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Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience
Edited by Bernard J. Baars and Nicole M. Gage
2007 Academic Press
Chapter 4 The Tools: Imaging the Living Brain
“I believe the study of neuroimaging has supported the localization of mental operations within the human
brain.”
-Michael I. Posner, 2003
Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience
Edited by Bernard J. Baars and Nicole M. Gage
2007 Academic Press
Chapter Outline
1.0 Introduction
2.0 A range of useful tools -- measuring electric and magnetic signals
3.0 fMRI and PET: indirect signals for neural activity
4.0 Conscious vs. unconscious brain events
5.0 Correlation and causation
6.0 Summary
Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience
Edited by Bernard J. Baars and Nicole M. Gage
2007 Academic Press
1.0 Introduction
Brain recording: more and less direct measurements
How do brain recordings reflect
human cognition? While they are
indirect measures, each type of
brain recording tells us part of the
story of how the brain works.
Here is an image of the brain using
diffusion tensor imaging: this
technique allows us to view white
(myelinated) fiber tracts.
Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience
Edited by Bernard J. Baars and Nicole M. Gage
2007 Academic Press
1.0 Introduction
The time-space tradeoff: some techniques provide high temporal resolution of brain
activity (such as EEG) while others provide higher spatial resolution (such as
fMRI).
Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience
Edited by Bernard J. Baars and Nicole M. Gage
2007 Academic Press
2.0 A range of useful tools -measuring electric and magnetic signals
Single-unit recording:
Recording from individual neurons can
tell us about spiking patterns in the
brain. Here you see that the activity in
this single unit is most active (shown in
red) during the delay period. Such
neurons are thought to be involved in
the working memory system.
Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience
Edited by Bernard J. Baars and Nicole M. Gage
2007 Academic Press
2.0 A range of useful tools -measuring electric and magnetic signals
Human
Animal and human studies cast light
on each other
While humans and monkeys are very
different, some monkeys, such as the
macaque, are extensively studied
because of the similarity between their
brains and human brains.
Macaque
Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience
Edited by Bernard J. Baars and Nicole M. Gage
2007 Academic Press
2.0 A range of useful tools -measuring electric and magnetic signals
Animal and human studies cast light
on each other
Some macaque behaviors are similar
to humans as well, such as close
infant-mother bonding.
Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience
Edited by Bernard J. Baars and Nicole M. Gage
2007 Academic Press
2.0 A range of useful tools -measuring electric and magnetic signals
Electroencephalography (EEG) recordings reveal brain rhythms such as Gamma
(40Hz). Gamma activity is thought to signal exchange of information between cortical
and subcortical regions.
Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience
Edited by Bernard J. Baars and Nicole M. Gage
2007 Academic Press
2.0 A range of useful tools -measuring electric and magnetic signals
Magnetoencephalography (MEG)
MEG recordings reflect magnetic -- not
electric -- cortical activity. MEG has higher
source localization capabilities than EEG.
Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience
Edited by Bernard J. Baars and Nicole M. Gage
2007 Academic Press
2.0 A range of useful tools -measuring electric and magnetic signals
Zapping the brain -- Transcranial Magnetic Stimulation (TMS)
TMS uses brief magnetic pulses over the scalp to inhibit or excite a small region of
cortex. TMS is used to test causal hypotheses about the contribution of specific brain
regions to complex cognitive processes.
Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience
Edited by Bernard J. Baars and Nicole M. Gage
2007 Academic Press
3.0 fMRI and PET: indirect signals for neural activity
PET was developed before fMRI and
provides a measure of metabolic activity
in the brain. It is very expensive to use
and is invasive, requiring subjects to be
injected with a radioactive tracer.
PET is used less often in research
studies today, but remains an important
clinical and research tool.
Both PET and fMRI rely on a subtraction
method where brain scans for different
experimental contrasts are subtracted
from each other.
Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience
Edited by Bernard J. Baars and Nicole M. Gage
2007 Academic Press
3.0 fMRI and PET: indirect signals for neural activity
fMRI provides a measure of hemodynamic (blood
based) activity in the brain and is based on the premise
that neuronal activation increases oxygen demand of
neurons and related cells, leading to additional blood
flow carrying oxygen molecules to the region. This can
be measured using BOLD -- Blood Oxygen Level
Dependent -- activity.
fMRI is the dominant neuroimaging technique today in
research.
Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience
Edited by Bernard J. Baars and Nicole M. Gage
2007 Academic Press
3.0 fMRI and PET: indirect signals for neural activity
Regions of interest:
The brain is a dynamic, complex
entity. How do you know which brain
activity corresponds to your research
experiment? One technique is to
define regions of interest (ROIs)
before scanning to identify which
areas you expect to see changes in
activation.
Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience
Edited by Bernard J. Baars and Nicole M. Gage
2007 Academic Press
3.0 fMRI and PET: indirect signals for neural activity
The resting brain is not silent …
Many fMRI and PET research
protocols subtract an experimental
condition from a baseline -- frequently
a ‘resting’ state where the subject
does not have a task to perform.
But, is the brain resting? While activity
during a resting state may not be
directly related to the tasks being
performed in other states, we know
that humans are constantly thinking,
imagining, feeling, anticipating and
remembering.
Background activity in the left and right
hemispheres during a resting state
Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience
Edited by Bernard J. Baars and Nicole M. Gage
2007 Academic Press
4.0 Conscious and unconscious brain events
A recent wave of brain studies are
investigating conscious and
unconscious phenomena in the brain.
For example, a fMRI study compared
brain activation for conscious and
unconscious events: unconscious
viewing of words activated visual areas
only, while conscious viewing activated
expanded regions in the cortex.
Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience
Edited by Bernard J. Baars and Nicole M. Gage
2007 Academic Press
5.0 Correlation and Causation
Brain damage and causal inferences
Brain injuries can provide evidence that areas are necessary for certain cognitive
functions, however it is important to keep in mind that studies of brain-damaged
individuals provide correlational, not causal, explanations about brain function.
Cognition, Brain and Consciousness: An Introduction to Cognitive Neuroscience
Edited by Bernard J. Baars and Nicole M. Gage
2007 Academic Press
6.0 Summary
The advent of brain imaging has transformed the study of human cognition. New
and refined methods are constantly being produced.
There is a wide array of methods and techniques for brain recording: brain imaging
techniques allow us measure single neurons as well as large cortical activations,
brain structures as well as dynamic brain activity.
A powerful use of brain imaging is to provide converging evidence, across
techniques and research populations, to better understand human cognition.