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Banich & Compton (2011) Cognitive Neuroscience, 3

Rd

Jamie Ward (2010)
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Wadsworth Cengage
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Psychology Press
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Ed
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Brain tissue is less dense
than blood
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Tissue that is dense will appear white and tissue/material that is more dense will
appear black
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It causes all the magnetically sensitive particles to align themselves in
the same direction
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The time it takes for the protons to go
back to their original state (relaxation time) is recorded through a radio-frequency coil
that acts as a receiver coil (positioned around or near to the persons head)
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Gradient field – varies in intensity over the area being imaged
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A 3-d image of the brain is able to be formed due to spatial
information and signal intensity received
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This detects the
main axis or direction along which water diffuses in nerve fibers
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Techniques for assessing physiological Function
Functional Brain Imaging Methods
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Used to determine which methods discern which areas of the brain are physiologically
active by measuring changes related to blood flow and the metabolic changes in
compounds used by different brain regions
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Developed earlier than fMRI
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Positron emission tomography (PET)
Greatest advantage researches can determine the amount of a specific compound of
interest, such as a neurotransmitter for example
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The resolution is lower than that of the functional MRI
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Functional Magnetic Resonance Imaging (fMRI)
The use of fMRI requires that we always compare two conditions: the condition of
interest to a baseline
Researchers carefully pick a baseline task against which to measure changes in brain
activation associated with the task of interest
fMRI cannot measure a neuronal response directly indexes a hemodynamic response
(response of the vascular system to the increased need for oxygen of neurons in a
local area)
this response is slow

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however, the temporal resolution is much faster than PET
fMRI is a widely available method, non-invasive technique that does not involve high
radiation and multiple scans can be done an individual unlike PET and it is quicker
than PET
the precision of scans obtained by fMRI allows us to examine brain-behaviour
relationships in individuals useful for clinical interventions such as neurosurgery
disadvantage only provides information about the relative concentration of
oxygenated and deoxygenated blood

Electromagnetic Recording Methods
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used to record the electrical activity of the brain that results from neuronal firing or
the magnetic fields induced by hat electrical activity
offer scientists the best available temporal resolution of brain activity
Single-Cell Recordings
Once a baseline firing for a given cell has been established, researchers then
determine what properties of a stimulus make the cell fire maximally above that
baseline
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Opportunities for studies with humans is limited but in animals there is a lot of
research and studies that have conducted testing the sing-cell recordings
However, there are cases where electrodes have been implanted into the brain for the
removal of epileptic tissue and cases in which electrodes are placed on the surface of
the brain during an operation to better isolate the source of seizure activity
Such procedures allow scientists to acquire knowledge of the stimulus properties that
make cells fire in a given brain region
Electroencephalography (EEG)
Recordings of the brains electrical activity are often used clinically to detect aberrant
activity such as that associates with epilepsy and sleep disorders
In EEG electrical signals produced by brain are recorded by metal electrodes
positioned on the scalp
The number of electrodes used varies form 20 to more than 100 in high-density-array
recording systems
One electrode is connected to an electrically inactive site such as the mastoid bone
(behind the ear) which acts as a reference that provides a base-line against which the
activity at each of the other electrodes can be compared
The electrical potential recorded at an electrode on the scalp is the summed or
superimposed signal of the postsynaptic electrical fields of similarly aligned neuronal
dendrites
The electrical potential which is recorded as a waveform, has a voltage and a
frequency it oscillates at a specific rate (measured in hertz)
Frequency of EEG varies depending on the persons state
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When person is awake
can be 15 Hertz (beta activity, more fast)
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Recent research ahs shown that synchronous oscillations between groups of neurons
in the 30-100 Hertz range gamma activity play an important role in perception and
attention
Clinically EEG can detect epilepsy which can be conceptualized as a electrical storm
in the brain
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After individual is treated with anticonvulsants, the EEG can be performed
again to make sure that the spiking has decreased
The degree of alpha suppression is examined o determine how active the brain is
under different conditions
Event-Related Potentials(ERP)
Recorded in reference to a specific event
Recordings of the brains activity that are linked to the occurrence of an event such as
the presentation of a stimulus
Can provide some idea of when processes occur in the brain
Dipole small region of electrical current with a relatively positive end and a relatively
negative end which is caused by the alignment and firing of dendritic fields in the
brain
The waveform created can be divided into components characteristic portions of the
wave that have been linked to certain psychological processes such as attention and
memory
Components are always given a letter (P or N for positive or negative) and a number
(he milliseconds after stimulus presentation that the the component appears)
Components are often divided into two categories: exogenous components (linked to
physical characteristics of stimulus and occur in waveform
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Also been used to understand more
about the neurophysiology underlying psychiatric disorders such as schizophrenia

Optical Recording Methods
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Allows neuroscientists to simultaneously obtain information about the source of
neural activity and its time course
Method is called optical imaging
Can provide two types of information: first is similar to that obtained by the BOLD
signal in fMRI by measuring absorption of light (slow signal)
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Although TMS can facilitate brain activity it can also disrupt it
TMS can also provide important information about whether a behavior is critically
dependent on a particular brain region or whether it results from the interaction
between brain regions
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As currently
designed, the stimulating coils affect only the region of the brain closest to the
surface
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Also, it is
not possible to precisely control what regions of the brain are affected by TMS

Multimethod Approaches
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using multiple tools in tandem

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One common coupling combines electromagnetic methods of recording brain activity,
which provide excel- lent information about the timing of brain events, with fMRI,
which is better at providing information about the location of brain activity
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Another multimethod approach involves combining TMS with other methods to
provide information on the connectivity between brain regions
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Assessment of behaviour in Brain-damaged populations
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the job of both clinical and experimental neuropsychologists is to carefully tease apart
the possibilities and pinpoint the probable locus of the deficit
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This assessment is designed to provide a profile of which abilities have been
compromised and which ones are intact

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with the goal of casting a wide net to detect any type of brain dysfunction of either
neurological or psychiatric origin
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When deficits are more subtle, they may be difficult to detect
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the examiner initially uses information from a small set of tests (e
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, WAIS-IV,
Boston Diagnostic Aphasia Exam) to generate hypotheses about the set of particular
abilities that were compromised by the brain damage
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Researchers create simulations generally known as neural networks, to help them
test theories of neuropsychological functioning and to derive general principles
regarding brain-behaviour relationships

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Computational modelling has a number of important strengths
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Second, models can be manipulated systematically in ways that may be impossible to
do with animals or people

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Finally, the outcome of modelling can provide researchers with novel predictions
about the relationship between the brain and behaviour that can be tested

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A variety of computational models can be used to simulate mental functions in
humans

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connectionist networks are composed of interconnected layers of units that exhibit
neuron-like behaviour

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One of the most common methods for learning in computational models is supervised
learning

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the system is provided with an input and allowed to compute through to a final output

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output obtained is then compared to the output that should have been given

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Other computational models work by an alternative process called Hebbian learning,

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in Hebbian learning models, when the activity of units co-occurs frequently, the
connection strength of one unit upon the other is increased

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