Cognitve Neuroscience Flashcards
L2:
Outline the learning objectives of Lecture 2: Cognitive Neuroscience
- Describe the basic principles of how information travels around the brain (neurons)
- Explain how fMRI can help us understand cognitive processes (fMRI)
- Explain how TMS is used to alter cognitive processes (TMS)
- Explain what an ERP is and what ERPs can tell us about early visual processing and face processing (Visual evoked potentials, N170)
- Explain how we know where early visual processing and face processing occurs in the brain (specialisation of cortical regions - knowledge acquired via fMRI)
L2:
Describe the basic principles of how information travels around the brain
Neural activity is both chemical and electrical. The chemicals are called neurotransmitters, which are first brought to the cell via the dendrites. The neurotransmitters provide signals to the cell (excitatory or inhibitory). The cell body takes the chemical signals from the dendrites and determines whether there’s enough of a signal to allow the neuron to fire (reaching the action potential threshold). If the threshold is met, then an action potential creates the electrical signal that then travels down the axon to the terminal buttons, which then release neurotransmitters to communicate with other neurons.
L2:
Describe the basic principles of fMRI
- SO… when neurons are active, they metabolise (burn energy), which is automatically replenished by the blood (after a few seconds).
- Blood contains haemoglobin (which contains iron) so it’s possible to detect blood flow via magnetic fields and distinguish between oxygen-rich/ oxygen-depleted blood.
- By measuring BOLD (blood oxygen level dependent) response in an fMRI scanner, we can work out which areas of the brain were active recently
There are also other methods, but BOLD is by far the most common
L2:
Describe an example of an fMRI study
(Houdé et al)
USED A NEO-PIAGETIAN APPROACH
Number conservation in children (ie. working out that if coins are more spread apart etc, they are still the same quantity)
Children were prepped to stay still and calm inside the fMRI machine. Preparation:
A – initially set up a tunnel in the childs school
B - brought into lab environment, played the “statue game” with a simulation scanner (cardboard)
C – scanner can eventually be used, has child friendly imaged on it (planets etc)
PIAGET’S CONS. OF # TASK
Children had to indicate if they thought that lines of dots had the same number or different, via a button inside the machine. In the first stage, the lines are the same length with the same number of dots. An inter-stimulus interval of less than a second (750ms +/- 250 ms).
Second stage, rows are now either same or spread apart, asked to indicate again. Intertrial interval of 9 seconds +/- 1sec - to allow for BOLD response (takes 4-5 seconds).
Control condition - Everything is the same but the task was to identify whether the dots were the same colour across the two rows.
Results:
- 2.5% of 5-6 year olds could number conserve
- 97% of 9-10 year olds could number conserve
- Both groups equally adept in colour condition
Brain response:
- some of the active areas are the same across the task type (most likely these areas are not to do with the tasks but button pressing or something else more general)
- activity was very different between number conservers and non-number conservers, by comparing scans we can localize active areas
L2:
Evaluate fMRI as a brain scanning technique
Advantages:
- tells us which parts of the brain are used in which tasks
- reasonable temporal resolution
- get structural data within the same trial
Disadvantages:
- claustrophobic, noisy, movement artefacts (difficult for button-press)
- can’t have any metal stimuli
- BOLD isn’t a direct measure of activity, we can only infer
L2:
Describe the basic principles of transcranial magnetic stimulation (TMS)
- Non-invasive method causing depolarisation or hyperpolarisation of neurons in the brain i.e. decrease or increase in activity.
- Uses electromagnetic induction to induce weak electrical currents into the brain cortex
- can cause motor evoked potentials (limb twitches)
- can produce a simulated temporary “lesion” of the brain by preventing normal function of that region (thought to have no long lasting adverse affects)
This technique was invented at the Uni of Sheffield in 1985
L2:
Describe an example of a TMS study
(Rossi and Rossini)
Investigated spatial neglect following strokes
- this tends to occur on the left-hand side, as lesions tend to occur on the right hemisphere of the brain
Using TMS to treat spatial neglect
- neurons are activated on the left-hand side of the brain if the left-hand side of the drawing space is being neglected
Currently only used as a temporary phenomenon
L2:
Evaluate TMS as a technique
Advantages:
- near portable
- can ‘stimulate’ or ‘lesion’
Disadvantages:
- difficult to specify precise regions
- only surface regions
- unknown long-term effects
L2:
Describe the basic principles of electroencephalography (EEGs)
Principles:
EEG measures electrical signals generated by the brain through electrodes placed on the scalp. Signals are produced by partial synchronisation of cortical field activity and are measured as changes in voltage, recorded at the scalp, over time. Analysis of EEG signals may be task-dependent or task-independent.
> How are EEG signals detected?
Electrodes are placed on the scalp, connected with gel or a conductive solution. EEG signals are transported to an amplifier. The amplifier measures the difference in voltage between the active electrode and the reference electrode. The frequency of measurements is up to 2000Hz.
Electrodes are labelled according to their placement on the scalp.
L2:
Evaluate EEG as a technique
Advantages:
- very good temporal resolution
- less subject to motion artefacts, not claustrophobic, can even be used on infants
- the major artefact is eye-blinks but can be monitored and accounted for
Disadvantages:
- poor spatial resolution
- inverse problem -> given a pattern of activity, how do you determine which brain regions caused it?
L2:
What is a visual evoked potential? What does it look like?
When looking at a stimulus, it takes the brain a little bit of time to respond. There is a small negative deflection initially, then a strong positive response from the visual cortex around 100ms after a change in visual stimuli occurs (consistend between individuals, and stays contant throughout lifetime).
L2:
What is an ERP?
Event-related potential - beginning as postsynaptic potentials generated during neurotransmission, they travel through the brain and skull to the scalp, contributing to an overall encephalogram
A visual evoked potential, is, therefore, a kind of ERP, an event-related potential resulting from a visual stimulus
Been used to study attention since the 1960s
P1 = first positive ERP peak N1 = first negative ERP peak N170 = precise timing of peak
L2:
What can ERPs tell us about face processing and where it occurs in the brain?
Include reference to research evidence
(Nguyen et al)
Nguyen et al - Looked at ERP of upright, inverted and scrambled faces (with chair image control)
Looked at the difference in activation between different stimuli. For the different categories of images, there are different kinds of traces from the ERPs. The brain starts to differentiate between the different kinds of stimuli around 170ms (N170 - the point at which neural processing of faces begins), the largest difference was between the categories of faces (upright or inverted) and the non-faces. Small difference between upright and inverted faces processing time (upright was slightly quicker). The combined EEG and fMRI findings show which areas of the brain are activated when processing upright and inverted faces.
Combined data from EEG and fMRI show that face processing mainly in the fusiform face area (FFA) but also partially in the superior temporal sulcus (STS) and medial fusiform gyrus (mFG).
Responses were greatest to normal faces in the FFA, inverted faces in the mFG.
L2:
What can ERPs tell us about early visual processing?
Include reference to research evidence on ERPs generally and the gain control theory
(Luck et al)
Luck et al - Lit Review of ERP studies into Attention
Does attention modulate information processing at a sensory stage or at a later stage?
It is obvious that sometimes attention operates after perceiving a stimulus e.g. we may see something and choose not to attend to it overtly. But can attention sometimes suppress the sensory processing of a stimulus?
ERPs are well suited to addressing this ‘locus-of-selection’ issue… you can compare the ERP waveform elicited by an ‘attended to’ stimulus to that of a physically identical ‘unattended to’ stimulus. The earliest point at which the two waves differ provides an upper bound on the initial effect of attention on the neural processing of the stimulus.
Example: comparison of “attended to” and “unattended to” rectangles showed that the waveforms began to differ in the latency range (before it starts) of the P1 wave (between 60-100ms after stimulus presentation) - indicates that attention modulates processing at or before this time… there may be earlier differences that don’t show up on the ERP wave.
Gain control theory:
Suggests the system is merely a mechanism that causes larger P1 responses for ‘attended to’ stimuli vs ‘non-attended to’ stimuli, increasing sensory gain.
Evidence: stimuli presented, when lots of noise (visually and neurally) accuracy is limited by visual noise (increasing sensory gain here would amplify both noise and signal). When there is little noise, accuracy is limited by neural noise (increasing sensory gain here would amply signal only).
L2:
Outline tDCS (+ advantages and disadvantages)
Delivers a small electric current to the brain through electrodes attached to the scalp, can either excite or inhibit neuron activity.
Advantage - Cheaper and easier to use than TMS.
Disadvantage - Has a weaker effect on neuron activity.
