The effects of atropine microinjections into the motor cortex of rats on the development of a motor habit.

Acetylcholine modulates the responses of motor cortex neurons during learning. Studies were carried out on the effects of atropine microinjections into the motor cortex on the development of a habit consisting of procuring food with the forelimbs in freely mobile rats. Animals received unilateral intracortical injections of atropine (5 and 15 micrograms in 0.6 microliter over 40 sec) in the forelimb representation area of the motor cortex. Rats were trained to procure food from a horizontal tube, using the forelimb contralateral to the injection site. Data were obtained which suggested that atropine has a dose-dependent effect on the development of this movement habit. The general effect of atropine doses consisted of suppressing the inhibition of concurrent movements during learning. The higher atropine concentration had a depressive effect on the initiation of the learned movement.