spatiotemporal distribution of the differences between young and old group (p3a)

Increased frontal activation in old compared to young group

FRONTAL SHIFT?

Female

25 years

Female

74 years

Young vs old

Cortical thicknessYoung Old

General Linear Model testing the effect of group

Thickness (vertexn) = (young × β1) + (old × β2) + error

H0: β1 = β2 (no difference between group)

Mean young group

Mean old group

Young Old

Young > Old

General Linear Model testing the effect of group

Colored areas:

p(β1= β2)< 5%

(here we reject H0)

FA

Red 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)

Young Old p

FA 0.49 (.02)

0.45 (0.01)

<.001

Independent samples t-test

NB! Life-span changes in FA are not linear

FA increases until ~30 years

Y O

General Linear Model testing the effect of P3a amplitude on thickness within and between groups

Thickness (vertexn) = (young×β1) + (old×β2) + (ERPy× β3) + (ERPo × β4) + error

Within groups:

H01: β3 = 0 (no relation between amplitude and thickness in young group )

H02: β4 = 0 (no relation between amplitude and thickness in old group )

Between groups

H03: β3 = β4 (no difference between β3 and β4)

Cortical thickness vs P3a amplitude

Cortical thickness vs P3a amplitude

H0: β3 = 0 (no relation between amplitude and thickness in young group )

Colored areas: the probability (p) of H0 < 5 %

Young

Cortical thickness vs P3a amplitude

H0: β4 = 0 (no relation between amplitude and thickness in old group )

Colored areas: the probability (p) of H0 < 5 %

Old

p(β3)=0 p(β4)=0

Between groups

H03: β3 = β4 (no difference between the amplitude × thickness correlations between groups)

Within groups

young old

p(β3 = β4) < 5%

Red areas: thickness stronger related to amplitude in young than in old group

p(β3 = β4) < 5%

Red areas: thickness stronger related to amplitude in young than in old group

p(β3)=0

p(β4)=0

FA vs P3a amplitude in young group

Green areas: negative correlation between amplitude and FA

FA vs P3a amplitude in young group

β= -.67, p < .01

FA vs P3a amplitude in old group

Red areas: negative correlation between amplitude and FA

FA vs P3a amplitude in old group

β= -.71 p < .01

Low FA

High FA

High FA

Tract 1

Tract 2

Crossing fibres?

How do we explain the negative correlations between amplitude and FA?

How do we explain the negative correlations between amplitude and FA?

Radial diffusion Radial diffusion

Increased radial diffusion?

How do we explain the negative correlations between amplitude and FA?

Radial diffusion Radial diffusion

AlongP

erpe

ndic

ular

Positive correlation between radial diffusion and P3a amplitude

Increased axonal calibre/diameter?

FA/thickness: Young > old

P3a positively correlated with thickness

Summary

P3a negatively correlated with FA

P3a positively correlated with radial diffusion

Young Old

Young vs old

OldYoung

Q: How could we improve the study?

The inverse problem

Theoretical source 1

Theoretical source 2

Scalp electrodesScalp EEG

Question: 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 groups

A) 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 years

Female

74 years

Young 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