Welcome to this module,
in which we will discuss the terminology of brain organization.
To describe the locations and physical relationships in the brain,
a standard set of nomenclature is often used for
vertebrate nervous systems particularly in MRI research.
In this module, we will step through some of those terms
to make you familiar with that language.
These terms are commonly used in MRI research to denote relative locations of structures
and when we're talking about activations findings or
areas of activation in the brain when we're talking about fMRI research.
The major axis of the body is called the rostral-caudal axis with the rostral side,
the rostrum or beak,
representing the front side of the animal and the caudal or cauda tail,
the backside of the animal.
The second access, the vertical axis of
the body is referred to as the dorso-ventral axis.
With the dorsal, the back side of the animal
and the ventrum refer to as the belly of the animal.
So these are four dimensions that are commonly used when
we're talking about the anatomy of the animal nervous system.
Now in humans, this is a little bit more difficult
because we are upright and our brain is tilted,
a little bit relative to the animal,
we use a slightly different nomenclature to indicate those positions.
Caudal can still be the back side if we were to apply
the terminology used in animals to humans.
Dorsal can still be the top of the head,
rostral would still be the front side but ventral then would also be
the front side if we use that for the belly side of the human.
So in humans, we basically need a slightly different set of
terms to indicate similar relative positioning.
In humans, we use anterior for the front,
posterior for the back side,
superior for the top side of the brain,
and inferior for the bottom side.
Medial is referred to as towards
the center axis of the body or towards the center axis of the brain,
whereas lateral is referred to as moving away from the center axis of the body or brain.
In addition to those locations of front and back,
and superior and inferior,
there are also specific terms for the planes that
were going to be studying using fMRI or MRI research.
We have the frontal plane,
the transverse plane, which is essentially the horizontal plane,
and then there's a sagittal plane,
which is sometimes also called the sagittal midline which runs from the back of
the head essentially through
the nose and this plane is referred to as the sagittal plane.
When we apply this to MRI images,
the planes of orientations are commonly labeled as coronal,
which is the same as the frontal plane,
axial which is the same as it transverse first plane or sagittal
which is again the plane that runs from the nose through the back of the head vertically.
These terms allow us to make statements about
relative positioning in the brain of
either structure or activation findings when we're talking about fMRI.
For example, we could say that this sagittal view of the brain shows the cerebellum,
which you will see in the white box at the bottom,
which is posterior as well as ventral to the frontal cortex.
Similarly, it allows us to say that the hippocampus in this coronal slice of the brain,
is both inferior and lateral to
the third ventricles which you see in the white box at the top of the image here.
Now, when you notice this image of the coronal plane of the human MRI,
note that it is impossible to tell what is
the left side of the brain and what is the right side of the brain.
You could create this image by standing behind the person but it
would look identical if you were to stand in front of the person looking at their brain.
So left versus right is a very important issue in MRI studies.
As it's impossible to see from the image
itself which side is left and which side is right.
Again the same image could be generated by looking,
standing behind the person or facing the person,
looking at the person from the front.
So, how's this situation resolved?
Well, there are two conventions that are commonly used to address this issue.
If the image follows a radiological convention,
it means that the left side of the image represents the right side of the person.
So the left side of the picture here would represent the right side of the person's face.
In counterparts, the neurological convention states that
the left side of the image also corresponds with the left side of the person.
So in radiological convention,
the image would be presented as if you were facing the person,
standing in front of the person,
whereas the neurological convention
essentially it says that you're standing behind the person,
looking in the brain and left is left and right is right.
In research, both conventions are used and it's usually defined
by the analysis software that you're using to process the MRI images.
But care must be taken to consistently apply
these preferences to accurately report the results.
For example, if images are in
radiological convention but are mistakenly read as neurological convention,
the results of an fMRI study could mistakenly
label as findings on either on the left or on the right.
To make sure that this is not an issue in reporting results,
a lot of studies use what's called a fiduciary marker.
This is a magnetic or a metallic object
or in some cases a vitamin pill that is placed in the field of view when
the image is acquired on the right side of the brain to make sure that on
the MRI images it is clearly visible what
is the right side and what is the left side of the image.
Other commonly used terms in brain organization include proximal,
which refers to closer to the point of attachment,
distal which refers to further from the point of attachment,
ipsilateral which refers to the same side of the brain,
contralateral referring to the other side of the brain,
and an oblique plane which is a plane that is neither
horizontal nor vertical but is at an angle relative to the brain.
So we've discussed some basic terminology that is very
commonly used in MRI research and MRI data processing.
We've now essentially concluded the description of
the anatomy and the vascular developmental organization as well as terminology.
And in the next module,
we will move on to discuss how
neurons and cells in the brain communicate with each other.
Arnold BakkerAssistant Professor
