Cortex: Statistics and Geometry of Neuronal Connectivity

Braitenberg,; Schüz, Almut

doi:10.1007/978-3-662-03733-1

Cited by 1,023 publications

(1,098 citation statements)

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“…Furthermore, the ability of MK-801, given alone or prior to NMDA, to significantly reduce k* for AA by 16-49%, suggests that NMDA-initiated PLA 2 activation contributes substantially to the baseline release of AA in control brain. This interpretation is consistent with evidence that glutamatergic receptors constitute about 75% of the synapses in the mammalian cortex, and that many of these synapses include NMDARs (Braitenberg and Schüz, 1998;Fonnum, 1984;Raichle and Gusnard, 2002).…”

Section: Discussionsupporting

confidence: 90%

Chronic Lithium Chloride Administration Attenuates Brain NMDA Receptor-Initiated Signaling via Arachidonic Acid in Unanesthetized Rats

Basselin

Chang

Bell

et al. 2005

Neuropsychopharmacol

106

132

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It has been proposed that lithium is effective in bipolar disorder (BD) by inhibiting glutamatergic neurotransmission, particularly via N-methyl-D-aspartate receptors (NMDARs). To test this hypothesis and to see if the neurotransmission could involve the NMDARmediated activation of phospholipase A 2 (PLA 2 ), to release arachidonic acid (AA) from membrane phospholipid, we administered subconvulsant doses of NMDA to unanesthetized rats fed a chronic control or LiCl diet. We used quantitative autoradiography following the intravenous injection of radiolabeled AA to measure regional brain incorporation coefficients k* for AA, which reflect receptormediated activation of PLA 2 . In control diet rats, NMDA (25 and 50 mg/kg i.p.) compared with i.p. saline increased k* significantly in 49 and 67 regions, respectively, of the 83 brain regions examined. The regions affected were those with reported NMDARs, including the neocortex, hippocampus, caudate-putamen, thalamus, substantia nigra, and nucleus accumbens. The increases could be blocked by pretreatment with the specific noncompetitive NMDA antagonist MK-801 ((5R,10S)-( + )-5-methyl-10,11-dihydro-5H-dibenzo[a,d] cyclohepten-5,10-imine hydrogen maleate) (0.3 mg/kg i.p.), as well by a 6-week LiCl diet sufficient to produce plasma and brain lithium concentrations known to be effective in BD. MK-801 alone reduced baseline values for k* in many brain regions. The results show that it is possible to image NMDA signaling via PLA 2 activation and AA release in vivo, and that chronic lithium blocks this signaling, consistent with its suggested mechanism of action in BD.

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Section: Discussionsupporting

confidence: 90%

Chronic Lithium Chloride Administration Attenuates Brain NMDA Receptor-Initiated Signaling via Arachidonic Acid in Unanesthetized Rats

Basselin

Chang

Bell

et al. 2005

Neuropsychopharmacol

106

132

View full text Add to dashboard Cite

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“…Within-(recurrent) and between-area synaptic connections are not "allto-all" but random, patchy and topographic, as typically found in the mammalian cortex (Gilbert & Wiesel, 1983;Braitenberg & Schüz, 1998). Local reciprocal connections between excitatory and inhibitory layers of each area realise lateral inhibition (Braitenberg & Schüz, 1998), as follows: each inhibitory cell I receives excitatory input from all excitatory cells situated within an overlying 5x5 neighbourhood and projects back to the single excitatory cell E located directly above it. The parameter w I , indicating the weight of the projection I→E (identical across all cells and areas) was manipulated in the simulations to modulate local inhibition strength.…”

Section: Experiments 1 -Mmn To Frequency Change In Auditory Areasmentioning

confidence: 98%

“…Each cell or "node" of the network represents a cortical column of approximately 0.25mm 2 size (Hubel, 1995), containing ~2.5⋅10 4 neurons (Braitenberg & Schüz, 1998) 9 . The state of each cell x is uniquely defined by its membrane potential V(x,t), representing the average of the sum of all excitatory and inhibitory postsynaptic potentials acting upon neural pool (cluster) x at time t. The membrane potential V (x,t) at time t of a model cell x with membrane time-constant τ is governed by the equation:…”

Section: Appendix Amentioning

confidence: 99%

From sounds to words: A neurocomputational model of adaptation, inhibition and memory processes in auditory change detection

Garagnani

Pulvermüller

2011

NeuroImage

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Most animals detect sudden changes in trains of repeated stimuli but only some can learn a wide range of sensory patterns and recognize them later, a skill crucial for the evolutionary success of higher mammals. Here we use a neural model mimicking the cortical anatomy of sensory and motor areas and their connections to explain brain activity indexing auditory change and memory access. Our simulations indicate that while neuronal adaptation and local inhibition of cortical activity can explain aspects of change detection as observed when a repeated unfamiliar sound changes in frequency, the brain dynamics elicited by auditory stimulation with well-known patterns (such as meaningful words) cannot be accounted for on the basis of adaptation and inhibition alone. Specifically, we show that the stronger brain responses observed to familiar stimuli in passive oddball tasks are best explained in terms of activation of memory circuits that emerged in the cortex during the learning of these stimuli. Such memory circuits, and the activation enhancement they entail, are absent for unfamiliar stimuli. The model illustrates how basic neurobiological mechanisms, including neuronal adaptation, lateral inhibition, and Hebbian learning, underlie neuronal assembly formation and dynamics, and differentially contribute to the brain's major change-detection response, the mismatch negativity.

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“…Numbers of MR images acquired were in the range 10À15, with the time between inversion and readout varying from 23 to 3000 ms. With a repetition time of 10 s, 15 echoes were acquired per scan and averaged six times. All experiments scanned 256 2 voxels in a field-of-view of 110 mm in both directions, resulting in a voxel volume of 0.6 Â 0.6 Â 1 mm 3 .…”

Section: Synthesis Of Ligand (S)-methyl 2-(benzyloxycarbonylamino)-6mentioning

confidence: 99%

“…1,2 In particular, the profuse pattern of connections of the cerebral cortex plays an important role for cognitive functions. 3 Research over the past few years has added additional complexity to the connectivity problem, challenging the view of the brain as a rigid system and demonstrating that it is rather a plastic structure with connections adapting to the environment. For instance, connectivity can change in the course of learning, drug addiction, epilepsy, and other neurodegenerative diseases.…”

mentioning

confidence: 99%

Biocytin-Derived MRI Contrast Agent for Longitudinal Brain Connectivity Studies

Mishra

Schüz

Engelmann

et al. 2011

ACS Chem. Neurosci.

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T here is a general consensus in the neuroscientific field on the prime importance of understanding brain connectivity to advance our understanding of brain function and disease. 1,2 In particular, the profuse pattern of connections of the cerebral cortex plays an important role for cognitive functions. 3 Research over the past few years has added additional complexity to the connectivity problem, challenging the view of the brain as a rigid system and demonstrating that it is rather a plastic structure with connections adapting to the environment. For instance, connectivity can change in the course of learning, drug addiction, epilepsy, and other neurodegenerative diseases. 2,4À6 In order to better relate the anatomical structure of the brain to a particular functional outcome and to follow changes with development and aging, longitudinal studies on an individual basis are required. There are not many techniques that give us the opportunity of approaching this goal. For its broad spatial coverage and 3D noninvasive nature, magnetic resonance imaging (MRI) stands as an excellent candidate for dynamic investigations of brain connectivity.We report here a strategy to produce novel MR contrast agents to dynamically trace brain connectivity in vivo by functionalizing classical neuroanatomical tracer molecules. Classical tracers are taken up by neurons and transported from the soma and dendrites to the distant synaptic terminals (anterograde tracers) or toward the soma (retrograde tracers). 7 These compounds are visualized with conventional histological techniques in post-mortem samples. Thus, the outputs from and inputs to a particular brain area are delineated only after processing of the fixed brain tissue. Previous and successful attempts to investigate neuronal connectivity in vivo using MRI and the paramagnetic ion manganese (Mn 2+ ) have been reported. 8 In manganese-enhanced MRI (MEMRI), Mn 2+ is taken up by neurons and transported to the distant synaptic terminals where it accumulates and reveals the projection fields. 8À14 Combined anterograde and retrograde transport has also been reported using MEMRI. 15 Also reported is, however, the toxicity associated with high concentration of Mn 2+ in tissue that challenges the applicability of the MEMRI technique. 10,16,17 Although some strategies have been reported to decrease the impact of Mn 2+ toxicity on MEMRI experiments, 10,18À20 new nontoxic paramagnetic tracers are desirable.To develop new neuronal tracers for connectivity studies in living animals, we have focused, as a proof of concept, on the wellknown classical tracer biocytin. 21 The backbone of this structure was functionalized by covalently linking the gadolinium (Gd 3+ )Received: March 7, 2011 Accepted: August 3, 2011 ABSTRACT: To investigate the connectivity of brain networks noninvasively and dynamically, we have developed a new strategy to functionalize neuronal tracers and designed a biocompatible probe that can be visualized in vivo using magnetic resonance imaging (MRI). Furthermore, the multi...

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Cortex: Statistics and Geometry of Neuronal Connectivity

Cited by 1,023 publications

References 0 publications

Chronic Lithium Chloride Administration Attenuates Brain NMDA Receptor-Initiated Signaling via Arachidonic Acid in Unanesthetized Rats

Chronic Lithium Chloride Administration Attenuates Brain NMDA Receptor-Initiated Signaling via Arachidonic Acid in Unanesthetized Rats

From sounds to words: A neurocomputational model of adaptation, inhibition and memory processes in auditory change detection

Biocytin-Derived MRI Contrast Agent for Longitudinal Brain Connectivity Studies

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