From chemotaxis to the cognitive map: The function of olfaction

Abstract

A paradox of vertebrate brain evolution is the unexplained variability in the size of the olfactory bulb (OB), in contrast to other brain regions, which scale predictably with brain size. Such variability appears to be the result of selection for olfactory function, yet there is no obvious concordance that would predict the causal relationship between OB size and behavior. This discordance may derive from assuming the primary function of olfaction is odorant discrimination and acuity. If instead the primary function of olfaction is navigation, i.e., predicting odorant distributions in time and space, variability in absolute OB size could be ascribed and explained by variability in navigational demand. This olfactory spatial hypothesis offers a single functional explanation to account for patterns of olfactory system scaling in vertebrates, the primacy of olfaction in spatial navigation, even in visual specialists, and proposes an evolutionary scenario to account for the convergence in olfactory structure and function across protostomes and deuterostomes. In addition, the unique percepts of olfaction may organize odorant information in a parallel map structure. This could have served as a scaffold for the evolution of the parallel map structure of the mammalian hippocampus, and possibly the arthropod mushroom body, and offers an explanation for similar flexible spatial navigation strategies in arthropods and vertebrates.sensory | memory | orientation | limbic

Multimodal sensory reliance in the nocturnal homing of the amblypygid Phrynus pseudoparvulus (Class Arachnida, Order Amblypygi)?

“…In insects, mushroom bodies are known to be involved in contextual information processing, learning, and memory-including spatial memory (de Belle and Heisenberg, 1994;Heisenberg, 2003;Mizunami et al, 1998;Pascual and Preat, 2001;Zars et al, 2000). In fact, the size of arthropod mushroom bodies has recently been proposed to reflect the complexity of spatial navigation strategies (Jacobs, 2012). This "spatial orientation" hypothesis is consistent with our current knowledge of amblypygid neuroanatomy (i.e., large mushroom bodies) and their seemingly complex navigational capacities (present study).…”

The behavioral ecology of amblypygids

“…The size of arthropod mushroom bodies has been hypothesized to reflect their spatial navigation strategies (Jacobs 2012), and amblypygids are well-known for their enlarged mushroom bodies (Strausfeld 1998). In the visually guided desert ant, Cataglyphis bicolor (Fabricius, 1793), researchers were able to demonstrate a remarkable increase in mushroom body size during the extremely short lifespan (ca.…”

Physical evidence of predatory behavior in Tyrannosaurus rex

“…Horner also suggested that the enlarged olfactory lobes in T.rex were characteristic of scavengers (25). More recent studies (28,29) determined the olfactory lobes of modern birds are "poorly developed," inferring that enlarged olfactory lobes in T. rex are actually a secondary adaptation for predation navigation "to track mobile, dispersed prey" (30). T. rex has a calculated bite force stronger than that of any other terrestrial predator (7), between 35,000 and 57,000 Newtons (30,31), and possible ambulatory speeds between 20 and 40 kph (7,15,16), documenting that it had the capability to pursue and kill prey items.…”