Submitted on January 18, 2005
Accepted on October 11, 2005
Activity of the motor cortex during scratching
Mikhail G. Sirota1, Galina A. Pavlova2, and Irina N. Beloozerova1*
1 Barrow Neurological Institute, St. Joseph Hospital and Medical Center, Phoenix, Arizona, USA
2 A.N.Belozersky Institute of Physical-Chemical Biology, Moscow State University, Moscow, Russian Federation
* To whom correspondence should be addressed. E-mail: ibelooz{at}chw.edu.
In awake cats sitting with the head restrained, scratching was evoked using stimulation of the ear. Cats scratched the shoulder area, consistently failing to reach the ear. Kinematics of the hind limb movements and the activity of ankle muscles however were similar to those reported earlier in unrestrained cats. The activity of single neurons in the hind limb representation of the motor cortex, including pyramidal tract neurons (PTNs), was examined. During the protraction stage of the scratch response the activity in 35% of the neurons increased and in 50% decreased as compared to rest. During the rhythmic stage, the motor cortex population activity was approximately two times higher as compared to rest, as the activity of 53% of neurons increased and that of 33% decreased in this stage. The activity of 61% of neurons was modulated in the scratching rhythm. The average depth of frequency modulation was 12.1±5.3%, similar to that reported earlier for locomotion. The phases of activity of different neurons were approximately evenly distributed over the step cycle. There was no simple correlation between resting receptive field properties and the activity of neurons during the scratch response. We conclude that the motor cortex participates in both the protraction and the rhythmic stages of the scratch response.
