Origin of the early component of associative cortical responses in cats

Abstract

1. In response to different peripheral stimuli (flashes, electrical stimulation of contralateral fore- and hind limbs) a complex associative response consisting of early and late components is recorded in the cat association cortex (anterior divisions of the marginal and suprasylvian gyri). The early component is observed in both anesthetized and unanesthetized animals; the late component is absent under nembutal anesthesia. 2. In unanesthetized and chloralose animals most responding neurons generate a late component, and only a few generate the early component of the associative response. 3. The early component of the associative response coincides with discharge of neurons responding after a short latent period and only to stimulation of one modality. The late component is due to activity of polysensory, bisensory and monosensory neurons having a longer latency. 4. In unanesthetized animals and, in particular, under chloralose anesthesia, the polysensory activity of the neurons is improved; under nembutal anesthesia no polysensory response was observed under the experimental conditions used. 5. It follows from the facts described above that formation of the late component of the associative response is connected with the state of cortical function favoring the formation of polysensory unit activity. The early component is also generated by neurons exhibiting monosensory activity. 6. Polysensory neurons responsible for the late component of the associative response are found more frequently in layer IV, whereas neurons generating the early component are more numerous in the upper (III) and lower (VI) layers of the cortex.