W1: What is Cognitive Neuroscience: Emergence of Cognitive Neuroscience Methods Flashcards
During the emergence of techniques to measure brain activity, behaviourism was the
dominant psychological approach.
Behaviourists tried to explain behaviour using only stimulus and response avoiding any reference to the
underlying mental states, because mental states could not be defined independently.
Cognitive scientists on the other hand (as compared to behaviourists) try to explain behaviour based on models
of mental states.
Methods in cognitive neuroscience allow scientists to measure
mental states directly
- Behaviorists did not deny the existence of internal mental states but argued that
mental states are inappropriate topics for scientific study
Behaviourism Ignoring complex mental states made experiments more controlled but reduced the scope of
psychology by excluding the study of cognitive functions other than learning.
The emergence of cognitive neuroscience began with the development of techniques
to measure brain activity.
to measure brain activity.
electrophysiological recording
The most popular modern use of electrophysical recording is been
single-neuron electrical recording
single-neuron electrical recording entails
measuring Aps produced by individual neurons
Single-neuron recordings can record neuronal firing either …. OR…. - (2)
extracellularly (from extracellular space next to active neurons) or
intracellularly (from inside a single neuron)
- Recently, most electrophysiological experiments have been focused on studies in
awake behaving animals performing tasks, typically after extended periods of training
- In the past, extracellular and intracellular recordings were performed on
anesthetised animals which prevented experiments on cognitive functions that relied on animals to execute behaviours e.g., reacting or perceiving stimuli.
There are two useful approaches where single-unit data can be acquired and analysed - (2)
- peristimulus time histogram (PSTH)
- Tuning curve
Single-neuron recordings have the activity from individual neurons is acquired in the form of peristimulus histograms, in which - (2)
the number of action potentials that occur after stimulus onset is determined over many trials.
This provides the response to one stimulus.
Data from neuron in visual cortex where monkey moves eyes to visual stimulus and trained to press lever for reward PSTH
In each plot, each row corresponds to a single trial and displays a tick for each
for each recorded AP following a single presentation of the stimulus
The responses of single neuron’s APs in monkey’s visual cortex are summed vertically across the trials aligned in time with stimulus onset (i.e., time-locked) yielding a
peristimulus time histogram of responses of stimulation (bottom)
PSTH allows the activity of neurons to be
linked to stimulus processing and demands of task being performed.
The response to many stimuli shows what type of stimulus the neuron
is sensitive to.
Can do single-neuron recordings in human if they are
going to suregrey
There are neurons from single-neuron recordings that
respond specifically to Jennifer Anderson
A way to study human brain activity that is linked with cognitive processes is done through
electroencephalographic (EEG) recordings
EEG utilises a set of surface electrodes , ranging in numbers from a few to as
many as 256
EEG surface electrodes are usually embedded in a elastic cap fitted over
the scalp shown below:
- The electrodes are brought into electrical contact with the skin via
conducting gel or salt paste and pressure from the elasticity of the cap
There is also a reference electrode in EEG which provides a
a constant defined potential
The invasive nature of single neuron recordings is that
it is restricted to animals or humans undergoing surgery.
EEG or MEG provide non-invasive methods to record
electrical activity from the brain
Unlike single neuron recordings, the activity in EEG and MEG is based on
the activity of many active neurons.
The signal in EEG and MEG is based on the
flow of electrical charge along the dendrites of pyramidal neurons in the cerebral cortex.
- The dendritic trees of the larger cortical neurons are generally oriented
perpendicularly to the cortical surface.
ERPs are based on
averaging the response from a single EEG electrode across many trials
ERPs are small voltage fluctuations in
an ongoing EEG which is triggered by sensory and cognitive events
An ERP is revealed by extracting
portions, or epochs, of the ongoing EEG time-locked to repeated occurrences of a sensory, cognitive, or motor event and averaging the epochs together.
- Visual ERP comprises a series of
negative and positive peaks that are named according to electrical polarity (N for negative, P for positive) and their latency (delay)
- An advantage of the EEG/ERP technique is that it has good temporal resolution: it - (3)
takes readings every millisecond, meaning it can record the brain’s activity in real time as opposed to looking at a passive brain.
Thus especially useful for studies when timing and sequence of functional brain activity is particularly important,
ERPs can indicate how early attention can exert an influence on processing of sensory input
Contour maps of ERP/EEG activity can be made to show the
The patterns can be used to infer (2)
spatial and temporal pattern of activity across many electrodes
which regions of the brain are active.
MEG is a variant of EEG and measures the
magnetic signal associated with electrical signals
- Another way to measure the electrophysiological brain activity noninvasively is to record the magnetic counterpart of EEG which is
magnetoencephalography or MEG
- Much like ERPs extracted from EEG recordings by time-locked averaging to set of stimulus events , this method can be used to extract time-locked responses called
event-related magnetic field responses (ERFs) from ongoing MEG signals
Differences between MEG/EEG is that - (2)
MEG is sensitive to mainly neuronal activity in cortical valleys or sulci and relatively insensitive to the activity in gyri
, EEG picks up voltage fluctuations from sources in both cortical gyri and sulci, although it tends to be more sensitive to the former (gyri)
The advantage of MEG is that magnetic fields are not
affected by the skull/scalp.
MEG and EEG based on same principle as they look at
post-synaptic potentials like IPSPs and EPSPs
In EEG, place electordes on scalp and looking at electrical activity taking place, recording from..
thousands of neurons
If you average each time locked to stimulus onset, you can get
profile of peaks which increase and decrease in electrical potential and relating to cognitive events when processing a specific stimulus
MEG measures magnetic field associated with electrical field and looking what
region of brain is active = spatial info
Libet experiment on when we consciously deicde to move our bodies and found that
Record EEG potentials before you are consciously going to move
Although the brain is only 2% of body weight, it consumes 20% of the body’s energy resources such as
20% oxygen and 20-25% glucose.
Neurons require a constant energy supply to maintain the
resting membrane potential.
However, when they neurons become active and produce post-synaptic/APs they
use even more energy
The brain
does not store energy.
ATP is the principal form of energy for
neurons.
In the brain, ATP is dervived predominantly from
glucose and oxygen
when a region in the brain becomes active it
needs more glucose and oxygen.
the most widely used and popular method for assessing brain activity linked to cognitive functions is
functional brain imaging.
- Detecting and mapping these local changes in the cerebral metabolism and blood flow is the
hemodynamic basis of two functional neuroimaging techniques that have been commonly used (fMRI and PET)
- To meet the increased metabolic demands of active neurons, the local flow of blood to the relevant brain area
increases
fMRI measures the changes
Neural activity uses …
Energy is replenished by.. (3)
in blood flow that accompany changes in neural activity
Neural activity uses energy.
This energy is replenished by nutrients (glucose and oxygen) in the blood.
- fMRI is based on the fact that oxyhaemoglobin and de-oxyhaemoglobin have
different magnetic resonance signals
- The active brain areas use more oxygen than relatively inactive area and thus require more
local blood flow
PET involves injecting a
radioactive atom that is incorporated into water or other nutrients in the blood.
How does PET work and tell which reigon is active?
Changes in the emission of the radioactive atom indicate which regions of the brain are active
fMRI detects changes in
magnetic signal
fMRI measures the change in magnetic signal caused by ratio of
oxy/deoxyhaemoglobin.
Diagram of how fMRI/PET signal works
fMRI offers better … than PET and better… (2)
spatial localisation
temporal resolution
fMRI uses endogenous (internal) signals that are inbuilt to normal brain functions rather than
signals originating from exogenous (external) radioactively labelled probes (PET)
PET often uses ratioactive isoptope such as
O15
How does PET work? - (3)
- When unstable isotope decays, once injected, the extra proton breaks down into a neutron an emitted positron
- emitted positron travels a long distance until it collides with an electron
- collision destroys both paeticles and emits two gamma rays that travel in opposite direction on the site on the collision
- By reconstructing the density of these collision lines using computer algorithms, the location of the active regions can be imaged:
Transcranial magnetic stimulation provides a non-invasive approach to
disrupt brain processing.
A typical TMS experiment probes the role of particular brain regions in
specific behaviours
EPSPs causes a neuron to become
A. depolarised
B. hyerpolarised
C. hypopolarised
D. Unpolarised
A
Which of the following people can be described as a dualist?
A. Rene Descartes
B. Freud
C. Broca
D. Gall
A
The influx of the following ion is critical for neurotransmitter release
A. Calcium
B. Chloride
C. Potassium
D. Sodium
A
Which of the following researchers was the first to describe differences in cytoarchiture across the brain?
a. Cajal
B. Golgi
C. Freud
D. Brodman
D
