Dissociating the neural processes associated with attentional demands and working memory capacity
Gál ViktorKóbor István
Vidnyánszky Zoltán
SE-MRKKPPKE-ITK
Budapest, 2011
Working memory is affected by several CNS disorders
WM tasks (e.g. delayed match to sample) are important part of neuropsychatric tests
The goal is to show that fMRI can be used to measure:
-Subtle changes in the neural responses in specific brain regions associated with memory-load dependent modulation of the performance in a working memory tasks.
-Neural correlates of the individual differences in WM capacity.
Measuring the neural effect of working memory load using fMRI.
VSTM experiment
• 13 subjects, 3 excluded(poor behavioral performance and scanning artifacts)
• Plan: to have at least 20-25 subjects in the analysis• Main experiment + independent ROI localizer scan• Standard GLM analysis protocols
fMRI measurements, analysis
• Scanning parameters:– Philips Achieva 3T, 36 functional axial slices, TR: 2 s,
resolution: 3 x 3 x 3.5mm.• Preprocessing, analysis:
– Functional data was preprocessed using standard procedures in SPM8.
– Data was analyzed by standard GLM procedures via customized SPM8 scripts.
– Statistical parametric maps were transformed to the MNI space using the transformation parameters of the normalized high resolution T1W anatomical scans.
Behavioural results
FHSK
where K is the memory capacity, S is the size of the array, H is the observed hit rate and F is the false alarm ra
1 2 3 4 50.5
1
1.5
2
2.5
3
memory load
mem
ory
cap
acit
iy
memory capacity1 2 3 5
0
0.5
1
1.5
2
2.5
3
3.5
4MEMORY CAPACITY
memory load
mem
ory
capa
city
(K
)
1 2 3 50
10
20
30
40
50
60
70
80
90
100
110PERFORMANCE
memory load
corr
ect
answ
ers
%
Localization of VSTM related BOLD activity
Random effect group results of the memory load 5 > baseline contrast map group-wise analysis at a threshold of FDR=0.05.
Localization of VSTM related BOLD modulation
Random effect group results of the memory load 5 > memory load 1 contrast map group-wise analysis at a threshold of p<0.001.
Evoked fMRI responses at different memory loads
1 2 3 4 5 6 7 8-0.3
-0.2
-0.1
0
0.1
0.2
0.3
parietal_left
1 2 3 4 5 6 7 8-0.2
-0.1
0
0.1
0.2
0.3
0.4
parietal_right
1 2 3 4 5 6 7 8-0.1
-0.05
0
0.05
0.1
0.15
0.2
insula_left
1 2 3 4 5 6 7 8-0.1
-0.05
0
0.05
0.1
0.15
0.2
insula_right
1235
Memory load dependent fMRI responses
0 50
0.2
0.4
0.6
bo
ld s
ign
al
parietal_left
0 50
0.2
0.4
0.6
bo
ld s
ign
al
parietal_right
0 50
0.5
memory load
bo
ld s
ign
al
insula_left
0 50
0.5
memory load
bo
ld s
ign
al
insula_right
BOLD response, memory capacity and error rate
1 2 3 50
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2IPS_left
memory load
bold
memory capacityerror rate
1 2 3 50
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2IPS_right
memory load
bold
memory capacityerror rate
1 2 3 50
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2insula_left
memory load
bold
memory capacityerror rate
1 2 3 50
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2insula_right
memory load
bold
memory capacityerror rate
1 2 3 50
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2SMA
memory load
bold
memory capacityerror rate
Correlation of bold responses and behavioral performance
• Correlation between the memory load induced modulation of bold responses and behavioral performance R=0.64, p=0.048
1 2 3 40
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
WM capacity
Lo
ad d
epen
den
t m
od
ula
tio
n o
f fM
RI
resp
on
ses parietal_left
1 2 3 4-0.05
0
0.05
0.1
0.15
0.2
WM capacityL
oad
dep
end
ent
mo
du
lati
on
of
fMR
I re
spo
nse
s parietal_right
Conclusion• It was found that fMRI responses:• in the visual cortex showed early saturation: increasing the number of
objects to be remembered above two resulted in a very small modulation of the BOLD responses in these regions
• in the bilateral supplemental motor area extending into middle cingulated cortex and the right anterior insula gradually increased with increasing the WM load, independently of the subjects’ WM capacity.
• in the bilateral intraparietal sulcus and in the left anterior insula closely associated with the subjects’ WM capacity and not with the overall attentional demands.
• To conclude the results provide evidence that different neural networks are involved in the processes associated with WM capacity and changes in overall attentional demands
Restingstate fcMRI (rs-fcMRI) studies measure the correlations in spontaneous activity between brain regions . These rs-fcMRI measurements are reliable across scans and institutions and are thought to have been shaped by the cumulative effect of experiences across one’s lifespan.
Important group-level rs-fcMRI studies have already shown differences in spontaneous activity in disorders such as autism, schizophrenia, depression, and attention-deficit hyperactivity disorder.
Functional connectivity magnetic resonance imaging (fcMRI)
fcMRI parameters, preprocessing
• 11 subjects, 15min• Scanning parameters:
– Philips Achieva 3T, 28 functional axial slices, TR: 1.5 s, resolution: 3 x 3 x 4mm and 36 functional axial slices, TR: 2 s, resolution: 3 x 3 x 3.5mm
• Preprocessing, analysis:– Functional data was preprocessed using standard procedures in SPM8.– Noise (artificial correlation) was attenuated by:
– Regressing out– Motion correction parameters– Phys. monitoring data (respiration, pulsoxy)– White matter signal– Global gray matter signal
– Bandpass filter: [0.009Hz 0.08Hz]
fcMRI parameters, preprocessing
• Seed ROI: left and right insula anterior based on main memory experiment group results• backprojected from MNI to single subject space
• Correlation between seed voxels and all other gray matter voxels were calculated and entered in second level analysis
• Group level statistical parametric maps were created after random effects analysis of the individual SPMs
Seed voxel: insula anterior
Seed voxel: insula anterior
