Some thoughts on cortical minicolumns

Rockland, Kathleen S.; Ichinohe, Noritaka

doi:10.1007/s00221-004-2024-9

Cited by 105 publications

(105 citation statements)

References 70 publications

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“…Finally, computational models of cortical connectivity often underestimate the extent of long-range connectivity. Motivated by the notion of structural columns [e.g., minicolumns (19,38,39)] and functional columns [e.g., orientation and ocular dominance (40)] in the cortex, such models often assume that the majority of synaptic connections are made within columnar units (roughly 500 m in diameter; see, e.g., ref. 41) that are only weekly interconnected with one another.…”

Section: Discussionmentioning

confidence: 99%

The fractions of short- and long-range connections in the visual cortex

Stepanyants

Martı́nez

Ferecskó

et al. 2009

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

195

168

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When analyzing synaptic connectivity in a brain tissue slice, it is difficult to discern between synapses made by local neurons and those arising from long-range axonal projections. We analyzed a data set of excitatory neurons and inhibitory basket cells reconstructed from cat primary visual cortex in an attempt to provide a quantitative answer to the question: What fraction of cortical synapses is local, and what fraction is mediated by long-range projections? We found an unexpectedly high proportion of nonlocal synapses. For example, 92% of excitatory synapses near the axis of a 200-m-diameter iso-orientation column come from neurons located outside the column, and this fraction remains high-76%-even for an 800-m ocular dominance column. The long-range nature of connectivity has dramatic implications for experiments in cortical tissue slices. Our estimate indicates that in a 300-m-thick section cut perpendicularly to the cortical surface, the number of viable excitatory synapses is reduced to about 10%, and the number of synapses made by inhibitory basket cell axons is reduced to 38%. This uneven reduction in the numbers of excitatory and inhibitory synapses changes the excitationinhibition balance by a factor of 3.8 toward inhibition, and may result in cortical tissue that is less excitable than in vivo. We found that electrophysiological studies conducted in tissue sections may significantly underestimate the extent of cortical connectivity; for example, for some projections, the reported probabilities of finding connected nearby neuron pairs in slices could understate the in vivo probabilities by a factor of 3.axon ͉ connectivity ͉ local ͉ slice W hen examining drawings (1) and 3-dimensional reconstructions (2, 3) of cortical excitatory neurons, it is difficult to evade the impression that most of the excitatory neurons' axons, and, consequently, most of their synapses, are confined to a few hundred micrometer columnar domains surrounding the neurons' somata (Fig. 1A). Only a few branches occasionally escape through the boundaries of the local domain. This interpretation of neuron images can be misleading, however. The few axonal branches that extend beyond the local domain could ramify over large territories (e.g., the entire cortex) and thus could carry a significant fraction of all synapses. Such long-range projections may include interareal and intraareal connections, feedback from higher cortical areas, interhemispheric projections, and feed-forward inputs from subcortical structures. These projections can be easily observed with single neuron or bulk injections of tracers (4-6), but quantifying their fraction is difficult. This is because an accurate estimate of the amount of long-range axons must be made on the scale of the entire cortex, which presents a significant challenge. In practice, long-range axons are truncated in the reconstruction process, and thus their length and richness (density), and the number of synapses that they mediate, cannot be estimated reliably.We devised an approach to deli...

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Section: Discussionmentioning

confidence: 99%

The fractions of short- and long-range connections in the visual cortex

Stepanyants

Martı́nez

Ferecskó

et al. 2009

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

195

168

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“…If we consider the columnar organization of the input connections, the differences in connectivity between neighboring neurons, and the combinations of the interlaminar connections of both pyramidal and nonpyramidal neurons, it is clear that neurons in different layers do not process the same information (29,30). Furthermore, pyramidal neurons located in different layers project to different cortical and subcortical nuclei (31-33).…”

Section: Discussionmentioning

confidence: 99%

Gender differences in human cortical synaptic density

Alonso‐Nanclares

González‐Soriano²,

Toledo-Rodriguez³

et al. 2008

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

190

153

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Certain cognitive functions differ in men and women, although the anatomical and functional substrates underlying these differences remain unknown. Because neocortical activity is directly related with higher brain function, numerous studies have focused on the cerebral cortex when searching for possible structural correlates of cognitive gender differences. However, there are no studies on possible gender differences at the synaptic level. In the present work we have used stereological and correlative light and electron microscopy to show that men have a significantly higher synaptic density than women in all cortical layers of the temporal neocortex. These differences may represent a microanatomical substrate contributing to the functional gender differences in brain activity.electron microscopy ͉ neocortex ͉ neuronal density ͉ sex

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“…3), within which the autonomy of individual neurons is reduced [163] due to dense intrinsic connectivity [164][165][166]. It is supposed that minicolumns possess relatively stereotypic internal processing, and maintain generic patterns of inputs and outputs with minicolumns in other regions [167,168].…”

Section: Spatial Structure Of Neuronal Assembliesmentioning

confidence: 99%

Natural world physical, brain operational, and mind phenomenal space–time

Fingelkurts

Neves

2010

Physics of Life Reviews

166

233

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Concepts of space and time are widely developed in physics. However, there is a considerable lack of biologically plausible theoretical frameworks that can demonstrate how space and time dimensions are implemented in the activity of the most complex life-system -the brain with a mind. Brain activity is organized both temporally and spatially, thus representing space-time in the brain. Critical analysis of recent research on the space-time organization of the brain's activity pointed to the existence of so-called operational space-time in the brain. This space-time is limited to the execution of brain operations of differing complexity. During each such brain operation a particular short-term spatio-temporal pattern of integrated activity of different brain areas emerges within related operational space-time. At the same time, to have a fully functional human brain one needs to have a subjective mental experience. Current research on the subjective mental experience offers detailed analysis of space-time organization of the mind. According to this research, subjective mental experience (subjective virtual world) has definitive spatial and temporal properties similar to many physical phenomena. Based on systematic review of the propositions and tenets of brain and mind space-time descriptions, our aim in this review essay is to explore the relations between the two. To be precise, we would like to discuss the hypothesis that via the brain operational space-time the mind subjective space-time is connected to otherwise distant physical space-time reality.Key words: spatial, temporal, consciousness, cognition, operation, architectonics, EEG, field, metastability, physics, coordinative dynamics, self-organization, cortex.

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Some thoughts on cortical minicolumns

Cited by 105 publications

References 70 publications

The fractions of short- and long-range connections in the visual cortex

The fractions of short- and long-range connections in the visual cortex

Gender differences in human cortical synaptic density

Natural world physical, brain operational, and mind phenomenal space–time

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