Orientation selectivity in the visual cortex of the nine-banded armadillo

Orientation selectivity in primary visual cortex (V1) has been proposed to reflect a canonical computation performed by the neocortical circuitry.  While orientation selectivity has been reported in all mammals examined to date, the degree of selectivity and the functional organization of selectivity varies across clades. The differences in degree of orientation selectivity are large from reports in marsupials that only a small subset of neurons are selective to studies in carnivores in which it is rare to find a neuron lacking selectivity. Further, the functional organization in cortex varies in that the primate and carnivore V1 is characterized by an organization in which nearby neurons share orientation preference while other mammals such as rodents and lagomorphs either lack or have only extremely weak clustering. To gain insight into the evolutionary emergence of orientation selectivity we examined a member of Xenarthra, an early placental clade whose members are rod monochromats. Here, for the first time, we use a combination of neuroimaging, histological, and electrophysiological methods to identify the retinofugal pathways, locate V1, and examine the functional properties of V1 neurons in the armadillo (Dasypus novemcinctus) V1. Individual neurons were strongly sensitive to the orientation and often the direction of drifting gratings. We uncovered a wide range of orientation preferences, but found a bias for horizontal gratings. The presence of strong orientation selectivity in armadillo suggests that the circuitry responsible for this computation is common to placental mammals, and may reflect a difference in the cortical circuitry of marsupial and placental cohorts.

from Physiology via xlomafota13 on Inoreader http://ift.tt/2jcnmVj
via IFTTT