Zusammenfassung
Summary LITERATURE & LECTURES B&C3: Cognitive Neuropsychology (Radboud University Nijmegen)
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College aantekeningen Brain & Cognition Part 2 (7201702PXY) Cognitive Neuroscience
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Summary Cognitive Neuroscience
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cognitive neuroscience week 1 summary
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Intro / tools of neuropsychologyWhy cognitive neuropsychology ? Mind vs. Brain:
- Descartes thought inputs are passed on by the sensory organs in the brain and from there to
the immaterial spirit (mind)
- Gall introduced the idea of localization of function → phrenology. He observed that some
people were good at doing something, but really bad at doing other things. He realized that
because of that there had to be some sort of specialization in certain parts of the brain.
- Broca found evidence for localization → found several patients with lesions in left frontal
cortex (Broca´s area)
→ if you want to understand behavior, you need to understand the brain!
Example for the fact that behavior arises from the brain: sea squirt eating its own brain once it
settled down at a spot where it can “rest”
Toolbox:
- To understand the brain and behavior, we have to combine different methods (converging
evidence: conclusions are stronger when supported by different approaches)
Cognitive psychology and behavioral research:
- We do not directly perceive the world, but interpret the incoming information
- Mental we can think of as an information processing problem → information processing
depends on pre-existing internal representations (beliefs, concepts, desires etc.).
- These mental representations undergo transformations
Case study: memory comparison task (Sternberg):
- Participant is presented with a set of one, two or four letters and asked to memorize them.
After a delay, a single probe latter appears and the participant indicates whether that letter
was a member of the memory set.
- Reaction time increases with set size, indicating that the target letter must be compared with
the memory set sequentially rather than in parallel.
- Encode: identify the visible target
- Compare: compare the mental representation of the target with the representations of the
items in memory
- Decide: decide whether the target matches one of the memorized items
- Respond: respond appropriately for the decision made in step 3
- Word superiority effect → participants are most accurate in identifying the target letter
when the stimuli are words
,Limitations in information processing also inform us about mental transformations:
- Incongruent Stroop condition shows that 2 representations are activated. “word”
representation is dominant, at least when reporting verbally.
Cognitive psychology uses behavioral tasks to study mental representations and transformations,
however, it cannot probe anything that is not expressed in behavior → no insight in how these
processes are implemented in the brain!
Context matters for information processing, because multiple representations may be activated by a
simple stimulus → letter-matching task (Michael Posner): participants press one of two buttons to
indicate if two letters belong to the same or different categories. Results showed that participants
respond fastest to the physical-identity (AA) condition and slowest to the same-category (SC) with
both consonants
Patient studies:
- Study how cognition breaks down may tell us about how it is organized
- Study the cognitive function of brain regions through brain damage
- Angiography → imaging method to evaluate the circulatory system in the brain and diagnose
disruptions in circulation
- Cerebral vascular accidents → occur when blood flow to the brain is suddenly disrupted
- Degenerative disorders → result from progressive disease and associated with both genetic
aberrations and environmental agents (Alzheimer´s, parkinson´s, Huntington´s etc.)
- Traumatic Brain Injury → the skull remains intact, but brain is damaged; increased pressure
causing decreased blood flow are the consequences
- Lesion studies may be used to link certain mental functions to specific brain structures
(comparing brain lesioned patients with healthy individuals). Limitations → analyzing
functions may not be easy since only the functional consequences are observable, lesions
may alter connected regions, there may be compensatory processes at play and there is
great variability in naturally occurring lesions
Cognition breaking down: single vs. double dissociation:
- Functions often have many components → what component leads to the disability in the
patient ? (bad performance on reading test may be caused by blindness, language disorder
etc.)
- Task sensitivity (is the task just more or less difficult) or selective impairment (is there really
a selective impairment)?
- People with damaged temporal lobe (important for memory). Temporal lobe patients are
particularly bad at familiarity memory, but not at recency memory. We could then conclude
that patients are particularly bad at familiarity memory tests (selective impairment), but we
could also conclude that familiarity memory tests are more difficult than recency memory
tests (task sensitivity).
- Frontal lobe patients have no problem with familiarity memory tests, but with recency
memory tests.
- In a single dissociation task, participants perform bad on only one task, so there is a
between-group difference in one task → conclusion could be that temporal lobe patients
have a problem with familiarity memory, but it could also be that familiarity tests are more
difficult than recency memory tests
, - Establishing a single dissociation between two functions provides limited and potentially
misleading information, whereas a double dissociation can conclusively demonstrate that the
two functions are localized in different areas of the brain.
- Double dissociation → one group of patients has a problem with one task and the other
with another task. That means it isn’t just that one task is more difficult than the other, but
that there really is a selective impairment. So, the third patient group shows the opposite
picture and therefore demonstrates that it is not just the task that is more difficult, but that
there has to be a selective impairment for the temporal lobe damaged patients
Dependent or independent functions?
- HM: impaired long-term memory but intact priming
- MS: impaired priming but intact working memory
- That destroys this model of how we think this processing happens, because somehow the
sensory input can go directly into episodic memory without needing the working memory
where priming happens. So, this tells us something about the dependency/independency of
functions!
Patient lesion research:
- Study the functional role of brain regions through brain damage → if part of brain is
important for particular function, this function will deteriorate after damage to this region
- If a patient has a lesion and can perform a particular task that means that he doesn’t require
this region to perform the task. However, that doesn’t mean that this brain region is not used
for the task in “normal” people. (patient without arms can open bottle with mouth, but that
doesn’t mean that people with two arms won´t open the bottle with their arms)
- Limitations → there are all sorts of compensation mechanisms when there are brain
lesions; damage location may vary between patients and there are no controlled ways of
studying brain damage!
- Solution animal studies ? → controlled, localized, replicable lesions
Methods to perturb mental function:
Example study for pharmacology:
- Dopamine has a selective reward-driven learning effect
- Group 1 was given Haloperidol (dopamine antagonist) and group 2 L-Dopa (dopamine
agonist) → group 2 won more in the learning task where the aim was to gain monetary
reward
- Shows the influence of pharmacology, however, a drawback is that you do not know how
much drug makes it to the point of interest in the brain
, - Knockout procedures → specific genes are manipulated so that they are no longer
present/expressed, so one can study the consequences of that gene
Correlation vs. causation:
- It is tempting to conclude a causal link in the absence of a manipulation
Relation PTSD and hippocampal size:
- So, you might conclude more PTSD → smaller hippocampus. But, when looking at twin you
see a similar hippocampal size without being exposed to combat (PTSD). So, this shows that
actually it is not the case that hippocampal size is smaller because of PTSD, but that actually
the smaller hippocampal size may predict the severity of PTSD.
Causal links after surgical intervention:
- Split brain and lobotomy patients
- Deep Brain Stimulation
Looking inside the brain:
- Brain region X is active during task Y, but that doesn’t mean that region X is necessary to
perform task Y. So, the brain might also solve the task without that region, you don’t know
that by just showing that the region is active.
- Lesion and fMRI studies answer the exact opposite question: Can the brain solve this
problem without this region? & Does the brain normally use this region to solve this
problem?
- Single cell recordings → rare in human brain studies, however, specific neurons in MTL were
found to respond selectively to specific familiar images
Additive logic → when using fMRI to find the region of color processing, people will at the same time
think about other things and other regions will light up as well. That is why you again do it in the
exact same way, but without showing colored pictures but this time black and white pictures. If
you than subtract these two conditions from one another, you will get the region responsible for
processing colors.
MRI → The proton in a hydrogen atom is in constant motion and creates a tiny magnetic field. When
a person is placed within the magnetic field of the MRI machine, a significant proportion of their
protons become oriented in the direction parallel to the strong magnetic force of the MRI machine.
Radio waves are then passed through the magnetized regions, and as the protons absorb the energy
in these waves, their orientation is perturbed in a predictable direction. When the radio waves are
turned off, the absorbed energy is dissipated and the protons re- bound toward the orientation of
the magnetic field. This synchronized rebound produces energy signals that are picked up by
detectors surrounding the head of the participant. By systematically measuring the signals
throughout the three-dimensional volume of the head, an MRI system can then construct an image
based on the distribution of the protons and other magnetic agents in the tissue.
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