Cortical Organization in the Etruscan Shrew (Suncus etruscus)

Abstract

Cortical organization in the Etruscan shrew is of comparative interest because of its small size and because the Etruscan shrew is an amazing tactile hunter. Here we investigated cortical organization in Etruscan shrews by electrophysiological mapping. We developed an anesthesia protocol for this very small mammal in which we combined massive application of local anesthesia, very slow induction of general anesthesia, and passive cooling. Under this anesthesia regime, we characterized auditory, visual, and somatosensory cortical responses. We found that large parts of shrew cortex respond to such stimuli. Of the responsive sites, a small fraction (∼14%) responded to visual stimuli in a caudally located region. Another small fraction of sites (∼11%) responded to auditory stimuli in a centrally located region. The majority of sites (∼75%) responded to tactile stimuli. We identified two topographically organized somatosensory areas with small receptive fields referred to as putative primary somatosensory cortex and putative secondary somatosensory cortex. In a posterior-lateral region that partially overlaps with piriform cortex, we observed large somatosensory receptive fields and often polysensory responses. In an anterior-lateral region that partially overlaps with piriform cortex, we observed large unimodal somatosensory receptive fields. Our findings demonstrate a remarkable degree of tactile specialization in Etruscan shrew cortex.

Brain Mass and Cranial Nerve Size in Shrews and Moles

“…Both groups spend much of their lives in tunnels and grassy runs, apparently requiring less visual information than most terrestrial animals. Both behavioral2637 and physiological data from the central nervous system383940 suggest that the visual system of shrews is poorly developed. Often these species forage at night or in low light conditions41, situations in which visual information would be less useful.…”

The Robot Vibrissal System: Understanding Mammalian Sensorimotor Co-ordination Through Biomimetics

“…Second, the shrewÕs brain is tiny (Roth-Alpermann, Anjum et al, 2010). Not only must its predation behaviour be accomplished with 20,000 times fewer neurons that a human might utilise for reach and grasp, we also know from the speed of the attack (which can be as little as 80 milliseconds (Anjum, Turni et al, 2006)) that the shrew achieves its goal in a far smaller number of processing steps.…”

Chemoarchitecture of Layer 4 Isocortex in the American Water Shrew <i>(Sorex palustris)</i>

“…This provides a contrast to the condition in small-brained rodents, which typically have prominent barrels in the somatosensory cortex, each delineating the representation of a single whisker [Woolsey and Van der Loos, 1970;Woolsey et al, 1975]. It should be noted in this The overall organization of water shrew isocortex is quite similar to that described in other shrews [Catania et al, 1999;Roth-Alpermann et al, 2010] and exhibits both conserved and derived traits when compared to other mammals. For example, the overall positions of V1, S1 and the auditory cortex are similar among shrews and other small mammals with V1 located in the caudal and somewhat medial cortex, S1 more rostrally located (with head and mouth represented more laterally and limbs and trunk represented more medially) and the auditory cortex found caudolaterally.…”

“…Despite this long-standing interest and the impression that modern soricine shrews may retain primitive characters, few studies have examined the details of their cortical organization [Catania et al, 1999;Roth-Alpermann et al, 2010]. Beyond the historical (though questionable) interest in shrews as representatives of ancestral mammals, shrews are of general interest for comparative studies aimed at reconstructing the most likely configurations of ancestral brains based on the distribution of characters across a wide range of mammalian lineages [Northcutt and Kaas, 1995;Krubitzer et al, 1998Krubitzer et al, , 2009Kaas, 2005].…”