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The vertebrate nervous system evolved a highly complex hierarchical architecture. While considerable progress has been made in describing the representation of behaviorally relevant state-variables by high-level circuits, how these circuits interact with low-level networks and modulate behavior is still poorly understood. In this talk I will describe two studies that begin to address this issue by exploring the transformations of motion representation across different tiers of the neural hierarchy. In the first study, conducted at Ehud Ahissar's lab at the Weizmann Institute of Science, we explored the generation and processing of rhythmic phase coding, previously reported as a key state-variable in cortical processing of rodent vibrissal perception. Using closed-loop motion control in anesthetized rats, we found that the vibrissal mechanoreceptors generate this invariant phase representation, which is then differentially processed by the various secondary brainstem populations. In the second study, underway in Leonard Maler's lab at the University of Ottawa, we focus on the preglomerular complex (PG) of the weakly electric fish Apteronotus leptorhynchus. This small, densely packed diencephalic structure serves as an exclusive gateway from the hindbrain and midbrain circuits to the telencephalon, which is involved in memory formation and spatial navigation. We found both spatial and temporal compression of motion related information conveyed through the PG bottleneck, suggesting an effective 'division of labor' between the low and high levels of the hierarchy.

TBA

In the vastness of geological time, the biodiversity increased since the paucity of the Precambrian barren world until the richness of the biological species in the present. Along the last 540 million years, ie since there are abundant fossils in the record, many mass extinctions have been observed, whose proposed causes are mostly considered to have been the impact of large extraterrestrial objects.

The decrease in the diversity, especially among many mammals and birds, can arguably been assigned to the impact of humans. Such diversity crisis begun already in Pleistocene times as human populationd colonised new territories. In particular, the South American megafauna, an impressive array of many giant mammals of peculiar taxonomy, disappeared near the Pleistocene-Holocene limit, when the evidence of human presence started to be more profuse.

However, the evidence of such interaction between humans and the megafauna is scarce. Among them, a site in southern South America contributes to the debate with marks on megafaunal bones at an unexpectedly old age.