Lec 1 Intro and Neuroimaging Flashcards
MIND-body problem
how can a physical substance give rise to mental experiences
Mental experience arises from the heart according to who?
Aristotle (think aorta)
Where did Plato think mental experience arose from
The brain
Dual aspect theory
mind and body are two levels of explanation of the same thing (spinoza)
Who proposes phrenology originally?
What did it entail
Gall and Spurzheim
- different parts of cortex serve different functionsm with different personality traits manifesting in differences in cortical size, crude division of psychological traits
What part of phrenology was the only thing that was kept
functional specialisation- degree of specialiation of neurons in certain regions
Wilder Penfields work
direct electrical stimulation of cortex- produces mental sensations of thinking, perceiving
single cell recording
electrode implanted into axon to record neural activity but does NOT stimulate
EEG properties
Maps WHEN things happen
- measures electrical activity via electrodes on scalp, with resulting trace representing electrical signal fro large number of neurons
- EEG signals represent change in potential difference between two electrodes IN TIME
- EEG average from many trials form an ERP
Name some key ERPs that are processed quickly
N170 for faces
P300 famous./familiar faces , detecting targets
MEG properties
WHEN things happen in brian
- good for spatial and temporal resolution
- measures magnetic field (electrical activity in brain) via SQUIDS device
MRI properties (structural and functional)
Uses differential properies and types of tissues/blood to produce images of brain
- Structural- creates static map (CT and structural MRI)
of the different types of tissue (skull, grey/white matter, CFS fluid) and their properties
-fMRI goof for temporal changes in brain physiology
(PET
- measures concentration of deoxyhaemoglobin
BOLD stands for?
What is the change in BOLD response over time called?
Blood Oxygen level dependent contrast
- hemodynamic response function
(HRI peaks in 6-8 seconds so temporal resolution is limited
What is the measurement of brain activity called
voxels or voume pixels.
This build the 3D brain image
PET properties (part of MRI)
measures local blood flow (rCBF)
radioactive tracer injected into blood stream (takes about 30 secs). Once it has undergone radioactive decay, a positron is emitted. This is picked up by a detector
High radioactivity = brain activity in that area
Cognitive subtraction
Why is it needed?
Control task activity MINUS experimental task activity.
Control task will be similar to the experimental task, common method for fMRI tasks.
- It is needed because in order to infer functional specialisation, comparing relative differnce of exp and control in needed
Criticism of cognitive subtraction
Difficulty of the baseline task.
key to know- Activation in experimental condition must be relaitve to the control task
where has disagreement between imaging and lesion studies come from?
Semantic processign evidence i.e. semantic dementia
What is semantic dementia
Impairment/degeneration im anterior temporal lobes (left in particular), leading to inability to understand meaning (dont know how to use it, the action for it)
Devlin et al (2000) fMRI (structure) and PET (direct blood flow to region) results
Both scan showed anterior temporal area activated in semantic tasks showing this area is key for semantic meaning
TMS properties and advantages
Electrical current induced in area of coil not connected to the battery/energy source
Advantages:
temporary/transient lesion,
reversible, non-invasive
control location of stimulation,
transcranial electric stimulation (TES)
- At very low currents (1-2mA) applied to scalp via electrodes by changing the working potential.
- considered more as modulation rather than stimulation
-after block of lessons lead to changes in neuronal excitability- good for learning and for clinial therapy of migrained, dementia, stroke, parkinsons
TES protocols
Anodal- current goes from + electrode to -
(facilitation effects)
2) Cathodal- current goes from - to + (inhibition effects)
3) Sham- as control. usually cant tell if youve received sham or not
how we know anodal TES is facilitatory
Inhibits inhibitory neurotransmitters = excitation
Anodal stimulation seems to INHBIT GABA (primary inhibitory neurotrans) in motor cortex
How we know cathodal TES is inhibitory
cathodal stimulation seems to inhibit glutamate (primary excitatory neurotrans)
Neuropsychology
study of brain damaged patients, abnormalities to gain insight into normal functioning in healthy brains
2 traditions in neuropsychology
classical neuropsychology- what functions are disrupted by damage to region X
- addresses functional specialisation, group study methods used
cognitive neuropsychology- can a specific function be spared/impaired relative to other cognitive functions
- addresses building blocks of cognition (irrespecitve of WHERE they area) -single case methodology used
what 2 ways can brain damage via stroke occur
Ischemia (blood clot)- lack of glucose and oxygen supply
Hemorrhage- bleeding into brain tissue out of arteries, blood can eventually drain and recover brain tissue after some time
examples of neuropsychological testing (of intelligence, memory, visuospatial, executive function, sensation
semantic memory test- pyramids and palm trees
visuospatial test- figure of Ray (draw what you’ve just seen)
single dissociation
impaired in task A but spared in Task B
classical single dissociation
patient performs in normal range on task B
strong single dissociation
impaired on both tasks but significantly more impaired o one
What dissociation did famous Patient CF have?
Classic single dissociation- he suffered ischemic stroke to left parietal area. He was speechless but could still communicate in gesture
He would leave out the vowels i.e. bologna / blgna
A different patient made spelling errors on consenants only
What can be concluded from the patient CF’s evidence and others about independence of domains in brain
independence of domains can be assumed since single dissociations show difficulty relative to absence in difficulty in another domain. The cases show that the brain has separate neural response for processing written vowels relative to consenants
What dissociation do SD patients have
Strong single dissociation-
semantic impairment whilst attention/executive and visuospatial is spared
RFTD case study- what does impairment in this right hemispheric variant of semantic dementia show in patients
They are significantly worse in social discrimination tasks, often misunderstanding social cues and social scenarios
explain double dissociations
Two single dissociations or 2 single cases with complimentary profiles of strengths/weaknesses (i.e. one omits on consenant, other on vowels)
What is the best example of a double dissociation
Broca’s and Wernicke’s aphasia
What is affected in Broca’s aphasia
Speech production impaired, speech is effortful
What is affected in Wernicke’s aphasia
Meaning of words affected, speech is usually still fluent
Issue with single case studies
We can NEVER average performance from a series of single cases because lesions will never be in the same place
How are group studies possible:
1) group by syndrome-
useful to investigate neural correlates of a disease
2) group by behavioural symptoms-able to identify multiple regions that are implicated in a behaviour
3) group by lesion location- test predictions from functional imaging
