Synaptic Connections between Layer 5B Pyramidal Neurons in Mouse Somatosensory Cortex Are Independent of Apical Dendrite Bundling

Krieger, Patrik; Kuner, Thomas; Sakmann, Bert

doi:10.1523/jneurosci.1182-07.2007

Cited by 56 publications

(58 citation statements)

References 75 publications

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“…These pioneering observations raised the possibility that the septal region is a special passage site in layer 4. This possibility was reinforced by other previous studies demonstrating that apical dendrites of layer 5 pyramidal neurons also locate preferentially to the septal region in mice and rats (Escobar et al, 1986;Ito, 1992;White and Peters, 1993;Krieger et al, 2007) and that thalamocortical axons from POm are predominantly found in the septal region of the rat cerebral cortex (Koralek et al, 1988). Our results further support this possibility.…”

Section: Whisker-related Patterns Of Intracortical Connectionssupporting

confidence: 89%

Whisker-Related Axonal Patterns and Plasticity of Layer 2/3 Neurons in the Mouse Barrel Cortex

Sehara

Toda²,

Iwai³

et al. 2010

J. Neurosci.

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Elucidating neuronal circuits and their plasticity in the cerebral cortex is one of the important questions in neuroscience research. Here we report novel axonal trajectories and their plasticity in the mouse somatosensory barrel cortex. We selectively visualized layer 2/3 neurons using in utero electroporation and examined the axonal trajectories of layer 2/3 neurons. We found that the axons of layer 2/3 neurons preferentially run in the septal regions of layer 4 and named this axonal pattern "barrel nets." The intensity of green fluorescent protein in the septal regions was markedly higher compared with that in barrel hollows. Focal in utero electroporation revealed that the axons in barrel nets were indeed derived from layer 2/3 neurons in the barrel cortex. During development, barrel nets became visible at postnatal day 10, which was well after the initial appearance of barrels. When whisker follicles were cauterized within 3 d after birth, the whisker-related pattern of barrel nets was altered, suggesting that cauterization of whisker follicles results in developmental plasticity of barrel nets. Our results uncover the novel axonal trajectories of layer 2/3 neurons with whisker-related patterns and their developmental plasticity in the mouse somatosensory cortex. Barrel nets should be useful for investigating the pattern formation and axonal reorganization of intracortical neuronal circuits.

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Section: Whisker-related Patterns Of Intracortical Connectionssupporting

confidence: 89%

Whisker-Related Axonal Patterns and Plasticity of Layer 2/3 Neurons in the Mouse Barrel Cortex

Sehara

Toda²,

Iwai³

et al. 2010

J. Neurosci.

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“…We recorded simultaneously from up to 12 thick-tufted layer 5 pyramidal neurons in somatosensory cortical slices (300 μm thick) from Wistar rats (postnatal days [14][15][16] (Fig. 1 A and B)-a model system extensively used in previous studies of cortical neurons and plasticity (39,40,(45)(46)(47)(53)(54)(55)(56)(57)(58). Connectivity was determined by applying trains (5-15 spikes at 20-70 Hz) of pulses of current (∼2 nA for 2.5-4 ms) to each recorded neuron and measuring the response of the other neurons, in the form of excitatory postsynaptic potentials (EPSPs), in current-clamp mode ( Fig.…”

Section: Resultsmentioning

confidence: 99%

A synaptic organizing principle for cortical neuronal groups

Perin

Berger

Markram

2011

Proc. Natl. Acad. Sci. U.S.A.

668

819

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Neuronal circuitry is often considered a clean slate that can be dynamically and arbitrarily molded by experience. However, when we investigated synaptic connectivity in groups of pyramidal neurons in the neocortex, we found that both connectivity and synaptic weights were surprisingly predictable. Synaptic weights follow very closely the number of connections in a group of neurons, saturating after only 20% of possible connections are formed between neurons in a group. When we examined the network topology of connectivity between neurons, we found that the neurons cluster into small world networks that are not scale-free, with less than 2 degrees of separation. We found a simple clustering rule where connectivity is directly proportional to the number of common neighbors, which accounts for these small world networks and accurately predicts the connection probability between any two neurons. This pyramidal neuron network clusters into multiple groups of a few dozen neurons each. The neurons composing each group are surprisingly distributed, typically more than 100 μm apart, allowing for multiple groups to be interlaced in the same space. In summary, we discovered a synaptic organizing principle that groups neurons in a manner that is common across animals and hence, independent of individual experiences. We speculate that these elementary neuronal groups are prescribed Lego-like building blocks of perception and that acquired memory relies more on combining these elementary assemblies into higher-order constructs.cell assemblies | Edelman | Hebb | brain development | learning H ebb's (1) contributions to the theory of learning and memory have shaped psychological, philosophical, and neuroscientific theories for over 60 y. Three of the concepts that he put forward were particularly important. The first defines a correlation-based learning rule, namely that when one neuron persistently drives another, then the connection between them will be strengthened. The second states that this leads to the formation of clustered synaptic coupling of neurons into cell assemblies whose network topologies are molded by experience; the third suggests that such elementary cell assemblies are synaptically linked by the same learning rule to form trains of percepts (a phase sequence), constituting thoughts (1-6). There is a vast body of evidence for all three concepts (5, 7-10).Despite this evidence, theorists have pointed out that the first postulate would cause synapses within cell assemblies to saturate, restricting their dynamic range and limiting memory storage capacity (11)(12)(13)(14)(15)(16)(17)(18)(19)(20). Experimental studies have confirmed that saturated long-term potentiation (LTP) is unfavorable to learning and memory (21,22). Although Hebb (1) had suggested a mechanism for passive weakening of unused synaptic connections, these objections suggested the need for an active depressive mechanism (16,17,23), inspiring the discoveries of long-term depression (LTD) (24) and bidirectional and spike timing-dependent plastici...

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“…Two-photon microscopy has enabled the visualization of neocortical layer five pyramidal cells in living mice (Krieger et al 2007;Berglund et al 2008). This approach has been extended to image cerebellar granule cells in vivo ).…”

Section: In Vivo Imagingmentioning

confidence: 99%