Hirokawa, J. | Search bioRxiv

bioRxiv2017

Analysis of ipsilateral corticocortical connectivity in the mouse brain

In primates, proximal cortical areas are interconnected via within-cortex \"intrinsic\" pathway, whereas distant areas are connected via \"extrinsic\" white matter pathway. It is not well known how cortical areas are interconnected in small-brained mammals like rodents. In this study, we systematically analyzed the data of Allen Mouse Brain Connectivity Atlas to answer this question and found that the ipsilateral cortical connections in mice are almost exclusively contained within the grey matter with the exception of the retrosplenial area. We analyzed the layer-specific distribution of axonal projections within the grey matter using Cortical Box method and obtained the following results. First, widespread axonal projections were observed in both upper and lower layers in the vicinity of injections, whereas highly specific \"point-to-point\" projections were observed toward remote areas. Second, such long-range projections were predominantly aligned in the anteromedial-posterolateral direction. Third, in majority of these projections, the connecting axons traveled through layer 6. Finally, the projections from the primary and higher order areas to distant targets preferentially terminated in the middle and superficial layers, respectively, suggesting hierarchical connections similar to those of primates. Overall, our study suggests the conserved nature of neocortical organization across species despite conspicuous differences in wiring strategy.

neuroscience↗

bioRxiv2017

Categorical Representations Of Decision-Variables In Orbitofrontal Cortex

The brain creates internal representations of the external world in the form of neural activity, which is structured to support adaptive behavior. In many cortical regions, individual neurons respond to specific features that are matched to the function of each region and statistics of the world. In frontal cortex, however, neurons display baffling complexity, responding to a mixture of sensory, motor and other variables. Here we use an integrated new approach to understanding the architecture of higher-order cortical representations, and use this approach to show that discrete groups of orbitofrontal cortex (OFC) neurons encode distinct decision variables. Using rats engaged in a complex task combining perceptual and value guided decisions, we found that OFC neurons can be grouped into distinct, categorical response types. These categorical representations map directly onto decision-variables of a choice model explaining our behavioral data, such as reward size, decision confidence and integrated value. We propose that, like sensory neurons, frontal neurons form a sparse and over complete population representation aligned to the natural statistics of the world - in this case spanning the space of decision-variables required for optimal behavior.

neuroscience↗