Multisensory activation of pyramidal tract neurons in the cat

Extracellular unit recordings were made of the responses of pericruciate neurons to photic, auditory, and forepaw stimulation in chloralose-anesthetized cats. More than 70% of pyramidal tract (PT) neurons was activated by two or more different sensory modalities, whereas about 40% of other neurons had such sensory convergence. The majority of the responsive pericruciate, neurons was located in the lower one-half of the cortex. During sensory activation PT activity was found to precede the cortical-evoked response. The majority of the multisensory PT cells belonged to the "fast" group with conduction velocities between 25 and 50 m/sec. The results suggest that multisensory activation of certain pericruciate neurons provides a means of rapidly producing a state of "readiness to act" in the spinal cord.