Our Awareness and Motor Control

Hello World and Hello Rebel Fighters!

Today I will cover two topic of Cognitive NeuroPsychology, which is the Awareness and Motor Control system.

We will be taking some notes on few key areas of the brain that involves in movement, evaluating models of motor control and awareness and evidence of the model from both healthy and damaged/injured brain from individuals.

Starting with the basics...
As are we know the left hemisphere of the brain controls the RIGHT side of the body and the right hemisphere of the brain controls the LEFT side of the human body.

Picture by Sebastian023



 The brain area are generally divided into 4 lobes;
          1) Frontal lobes
          2) Parietal lobes
          3) Occipital lobes
          4) Temporal lobes






Image taken from http://quizlet.com/10829277/mbb-week-33-head-injury-flash-cards/

The image above shows the arrangement of Primary motor cortex, Supplementary motor cortex, Premotor cortex, and Posterior parietal  cortex in the brain. Motorneurons are nerve cell in the spinal cord that send their axons to innervate muscles. Action potential (AT) travel down the motoneuron which branches into many terminnal near its target. The neurotransmitter acetycholine (ACh) is released.

The Primary Motor Cortex (sometimes known as M1) is located in the posterior portion of the frontal lobe. It involved in implementation of movement by sending signals to muscles to move with the help of electronic impulses, which later ATP is then burned in the muscle cells to get the energy to make movement. Destruction of motor cortex (such as stroke) causes paralysis of muscle. With this we can see why some people became paralyze after a venom sting from snakes or scorpion.

The Basal Ganglia is a group of structures nuclei linked to the thalamus in the base of the brain and involved in coordination of movement. What is does is that, it will receive the input from the cortex and send info back to the cortex. Basal Ganglia becomes active after a movement has been initiated by the cerebral motor areas. Thus, the Basal Ganglia does not initiate movement but it back up the motor plan of the cortex with automatic adjustment. However, it also contribute to sequencing of movements and inhibiting competing response.

The Secondary Motor Areas involves with the movement planning. There are two main areas in the secondary motor area: Supplementary Motor Area (SMA) and Premotor Area (PMA)

The SMA simply incharge of the complex sequences of the movement. It also response to internal cues and active during mentally rehearsed movements even when not executed. While PMA on the other hand, is incharge planning when task depends on external cues. unlike SMA, the PMA is active when movement under guidance of visual auditory or somatosensory feedback. Extensive interconnections with areas where sensory input converge (i.e parietal cortex).

More recently the simple two-area conception of secondary motor cortex has become more complex . Research now suggest at least 8 areas of secondary cortex in each hemisphere (Graziano, 2006). To qualify as secondary motor cortex an area must be connected with association and secondary motor areas.

Parietal cortex role is two-fold depending on anatomically distinct areas. First part, the "Superior parietal cortex" which integrate sensory information with movements for that limbs can be guided correctly through space and ensure movements executed correctly and allow for correction if not. The Second part is the "Inferior parietal cortex" which incharge of the production of well learned motor acts. 'Motor programs' stored in left inferior parietal lobe of right handers (i.e theoretical store learned skilled movements). Damage to this area results the inability to perform complex, well-learned motor tasks (apraxia) and inability to imagine sequential movements.

Anterior cingulate gyrus of left cerebral hemisphere. Shown in red. This image was made out of, or made from, content published in a BodyParts3D/Anatomography web site.
Anterior cingulate cortex (ACC) does the selecting and monitoring actions, especially when movement is novel or unrehearsed. It links cognitive and motor behaviours, such as pressing red button in response to blue stimuli.

Prefrontal Cortex (PFC) produce the 'will' and 'desire' to move; spontaneous generation of 'willed' movement. It is active when individuals generate a series of actions at will. Damage to PFC often leads to utilization behaviour (i.e stimulus bound).

There cerebellum have multiple roles such as:
1) Posture
2) Smooth Movements
3) Co-ordination or multi-limb movements
4) Ballistic movements
5) Motor Learning
6) Sensorimotor Prediction

Summary of Motor Areas:
  • Primary Motor Cortex (M1) - implementation. Sends signals to muscles to move
  • Basal Ganglia (BG) - Initiate - movement gets adjusted
  • Secondary Motor Cortex (SMA & PMA) - Planning - movement needs planning
  • Parietal Cortex - memory store & integration (sensory & motor). negotiating the environment using well-learned skills and complex movements.
  • Anterior Cingulate Cortex (ACC) - Integration (cognitive & motor). Dealing with novelty. such as error detection, anticipation of tasks, attention, motivation, and modulation of emotional responses
  • Prefrontal Cortex (PFC) - Executive - the will to move
  • Cerebellum - multiple roles (including; co-ordination, learning and sensory prediction)

Motor commands comes from the primary motor cortex of the brain. Initiate movement in the muscles leading to the sensory feedback of movement. Copy of motor command created simultaneously (efference copy) which is use to predict expected sensory consequences of movement. actual and predicted sensory are then being compared. see image below:



Miall and Wolpert 1996
So why can't we tickle ourselves? Efference copies predict the sensory outcome of the tickle movement as a  result the brain reduce the tickle sensation. Likewise, if the prediction of the efference copies doesn't tally with the actual feedback, then we might experience some ticklish sensation. When both predicted sensory consequences match with the actual sensory feedback the cerebellum kicks in a mechanism to suppress the effects of the stimulation, and the end result is diminished activity in the somatosensory cortex and with it, diminished perception of the tickle. This cancellation of the sensory consequences of a motor command is a phenomenon known as "reafference".

Blakemore, Frith and Wolpert (1998-1999) examine on two different stimulation condition, the self produced stimulation and the externally produced stimulation(using robot). They then rank the tickle rating and found that self-produced stimulation is less tickly then those externally administered stimulus. On the next part, Blakemore et al looks up if the time delay and the degree of spatial changes will effect the ticklish rating. The image below is an example of the experiment:


It was found that the delays in time (100, 200, and 300ms) and the degree of spatial changes (30, 60, and 90 degree) in the tactile stimulus create a more ticklish effects than self-produced (but are still less than the robot-produced stimulus). The self-produced tactile stimulation results in less activation of somatosensory cortex than identical externally produced tactile stimulation. Tickle sensation association with increased activation of somatosensory cortex (the more activity in the somatosensory the more ticklish it is). In Blakemore et al experiment delays and the changes in spatial direction make efference copy increasingly inaccurate at predicting expected sensory consequences. Efference copy cannot be used to cancel the sensation stimulation feel more ticklish. Self-awareness of movement are basically common sense telling us that we are constantly aware of movement we have made. In fact, research suggest awareness regarding our actual movement is surprisingly poor.

Fourneret and Jeannerod (1998)

The above image shows the experiment conducted by Fourneret and Jeannerod (1998) whereby participant's hand is out of sight (below the mirror) and the view that the participant see is the mirror image of the 'starting point' and the 'target point' that was generated by the computer. Participants were asked to draw a straight line from s tart point to target point. A red line projects onto mirror coinciding with path of stylus.


However, the red line was actually a deception to the participants because it was not the real path of the stylus.
When asked the participants thought that the direction of their stylus was at 7 (even though the computer have mislead them to a certain degree of direction). That said, normal individual possess limited awareness of actual state of motor system. Awareness relies on movement we intent to make rather than those we actually make (provided that out goal is achieved). Most of the time we are not aware of what we are doing.

So how do we know if we are doing something wrong? the 'awareness of error' depends on detecting discrepancies between predicted and actual sensory consequences of movement. The awareness becomes available only when the discrepancy between intended and actual movement is large.



Anosognosia is a denial of own illness or disability (besides this, patient are generally sane/lucid). It is not a general cognitive impairment nor a lack of basic sensory feedback. Anosognosia for Hemiplegia (AHP) are the unawareness of contralesional paralysis following stroke.




Miall and Wolpert 1996

AHP results from a failure to register discrepancies between representations of intended movement and actual feedback (Frith et al, 2000; Berti and Pia, 2006).

Neuropsychological evidence:
  • Fotopoulo et al (2008) : AHP patients more likely to claim a motionless rubber hand had moved when intention to move was present. Non AHP patient did not claim rubber hand had moved when hand remained still (regardless of intention).
In conclusion, the finding support the idea that internal predictions about intended movement are intact in AHP and contribute to illusory awareness. Support idea that AHP can be explained in terms of a failure to detect discrepancies between intended (predicted ) and actual movement.


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Joe

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