The cortical angiome: an interconnected vascular network with noncolumnar patterns of blood flow.

What is the nature of the vascular architecture in the cortex that allows the brain to meet the energy demands of neuronal computations? We used high-throughput histology to reconstruct the complete angioarchitecture and the positions of all neuronal somata of multiple cubic millimeter regions of vibrissa primary sensory cortex in mouse. Vascular networks were derived from the reconstruction. In contrast with the standard model of cortical columns that are tightly linked with the vascular network, graph-theoretical analyses revealed that the subsurface microvasculature formed interconnected loops with a topology that was invariant to the position and boundary of columns. Furthermore, the calculated patterns of blood flow in the networks were unrelated to location of columns. Rather, blood sourced by penetrating arterioles was effectively drained by the penetrating venules to limit lateral perfusion. This analysis provides the underpinning to understand functional imaging and the effect of penetrating vessels strokes on brain viability.

Spectral mixing of rhythmic neuronal signals in sensory cortex.

The ability to compute the difference between two frequencies depends on a nonlinear operation that mixes two periodic signals. Behavioral and psychophysical evidence suggest that such mixing is likely to occur in the mammalian nervous system as a means to compare two rhythmic sensory signals, such as occurs in human audition, and as a means to lock an intrinsic rhythm to a sensory input. However, a neurological substrate for mixing has not been identified. Here we address the issue of nonlinear mixing of neuronal activity in the vibrissa primary sensory cortex of rat, a region that receives intrinsic as well as sensory-driven rhythmic input during natural whisking. In our preparation, the intrinsic signal originates from cortical oscillations that were induced by anesthetics, and the extrinsic input is introduced by periodic stimulation of vibrissae. We observed that the local extracellular current in vibrissa primary sensory cortex contained oscillatory components at the sum and difference of the intrinsic and extrinsic frequencies. In complementary experiments, we observed that the simultaneous stimulation of contralateral and ipsilateral vibrissae at different frequencies also led to current flow at the sum and difference frequencies. We show theoretically that the relative amplitudes of the observed mixture terms can be accounted for by a threshold nonlinearity in the input-output relation of the underlying neurons. In general, our results provide a neurological substrate for the modulation and demodulation of rhythmic neuronal signals for sensory coding and feedback stabilization of motor output.