Microelectrode investigation of motor cortex in unanesthetized rabbits

Abstract

1. A microelectrode investigation of the motor cortex of the unanesthetized rabbit has shown that 48% of the cells react to electrocutaneous stimulation by an increase in frequency. Of these cells, 75% are polysensory, i.e., they react also to photic and acoustic stimulation. Only 25% of the cells respond to electrocutaneous stimulation only. 2. The activity of the polysensory neurons is associated with the arousal reaction in the EEG: an increase in the frequency of their activity takes place only when the stimulus evokes an arousal reaction. 3. All the cells responding to electrocutaneous stimulation also modify their activity during a motor reaction. The increase in the frequency of the activity of the monosensory cells takes place simultaneously with the onset of the motor reaction, while in the polysensory cells it takes place before the beginning of the movement, coinciding with the beginning of the arousal reaction in the EEG. 4. The facts obtained suggest that most cells of the motor cortex of the rabbit are polysensory or “nonspecific,” and are connected with the reticular activating system of the brain stem. This diffuse, “nonspecific” activating system evidently plays an important role in the organization of motor reactions.