Visual evoked potentials in cortical auditory and anterior ectosylvian areas of cat (original) (raw)

POTENTIALS recorded in cortical primary areas and evoked by stimulation of different sensory afferences have been called "cross-modality non-primary responses" (BUSER and BIGNALL, 1967). They were first described by BREMER (1953) who recorded auditory responses in the visual primary area. Unit recordings in the visual area confirm the presence of neurons activated by auditory stimulation (BENTAL et al., 1968; SPINELLI et al., 1968). Visual evoked potentials have been recorded in the ectosylvian gyrus, which includes auditory areas AI, AI1 and EP, in animals under barbiturate anesthesia (MARSHALL et al., 1943), chloralose anesthesia (BUSER et al., 1959b) and the non-anesthetized animal (BUSER et al., 1959a, b; STERIADE, 1962a, b, 1964). MARSHALL et al, (1943) have called attention to the lack of interaction between auditory and visual evoked potentials of the ectosylvian gyrus suggesting that these responses are not "physiologically real". STERIADE (1964) has presented evidence that these potentials relay in the Iateral geniculate body, and in the pulvinar-later0 posterior nucleus complex. They are modulated by the reticular formation and the primary visual cortex. Nevertheless, there are still doubts concerning the definite cortical origin of photic responses in the ectosylvian gyrus, which could result from activity generated at a more distant source. DESMEDT and MECHELSE (1959) and WOOLSEY et al. (1961) have described auditory and photic evoked potentials in the "insular area". THOMPSON et al. (1963a) also observed responses to the three modafities in the insular area. The more inferior and anterior "orbital region" has been studied by KORN et al. (I 966) and BIGNALL et al. (1966,1967c) and BIGNALL (1967a). They defined it as a polysensory area activated by visual, auditory and somatic stimuli. These studies, however, have not clarified the relationship between polysensory responses, particularly photic potentials and cross-modality visual responses of the auditory area. The present work deals with photic evoked responses in the auditory fields of the ectosylvian gyrus and attempts to determine whether they originate in this cortex or somewhere else. It also describes a small area placed in the rostra1 and ventral end of MI, below and along the ectosylvian sulcus, probably continuous with the insular field previously reported. This is called "anterior ectosylvian association area" (AEA) in this work and is considered a polysensory field with special relevance for visual and auditory integrative processes.