Please enable JavaScript.
Coggle requires JavaScript to display documents.
INTRODUCTION TO METHODS: NEURO-IMAGING AND COGNITIVE TASK DESIGN - Coggle…
INTRODUCTION TO METHODS: NEURO-IMAGING AND COGNITIVE TASK DESIGN
1) Two
methods
in
comparison
fMRI
EEG / MEG
Strenghts
Spatial resolution
Usable to study where
Temporal resolution
Usable to study when
EEG mobile-devices: ecologity validity
Combining
methods means combining strenghts
2) Focus on fMRI
Different techniques with
MRI scanner
MRI
(brain's anatomy)
Partecipants lies in the scanner
Static 3D image with tissue contrast
fMRI
(brain's activity)
Partecipants do an activity in the scanner
Multiple 3D fewer detailed images with hemodynamic contrast
DTI
(brain's statical connectivity)
What we do in an fMRI study?
1) Partecipants
do
an
activity
in the
scanner
(this activity activates a cognitive process)
2) The activated process change the
oxygen level
in
blood surrounding neurons
(
BOLD signal
)
3) The
scans
during this phase are
compared
to the scans during control condition
4) We
identify
the
blobs
, where phase-areas differ from control-areas
Alternation
of
task scan - control scan
to study the validity of changes in brain activity (in the statistical analysis phase)
The multiple comparison
colored
the areas that are significatly different from the two conditions (blobs)
Combination
of
anatomical scan
to have greater spatial resolution
Colored the areas
stronger activated
(blood oxygen level changed) than in the control task
The area is not assolute, but
depends
on
control condition
Brain areas involved in the task requires oxygen, this determines a
LATER apport
of
fresh blood
in these areas
Difference in oxygenated vs deoxygenated blood
Oxy-Hb (diamagnetic)
Deoxy-Hb (paramagnetic)
Distorts magnetic field
, if it's more, low fMRI-signal
fMRI is an
indirect measure
3)
Cognitive task design
Basic logic
Using the
Donders' subtraction method
in the comparison experimental condition / control condition
Our
blobs scans
are always
relative
to this difference
Common design
Example of
2X2 design
(2 groups of partecipants / 2 task conditions to compare
Examples
Stroop Task
(children - adolescents / congruent - incongruent condition)
Stop Task
(controls - ADHD / succesful inhibition - failed inhibition)
4) Neuro-imaging:
interpretation ptifalls
4.1)
Reverse Inference
Different
from
forward inference
, going backwards from a brain activation to a particular cognitive function
If
task A
is activated by
brain area Z
and Brain area Z is activated by
cognitive processes X
this
DOESN'T MEAN
that cognitive processes X are engaged by task A
Brain area Z
can be activated in two different processes
4.2)
Correlation VS Causation
Neuroimaging techniques
are
correlational methods
, so we cannot conclude causal inference between brain areas and cognitive functions
4.3)
Individual Differences
At least
group differences
(not individual): individual diagnosis cannot be based on only one neuroimaging scan