It’s Professor Dave, let’s check out some research.
Now that we have some of the basics down in terms of how the brain works, it’s time
to start diving into some of the specific capabilities of the brain.
How do we learn?
What are emotions?
These are bold questions with fascinating answers, but before we get into all that,
we have to talk a bit about how exactly scientists come to know these things.
What kinds of experiments are done to gather information about the human brain?
What kinds of instruments are used?
Let’s take a moment to gather a basic vocabulary and understanding of the research methods
associated with biopsychological research.
Given the dual nature of biopsychology, research will focus on one of two things.
Sometimes it is the nervous system that is studied, when examining biological aspects
of the brain, and sometimes it is human behavior that is studied, when examining psychological
aspects of human behavior.
Starting with the first of these, how exactly is it that we study the brain?
Fortunately modern technology is powerful, so we have many ways of visualizing the brain
and documenting its activity.
The 1970s saw the development of computed tomography, which utilizes X-rays to produce
what we commonly refer to as a CT scan.
This revolutionized the field, as it was then finally possible to get actual images of the
brain inside a living person, and even three-dimensional representations when many cross-sectional
images are combined.
But much more relevant to psychology was the development of positron emission tomography,
or PET.
This utilizes a radioactive compound which is injected into the neck and accumulates
in active neurons, tracking cerebral bloodflow.
In this way, PET allows for the visualization of brain function.
Analyzing the regions of the brain that show activity while a person performs a specific
task tells us what part or parts of the brain are involved in the execution of that task.
A related technique is called magnetic resonance imaging, or MRI.
This utilizes the way that hydrogen atoms interact with a magnetic field to produce
images.
Of particular importance to biopsychology is functional MRI, or fMRI, which identifies
the regions of the brain experiencing increased oxygen usage.
We can refer to this as BOLD, or blood oxygen level dependent imaging.
This technique is very practical because it provides both structural and functional information,
all without injecting anything into the patient.
There is also diffusion tensor imaging, or DTI, which looks at the diffusion of water
molecules as an indicator of white matter structure.
With imaging in general, we should note the difference between structural imaging and
functional imaging.
This is essentially the difference between a photo and a video, since the first of these
gives good resolution and allows us to zoom in on specific areas, in order to get very
specific data.
By contrast, the latter allows us to see the brain in motion, in order to get the bigger picture.
That covers the primary brain imaging techniques, so let’s move on to methods of recording
psychophysiological data.
The most familiar of these will be the electroencephalogram, or EEG.
This technique places electrodes on the scalp in a non-invasive fashion to measure electrical
brain activity that originates from the cortex and conducts to the scalp.
Thus, EEG is actually measuring voltage differences between different scalp areas that result
from underlying brain activity.
The data appears as waveforms called brain waves that look like this, and the thing that
is very useful about this method is that different states of consciousness will produce quite
different and rather distinct waveforms, as will different cognitive activities, brain
disorders, and pharmacological manipulations.
Looking at the following data, we can first identify alpha waves.
These are waves of a frequency of around eight to thirteen hertz, which means cycles per second.
Beta waves fall at around fourteen to thirty hertz.
Theta waves fall at around four to seven hertz.
And delta waves are those around four hertz or less.
These are high-amplitude waves associated with a state of deep sleep or being under
anesthesia.
With this technique, we can also identify the perception of a stimulus when it happens.
This is called a sensory evoked potential, and in this case we can see the signal as
being distinct from the background activity, which we call the noise.
If the noise is too great, it becomes more difficult to distinguish such sensory evoked
potentials from the noise.
Methods such as signal averaging work to reduce noise, by recording noise in absence of stimulus
and mathematically removing it when the stimulus is present.
Other similar techniques also exist, like magnetoencephalography, or MEG, which measures
changes in magnetic fields at the scalp due to changes in neural activity below.
That covers the basics regarding non-invasive techniques for studying the brain.
Let’s take a look at a few that are quite a bit more direct, meaning techniques where
physical contact is made with the brain itself in some way, typically on a laboratory animal
like a rat.
Stereotaxic surgery is a method in which an experimental device, like an electrode, is
implanted in the brain.
If this electrode is placed somewhere in particular, like the amygdala, it can then stimulate that
area of the brain electrically, causing nearby neurons to fire, often having very specific
behavioral effects.
This can give us information about that part of the brain.
And of course small sections of the brain can be removed entirely, which produces similarly
valuable information about brain function, by examining how behavior changes in its absence.
These kinds of lesion studies are responsible for a lot of our knowledge regarding certain
regions like the amygdala.
The brain can also be manipulated chemically, by administering drugs which have an impact
on the levels of certain neurotransmitters.
We can then measure the chemical activity of the brain by a number of methods.
One method involves using a molecule called 2-deoxyglucose that has been labelled with
a radioactive isotope.
This is similar enough to glucose that neurons will absorb it, but because of the missing
hydroxyl, it can’t be metabolized, so it remains in the cell intact.
So upon performing autoradiography, we can see how the compound is distributed, and identify
things like tumor cells, which will have a higher glucose uptake.
Cutting edge techniques include genetic engineering.
We can produce organisms that overexpress a particular gene, or even completely lack
a particular gene, and thus lack the protein that would be produced when that gene is expressed.
We can therefore gain clarity on the role of a particular protein in carrying out some
physiological function.
We can even perform gene replacement, where a human gene is placed in a mouse so as to
perform studies on certain disorders.
Another important technique is called optogenetics, where light-activated ion channels are inserted
into neurons, and then blue or yellow light can be used to excited or inhibit specific
neurons.
Innovations like these may hold the key to better understanding a wide variety of neurological
disorders.
Lastly, a wide variety of experiments deal not with brain function, but strictly with
the behavior of an organism.
There are many tests relating to brain damage that work by examining the performance of
specific tasks to see how they line up with expectation.
This can include repeating sequences of digits, arranging blocks, performing arithmetic, or
improvising a story given a set of images.
These may assess memory, spatial reasoning, language skills, or other such things.
With animals like rats, certain types of behavior may be observed and measured.
This can relate to aggressiveness, defensiveness, sexual behavior, or the anxiety associated
with navigating a maze.
Later we will examine such studies in a more rigorous and quantitative way, in order to
contextualize certain information regarding human psychology.
But for now, with a basic knowledge of research methods acquired, let’s move forward into the mind.