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Front Neural Circuits. 2014 Mar 11;8:15. doi: 10.3389/fncir.2014.00015. eCollection 2014.

Spatial pattern of intra-laminar connectivity in supragranular mouse auditory cortex.

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Department of Biology, University of Maryland, College Park MD, USA.
Center for Biomedical Engineering and Technology, University of Maryland School of Medicine, Baltimore MD, USA ; Department of Physiology, University of Maryland School of Medicine, Baltimore MD, USA.
Department of Biology, University of Maryland, College Park MD, USA ; Institute for Systems Research, University of Maryland, College Park MD, USA.


Neuronal responses and topographic organization of feature selectivity in the cerebral cortex are shaped by ascending inputs and by intracortical connectivity. The mammalian primary auditory cortex has a tonotopic arrangement at large spatial scales (greater than 300 microns). This large-scale architecture breaks down in supragranular layers at smaller scales (around 300 microns), where nearby frequency and sound level tuning properties can be quite heterogeneous. Since layer 4 has a more homogeneous architecture, the heterogeneity in supragranular layers might be caused by heterogeneous ascending input or via heterogeneous intralaminar connections. Here we measure the functional 2-dimensional spatial connectivity pattern of the supragranular auditory cortex on micro-column scales. In general connection probability decreases with radial distance from each neuron, but the decrease is steeper in the isofrequency axis leading to an anisotropic distribution of connection probability with respect to the tonotopic axis. In addition to this radial decrease in connection probability we find a patchy organization of inhibitory and excitatory synaptic inputs that is also anisotropic with respect to the tonotopic axis. These periodicities are at spatial scales of ~100 and ~300 μm. While these spatial periodicities show anisotropy in auditory cortex, they are isotropic in visual cortex, indicating region specific differences in intralaminar connections. Together our results show that layer 2/3 neurons in auditory cortex show specific spatial intralaminar connectivity despite the overtly heterogeneous tuning properties.


auditory cortex; excitation; inhibition; intracortical; microcircuit; mouse

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