Progressive degradation of serial grooming chains by descending decerebration.

Rule-governed behavioral chains occur predictably within the grooming sequences of rats. Descending levels of decerebration were used to identify the minimum brain substrate needed to generate the sequential structure of a chain that connects up to 25 actions into a stereotyped grooming pattern. Full brain transections in the coronal plane isolated the decerebrate brainstem of rats at one of 3 different levels: mesencephalic (above the midbrain), metencephalic (above the hindbrain), and myelencephalic (above the medulla oblongata). Complete chain sequences were produced successfully by higher decerebrates, demonstrating that brainstem circuitry suffices for the basic generation of this sequential pattern. The pattern of sequential degradation across lower transection levels was gradual and continuous, raising the possibility that the generating circuitry for this chain may not be localized at a single level within the brainstem but rather may be distributed across the hindbrain as a degenerate or parallel network. The competence of this network appears to be reduced merely in increments by descending transections. This possibility is compared to localized generator alternatives.

Brain evolution relating to family, play, and the separation call.

Mammals stem from the mammal-like reptiles (therapsids) that were widely prevalent in Pangaea 250 million years ago. In the evolutionary transition from reptiles to mammals, three key developments were (1) nursing, in conjunction with maternal care; (2) audiovocal communication for maintaining maternal-offspring contact; and (3) play. The separation call perhaps ranks as the earliest and most basic mammalian vocalization, while play may have functioned originally to promote harmony in the nest. How did such family related behavior develop? In its evolution, the forebrain of advanced mammals has expanded as a triune structure that anatomically and chemically reflects ancestral commonalities with reptiles, early mammals, and late mammals. Recent findings suggest that the development of the behavioral triad in question may have depended on the evolution of the thalamocingulate division of the limbic system, a derivative from early mammals. The thalamocingulate division (which has no distinctive counterpart in the reptilian brain) is, in turn, geared in with the prefrontal neocortex that, in human beings, may be inferred to play a key role in familial acculturation.

Quantitative analysis of orb web patterns in four species of spiders.

The orb webs of the four species Araneus pima (species nova), Araneus diadematus (Clerck), Argiope aurantia (Lucas), and Neoscona domiciliorum (Hentz) built under controlled laboratory conditions were compared and evaluated quantitatively at two different points in the life cycle in regard to size, regularity, shape, and fine structure. Orb webs of two species from one genus can be distinguished, but are more alike than webs from different genera. Mature spiders built highly specific webs, a fact which may play a role in species isolation during courtship. In adults, web measures correlated in size with the spiders' taxon; young spiders' web size measurements corresponded rather to their body weight or leg length. A web's regularity seemed to be closely related to age. Adult and young spiders built oval-shaped webs with eccentric hubs. Mesh width was correlated with leg length at both age levels. Web data support the likelihood of a monophyletic evolution of the four species.