The Thinking Brain - Part 2 - Movement
Over the past few weeks, we have been looking at The Thinking Brain (The Cerebral Cortex).
We examined how we sense things in our environment, both visual and auditory, and how we move our body in response to them.
This week we will look at the association areas which intervene between the sensory inputs and motor outputs and perform high-level integration tasks.[i]
When we perceive an object, our brains perceive a single option from all our senses. How this happens is called the binding problem.
Originally, researchers thought that information converged into the association areas.
However, more recent research has found that the association areas perform advanced processing in vision or hearing.[ii]
But that leaves the question of how senses are associated with each other.
While researchers cannot fully explain why this happens, we know that it does happen from experiments and from people who unfortunately lose their ability to do some associations.
Binding in Action
Here are some examples demonstrating this.
When we watch a ventriloquist, we associate the sound from the ventriloquist with the movement of the dummy’s mouth.[iii] Contrast this with watching a badly dubbed foreign movie where the lips don’t move at the same time as the speech and you perceive that the words are not coming from those lips.[iv]
You can examine this yourself. If you see a light flash once while hearing two beeps, you can sometimes think the light flashed twice. If the tone is soft, the opposite can happen.[v]
Another way is to sit next to a large mirror so that you can see your right hand in the mirror. Keep your left hand out of sight.
Squeeze your and release both hands in unison.
Wiggle your fingers and touch your thumb to each finger with both hands at the same time.
Because you feel your left hand doing things while seeing the reflection of your right hand in the mirror.
After a few minutes, you can start to feel that the mirror hand is your own left hand.
When things go wrong
One of the other ways we know that binding takes place is in cases when it goes wrong.
Prosopagnosia – An inability to recognise faces
When people have issues with their visual posterior association area, it can result in them not being able to recognise familiar faces. This is called prosopagnosia.
This has nothing to do with their vision.
They CAN
Identify a face is a face and the parts of a face.
Identify emotions from facial expressions, however,
They CANNOT
Identify a face of a particular person including recognising their relatives and sometimes even their own face.[vi]
Associative Agnosia – An inability to name objects they see
Another example is when there are issues with the posterior parietal cortex.
People with this issue can draw and perceive objects but CANNOT anme them. This is known as associative agnosia.[vii]
They can name the object if they touch them but not if they see them.
Apperceptive Agnosia – An inability to name objects they see
In the opposite case, damage to the occipital lobes can lead to people being able to name an object but not draw them (apperceptive agnosia).[viii]
Contralateral Neglect – Missing half of the world
This is one of the more dramatic examples of issues with associative areas.
When people have damage to the right posterior parietal visuocortex, then can end up neglecting the left part of the world. This can result in them:
Completely ignoring the left side of objects and their body – contralateral neglect syndrome,
No washing or dressing the left side of their body – personal neglect syndrome, and
Disowning the left side of their body to the extent where they remark, ‘Who put this arm in my bed?’ when they see their left arm.
However, it is not that they cannot sense the left part (it is not a sensory problem).[ix]
In a study, people were asked to imagine themselves at famous landmark (the Piazza del Duomo Public Square).
When they imagined themselves facing the cathedral in the square, they could recall only the buildings on their imagined right.
However, when they imagined themselves at the cathedral looking out at the square (facing the opposite direction), they could still only recall the buildings on their imagined right (which were the same building they were unable to recall in the first activity).
So they knew all of the buildings but what they could recall was dependent on which way the imaginedthemselves standing.[x]
Conclusion
When we perceive an object, our brains perceive a single option from all our senses. How this happens is called the binding problem. While researchers cannot fully explain why this happens, we know that it does happen. We can demonstrate how our brain associates inputs and we can also see what happens when brain damage occurs and association does not occur. So while we know that we bind two experiences that occur at the same time, we are still unsure about how exactly we to this.
[i] https://nba.uth.tmc.edu/neuroscience/m/s4/chapter09.html
[ii] Blanke, 2012 cited in Kalat, J. W. (2015). Biological psychology. Nelson Education.
[iii] Kalat, J. W. (2015).
[iv] Kalat, J. W. (2015).
[v] Kalat, J. W. (2015).
[vi] https://nba.uth.tmc.edu/neuroscience/m/s4/chapter09.html
[vii] https://nba.uth.tmc.edu/neuroscience/m/s4/chapter09.html
[viii] https://nba.uth.tmc.edu/neuroscience/m/s4/chapter09.html
[ix] https://nba.uth.tmc.edu/neuroscience/m/s4/chapter09.html
[x] https://nba.uth.tmc.edu/neuroscience/m/s4/chapter09.html
Photo by Siri Stafford/Photodisc / Getty Images
Photo by AntonioGuillem/iStock / Getty Images
To demonstrate how complicated this actually is, despite the ability of robots to manipulate objects in factories to build our cars and electronics, even the most hi-tech robot is unable to get you a glass of water![iii] (Note: This is from 2007 so may not still be the case…but you see the point).
Photo by ka_ru/iStock / Getty Images
The motor cortex (part of the brain) is made up of different areas in the frontal lobe (the front part of our cerebral cortex). These are:
The Primary Motor Cortex,
The Posterior Parietal Cortex,
The Premotor Cortex, and
The Supplementary Motor Area.[iv]
The Primary Motor Cortex (Initiates movements)
This important part of the brain is one of the principle brain areas involved in motor function.[v]
While it does not directly tell the muscles to move, its role is to generate the brain signals (neural impulses) to start movement.[vi] Its neurons extend to the brain stem and spinal cord which in turn generate the impulses that control our muscles.[vii]
The motor cortex is mapped out so different parts control different parts of the brain. These lie right next to the corresponding part of the brain that helps us feel that body part.
For example, the part of the motor cortex that controls our left index finger, is right next to the part of the brain that feels the left index finger. Now, this does not mean each part controls a particular muscle as the regions overlap but it is somewhat localised.[viii] The motor cortex orders an outcome, but the spinal cord and other areas determine which muscles to activate to achieve the result.[ix]
Additionally, the left part of the brain controls the right side of the body.[x]
The Posterior Parietal Cortex (Transforms what we see into movement)
This part of the brain helps us plan to move. It helps us prepare for movement.[xi]
It is also involved in changing the visual information we get into motor commands.[xii] In the case of drinking a glass of water, this would involve locating the glass and steering our hand toward it. People with damage to this area can describe an object but are unable to find it in space.[xiii]
The Premotor Cortex
This part of the brain is most active just before we move.[xiv]
It gets the information about where an object is as well as information about where the body is currently in space.
In the water example, it finds out where the glass is and where the body is in relation to that before we reach for the glass of water.[xv]
The Supplementary Motor Area
This is the part of the brain that is important for planning complex, rapid movement sequences.[xvi] It is involved, especially, in movements requiring both hands.[xvii] It is also involved in stopping habitual patterns such as when you move desks and have to turn right instead of left at the end of the hallway.[xviii]
Photo by badmanproduction/iStock / Getty Images
Conclusion
Movement is almost essential to mostly everything we do in life. Simple tasks such as reaching out and picking up a glass of water actually involve very complicated processes in our brain. The Posterior Parietal Cortex locates the glass and plans to reach for the glass. The Premotor Cortex uses this information about the glass and combines it with information on where our body is to plan the move. Then the Primary Motor Cortex generates the signals to start the movement. All this needs to take into account the type of glass and how full it is. A simple task that takes a lot of complex processes to achieve.
[i] https://www.neuroscientificallychallenged.com/blog/know-your-brain-cerebral-cortex
[ii] https://brainconnection.brainhq.com/2013/03/05/the-anatomy-of-movement/
[iii] Kemp, C. C., Edsinger, A., & Torres-Jara, E. (2007). Challenges for robot manipulation in human environments [grand challenges of robotics]. IEEE Robotics & Automation Magazine, 14(1), 20-29.
[iv] https://nba.uth.tmc.edu/neuroscience/m/s3/chapter03.html
[v] https://brainconnection.brainhq.com/2013/03/05/the-anatomy-of-movement/
[vi] https://brainconnection.brainhq.com/2013/03/05/the-anatomy-of-movement/
[vii] Kalat, J. W. (2015). Biological psychology. Nelson Education.
[viii] Kalat, J. W. (2015).
[ix] Kalat, J. W. (2015).
[x] https://brainconnection.brainhq.com/2013/03/05/the-anatomy-of-movement/
[xi] Kalat, J. W. (2015).
[xii] https://brainconnection.brainhq.com/2013/03/05/the-anatomy-of-movement/
[xiii] Kalat, J. W. (2015).
[xiv] Kalat, J. W. (2015).
[xv] https://brainconnection.brainhq.com/2013/03/05/the-anatomy-of-movement/
[xvi] Kalat, J. W. (2015).
[xvii] https://brainconnection.brainhq.com/2013/03/05/the-anatomy-of-movement/
[xviii] Kalat, J. W. (2015).