The mammalian Neocortex has a six-layered structure that has developed from a simpler cortex with less layers during brain evolution. Research in the mammalian cortex revealed the presence of specialised cell assemblies in the visual and somatosensory areas e.g. ocular dominance columns or whisker barrels with clear modular and functional borders. In the auditory cortex, clear evidence for modular borders in form of cortical columns and functional borders in form of a layer related processing is still missing.
In my PhD project I will investigate columnar organization of the auditory cortex by characterizing responses from neurons at different cortical depths. To assess if auditory columns are a generalized feature of mammals, I will carry out experiments in two mammalian species and compare their auditory cortices. One species with a hearing range that extends into the low frequency human hearing range (Mongolian Gerbil) versus a highly specialised high frequency auditory system, capable of processing echo-delays in a “chronotopically” organised area (Short-Tailed Fruit Bat). One could hypothesize, that columnar and laminar organisation is similar in the cochleotopic cortical map of bats and gerbils, but that such organisation might differ from that of “chronotopic” maps that are computational and unique to bats. In order to determine layer specific neuronal responses bearing information for identifying possible columnar borders, local field potentials and multiunit activity are sampled during perpendicular single- and multielectrode penetrations of primary auditory cortex and echolocation-processing areas. Based on the local field potentials current source density analysis will reveal cortical synaptic currents and input versus output circuitry. For further investigation, using piggy-backed electrodes potential cortical input synapses will be pharmacologically activated or deactivated with focus on GABAergic and glutamatergic system.
Kössl M, Hechavarria J, Voss C, Schaefer M, Vater M (2015) Bat auditory cortex - model for general mammalian auditory computation or special design solution for active time perception? European Journal of Neuroscience 41(5):518-32. doi: 10.1111/ejn.12801.
Schaefer M, Hechavarria JC, Koessl M (2015) Quantification of mid and late evoked sinks in laminar current source density profiles of columns in the primary auditory cortex. frontiers in Neural Circuits. doi: 10.3389/fncir.2015.00052
Schaefer M., Voss C., Kössl M. (2013): Bat VS Gerbil - A comparison of laminar response properties of auditory cortex neurons between a high frequency hearing specialist and a generalist. Treffen der deutschen Fledermausforscher 2013 in Rottenburg
Schaefer M., Voss C., Kössl M. (2012): Laminar differences in the response properties of auditory cortex neurons in the short-tailed fruit bat during stimulation with echolocation signals. 2nd Rhine - Main Neuroscience Network (rmn²) in Oberwesel: #58