A laminar analysis of the number of round‐asymmetrical and flat‐symmetrical synapses on spines, dendritic trunks, and cell bodies in area 17 of the cat

Beaulieu, Clermont; Colonnier, Marc

doi:10.1002/cne.902310206

Cited by 233 publications

(173 citation statements)

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“…This is a small number of synapses, Ͻ10% of the asymmetric synapses that SSs are expected to receive (Beaulieu and Colonnier, 1985;Anderson et al, 1994;Binzegger et al, 2004), and is comparable to previous estimates for cat visual cortex: 80 -100 (Binzegger et al, 2004), 100 -125 (Peters and Payne, 1993), and 286 (Ahmed et al, 1994). The number of thalamocortical synapses per neuron is also small for the primate visual cortex:18 -188 synapses (Peters et al, 1994;Latawiec et al, 2000).…”

Section: Discussionsupporting

confidence: 82%

How Thalamus Connects to Spiny Stellate Cells in the Cat's Visual Cortex

Costa¹,

Martin²

2011

J. Neurosci.

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In the cat's visual cortex, the responses of simple cells seem to be totally determined by their thalamic input, yet only a few percent of the excitatory synapses in layer 4 arise from the thalamus. To resolve this discrepancy between structure and function, we used correlated light and electron microscopy to search individual spiny stellate cells (simple cells) for possible structural features that would explain the biophysical efficacy of the thalamic input, such as synaptic location on dendrites, size of postsynaptic densities, and postsynaptic targets. We find that thalamic axons form a small number of synapses with the spiny stellates (188 on average), that the median size of the synapses is slightly larger than that of other synapses on the dendrites of spiny stellates, that they are not located particularly proximal to the soma, and that they do not cluster on the dendrites. These findings point to alternative mechanisms, such as synchronous activation of the sparse thalamic synapses to boost the efficacy of the thalamic input. The results also support the idea that the thalamic input does not by itself determine the cortical response of spiny stellate cells, allowing the cortical microcircuit to amplify and modulate its response according to the particular context and computation being performed.

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Section: Discussionsupporting

confidence: 82%

How Thalamus Connects to Spiny Stellate Cells in the Cat's Visual Cortex

Costa¹,

Martin²

2011

J. Neurosci.

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“…The number of asymmetric and symmetric synapses under a square millimeter of cortical surface was counted for each cortical layer in cat area 17 by Beaulieu and Colonnier (1985). Again, we multiplied these numbers by the total cortical surface area.…”

Section: Basic Properties Of Cortical Layersmentioning

confidence: 99%

“…Using stereological studies, Beaulieu and Colonnier (1985) estimated the number of symmetric and asymmetric synapses in each cortical layer of cat area 17 (see Materials and Methods). Using Figures 4 and 6 A, we can also make estimates of these numbers.…”

Section: Overall Statistics Of Synapses and Dendritesmentioning

confidence: 99%

“…In addition, some unassigned asymmetric synapses may be attributed to the spiny neurons of layer 1, the only cortical cell type for which we do not have reconstructed samples. However, the number of spiny neurons in layer 1 is tiny (ϳ3% of all neurons in layer 1) (Beaulieu and Colonnier, 1985;Gabbott and Somogyi, 1986), and they are unlikely to account for many of the unassigned asymmetric synapses in layer 1 and layer 6.…”

Section: Overall Statistics Of Synapses and Dendritesmentioning

confidence: 99%

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A Quantitative Map of the Circuit of Cat Primary Visual Cortex

Binzegger¹,

Douglas²,

Martin³

2004

J. Neurosci.

791

996

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We developed a quantitative description of the circuits formed in cat area 17 by estimating the "weight" of the projections between different neuronal types. To achieve this, we made three-dimensional reconstructions of 39 single neurons and thalamic afferents labeled with horseradish peroxidase during intracellular recordings in vivo. These neurons served as representatives of the different types and provided the morphometrical data about the laminar distribution of the dendritic trees and synaptic boutons and the number of synapses formed by a given type of neuron. Extensive searches of the literature provided the estimates of numbers of the different neuronal types and their distribution across the cortical layers. Applying the simplification that synapses between different cell types are made in proportion to the boutons and dendrites that those cell types contribute to the neuropil in a given layer, we were able to estimate the probable source and number of synapses made between neurons in the six layers. The predicted synaptic maps were quantitatively close to the estimates derived from the experimentalelectronmicroscopicstudiesforthecaseofthemainsourcesofexcitatoryandinhibitoryinputtothespinystellatecells,whichform a major target of layer 4 afferents. The map of the whole cortical circuit shows that there are very few "strong" but many "weak" excitatory projections, each of which may involve only a few percentage of the total complement of excitatory synapses of a single neuron.

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“…The appealing alternative view that total connectivity, gauged from the total number of synapses in the brain, should be a direct determinant of brain processing capabilities runs into the same difficulty. Although this possibility remains to be examined systematically, the few pieces of evidence available in the literature suggest that synaptic density is constant across species (14)(15)(16)(17). If that is indeed the case, the total numbers of brain synapses would be simply proportional to brain size and the differences in cognitive abilities between brains of a similar size would, again, be left unaccounted for.…”

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confidence: 99%

The remarkable, yet not extraordinary, human brain as a scaled-up primate brain and its associated cost

Herculano‐Houzel

2012

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

496

372

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Neuroscientists have become used to a number of “facts” about the human brain: It has 100 billion neurons and 10- to 50-fold more glial cells; it is the largest-than-expected for its body among primates and mammals in general, and therefore the most cognitively able; it consumes an outstanding 20% of the total body energy budget despite representing only 2% of body mass because of an increased metabolic need of its neurons; and it is endowed with an overdeveloped cerebral cortex, the largest compared with brain size. These facts led to the widespread notion that the human brain is literally extraordinary: an outlier among mammalian brains, defying evolutionary rules that apply to other species, with a uniqueness seemingly necessary to justify the superior cognitive abilities of humans over mammals with even larger brains. These facts, with deep implications for neurophysiology and evolutionary biology, are not grounded on solid evidence or sound assumptions, however. Our recent development of a method that allows rapid and reliable quantification of the numbers of cells that compose the whole brain has provided a means to verify these facts. Here, I review this recent evidence and argue that, with 86 billion neurons and just as many nonneuronal cells, the human brain is a scaled-up primate brain in its cellular composition and metabolic cost, with a relatively enlarged cerebral cortex that does not have a relatively larger number of brain neurons yet is remarkable in its cognitive abilities and metabolism simply because of its extremely large number of neurons.

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A laminar analysis of the number of round‐asymmetrical and flat‐symmetrical synapses on spines, dendritic trunks, and cell bodies in area 17 of the cat

Cited by 233 publications

References 48 publications

How Thalamus Connects to Spiny Stellate Cells in the Cat's Visual Cortex

How Thalamus Connects to Spiny Stellate Cells in the Cat's Visual Cortex

A Quantitative Map of the Circuit of Cat Primary Visual Cortex

The remarkable, yet not extraordinary, human brain as a scaled-up primate brain and its associated cost

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