The journal of neuroscience : the official journal of the Society for Neuroscience.

Since the first place cell was recorded and the cognitive-map theory was subsequently formulated, investigation of spatial representation in the hippocampal formation has evolved in stages. Early studies sought to verify the spatial nature of place cell activity and determine its sensory origin. A new epoch started with the discovery of head direction cells and the realization of the importance of angular and linear movement-integration in generating spatial maps. A third epoch began when investigators turned their attention to the entorhinal cortex, which led to the discovery of grid cells and border cells. This review will show how ideas about integration of self-motion cues have shaped our understanding of spatial representation in hippocampal-entorhinal systems from the 1970s until today. It is now possible to investigate how specialized cell types of these systems work together, and spatial mapping may become one of the first cognitive functions to be understood in mechanistic detail.

/pdf/spatial-representation-in-the-hippocampal-formation-a-11pp50774t.pdf

Spatial Representation in the Hippocampal Formation: A History

A study of mouse visual cortex relating patterns of excitatory synaptic connectivity to visual response properties of neighbouring neurons shows that, after eye opening, local connectivity reorganizes extensively: more connections form selectively between neurons with similar visual responses and connections are eliminated between visually unresponsive neurons, but the overall connectivity rate does not change. Intrinsic and experiential factors guide the patterning of neural pathways and the establishment of sensory response properties during postnatal development. Although sensory processing is known to depend on the precise wiring of cortical microcircuits, how this functional connectivity develops remains unclear. Based on electrical recordings of neighbouring neurons and changing network dynamics measures using calcium imaging, Thomas Mrsic-Flogel and colleagues offer a proposal that neuronal feature preference is initially acquired before sensory experience in a feed-forward manner, and with patterned input later driving the formation of precision within the network following the appropriate re-arrangement of synaptic connections. Sensory processing occurs in neocortical microcircuits in which synaptic connectivity is highly structured1,2,3,4 and excitatory neurons form subnetworks that process related sensory information5,6. However, the developmental mechanisms underlying the formation of functionally organized connectivity in cortical microcircuits remain unknown. Here we directly relate patterns of excitatory synaptic connectivity to visual response properties of neighbouring layer 2/3 pyramidal neurons in mouse visual cortex at different postnatal ages, using two-photon calcium imaging in vivo and multiple whole-cell recordings in vitro. Although neural responses were already highly selective for visual stimuli at eye opening, neurons responding to similar visual features were not yet preferentially connected, indicating that the emergence of feature selectivity does not depend on the precise arrangement of local synaptic connections. After eye opening, local connectivity reorganized extensively: more connections formed selectively between neurons with similar visual responses and connections were eliminated between visually unresponsive neurons, but the overall connectivity rate did not change. We propose a sequential model of cortical microcircuit development based on activity-dependent mechanisms of plasticity whereby neurons first acquire feature preference by selecting feedforward inputs before the onset of sensory experience—a process that may be facilitated by early electrical coupling between neuronal subsets7,8,9—and then patterned input drives the formation of functional subnetworks through a redistribution of recurrent synaptic connections.

/pdf/the-emergence-of-functional-microcircuits-in-visual-cortex-46s05kssj6.pdf

The emergence of functional microcircuits in visual cortex

Cell-Type-Specific Activity in Prefrontal Cortex during Goal-Directed Behavior.

One of the grand challenges in neuroscience is to comprehend neural computation in the association cortices, the parts of the cortex that have shown the largest expansion and differentiation during mammalian evolution and that are thought to contribute profoundly to the emergence of advanced cognition in humans. In this Review, we use grid cells in the medial entorhinal cortex as a gateway to understand network computation at a stage of cortical processing in which firing patterns are shaped not primarily by incoming sensory signals but to a large extent by the intrinsic properties of the local circuit.

/pdf/grid-cells-and-cortical-representation-4o1mv09pi6.pdf

Grid cells and cortical representation

A fundamental feature of the mammalian neocortex is its columnar organization. In the visual cortex, functional columns consisting of neurons with similar orientation preferences have been characterized extensively, but how these columns are constructed during development remains unclear. The radial unit hypothesis posits that the ontogenetic columns formed by clonally related neurons migrating along the same radial glial fibre during corticogenesis provide the basis for functional columns in adult neocortex. However, a direct correspondence between the ontogenetic and functional columns has not been demonstrated. Here we show that, despite the lack of a discernible orientation map in mouse visual cortex, sister neurons in the same radial clone exhibit similar orientation preferences. Using a retroviral vector encoding green fluorescent protein to label radial clones of excitatory neurons, and in vivo two-photon calcium imaging to measure neuronal response properties, we found that sister neurons preferred similar orientations whereas nearby non-sister neurons showed no such relationship. Interestingly, disruption of gap junction coupling by viral expression of a dominant-negative mutant of Cx26 (also known as Gjb2) or by daily administration of a gap junction blocker, carbenoxolone, during the first postnatal week greatly diminished the functional similarity between sister neurons, suggesting that the maturation of ontogenetic into functional columns requires intercellular communication through gap junctions. Together with the recent finding of preferential excitatory connections among sister neurons, our results support the radial unit hypothesis and unify the ontogenetic and functional columns in the visual cortex.

/pdf/clonally-related-visual-cortical-neurons-show-similar-n94tm62l5c.pdf

Clonally related visual cortical neurons show similar stimulus feature selectivity

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Clonally related visual cortical neurons show similar stimulus feature selectivity