reading electric minds: how blood reveals the spark michelle rigozzi integrating the evoked response...
Post on 20-Dec-2015
215 Views
Preview:
TRANSCRIPT
Reading electric minds:
How blood reveals the spark
Michelle Rigozzi
Integrating the evoked response potential (ERP) with the functional magnetic resonance imaging blood oxygen level dependent (fMRI BOLD) response
In the beginning…• Stimulus
• Neurons fire
• Oxygen deficiency.
Increase in dHb
• Blood rushes in
• Oxygen excess. dHb
drops
ERP
• Evoked response potential reads neuronal activity
• Advantage:– High temporal
resolution
fMRI
BOLD
• Functional magnetic resonance imaging
• Blood oxygen level dependent reads dHb levels
• Advantage: High spatial
resolution
What we know
Yet we are still to uncover…
…the gap• Is one really just a slow version
of the other?
• How is the underlying neuronal activity (ERP) manifested through the haemodynamic BOLD response?
• New insights for future models?
Super models
• Robinson & Rennie – neuronal model– P. A. Robinson, C.J. Rennie et al., 2002.
Neurophysical Modeling of Brain Dynamics. Phys. Rev. E.
• Friston – haemodynamic model– Friston, K.J., 2003. Dynamic Causal
Modelling. NeuroImage 0.
Real sparky
Friston
Robinson & Rennie
Neuronal networksElectricalResponse(Activity)
input BOLD
∫ing models…
Testing, testing…
• General behaviour, reliability and limits of equations
• ERP v BOLD response when changing:– Overall amplitude of a biphasic ERP – ERP peak ratio– Width of ERP
Changing ERP amplitude
• Fix peak ratio
ERP = BOLD• Hypothesis
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
Increasing ERP amplitude -->
BO
LD
am
pli
tud
e
Changing ERP peak ratios
• Vary height of 2nd peak
• Hypothesis:
– Area of ERP BOLD
0
0.5
1
1.5
2
2.5
3
3.5
0 5 10 15 20 25 30 35
Height of 2nd peak
BO
LD
am
pli
tud
e
Changing ERP width
• Amplitude same, width stretched
• Hypothesis:ERP = BOLD
0.001
0.01
0.1
1
0.01 0.1 1
Decreasing ERP width -->
BO
LD
am
pli
tud
e0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
Decreasing width of ERP -->
BO
LD
am
pli
tud
e
Log-log
Linear-linear
What the future holds…
• We now know:– The peak amplitudes are linearly related– BOLD reflects integral of ERP– Linearity is lost once stimulation
lengthens
• Shape of ERP is critical –The relationship still has much to reveal!
Got you thinking?
top related