Cognitive Neuroscience Flashcards
What does MRI provide?
Provides structural images of the brain as well as measures brain activation as well as how the brain responds to different cognitive conditions
Why should we study the brain?
Knowing when and where cognitive processes occur in the brain can help us understand the nature of those processes
What does the understanding of the neural basis of behaviour allow us to understand?
Allows us to understand cognitive disorders and to predict effects of damage to the brain
What is the N400?
It is an electrophysical signal that occurs when we hear an unexpected word
What is the N400 used for?
It is widely used to study how and when prediction occurs in language
When designing an experiment to investigate how neural activity and cognitive functions relate to one another, what are the two ways we can go?
(1) We can change behaviour and measure the effect on the brain
(2) Or we can change the state of the brain and measure the effect of behaviour
What is a recording study?
It is the first type of study where we manipulate behaviour and record what is going on in the brain
What are the causes of brain damage?
Surgery, tumour, stroke, traumatic brain injury, neurodegeneration
What are the two main types of stroke?
Ischemic and haemorrhagic stroke
What is an ischemic stroke?
Blockage in the blood vessel
What is a haemorrhagic stroke?
The wall of the blood vessel becomes weakened, and it bursts in the artery, depriving parts of the brain of oxygen
What is neuropsychology?
Learning about people with brain damage
What does cognitive neuropsychology rely on?
It relies on identifying dissociations and associations between different cognitive abilities
When studying single cases, we are looking at patients and looking for impairments in different areas of cognition. Alfonso Caramazza proposed 3 major assumptions that we need to make when we are doing this kind of single case research?
(1) Fractionation assumption –brain damage can selectively affect different cognitive/ neural systems
(Neural specialisation is a basic principle in cognitive neuroscience, and is agreed by many)
(2) Transparency assumption – brain lesions can affect existing cognitive systems but do not create new systems
(3) Universality assumption – all cognitive systems are basically the same
What does lesion-symptom mapping tell us?
Tell us important clinical-information about what deficits is likely to result from particular areas of damage
Aside from telling information about what deficits are likely to results from areas of damage, what else does lesion-symptom mapping tell us?
Tells us information about which cognitive processes are associated with which brain areas:
- important for developing theories of brain organisation
- but also, for testing cognitive level theories of processing
What are natural lesions?
Lesions that have been acquired through some sort of injury or disease?
What are limits of natural lesions?
1) we are limited to between-subject designs
2) damage frequently extends across multiple areas of the brain
3) possibility of reorganisation of function in people with long-standing neurological conditions (neural plasticity)
What is Transcranial Magnetic Stimulation (TMS)?
This is a safe, commonly used technique for temporarily disrupting neural activity in healthy participants
What happens in Transcranial Magnetic Stimulation (TMS)?
The function of a small area of cortex is disrupted through application of a rapidly changing magnetic field
In TMS what does the disruption of the small cortex measure?
This measures effects of disruption on particular cognitive processes or behaviours
What is TMS based on?
It is based on the principle of electromagentic induction
How does TMS work?
Alternating electrical current passed through a coil creates a rapidly changing magnetic field which will induce a current in a nearby coil
In TMS, the second coil is replaced with a brain: the magnetic field induces current in underlying brain tissue
What can we do with TMS?
We can create temporary ‘virtual lesions’ to small areas of the brain
What are the benefits of TMS?
1) we can choose where the lesions are
2) Because the effects are temporary, participants can act as their own control [within-subjects design]
3) Because the participants have healthy brains, there are no complications from recovery or plasticity that would affect results
4) can compare the baseline performance to post TMS performance
In TMS what are we observing?
We want to observe whether our participants slow down or make more errors after stimulation.
In TMS what do we want to infer?
We want to infer that the region we have stimulated must be very important for performing that task
What are possible alternative explanations of TMS effects?
(1) brain stimulation is a weird experience – maybe people are distracted and perform worse afterwards
(2) people may feel anxious beforehand – then they might be distracted before and perform better afterwards
(3) there may be a placebo effect – what if people expect to perform worse after receiving brain stimulation?
What are two control conditions you can use in TMS?
- control site : stimulate a region that we don’t think is involved in our task
AND/OR - control task : use an additional task that we don’t think our region is involved in
What are the limits of TMS?
- Stimulation only penetrates 2-3cm below the skull, so deeper brain structures cannot be investigated
- Effects on higher cognitive functions are very small – needs careful task design and measurement
- Effects are transient (10-15mins) so can’t study long-term processes like learning
What does neural representation consist of?
Consists of some sort of neural code
What do neurons do?
Neurons in the brain encode information by communicating with each other through brief electrical impulses which are coordinated across large swaths of neurons
How do neurons communicate with each other?
- Neurons communicate with each other by:
(1) Receiving electrical potentials (excitatory or inhibitory) from other neurons
(2) Once a threshold for excitation is surpassed, an action potential propagates along the axon
(3) This triggers the release of neurotransmitters at the synapses with other neurons.
What is the triggering of an action potential called?
Firing or spiking
In animals, how do we measure the firing rates of individual neurons?
With single cell recoridng
What is it called when we record from multiple cells at the same time and look at how their firing might correlate?
Multi-cell recording
In humans, how do we measure the summed activity of large populations of neurons?
EEG and MEG
What does EEG records?
It records electrical activity
What does MEG monitor?
Monitors magnetic field
How does single cell recording in animals work?
Electrodes are surgically implanted in the brains of experimental animals
This is typically done in rodents or non-human primates
What is measured in single cell recording? and what information is provided?
We can monitor firing rates of neurons when the animal perceives different stimuli.
This provides information on how and where different classes of stimulus are coded in the brain
What are the two things we observe from single cell recordings?
(1) Selectivity: specific neurons respond to particular types of visual stimulus
(2) Hierarchical organisation: higher-level neurons respond to increasingly complex stimuli
What is grandmother cell hypothesis?
The logical continuation of this hierarchical model is that neurons at the top of the hierarchy only respond to one specific stimulus
What happens in EEG?
This is where we place lots of electrodes on a person’s skull and then we record tiny electrical signals coming from the brain
Why does EEG have poor spatial resolution?
This is as a consequence of the fact that signal is generated inside the grey matter of the brain, but we measure it from quite far away, from the surface of the head
Typically how many electrode places do you use in EEG studies?
32 or 64
What is the most useful thing about EEG?
EEG is most useful for learning about when neural activity occurs, rather than where
EEG signals are noisy. What are 3 potential sources of noise?
(1) Random, spontaneous neural firing – represent neural noise
(2) Electrical activity from movements of the eye and facial muscles
(3) Inference from nearby electrical equipment
What are event-related potentials?
When we show different stimuli, or participants do different tasks, we often record a similar-looking change in the response pattern. Those particular potentials associated with certain processes has kind of become your dependent variables which tell you about how the brain is processing information at that particular point in time
How are event-related potentials named?
These are generally given names that reflect their polarity and timing (N1170, P600, N400 etc.) and sometimes also the location of electrodes on which they are observed (N2pc)
What are event-related potentials used to track?
ERP’s are often used to track the time course of cognitive processes involved in a task
What is magnetoencephalography?
This is another technique that records activity related to the firing of our neurons. Same basic principles of EEG but signals are measured by SQUID sensors that record fluctuations in the magnetic field
What happens when brain regions are highly active?
Their metabolic demands increase and the delivery of oxygen to them increases
What do PET and fMRI measure?
They measure the changes in blood supply in brain regions and use them to make inferences about the activity of brain regions
What is positron emission tomography? (PET)
It is the first technique developed to measure cerebral blood flow
What happens in PET?
Using a cyclotron, we can make a certain substance (that would otherwise be normal such as oxygen or glucose or any neurotransmitter) into a radioactive version of itself. This is called a radioactive tracer.
The participant is injected with a radioactive tracer which enters the bloodstream and flows to the brain. The idea here is that it will go to the part of the brain that is currently active
What happens once the radioactive tracer is injected into a participant in PET?
- The radioactive nucleus has been marked with the radioactive tracer
- The substance is travelling to the brain during the same time that the radioactive tracer is emitted
- As it decays it emits a positron (essentially the opposite of an electron, a positive particle)
- As the positron travels away from the nucleus, it bumps into an electron
- This will happen after two or three millimetres after leaves the positron
- When the positron and electron bump into each other, they annihilate each other, emitting 2 photons
- The two photons then travel in diametrically opposite directions from this point at the exact same speed
How is blood flow in a brain region calculated in PET?
It is calculated by the measuring the particles emitted as the tracer decays
What are potential negatives of PET?
- participants are exposed to radiation
- it is expensive
- tasks must be performed for at least a minute
- rarely used in cognitive neuroscience
What does a structural MRI use and what is it used for?
Uses strong magnetic fields to generate detailed images of soft tissue – this is the structural part of the image
What is a functional MRI used for? and what does it allow?
It is used to measure changes in blood supply, allowing inferences about neural activity
What can MRIs detect?
Can also detect the different signatures emitted by oxygenated and deoxygenated blood
What is the BOLD signal?
When neurons are highly active, their demand for oxygen increases. The vascular system responds by increasing the ratio of oxygenated to deoxygenated blood.
What does the BOLD signal stand for?
Blood Oxygen Level Dependent response
What are the little areas of volume that the brain can be divided into be called?
Voxels
How does fMRI studies work?
(1) The MRI scanner provides data on the BOLD response in each voxel in the brain and how it changes over the course of our experiment
(2) Changes in the BOLD response indicate when neural activity has taken place
(3) To analyse the results, we create a predicted BOLD response for each of our experimental conditions
(4) We then test whether the actual BOLD signal from each voxel matched any of our predictions
(5) By repeating this process throughout the brain, we produce an image of which voxels are activates to what degree in each condition
What does subtraction analysis allow us to identify?
- regions where the BOLD response is greater for faces compared with scenes
(You look at which voxels are active, fitting one or the other prediction and perform some sort of statistics against what the false detection rate could be, and then compare) - regions where the BOLD response is greater for scenes than for faces
Since there is no absolute baseline in brain studies, as the brain is never off, what do researchers use as a baseline?
They use a resting baseline, in which the participant lies in the scanner doing nothing
What is the default mode network?
This is the brain network that is most active when you’re not really doing anything
What do traditional fMRI studies tell us?
They tell us whether a brain region is engaged by a particular task/stimulus and multivariate fMRI studies tell us what information is actually available
