Cytoarchitecture and Connexions Of the Teleostean Optic Tectum

Abstract

More than a plain “roof” the teleostean optic tectum is an ample double-dome whose sides are supported by the midbrain tegmentum and whose front edges lean upon the diencephalon. It is made of several thin concentric strata (Fig. 1) which are known as: stratum marginale (SM), stratum opticum (SO), stratum fibrosum et griseum superficiale (SFGS), stratum griseum centrale (SGC), stratum album centrale (SAC) and stratum periventriculare (SPV). In general terms, three types of neurons are found within such strata (Fig. 1): vertical neurons, which have a long axis oriented radially with respect to the dome’s curvature; horizontal neurons, which extend in the plane of the layers; and multipolar neurons. Needless to say, the handling of information which the tectum receives from the retina, the confrontation of such information with data which arrive on — line from other neural areas plus data which are retrieved from past experience, and the addressing of messages which will ultimately result in the animal’s behaviour, are all based upon the manner in which tectal neurons extend and interconnect, upon the distribution of afferent terminals among the neurons’s processes, and upon the targets which finally receive the tectal outflow. Such aspects will be reviewed in the present article.