1
Q
what are the goals of structural imaging with non-invasive methods
A
- to study anatomy
- to identify abnormalities
- to follow development
- to show plasticity
2
Q
what does structural MRI rely on
A
contrast between tissue types (white matter vs gray matter vs cerebrospinal fluid)
3
Q
what is an application of structural MRI
A
brain plasticity after motor learning - juggling
4
Q
structural MRI- how does learning to juggle change the brain
A
clusters of statistically significant expansion of gray matter
- not to be confused with functional MRI (similar display but different method)
- observed in volunteers who have learned to juggle
- correspond to area hMT/V5, a visual motion area
- after juggling - significantly increase in gray matter
5
Q
what is the ventral pathway and where does it travel to
A
- what pathway
- travels to the temporal visual areas
- responsible for recognition, such as identifying shapes and colours
6
Q
what is the dorsal pathway and where does it travel to
A
- where/how pathway
- travels to the parietal visual areas
- responsible for action and spatial awareness, such as reaching for an object
7
Q
what is area MT/V5 and where is it located
A
- critical component of dorsal pathway
- primary role is processing of movements and motion
- located in mid-temporal region, acting as a bridge towards the parietal lobe
8
Q
what are extrastriate visual areas
A
regions of the brain that process visual information after it leaves the primary visual cortex via the geniculostriate system
9
Q
what are the two primary components necessary for generating structural MR contrast
A
- the magnet - produces powerful, static external magnetic field, referred to as B0
- radio frequency coil - used to transmit pulses and receive signals from the brain to create this image
10
Q
how does the scanner work
A
- magnetic alignment
- signal collection
11
Q
what is magnetic alignment
A
the patient lies on a table within the bore of the scanner, where their body is subjected to B0 magnetic field
12
Q
what is the signal collection
A
- the RF coil interacts with the magnetic alignment of atoms in the body to generate the ‘contrast’ needed to distinguish between different types of tissue, such as gray matter and white matter
13
Q
what atoms does MRI focus on
A
hydrogen protons
14
Q
how does the role of the magnet change the behaviour of protons in the body’s soft tissue
A
- natural state - outside a magnetic field, the ‘spin’ or magnetic orientation of protons is random
- inside the scanner - when a patient is placed inside the B0 field, the protons align with the direction of the external field
- net magnetisation - this alignment creates a net magnetisation vector, which is the sum of the magnetic signals from the aligned protons. this vectors serves as the baseline for creating an image
15
Q
what is the MRI process in terms of excitation and relaxation
A
- initial alignment - protons are aligned 100% in the direction of the external B0 field, creating a net magnetisation
- the RF pulse - coil sends a pulse that tips net magnetisation perpendicular to the external field
- relaxation - once the pulse stops, the net magnetisation begins to recover or realign with the B0 field
- readout - the MR signal is measured during this recovery period. a specific sequence of these pulses and readouts is called an MR protocol
16
Q
how do technical components create contrast
A
- radio frequency coil - used to disturb the aligned protons with radio waves and the listen for the signal they emit as they realign
- the target - MRI focuses on protons because of the high water content in the brain
17
Q
what is T1 relaxation (spin-lattice relaxation)
A
- after a radio frequency pulse tips the protons, they begin to realign with the external magnetic field. this increase in the magnetisation parallel to the external field is called longitudinal magnetisation or T1 relaxation
18
Q
what are the structural-specific time courses of spin-lattice relaxation
A
- brain tissue faster relaxation than in ventricles (cerebrospinal fluid)
19
Q
what is the goal of functional MRI
A
- identify brain areas that support sensory and cognitive processes, derive models of brain function
- blood flow
- need contrast that separates non-activated tissue
20
Q
what are the 3 scientific problems with functional imaging
A
- measurement
- generation
- identification
21
Q
what is BOLD
A
blood oxygen level dependent
22
Q
what does the BOLD signal rely on
A
the magnetic properties of hemoglobin in the blood
23
Q
how to measure neural activity in functional contrast
A
- T2 contrast
24
Q
what is T2 contrast
A
- depends on the balance of deoxygenated to oxygenated hemoglobin with blood in a voxel
- this in turn depends on local regulation of arterial width
25
what happens during local neuronal activation in functional contrast
- flow is increased, more oxy-Hb in capillaries
- oxy-Hb is diagmagnetic whereas deoxy-Hb is paramagnetic, making field inhomogenous
- in inhomogeneous field, horizontal magnetisation decays faster
- slower T2 decay; increased MR signal intensity =blood oxygen level dependent effect
26
what are significant hurdle in capturing high-quality functional data
- small signal change
- poor temporal resolution
- the 6 second peak
- long trials
27
what is small signal change in functional imaging
the actual change in signal intensity during brain activity is very small, often around 2%
28
what is poor temporal resolution in functional imaging
- huge temporal delay between the neural activity in the peak of the measurable BOLD signal
29
what is the 6 second peak in functional imaging
in the visual cortex, the maximum BOLD signal is not instantaneous, it occurs approximately 6 seconds after the visual stimulus is presented
30
how long can a single trial in functional imaging take up to
24 seconds
31
what is space event-related design
- stimuli are presented individually with enough time between them to allow the BOLD signal to return to baseline
32
what is block design
- stimuli of the same condition are grouped together in blocks
- blocks of rest alternating with blocks of stimuli
- more stimuli = more signal
- for example, a 20 second rest period followed by a 20 second block of stimulus A, another rest and then a block of stimulus B
- this creates a strong sustained signal
33
what is rapid event related design
- different stimuli are presented quickly and in a randomised order
- this design uses random stimulus onset asynchrony tot untangle the overlapping BOLD responses from different events
34
advantage of block design
- good statistical power, robust, continuous activation
35
disadvantages of block designs
they are inflexible and limit the number of different conditions a researcher can test in one session
36
how do researchers solve overlap in event-related designs
- using long intervals between stimuli or by randomising the timing and trial types to give each response a unique time course
37
advantages of event related design
- help avoid habituation and allow researchers to analyse specific types of responses, such as comparing correct vs incorrect trials
38
what are disadvantages of event related designs
- they generally have reduced sensitivity to neural events compared to block designs
39
what are the overarching aims of FMRI design
- optimisation
- control
- efficiency
40
how to identify areas that show functional contrast
- spatial preprocessing
- FMRI statistics
41
what does spatial preprocessing involve
- motion correction
- coregistration
- normalisation
- spatial smoothing
42
what is motion correction
- align each volume of the brain to target volume
- detects subject movement
- adjusts for small head movement the participant might have during scan to ensure each voxel remains aligned across time
43
what is coregistration
- BOLD image results superimposed on structured image
- aligns the functional FMRI data with the high resolution structural anatomical scans of the same subject
44
what is normalisation
since every brain is shaped differently, researchers warp individual scans into a standard template space so results from different people can be compared directly
- once all subjects are aligned to the same template space, researchers can calculate the average activation across the entire group
45
what is spatial smoothing
a technique used to blur the data slightly, which helps suppress noise and accounts for small residual differences in anatomy
46
what is the process of FMRI statistics
- statistical analysis on each voxel
- analysis across subjects
47
what is statistical analysis on each voxel
- computers test every single voxel in the brain to see if it's signal changes in a way that correlates with the experimental task
48
what is analysis across subjects
researchers then determine if these patterns are consistent across all pps to draw broader conclusions about human brain function
49
in FMRI data analysis how is a specific voxel identified as being activated
by comparing voxel's observed timecourse against predicte timecourse
50
what statistical model is typically used to test if a voxel's signal follows a predicted timecourse
the general linear model
51
why is it said that FMRI analysis has low power in terms of voxel count
a typical whole brain scan contains a massive number of voxels, making it difficult to detect true effects amidst the noise
52
what does a significant FMRI result generally imply about a brain region
it implies that a certain brain region is involved in that specific task being performed
53
what two primary factors determine the appearance of a final FMRI statistical map
amplitude and noise
54
what are three common clinical tests used to assess cognitive deficits following brain damage
- copying task
- albert task
- line bisection
55
what is the copying task
- a patient is asked to replicate a simple drawing
56
what is the albert task
- a cancellation task where patients must cross out lines scattered across a page
57
what is line bisection
patients are asked to mark the midpoint of horizontal lines
- consistent errors in finding the true center can reveal specific spatial processing issues
58
what are the 2 distinct types of methods required for neuropsychological study
- assessing brain anatomy
- behavioural testing
59
what is the goal of neuropsychology
- localise impaired behaviour to damaged regions (but lesion may affect a relay station rather thana originally functional region)
- exclude localisation of preserved skills to damaged regions (but other regions may have re-organised to perform functions that were originally localised to damaged region
60
what is association in neuropsychology
- damage to a single brain region, but multiple deficits
61
what is dissociation in neuropsychology
- damage leads to impaired performance in task A but performance in task B is normal
62
what is Balint's syndrome
characterised by a co-occurrence of three distinct neurological deficits that result from bilateral damage to the posterior parietal cortex
63
what are the three hallmarks of Balint's syndrome
- simultanagnoisa
- oculomotor apraxia
- optic ataxia
64
what is simultanagnosia
- the inability of a patient to perceive more than one item in their visual field at a singe time
65
what is oculomotor apraxia
- sever difficulty or failure to initiate voluntary, purposeful eye movements
66
what is optic ataxia
- the inability to accurately reach for a seen target in space, despite having normal muscle strength and no primary sensory loss
67
what are the core principles of associations
- primary inference
- alternative I
- alternative II
68
what is primary inference in association
task a, b and c all require the same underlying neural circuit to function correctly
69
what is alternative I in associations
functions a, b and c might be processed by separate, distinct functional regions that just happen to be anatomical neighbours
- a large lesion in that area would naturally hit all three neighbouring spots
70
what is alternative II in associations
region x might serve as a common relay station or hub for several regions that are otherwise anatomically and functionally distinct
71
what is the visual pathway in the dorsal stream
m-ganglion cells - magno LGN - V1/V2/V3 - MT/V5
72
what is the visual pathway in the ventral stream
p-ganglion cells - parvo LGN - V1/V2 - V4
73
what was the experimental set up to test double disocciations
- task 1 - discriminate shapes visually - testing the ability to recognise if two shapes are the same or different
- task 2 - grasp object
74
what happened to patient DF in the experiment
- visual agnosia
- lesion in ventral-occipital
- failed to recognise shapes
- could grasp objects
75
what happened to patient RV in the experiment
- optic ataxia
- lesion in bilateral occipitoparietal
- could discriminate between different shapes
- unable to use shape info to control movement
76
what are the challenges in neuropsychology
- variation in pathology
- weak inferences from single patient
- difficulty in grouping - due to lesion size and location variable
- normalisation issues - weakens anatomical variable
77
how does lesion size effect behaviour outcome
- small lesions may have little effect on behaviour
- small lesions in strategic locations may cause deficits
- in many cases large lesions, damage to several centres
- reorganisation may occur, intact regions change their behaviour
neuroscience and behaviour
flashcards
Decks in class (19)
# Cards
-
emotion46
-
sex differences33
-
methods50
-
methods77
-
alzheimer's62
-
neurodegenerative disorders44
-
schizophrenia56
-
decision making42
-
anxiety disorders27
-
introduction to learning12
-
classical conditioning21
-
instrumental conditioning37
-
numbers and counting17
-
time15
-
theory of conditioning19
-
pavlovian and instrumental interactions56
-
categorisation39
-
successes of rescorla-wagner model69
-
attention55
