Lecture 7 - Research Methods Flashcards
Methods – what questions can we ask?
- Santiago Ramon y Cajal said we can ask how but not why questions.
- But how questions can be asked on many different levels.
- Cellular
- Anatomical
- Functional
- Systemic
Santiago Ramon y Cajal said we can ask ___ but not ___ questions
HOW
WHY
Who is Santiago Ramon y Cajal?
father of modern day neuroscience
Cellular q’s
how do neurons communicate?
Anatomical q’s
how are different areas interconnected (cytoarchitectonics)?
Functional q’s
how do certain areas mediate certain behaviours?
Systemic q’s
how do disease processes affect brain function?
Cellular methods
histology and staining.
- ways to prepare tissue so that we can view the tissue under a microscope & see what’s gone on after our intervention/experiment
Anatomical methods
autopsy of healthy and diseased brains.
Functional methods
human (natural/rarely induced - stroke, bullet wound, car accident etc.) and animal (induced - specific areas) brain lesions.
neural stimulation – animal studies (single units) and human studies (disruption to networks – TMS).
- TMS = transcranial magnetic stimulation - way of temporary lesioning or existing cells
Systemic methods
neuroimaging – the brain in action
- what happens in brain when performing various activities/tasks
Lesion methods
removal of tissue (ablation), radio frequency lesions (blast of radiowaves - quite damaging/destructive), chemical lesions (more subtle - can target certain transmitters), reversible chemical lesions, cooling.
What does reversible chemical lesions & cooling do?
can use animal as its own control subject - reversible
Lesion studies
Assume that if cognition X is disrupted by a lesion to a brain area Y then region Y “supports” function X.
- meaning: if there’s an area of the brain, ex. primary visual cortex & lesioning that area of the brain, if that affects vision, then the primary visual cortex affects the visual system
- so the visual system must be tightly linked to that area of the brain
Modular concept of brain organization – a place for everything and everything in its place.
Shouldn’t forget that many functions are highly distributed throughout the brain!
Shouldn’t forget that many functions are highly ______ throughout the brain!
DISTRIBUTED
Animal lesion studies
& what may it be due to?
experimental ablation. (removal of tissues - causes changes in the behaviour that can be due to a few things)
caution in interpretation – change in behaviour after a lesion could be due to many things:
- the loss of function supported by that particular region.
- the loss of a sub-component necessary for the behaviour caused by disruption to the network.
- co-existing behavioural changes unrelated to the particular region.
Animal lesion models
Lesions may also change behaviour (adaptation to the deficit).
Monkeys deprived of sensory feedback to one limb will favour use of the other limb.
When deprived of sensory feedback to both limbs they will not favour one over the other.
- haven’t knocked out the ability for that monkey to use that limb, but it’s had a preference now for using the other limb
- but if you knock out sensory feedback, it uses both
Methodological limitation – correspondence between animals and humans may be low (e.g., right parietal lesions in monkeys does not produce neglect).
Methodological limitation
correspondence between animals and humans may be low (e.g., right parietal lesions in monkeys does not produce neglect).
- not a 1:1 coorespondence
Animal lesion studies types
- high frequency radio pulse
- chemical lesions
- excitotoxic lesion
- reversible lesions
High frequency radio pulse
destroys everything.
Chemical lesions
targets specific neurotransmitters neurons.
Excitotoxic lesion
spares axons that are passing through area.
- think: head is lesion (sparing axons passing through)
Reversible lesions
anesthetic or cooling (neurons not firing as much - almost temporarily inactivating that area of the brain).
Reversible Lesions
Within-subjects designs (subject is acting as its own control)
- test with the lesion and without (to see diff. in their beh’s)
- increased statistical power
Reversible Lesions: Design Issues Disadvantage
don’t euthanize the animal, stain the brain, and determine that the lesion was in the desired location.
- hard to know if you hit the right area
Stereotaxic Surgery
- helmet like mount on a person’s shaved head
- purpose: so surgeon can use a map of the brain to know where they’re doing the implantation
- use a particular seam in the skull (a SUTURE) as a landmark.
- BREGMA - the junction of the coronal and sagittal sutures (fontanel in infants).
A suture
use a particular seam in the skull (a suture) as a landmark.
Bregma
the junction of the coronal and sagittal sutures (fontanel in infants).
Skull Sutures: Targets for Lesion or Electrode Placement
- Cut scalp of rat open so we are looking at the skill
- Use bregma as 0.00 point
- Lower an electrode so that the tip touches the edge of the skull
- We take a recording of that
- If we use that as our 0 point, we can then use a map/altus of the brain to figure out how far down/left or right, forward or back etc. we have to go to hit the area we want to hit
- Have to figure out where to drill the hole & how far down do we have to send it in order to target that specific area of interest
Stereotaxic Atlas
google maps for the brain
- breaks brain down in diff. quadrants so you could use those #’s to figure out how to adjust your electrode or stereotaxic device to lesion the areas your interested in lesioning
Rats are…
anesthetized, holes are drilled and the tip of the electrode is sunk down to the level specified in the stereotaxic atlas.
Current is turned on, ablating the structure.
Rat is sutured and is tested after a couple of days.
essentially - putting rats head in the position that matches the head that was used in the stereotaxic axis
Animal Studies: Sham Controls
control animals must undergo all aspects of the lesion study except the lesion itself.
control/sham group: want to make sure the change in beh. is b/c of the lesion itself & not something else like antiobiotics etc.
LESION GROUP:
Anesthesia –> Incision –> Lesion –> Sutures & Stitches
SHAM (control) GROUP:
Anesthesia –> Incision –> Sutures & Stitches
*only diff is that there is no lesion itself
Note the incision in the sham group includes…
lowering the electrode or cannula to the appropriate depth.
Stereotaxic surgery in humans
- Take skull
- Screw stereotactic devices into the skull
- Align skull in the position that’s in your atlas to use that atlas to figure out where to go in the brain
Common Tests of Lesioned Animals
Radial arm maze
- Remembering places visited.
- learn to only go down the wells that had food in them (creates a food map) –> after surgery they can test if they still can run through wells with food
- good for spatial memory
Morris Winter Maze
Spatial orientation and spatial memory
- use room cues to create a spatial map (so they can determine where they should go)
- quick to learn
Bar pressing task: Effects of reinforcement…
- people who are interested in learning
- several diff. methods
1. rat press on bar to get food/drink reward
2. “ “ to stop electrical shock from happening
Histology – slicing and staining the brain
to determine if lesions were made in the correct location (or that the appropriate cells were targeted) the brain is fixed, sliced and stained.
Destroy autolytic enzymes that will turn the deceased brain into mush.
Place the brain in a fixative, formalin
- halts autolysis
- kills micro-organisms
- hardens the fragile brain
Perfusion
Perfusion
draining the blood and replacing it with another fluid. (fermaldahid process to preserve it, then freeze so it can slice v. thin with a microtome blade)
Perfusion
draining the blood and replacing it with another fluid. (fermaldahid process to preserve it, then freeze so it can slice v. thin with a microtome blade)
A microtome…
v. sharp razor blade that makes v. thin slices of brain
Staining – Nissl stain
- tissue section is placed in various chemical solutions to highlight specific details.
- Nissl (German neurologist) stain – highlights cell bodies – assumption is if the lesion was in the right place the cell count should be low.
- methylene blue or cresyl violet.
- shows off the different layers of the cortex.
- shows off nuclei. (grey matter)
Staining – myelin stain
- specifically stains myelin.
- not too useful for tracing pathways in any detail.
- b/c it blast everything black that has myelin
- can’t see cell bodies
Nissl and myelin stains
same area of brain but diff. aspects get highlighted
Staining – Golgi stain
- shows up the neuron in great detail including DENDRITIC BRANCHES.
- for reasons unknown it only stains a small number of cells at a time making easy to examine them in detail.
Single cell neurophysiology
visual experiment - focus on fixation point
- receptive field - area of space that the cell is turned for
- record response of single neuron (or multiple neurons) to specific tasks.
- can also stimulate one neuron and examine the effect of stimulation on a neuron in a different brain region.
- Neuron is said to “prefer” a given stimulus
Single cell neurophysiology q’s
- do single cell responses reflect what happens at the population level?
- to what extent are human and monkey brains alike?
- high degree of training required for the monkey to perform a given task – ecological validity?
Human lesion models (+ 2 approaches)
Naturally occurring lesions – no control on location, extent or cause
Two approaches:
- What function is supported by a given brain region?
- examine a group of individuals with similar lesions
- control group of patients with different lesions - control group of patients with different lesions
- examine a group of individuals with similar cognitive impairment
- can then examine the brain regions common to this deficit
Naturally occurring lesions
no control on location, extent or cause
ex’s: stroke & car accidents etc.
Two approaches of human lesion models
Two approaches:
- What function is supported by a given brain region?
- examine a group of individuals with similar lesions
- control group of patients with different lesions - control group of patients with different lesions
- examine a group of individuals with similar cognitive impairment
- can then examine the brain regions common to this deficit
Double Dissociations
Patient with damage to area X is impaired for cognition A but not cognition B.
Patient with damage to area Y is impaired for cognition B but not cognition A.
- e.g., lesion to Broca’s area (X) impairs speech production (A) but not comprehension (B).
- Lesion of Wernicke’s area (Y) impairs comprehension (B) but not production (A).
Limitations of the lesion method
Variability in patients and lesions.
Examples of lesion variability from a study on EXTINCTION (left) and NEGLECT (right).
- not in same spot
Possible solutions to variability in patients and lesions:
- group studies can control for age, IQ, handedness etc.
- compare a group of patients with different lesions (assumptions made about the REGION OF OVERLAP for the ‘CRITICAL’ lesion).
Must infer the functions of the damaged region from observed impairments.
Can determine if region X is “critical” for cognition A? (i.e., does the lesion disrupt the cognition?)
- But other brain regions may also be critical (i.e., area X may be NECESSARY but not SUFFICIENT for cognition A).
Disconnections – area X may not participate directly in cognition A but may disconnect two critical brain regions that are critical for cognition A.
More than one way to skin a cat! Cognition A could be performed by multiple brain regions.
Disconnections
area X may not participate directly in cognition A but may disconnect two critical brain regions that are critical for cognition A.
Split-brains – disconnection syndrome.
Severing the white matter fibres of the corpus collosum leads to certain cognitive impairments.
- But it’s not the corpus collosum that carries out these functions!
ex: reach out to grab an outfit with RH & LH will try to push it back or try to grab a separate outfit
- contact is stopped b/t the 2 hemispheres
Single-case vs. Group studies
- Choice of single case vs. group studies depends on the nature of the brain damage and the question being asked:
- Focal brain damage (e.g., from stroke, tumor, missile wound, etc.) is well suited to single case studies – no two patients are alike!
- Systemic disease processes (e.g., degenerative diseases, psychiatric disorders, infections, etc.) are well suited to group studies – no two processes are alike?
- Questions regarding cognition of the type “What CAN the brain do?” are well suited to single cases whereas questions of the type “What DOES the brain NORMALLY do?” requires group studies. This is the problem of generalization.
Questions regarding cognition of the type “What CAN the brain do?” are well suited to ___ cases whereas questions of the type “What DOES the brain NORMALLY do?” requires ___ studies. This is the problem of generalization.
SINGLE
GROUP
Heterogeneity of groups
the group average is same but if you look at case by case patients you see patients perform v. diff. on the tasks
Neurologically intact individuals
- necessary control group.
- normal functioning.
- anatomical morphology (e.g., planum temporale reduced and ventricles increased in schizophrenia, hippocampal sclerosis in epilepsy, etc.).
Cognitive Psychology
- reaction time mental chronometry
- accuracy
- mental operations – (e.g., visually process letter, match to template, make category decision, execute action).
- parallel vs. serial processing
- exploring the limits on information processing (e.g., capacity limits, automatic vs. controlled processes, etc.).
RED in green - harder time to say green causes says red
Cognitive psychology helps…
determine the processes involved in a given cognition, the limits to information processing (i.e., boundary conditions) and the normal patterns of performance.
Computer modeling
Neural Network models STIMULATE cognition
- Can also simulate lesions at different levels of the system or model (i.e., akin to different brain areas).
Explicit functions assigned to nodes of the network then performance is tested in relation to known inputs.
Computer modeling typically model…
Typically model known behaviours.
- So they rarely generate new hypotheses.
Computer modeling is limited in…
application to patient data.
No two patients are alike whereas the model must perform consistently!
Clinical testing
- Standardized tests (or test batteries) provide known “normal” performance.
- Patient with suspected brain injury are scored against these tests.
(to determine if they are behaving in normal way or are impaired)
An advantage of a reversible lesion is that
A) axons of passage are not affected by reversible procedures
B) each animal can serve as its own control
C) cell bodies are not affected by reversible procedures
D) such lesions affect brain tissue near the tip of the lesion device
E) All of the above are correct.
E) All of the above are correct.
The \_\_\_\_\_\_\_ is a device used to implant an electrode or cannula into the brain. A) stereotaxic apparatus B) electroencephalogram C) cryoloop D) macroelectrode E) oscilloscope
A) stereotaxic apparatus
\_\_\_\_\_\_ refers to a skull landmark which also serves as a reference point for stereotaxic surgery. A) Lambda B) The optic chiasma C) Bregma D) The parasagittal sutures E) The zero point
C) Bregma
The \_\_\_\_\_\_\_\_ instrument is used to slice the brain into thin pieces for later examination. A) microtome B) cryocoil C) microskim D) microionitrome E) stereotaxic
A) microtome
Dyes such as cresyl violet are useful for staining A) glutamate neurons B) axons of passage C) glial cells D) newly formed neurons E) cell bodies
E) cell bodies
