Defining structures 1: observing lesions

Question 1

What was the anatomical description that Broca provided for Tan?

Answer 1

-large lesion
-definitely including the third convolution of the frontal lobe (inferior frontal gyrus)

Question 2

What is a localist framing of broca’s area?

Answer 2

broca’s area is the portion of the left frontal lobe that is important for speech

Question 3

What was the contemporary criticism provided by a prominent holist Hughlongs Jackson of Broca’s area?

Answer 3

to locate damage which destroys speech and to locate speech are two different things (to say that this area is the reason he can’t speak is no to say this area is the reason he does speak)

Question 4

What was uncovered by Dronkers and his colleagues when looking at leborgne’s brain with broca’s lesion?

Answer 4

the lesion is very deep and includes the insula and there is alot of white matter damage to the superior longitudinal fasciculus (this basically connects the front and back of the cerebral cortex)

Question 5

What is a lesion in simple terms?

Answer 5

a brain injury

Question 6

What is a symptom?

Answer 6

a loss of function

Question 7

What is a voxel?

Answer 7

a volumetric pixel

Question 8

Bates, Dronkers and colleagues develop a technique for associating symptoms with lesion location using what?

Answer 8

MRI data

Question 9

What is magnetic resonance or how do you make pictures with a magnet?

Answer 9

-look at a magnetic field and you are being slid into that magnetic field and its job is to align a bunch of protons in one direction and a magnetic filed has two axes and protons line up on the third axes

Question 10

When a strong magnetic field is applied along two axes where do protons line up?

Answer 10

along the third axis

Question 11

If you apply an excitation or radio frequency pulse to proton temporarily what happens?

Answer 11

the protons flips from being lined up and they are then going to relax back and release the energy we put in them and then can have algorithims which determine where that energy came from and where that energy was released

Question 12

What is recorded by a receiving coil?

Answer 12

the energy released by the protons as they relax back to their longitudinal orientation with respect to the magnetization vector

Question 13

What are the different tissue types of the brain?

Answer 13

-fatty tissues
-white matter
-gray matter
-fluid

Question 14

What are the macronutrients of brain tissues?

Answer 14

fat and water in different concentrations

Question 15

Since different tissues have different relaxation times what happens?

Answer 15

when we take a snapshot of magnetization at any point in time contrast is readily observed between different tissue types

Question 16

With some additional nuances essentially the same kind of signal can be used to determine what?

Answer 16

the relative amount of deoxyhemoglobin in capillaries

Question 17

What is the basis of fmri?

Answer 17

the blood oxygen level dependent response (BOLD) - indicated brain activity

Question 18

What is a voxel in complex terms?

Answer 18

a 3d pixel created by the MR system when data are recorded digitally; virtually slice up brain and scan one voxel at a time and put a grid over each slice and each cube gives a signal intensity number of the amount of fat and water in that area

Question 19

What is the typical resolution for structural images in MRI and what does that mean about the information we are getting?

Answer 19

1mm^3 - thats a few million neurons worth of tissue so the info we are getting is not that great since synapses are important for explaining function but that might be a few million neurons off when localizing a particular areas function

Question 20

Can you get smaller than 1mm^3 in terms of resolution for MRI?

Answer 20

yes but lose contrast in doing so

Question 21

What is cytoarchitectonics? Who was it used by to divide the human brain into areas?

Answer 21

the organization and structure of cells - Used by Broadmann and a light microscope to divide the human brain into areas
-his map is still used today - broca’s area is referred to as BA 44/45

Question 22

What does the gross structure of the brain have?

Answer 22

sulci and gyri and the folding of tissue which allow us to pack a great SA into a small volume; the gyro can be seen via a light microscope

Question 23

What did Talairach and Tournoux set out to do?

Answer 23

produce an MRI based atlas

Question 24

What was the idea behind the talairach atlas?

Answer 24

the idea was that brain images could be aligned to a few landmarks and structures would fall roughly in line with the standard brain
-a certain slice has certain structures and line up everyone according to some landmarks and use computational tools to expand and contract the brain so it can fill the same space

Question 24

What are broadmann area labels?

Answer 24

the numbers along the outside of the blue strip (indicating grey matter)

Question 25

What are some of the issues behind the spatial normalization behind the talairach atlas?

Answer 25

-there are broad ethnic and age differences in the head shape so the standard brain might not fit
-voxels are not anatomically real but broad patterns of sulci and gyri are anatomically real

Question 26

What is the first thing they do in a spatial normalization program?

Answer 26

-they unfold the brain and then line up the sulci and gyri so you have confidence in that you are pointing to the same ones and then they refold it and shrink it back down

Question 27

When are standards useful to clinicians and scientists?

Answer 27

when they are telling us what you should expect and they are generally averaged our when you try to have one standard for everybody so a lot of statistical work goes into normalization

Question 28

When you are looking at an fMRI scan what are you looking at neuroanatomical orientation wise?

Answer 28

you are looking at a slice through the axial plane

Question 29

If you look at the right hemisphere what can you verify in an fMRI scan what can you verify>

Answer 29

that is the same structural image as this part of the brain - that includes mainly the parietal and frontal lobes - a bit of occipital as well but it is hard to tell

Question 30

On the left hemisphere of an fMRI map on slide 14 of this lecture is a statistical map, what can you see?

Answer 30

-each voxel is colored according to the value of a statistical test - in this case a t test - based on the result of a behavioral measure

Question 31

How come on slide 14 the fMRI statistical map was on the left hemisphere?

Answer 31

because the study from which these image were pulled from was a language based study so that is the side of the brain im[plicated in that

Question 32

How do they perform the t-test which provides the statistical map per voxel in an fMRI slice scan?

Answer 32

-they divide people into 2 groups and one group have visible damage in a voxel and the other group does not - so they can go in and draw a little volume for each lesion and put every lesion into a common space and then compare group i and group 2 using stats and ask is performance different between group i and group ii - you can try to map out the result of damage of a particular part of the brain to some cluster of symptoms shown behaviorally

Question 33

The study with bates et al. had participants complete a series of tests some related to fluency and some related to comprehension, what did they find?

Answer 33

-the symptoms tested were the first two components of the western aphasia battery test - spontaneous speech and auditory comprehension

Question 34

What makes up spontaneous speech on the western aphasia battery test?

Answer 34

broca’s area like things - like being able to answer open ended questions; to test this you can count the number of words they say and describe picture and the complexity and variety of the words used and the speed with which they can speak

Question 35

What makes up auditory comprehnsion on the western aphasia battery test?

Answer 35

answering yes no questions or identification of objects and picture and execution of commands of controlled complexity

Question 36

What does a t test compare?

Answer 36

compares the differences in the mean of two distributions to their variance
-so a t test where the means are close to each other and there is a lot of overlap would produce a low value while one where the distributions barely overlap would be considered to produce a statistically significant difference

Question 37

What is the similarity/difference between a t-test and subtraction method?

Answer 37

-both try to compare two groups to one another
-t-tests can quantify statistical difference between two groups via the relative difference in means relative to their respective dispersions of two groups while subtraction method does not quantify

Question 38

How do we formalize structure-function relationships in aphasia data (MRI data)?

Answer 38

-the symptoms are defined very broadly
-they tend to observe many patients or cases to abstract away from potential fake patterns specific to individual patients and rather observe broader patterns

Question 39

What regions of a brain tend to be likely damaged in individuals with fluency deficits?

Answer 39

the frontal area (left hemisphere)

Question 40

What regions of a brain tend to be likely damaged in individuals with comprehension deficits?

Answer 40

the back area (left hemisphere)

Question 41

What was the main finding of the voxel-based lesion symptom mapping study by bates et al.?

Answer 41

they found that fluency deficits were more strongly associated with the insula than with brocas area

Question 42

What does voxel-based lesion-symptom mapping allow for?

Answer 42

can move away from case studies and double dissociation logic and can now quantify and say these frontal areas are related to fluency and the back areas are related to comprehension

Question 43

What is the complementarity with perception/motor and speech?

Answer 43

-motor processing tends to run in a dorsal stream which has been found to run parallel to speech fluency since that has been found to run dorsal as well
-perceptive processing such as recognition of visual and auditory forms tends to run in a ventral stream which parallel to comprehension which has been also found to run ventrally

Question 44

Where is broca’s area found?

Answer 44

the front of the brain - left hemisphere - left inferior frontal gyrus

Question 45

Where is wernicke’s area found?

Answer 45

back of the brain in the superior temporal gyrus

Question 46

Where are the strongest associations found for fluency of speech?

Answer 46

they are in the medial area for broca and this is the insular cortex and has to do with the coordination of motor fluency for motor tasks

Question 47

Since voxels are made up and not biological - spatial normalization is performed and huge sample sizes are taken in order to perform a statistical test to see if an area is connected to a specific deficit - this may still not line up in each study - what does this result in?

Answer 47

take a poll of neuroscientists to identify brocas area and see that there is disagreement if it is the entire whole inferior frontal gyrus or part of it - this shows how there is a lot of slop on the literature in cognitive neuroscience about anatomical regions and structure relating to function