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Summary Neuropsychology and pharmacology
- Établissement
- Katholieke Universiteit Leuven (KU Leuven)
Samenvatting van het boek "The Student's Guide to Cognitive Neuroscience"
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Neuropsychology and pharmacologyChapter 1: introducing cognitive neuroscience
Cognitive neuroscience
Cognitive neuroscience: aims to provide a brain-based account of cognitive and behavioural
processes
- Made possible by technological advances in studying the brain that are safer
Historical foundations
Do mental experiences arise in the heart ((Aristotle) or in the brain (Plato)?
- Mind-body problem: how can a physical substance give rise to mental experience?
Dualism: mind and body are separate substances
Dual-aspect theory: mind and body are two levels of explanation of the same thing
Reductionism: mind eventually explained solely in terms of physical/biological theory
Scientific approaches to mind and brain
- Early anatomists believed ventricles were important -> they believed this was the place where
mental experiences resided
- Cortex was often schematically drawn or misrepresented like intestines until 18 th century
- Gall and Spurzheim (1810) provide an accurate depiction of the features of the brain
Phrenology
- Different parts of cortex serve different functions
- Differences in personality traits manifest in differences in cortical size and bumps on skull
- Crude division of psychological traits and not grounded in science
- Although phrenology is discredited -> the notion that different regions of the brain serve
different functions -> has stood the test of time
- Modern cognitive neuroscience uses empirical methods to ascertain different functions
- It does not assume that each region has one function, or that each function has a discrete
location -> but does assume some degree of functional specialization
For example: Broca area (production) vs Wernicke area (comprehension) -> suggests at
least two language faculties in the brain that can be independently affected by brain
damage
Minds without brains: the computer metaphor
Much of twentieth-century psychology was concerned with observations of behaviour, rather than
observations of the brain during behaviour
- This led to models of cognition that do not make direct reference to the brain -> information-
processing models
- The models were inspired by thinking of the mind as a series of routines (like those found in
computers)
Connectionist models: are mathematical in nature but don’t involve serial processing and discrete
routines
The return of the brain: cognitive neuroscience
1970s: structural imaging methods (CT, MRI) -> enable precise images of the brain
1980s: PET adapted to models of cognition developed by psychologists
1985: TMS is first used
1990: level of oxygen in blood used as a measure of cognitive function -> principle behind fMRI
Methods of cognitive neuroscience
Recording -> bringing in chart
Invasive -> inject something in the brain
Hemodynamic -> using nutrients actively through the blood
Method Type Invasiveness Brain property used
EEG/ERP Recording Noninvasive Electrical
Single-cell Recording Invasive Electrical
TMS Stimulation Noninvasive Electromagnetic
, tES Stimulation Noninvasive Electric
MEG Recording Noninvasive Magnetic
PET Recording Invasive Hemodynamic
FMRI Recording Noninvasive Hemodynamic
fMIRS Recording Noninvasive Hemodynamic
Temporal resolution -> refers to the accuracy with which one can measure when an event is
occurring
Spatial resolution -> refers to the accuracy with which one can measure where an event is
occurring
Chapter 3: the electrophysiological brain
Mental representation = the way in which properties of the outside world are copied/stimulated by
cognition
Neural representation = the way in which properties of the outside world manifest themselves in the
neural signal
In search of neural representations: single-cell recordings
Single-cell recordings:
- Electrodes placed in (intercellular) or near a neuron (extracellular)
- Measure number of action potentials per second
- Action potentials of single neurons = basis of neural communication
Electro-encephalography (EEG)
- Electrodes placed on the skull
- Measures summed electrical potentials from millions of neurons
Distributed versus sparse coding
Rolls and Deco (2002) summarize three different kind of neural codes:
- Local representation -> grandmother cells: all the information about a stimulus/event is
carried in one of the neurons
- Fully distributed representation: all the information about a stimulus/event is carried in all
the neurons of a given population
- Sparse distributed representation: a distributed representation in which a small proportion
of the neurons carry information about a stimulus/event
Rate coding = the informational content of a neuron may be related to the number of action
potentials per second
Temporal coding = the synchrony of firing may be used by a population of neurons to code the same
stimulus or event
Electroencephalography and event-related potentials
Electroencephalography used in 2 main research contexts in cognitive neuroscience:
- Analyses of rates of oscillation and links to cognitive function
- Event-related potentials (ERPs)
Records electrical signals generated by the brain through electrodes placed on different points
on the scalp
Figure 3.7:
- These three neurons are all firing at a similar rate
- But two neurons also fire at the same time -> these two neurons can influence each others
excitability and hence be said to ‘communicate’
- If there are enough synchronous neurons that repeatedly fire -> then this wave-like structure
can be detected in the EEG signal at a particular frequency range determined by the distance in
time between the peaks of activity
Advantages and disadvantages of EEG:
- EEG signal is directly related to neural activity and this electrical activity is conducted
instantaneously to the scalp
EEG has an excellent temporal resolution
- The EEG signal is derived from different sources in the brain and it is not possible to infer
exactly where these sources are from the scalp -> inverse problem
EEG has a poor spatial resolution
Rhythmic fluctuations in the EEG signal
Oscillation-based analyses
- Also called -> frequency bands
, - Neurons tend to fire in synchrony with each other -> but at different frequencies
- Different fluctuation frequencies characterise the different phases of sleep-wake cycle
- Different frequencies also characterise certain cognitive functions
Increased alpha -> linked to visual attention
Increased gamma -> linked to perceptual grouping
Event-related potentials (ERPs)
- Based on EEG recordings
- EEG signal is averaged over many events and aligned to some aspect of the event
- Electrodes record a series of positive and negative peaks
- Timing and amplitude of the peaks is related to different aspects of the stimulus and task
Mental chronometry in electrophysiology and cognitive psychology
Mental chronometry = can be defined as the study of the time-course of information processing in
the human nervous system
- Classic method is response time to a task/stimuli and measure changes in RT across conditions
- Attempts to decompose this single measure
- ERP signal is continuous over time and has some advantages over RT method
Figure 3.11:
- Sternberg’s additive factors method assumes that if two variables affect different stages of
processing then they should have an additive effect on the overall reaction time -> but if two
variables affect the same stage of processing then the factors should have an interactive effect
- His task involved comparing a probe digit with an array of one, two or four digits held in mind
In ERP -> different peaks may approximately reflect the functioning of different cognitive stages
But not a simple relationship between ERP peak and cognition -> because each peak is a sum of
different electrical activities
Investigating face processing with ERPS and reaction times
Different ERP peaks associated with different aspects of face processing
Serial processing:
N170:
- Negative dale on 170msec after we displayed a face -> face selective
N250:
- Effect of familiarity -> if you recognize the face it is a different strength then if you don’t
recognize it
P400-P600:
- Also, for names etc.
Chapter 4: the imaged brain
Structural imaging
= measures of the spatial configuration of different types of tissue in the brain -> these different
properties can be used to construct detailed static maps of the physical structure of the brain
- Most common structural imaging methods:
Computerized tomography (CT) -> these scans are constructed according to the
amount of X-ray absorption in different types of tissue
Magnetic resonance imaging (MRI)
- Advantages of MRI over CT:
Does not use ionizing radiation
Better spatial resolution
Better discrimination between white matter and gray matter
Adapted for use in fMRI
MRI physics for non-physicists
MRI is used to create images of soft tissue of the body, which X-rays pas through largely undistorted
Linking structure to function
Voxel-based morphometry (VBM)
- A technique for segregating and measuring differences in white matter and gray matter
concentration
- Voxel -> a volume-based unit in imaging research the brain is divided into many thousands of
these
, - Can search for differences between groups of correlates with cognitive actions
Diffusion tensor imaging (DTI)
- Uses MRI to measure white matter connectivity between brain regions
- Based on limited diffusion of water molecules in axons -> fractional anisotropy
Functional imaging
= measures the moment-to-moment variable characteristics of the brain that may be associated with
changes in cognitive processing
- Neural activity consumes oxygen as well as generating electrical signals
- In order to compensate for increased oxygen consumption, more blood is pumped into the
active region
- The time taken for this response is slow and so functional imaging has a poor temporal
resolution, but a good spatial resolution
Positron Emission Tomography (PET)
- Measures local blood flow (rCBF)
- Radioactive tracer injected into blood stream
- Tracer takes up to 30 seconds to peak -> very slow temporal resolution
- Effective spatial resolution around 1 cm
- Advantage:
Good spatial resolution
- Disadvantage:
Low temporal resolution
Functional magnetic resonance imaging (fMRI)
- Does not use radioactivity, but signal is affected by the concentration of deoxyhemoglobin in the
blood -> this is called the BOLD response (Blood Oxygen Level Dependent contrast)
- The change in BOLD response over time is called -> hemodynamic response function (HRF)
and it has a number of distinct phases
- The Hemodynamic Response Function peaks in 6-8 seconds -> this limits the temporal
resolution of fMRI
- Has a high spatial resolution for a noninvasive method
- Advantage:
Doesn’t use a radioactive material + good spatial resolution
- Disadvantage:
Low temporal resolution
What does it mean to say a brain region is “active”?
- The brain has a constant supply of blood and oxygen -> if it didn’t, it would die
- This means we cannot literally stick someone in a scanner and read their thoughts
- In order to infer functional specialization -> one needs to compare relative differences in brain
activity between two or more conditions: cognitive subtraction
- This involves selecting a baseline or comparison condition
- A region is “active” if it shows a greater response in one condition relative to another
- if the experimenter chooses inappropriate conditions the regions of activity will be meaningless -
> functional imaging isn’t foolproof
In some regions there is even more activity during rest -> Default Mode Network
From image to cognitive theory: experimental design
Studie from Petersen et al. -> was designed to look for brain regions specialized for the processing of
written and spoken words -> this study provides a good introduction to the principle of cognitive
subtraction
- Idea behind cognitive subtraction is that, by comparing the activity of the brain in a task that
utilizes a particular cognitive component to the activity of the brain in a baseline task that does
not, it is possible to infer which region are specialized for this particular cognitive component to
the activity of the brain in a baseline task that does not, it is possible to infer which regions are
specialized for this particular cognitive component
- Basic cognitive stages involved in reading written words aloud and producing spoken semantic
associates to written words
- Cognitive subtraction is founded on the assumption that it is possible to find two tasks that differ
in terms of a small number of cognitive components -> the results show several regions of
activity, but only the main results on the left lateral surface are depicted here
Cognitive conjunctions and factorial designs
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