Action IPN3012
,Brain Navigation
Modified from:
http://www.columbia.edu/cu/psychology/courses/1010/mangels/neuro/navigation/navigation.html
Sections
The brain, being a three-dimensional object, can be cut into three different planes of
orientation. They are:
o Coronal
o Sagittal
o Horizontal
o Coronal: Sections looking head-on toward an upright subject directly facing
you
o Sagittal: Sections looking head-on toward an upright subject facing sideways
o Horizontal: Also known as transverse or axial sections, are parallel to the floor
when the subject is standing upright. These views are very common with
imaging techniques such as CT or MRI.
Orientation
Sections can be viewed from different locations within the brain. They can be viewed from
the center (medial) toward the edge (lateral). When naming the different locations, the
convention taken is one of a brain within a four-legged animal. This can be confusing for a
human brain. (Simply assume the brain is located in a dog's head).
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, o Rostral: Also referred to as anterior. The frontal section of the brain closest to
the face, nose, and mouth. Rostrum is Latin for “beak” in certain animals and
for a speaker's platform, used for oration.
o Caudal: Also referred to as posterior. The rear section of the brain closest to
the back of the head. This refers to the tail in animals. Caudalis is Latin
for tail.
o Dorsal: Also referred to as superior. The upper section of the brain closest to
the top of the head. This refers to the back in animals. Dorsum is Latin
for back.
o Ventral: Also referred to as inferior. The lower section of the brain closest to
the neck. This refers to the belly in animals. Ventralis is Latin for belly.
The orientation is used in conjunction with a sectional view to navigate through the brain:
o Rostral/Caudal or Anterior/Posterior: Used to locate coronal sections.
o Dorsal/Ventral or Superior/Inferior: Used to locate horizontal sections.
o Medial/Lateral: Used specifically to locate sagittal sections, but in general to
differentiate between the center and the edge. The half-way sagittal section is
known as the midsagittal cut.
It could be interesting to know about the “3D Brain” app: App “3D Brain” by Cold Spring Harbor
Laboratory DNA Learning Center (Android & iOS).
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, Problem 1. Cortical voluntary motor control.
The first problem is about the global functional organisation of the voluntary action system. We do
not cover the spinal reflexes and pattern generators (first year course). Moreover, we do not have to
go into the nature of representations in M1, or the descending motor paths, all of which was
covered in the second year course Functional Neuroanatomy.
Instead, we focus on the functional organization of the cerebral motor system, covering such topics
as the dorsal “how” pathway, with a ventral and dorsal action subdivision, the division of labour
between the parietal (via PMA) and the medial frontal (supplementary motor area (SMA) control
of action, and the medial (pre)frontal cortex as the region where it is selected which action will be
executed and which supressed.
Pre-discussion
Example of a problem statement:
How does our brain transform perceptual information of an object into a movement directed at that
object?
A.
This part serves to revive the knowledge about the visual processing streams obtained in
the first year course sensation and perception and the second year neuroanatomy course.
These processing streams were identified based on lesion studies that demonstrated a
double dissociation between the effect of lesions to the inferior temporal cortex and the
partietal cortex.
In the lower two pictures, the association between the object and a particular action is not
immediately clear.
Questions to stimulate discussion:
How would the processing of the mug and the cactus be different?
While they have similar low level characteristics (contours), they will probably both activate the ventral stream to the same
extent, although their color, texture and identity obviously differ. Dorsal stream processing might be quite different, because
the mug is strongly associated with potential action and manipulation (picking up, drinking) whereas the cactus does not
immediately call for action, unless you are a gardener and wearing gloves.
Do you remember brain lesions that specifically interfere with object recognition? Do
you remember brain lesions that specifically interfere with object manipulation
and/or reaching for objects?
Lesions to the inferior temporal cortex (ventral stream) can produce object agnosia, inability to recognize objects, although
patients can still use the objects in an appropriate way. Lesions to the superior parietal cortex (dorsal stream) can lead to
problems with visually guided reaching (optic ataxia).
What is the difference in terms of object – action associations between the mug and
the lower pictures (door and faucet)? Would reaction times be slower for these
objects compared to normal doors/faucets? Why?
There are multiple, conflicting object-action associations. When we have a particular goal, for example to drink something, to
open a door to get inside or to wash our hands, we scan the environment for potential targets that might bring us closer to
achieving this goal. Once these targets have been identified and selected as motor goals, we have to plan the movement
towards them. This involves selecting which axction to perform and which limb to use. Once these two questions are answered
the movement trajectory follows in a straightforward manner here.
In case of the mug, the physical structure of the object is strongly associated with the act of picking it up at its ear with the
right hand in order to drink. However, in the case of the door knob, the action most strongly associated with its physical
features (‘push’) is in conflict with the action associated with the translation of the door label (‘pull’). So at least English
speaking people might show a delay in opening the door because they experience conflict between the actions associated with
the label and the physical features of the object.
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