cognitive neuroscience Flashcards
phinneas gauge
- survived an explosion and recovered fairly well
- despite severed optic nerve, had a strange lack of injury and cognitive damage
- however, his behaviour and personality changed extremely after the injury
- he went from being quiet, responsible and well liked - to erratic and unreliable
what is EEG and how to do it
place electrodes on scalp and record changes in electrical potentials caused by neural firing in brain - potentials are only around 2-10 microvolts
to generate a measurable response, a very large number of neurons would have to fire at the same time
cause a temporary deficit in a healthy brain which is used to measure the differences in performance of a cognitive task before and after the deficit
has poor spatial resolution - typically use 32 or 64 electrodes, because signals are conducted through the skulls so hard to determine where the neural activity is happening
good for knowing when neural activity takes place
signals are noisy - measures tiny signal that have to compete with many sources of noise (like random neural firing and activity for eye movements and facial muscles, interference from equipment) - signal to noise ration for single experimental event trail is poor (studies average measurements over number of trials)
why should we study the brain
psych - study of mental processes and behaviour
knowing when and where cognitive processes take place in the brain helps us to understand the nature of these processes
can be important for treating and understanding neurological disorders
cognitive neuroscience in theories of cognition
knowing when and where effects occur in the brain can constrain cognitive theories of those effects
e.g. the n400 is an electrophysiological signal that occurs when we hear an unexpected word (widely used to study how and when prediction occurs in language - the brain process the strange word roughly 400 ms after it has been said
cognitive neuroscience in clinical practice
understanding of the neural basis of behaviour allows us to understand cognitive disorders and predict the effects of damage on the brain
sometimes basic understanding of neural processes can have unanticipated applications
e.g. using EEG or fMRI to evaluate patient’s awareness/consciousness or even communicate with them
what are the 2 ways if investigating neural activity and cognitive functions
- change the behaviour and measure the effect on the brain
- change the state of the brain and measure the behaviour
what is a recording study - example
give the brain a stimulus (like a word) and look at where is activated in the brain as a response to the stimulus
for example if you read an action word (verb) there may be greater activity in the motor cortex when patients read this word so you could argue there is a correlation between the motor cortex and reading action words
an inference of this - when people process an action word, they simulate the action to help them understand the word
- but we don’t know is the simulation is necessary to understanding the word
what is an interference study - example
they are better for finding causal relationships
looking at a damaged brain to see if an impaired activity (like word understanding) is related or associated with the part of the brain that is damaged
for example, if patients have damage to their motor cortex, they may have an impaired understanding of action words
an inference of this - activation of the motor cortex is necessary to understand action words
- you must then assume there are no other difference between the 2 groups that could have cause the effect
recording methods
IV - conditions that manipulate behaviour/cognitive processes
DV - brain activity (EEG/MEG, blood flow fMRI)
causality - correlational technique
interference methods
IV - lesion and brain stimulation (conditions manipulating behaviour as validity check)
DV- behaviour or cognitive processes
causality - permits causal inference
are interference studies better
they do allow stronger inference about necessity of a brain region/causality
but they have limitations such as plasticity and reorganisation of function
are recording studies better
can allow for greater flexibility in experimental design and often richer sources of data
- you can sample across multiple brain regions with high spatial/temporal resolution
- sample at a very high temporal resolution
but cannot make causal inferences
converging evidence
comparing results from different techniques can reveal limitations in a theory
- can also reveal areas for improvement in applying analytical techniques to recorded data
what famous cases are most widely used in develop theories about brain and cognition and what areas did they supplement
phineas gauge - behaviour and planning
broca - language
hm - memory
df - vision
classical neuropsychology
mapping brain areas to cognitive functions
typically performed at group level
good at answering clinical questions
cognitive neuropsychology
determining which functions dissociate under damage - evidence for distinct cognitive processes
often relies on single case studies
focus on cognitive processes
doesn’t require information on location of damage
single dissociation - reading example
patient x has reading impairment
ability to read irregular words is impaired (like aisle) but ability to read non words is spared
how to draw inferences from single dissociations - reading example
x had damage to a neural system that is important for reading irregular words but not non words
reading irregular words require different cognitive/neural system than reading non words do
but what if reading irregular words is just harder than reading non words - well if this were the case, both types of reading would rely on the same system and damage to system would affect irregular words more
double dissociation - reading example
compare patient x with patient y who is impaired in reading non words but can read irregular words normally
this allows us to rule out task demand as an explanation (if irregular words are harder to read, they should always be harder to read than non words but this is not the case
double dissociation inferences - reading example
damage to different neural systems can selectively impair either irregular word reading or non word reading
- the brain processes these two classes of stimuli differently
associations - reading example
if patients are all equally bad at reading non words and irregular words
does existence of associations undermine finding of dissociations between x and y
not necessarily, patients who have associations may have damage to another neural system that is necessary for both types or damage to 2 different systems that are close to each other in the brain
* generally, dissociations are more informative than associations
caramazza (1986) - fractionation assumption
brain damage can selectively affect different cognitive/neural systems (like Broca’s area)
- neural specialisation -> basic principle in cognitive neuroscience
caramazza (1986) - transparency assumption
brain lesions can affect existing cognitive systems but do not create new systems
- existing systems can reconfigure -> neural plasticity
caramazza (1986) - universality assumption
all cognitive systems are basically the same
- questionable ? -> individual differences in how people perform at different cognitive operations
how do people vary
in cognitive abilities and the strategies they use to solve cognitive problems
dual route model of reading
connectionist (triangle) model (Plaut, McClelland, Seidenberg & Patterson, 1996)
- to read irregular words correctly, we have to activate their meanings (semantic reading)
dual route cascaded model (Coltheart, Rastle, Perry, Langdon & Ziegler, 2001)
- to read irregular words correctly, we do not have to activate their meanings (use lexical representations instead)
what results would you need to have to be able to suggest that an association exists between irregular reading and semantic knowledge
impaired semantic knowledge of word meaning and poor irregular word reading
- suggest that semantic knowledge is necessary to pronounce irregular correctly
patient EM - single case dissociation between irregular reading and semantic knowledge
had impaired semantic knowledge and spared irregular word reading
- suggests that semantic knowledge is not necessary
woolams et al argument against single case dissociations overturning large observed associations - reading example
occasional single cases do not invalidate theory supported by associations
claimed that while semantic knowledge is generally needed to read irregular words, there were individual difference in how much people rely on the semantic route of irregular word reading
- some people are so skilled at reading they do not need the semantic systems for irregular words
post hoc explanation of observed differences between single case dissociations and large observed associations - Coltheart et al
patients may not fit the predictions of the ‘semantic’ model
- this theory needs to predict who would show a dissociation and who would show a association for it to be an adequate explanation
it also illustrates the problem with single case studies - lesions may affect different people in different ways, if the cognitive systems were different to begin with
how do neurons communicate
by receiving electrical potentials (either exitatory or inhibitory) from other neurons
once a threshold of excitation is surpassed, an action potential spreads along the axon
this triggers a release of neurotrasnmitters at the synapses with other neurons
how to measure neural representations
firing/spiking of action potential (triggered)
in non humans - you can measure the firing rate of individual neurons with single cell recording
in humans - measure the summed activity of large populations of neurons with EEG or MEG
how to carry out single cell recording in animals
electrodes are surgically implanted in the brains of usually rodents of non human primates
monitor the firing rates of neurons when an animal perceives different stimuli
- demonstrates how and where different classes of stimulus are coded in the brain
Hubel and Weisel (1950s-60s) - mapping feline visual system
single cell recording has been instrumental in mapping cats organisation of visual cortex
- initially discovered by accident, found certain neurons in primary visual cortex fired strongly when the cat saw a straight line cause by projector fault
neurons in primary visual cortex are all tuned to a particular region and orientation is visual space
complex cells - pull info from simple cells - can respond to more complex stimuli because the receptive field is bigger
selectivity
specific neurons respond to particular types of visual stimulus
hierarchical organisation
higher level neurons respond to increasingly complex stimuli
- this was critically developed by measuring individuals responses
grandmother cell hypothesis
a logical continuation from the hierarchical model that neurons at the top of the hierarchy only respond the one specific stimulus
- idea that there is a neuron that only exists to respond to somebody’s gran
studies have found neurons that fire selectively for a small number of faces but hard to say whether it is truly specific for an indiviual
seems implausible to have a truly local code with one neuron for each person you know - these would not be very robust to damage
face selective neurons in primates (Chang and Tsao, 2017)
electrodes were implanted in inferotemporal cortex - highest stage of visual processing (where the representations are)
action potential was always fired when one person was shown, and still for different profiles and angles
- shows that the neurons respond to a single identity
Quiroga et al., 2005
single cell study in humans (MTL epilepsy patients)
- found that spikes of action potential occur for pictures of Jennifer anniston and not for other celebrities
similar study completed with pictures of the Sydney opera house compared to other famous monuments
ERP - face perception
n170 - peaks around 170 ms and is associated with facial perception
what are ERPs
different types of stimuli tend to produce characteristic ERPs at different points in time
given names which reflect polarity and timing and sometimes location of the electrode on which they are observed
can be positive or negative but doesn’t tell us anything about cognitive significance
polarity depends on spatial arrangement of the neurons which generate the activity
ERPs and tracking timing
they can be used to track the time course of cognitive processes in a task
components at different points in time may be influenced by different factors
stages of facial processing in terms of ERPs
perception (N170)- is it a face or not
recognition (N250) - is this a face i have seen before
person identity (P400-600)- who is this face and what do i know about them
magnetoencephalography
same basic principles of EEG but signals are measured by squid sensors that record fluctuations in magnetic field
(superconducting quantum interference devices)
advantages of magnetoencephalography
has the same high temporal resolution as EEG but with better spatial resolution too
disadvantages of magnetoencephalography
not so widely available and expensive
hard to install
