Research Methods
and the Tools Behind the Science
Opinion: a personal belief or judgment that is not founded on proof or certainty �
Hypothesis: a statement about the expected relationship b/w two (or a handful more) � variables – good hypothesis is supported with solid rationale based on � empirical evidence
Opinions, hypotheses, and theories
Theory: an attempt to explain the interrelationships between numerous variables which relate to a common
phenomenon & help us to understand the phenomenon
DA theory of addiction
Scientists rarely study whole populations. They study “samples”.
They uncover some “truth” in their sample, then estimate the probability that this “truth” would surface in the population.
Significant results or effects are those which would probably be found in the population
p < .05 … the probability that we’re wrong, that there’s actually no effect in the population, is less than 5%
Scientific “proof”: why scientists “hedge” so much
Statistics
The results suggest…
The results are consistent with…
One possible interpretation…
These results imply…
NEVER say “these results prove… unless???
Acceptable Hedge Words
Research Methods
and the Tools Behind the Science
Manipulate one or a few INDEPENDENT variables to see what effect they have on one or more DEPENDENT variables.
To “manipulate” an IV means to test at least two categories of the IV variable
Experiments
Important to eliminate or control all other EXTRANEOUS variables, so that they do not become CONFOUNDS
Example: lesion and sham lesioned rats
Do high GI foods elicit a higher CPR than low GI foods
Mice fed cheese and frootloops on alternating days
Test day – mice exposed to a container of one type of stimulus
Blood glucose measured before & after exposure to the stimulus
Mice exposed to the sight & smell of frootloops showed a greater CPR!
Variables are measured and recorded, but NOT manipulated
A correlation coefficient (r value) is calculated – this tells us how strong or weak the relationship is, as well as the direction of the relationship
The SIZE of the r value = strength -1 ……….. 0 ……….. +1
perfect no rel perfect
The SIGN of the r value = direction
positive = as scores increase for one variable, they increase for the other (and vs. versa)
negative = as scores increase for one variable, they decrease for the other
Correlational studies
Advantage Disadvantage
Experiments
Correlational
Studies
Help establish
cause & effect
So much control
makes them artificial
limiting their generalizability
Less artificial,
Good for making
predictions
Cannot establish
Cause & effect
Regardless, replication & converging lines of evidence
are necessary to establish a finding’s validity
Experiments vs. Correlational studies
Golgi stain
Myelin stain
Nissl stain
Myelin is stained blue
Black images are neurons
green-fluorescent
Nissl stain Stains only
cell bodies
Staining & Imaging Neurons
Autoradiography: using special x-ray techniques, allows us to see neurons, and identify
which neurons are active
Must inject a radioactively labeled substance like 2DG, then place
tissue slices onto special photographic film that picks up radioactivity
Autoradiograph of blood flow in the brain
Computer color-coded autoradiograph of nicotinic receptors in a section of rat brain.
Other neuronal imaging techniques
Immunocytochemistry: attach a dye to antibodies, inject the antibodies into the organism, � remove the tissue and observe
Rat cortical stem cell differentiation: monitored using multicolor immunocytochemistry
In situ hybridization: complementary strands of DNA are created and � made radioactive… these then bind with mRNA
inside the cell… pinpoints gene activity
Computed tomography (CT) scans
Why would a conventional x-ray of the brain not work?�
CT uses a computer to combine many 2D x-ray scans at �different angles to form a 3D image of the brain
Allows us to see structure but not function
One of the best ways of detecting tumors
Brain Imaging Techniques for Humans & Animals
Positron Emission Tomography (PET)
inject a radioactive labeled substance more active neurons take up more of the � substance – can see activity but not precise location
Magnetic Resonance Imaging (MRI)
measures radio-frequency waves emitted by different elements when subjected to � a magnetic field
allows greater imaging detail but very expensive and still cannot see function
CT scan
MRI
Functional MRI (fMRI)
Superimposes activity over structure
Experiments vs. Correlational studies
electroencephalography (EEG)
Relatively inexpensive and records in real time�
Does not record from deep in the brain, only from large areas of the cortex
Diffusion Tensor Imaging
A special type of MRI
Measures the diffusion of water within the tissues of the brain
Allows you to see white matter (neuronal tracts) within the brain
Manipulating the Brain
Positions instruments in 3D space
deep brain stimulation (DBS)�
Used for treatment-resistant major depressive disorder, Parkinson’s disease and chronic pain.
microdialysis probe
Sample fluids in the brain
microelectrodes
for stimulation or lesion
cannula
Inserting chemicals like drugs, neurotoxins, or neurotransmitters through a tube