A finding of Oligocene primates on the European continent

In this paper, we provide evidence that contrary to the current view, primates on the European continent did survive the dramatic extinction/origination event across the Eocene/Oligocene boundary 34 million years ago that severely affected the Eurasian mammal communities (the European “Grande Coupure” and the Asian “Mongolian Remodeling”). The survival of a mouse-sized omomyid for at least 2 million years, recorded in two localities of the Lower Stampian (Lower Oligocene) in a well dated stratigraphic series of fluviatile sediments in the north oriental sector of the Ebro Basin (Northeastern Spain), reflects the size-related survival pattern described recently for other coeval mammalian taxa.

Plasticity of the cochleotopic (frequency) map in specialized and nonspecialized auditory cortices

Auditory conditioning (associative learning) causes reorganization of the cochleotopic (frequency) maps of the primary auditory cortex (AI) and the inferior colliculus. Focal electric stimulation of the AI also evokes basically the same cortical and collicular reorganization as that caused by conditioning. Therefore, part of the neural mechanism for the plasticity of the central auditory system caused by conditioning can be explored by focal electric stimulation of the AI. The reorganization is due to shifts in best frequencies (BFs) together with shifts in frequency-tuning curves of single neurons. In the AI of the Mongolian gerbil (Meriones unguiculatus) and the posterior division of the AI of the mustached bat (Pteronotus parnellii), focal electric stimulation evokes BF shifts of cortical auditory neurons located within a 0.7-mm distance along the frequency axis. The amount and direction of BF shift differ depending on the relationship in BF between stimulated and recorded neurons, and between the gerbil and mustached bat. Comparison in BF shift between different mammalian species and between different cortical areas of a single species indicates that BF shift toward the BF of electrically stimulated cortical neurons (centripetal BF shift) is common in the AI, whereas BF shift away from the BF of electrically stimulated cortical neurons (centrifugal BF shift) is special. Therefore, we propose a hypothesis that reorganization, and accordingly organization, of cortical auditory areas caused by associative learning can be quite different between specialized and nonspecialized (ordinary) areas of the auditory cortex.