Central Pattern Generators

In Neuroscience yesterday, we learned about one of the coolest experiments ever done. The experiment was performed in 2007 (http://www.jneurosci.org/cgi/content/abstract/28/15/3976) to test a hypothesis that movement of the lower limbs is still possible in cats that have been paralyzed, do to a nerve root damage in the cervical spinal cord. The experiment was set up according to this picture:

The body core of the cat is stabilized, the front limbs are placed in a fixed position, and the hind legs are able to move on a treadmill. The experimenters had to start the hind legs moving in a normal walking movement according to the speed of the treadmill, but after this, the legs continued moving on their own in the rhythm of the treadmill. If the treadmill was sped up or slowed down, the hind legs adjusted their cadence accordingly! This shows that the movement is possible because of a stimulus that is occurring somewhere closer to the legs than the injury location at the spinal cord! After a lot more research, neuroscientists have discovered the existence of central pattern generators and have found more evidence that golgi tendon organs are also involved in regulating neurological stimulation instead of the BRAIN! I don't know if I can possibly explain the significance or coolness of this adequately!!!

Basically, a paralyzed cat can still run on a treadmill!
The mechanism of movement, therefore, does not require a stimulus from the brain (the higher center of control). Up until this point, it was not understood that complex neuronal circuits existed at the spinal cord that did not need to be continuously stimulated by signals from the brain. The brain does function to provide spatial awareness and alter movement patterns according to obstacles in the path. Without the brain, the subject of the experiment (the paralyzed cat) trips over simple obstacles like a change in level or a pencil.

As always, wikipedia does a great job covering central pattern generators. Check it out:

http://en.wikipedia.org/wiki/Central_pattern_generator#cite_note-10

Humans have too much control of movement by the brain in order to be able to design an experiment to get the same results. The human brain controls a lot more variables that are necessary for movement in walking bipedally (such as balance and coordination) than a cat who is quadrapedal. However, you do see evidence of central pattern generators in individuals who have partial paralysis of the extremities. See this link for more fascinating explanation:

http://www.harkema.ucla.edu/BRway1.html


**Pictures in this post are borrowed from a presentation by Marianne Beninato, DPT, PhD