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The anatomical problem posed by brain complexity and size: a potential solution.

DeFelipe J - Front Neuroanat (2015)

Bottom Line: Over the years the field of neuroanatomy has evolved considerably but unraveling the extraordinary structural and functional complexity of the brain seems to be an unattainable goal, partly due to the fact that it is only possible to obtain an imprecise connection matrix of the brain.The reasons why reaching such a goal appears almost impossible to date is discussed here, together with suggestions of how we could overcome this anatomical problem by establishing new methodologies to study the brain and by promoting interdisciplinary collaboration.Generating a realistic computational model seems to be the solution rather than attempting to fully reconstruct the whole brain or a particular brain region.

View Article: PubMed Central - PubMed

Affiliation: Laboratorio Cajal de Circuitos Corticales (Centro de Tecnología Biomédica: UPM), Instituto Cajal (CSIC) and CIBERNED Madrid, Spain.

ABSTRACT
Over the years the field of neuroanatomy has evolved considerably but unraveling the extraordinary structural and functional complexity of the brain seems to be an unattainable goal, partly due to the fact that it is only possible to obtain an imprecise connection matrix of the brain. The reasons why reaching such a goal appears almost impossible to date is discussed here, together with suggestions of how we could overcome this anatomical problem by establishing new methodologies to study the brain and by promoting interdisciplinary collaboration. Generating a realistic computational model seems to be the solution rather than attempting to fully reconstruct the whole brain or a particular brain region.

No MeSH data available.


Related in: MedlinePlus

Axonal arborizations of cortico-cortical cells in monkey sensory-motor cortex. These neurons were labeled after small extracellular injections of horseradish peroxidase into a stratum of corticocortical axons situated in the white matter immediately deep to area 3b (asterisks). (A) Retrogradely labeled corticocortical cell with soma (arrow) in area 1, a minor collateral to area 3b, dense boutonal clusters in areas 1 and 2, and major collaterals apparently continuing on toward area 5. (B) Retrogradely labeled corticocortical cells with somata (arrows) in areas 3b and 3a and focused concentrations of boutons in each area. The boutonal plots were produced from high-magnification drawings of the full collateral ramifications. Each dot indicates one bouton. Bar, 500 μm. Taken from DeFelipe et al. (1986).
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Figure 7: Axonal arborizations of cortico-cortical cells in monkey sensory-motor cortex. These neurons were labeled after small extracellular injections of horseradish peroxidase into a stratum of corticocortical axons situated in the white matter immediately deep to area 3b (asterisks). (A) Retrogradely labeled corticocortical cell with soma (arrow) in area 1, a minor collateral to area 3b, dense boutonal clusters in areas 1 and 2, and major collaterals apparently continuing on toward area 5. (B) Retrogradely labeled corticocortical cells with somata (arrows) in areas 3b and 3a and focused concentrations of boutons in each area. The boutonal plots were produced from high-magnification drawings of the full collateral ramifications. Each dot indicates one bouton. Bar, 500 μm. Taken from DeFelipe et al. (1986).

Mentions: If we were to follow the extrinsic axons entering the minicolumn that establish synapses with postsynaptic elements of the minicolumn, like motor thalamocortical axons in the rat (Kuramoto et al., 2009) for instance, we would have to face a similar difficulty due to the complexity and widespread axonal arborizations of these neurons (Figure 6). This problem would be even greater if we were to follow an extrinsic axon originating in the basal forebrain. For example, the studies of Wu et al. (2014)—using genetically-directed sparse labeling to examine the full morphologies of individual basal forebrain cholinergic neurons in the mouse—have shown that individual arbors innervate multiple cortical columns, and have >1000 branch points and total axon lengths of up to 50 cm. These authors have also estimated that basal forebrain cholinergic neurons in humans have a mean axon length of ~100 meters. Furthermore, the axons of most cortical neurons (i.e., pyramidal cells) give rise to local axonal arborizations (near the cell body of origin) but the number of axonal synaptic boutons is relatively low (in the order of a few hundreds; see e.g., DeFelipe et al., 1986; Figure 7). Thus, the majority of other synapses within the minicolumn are of extrinsic origin (i.e., axon terminals coming from neurons with a distant origin, like cortico-cortical neurons, thalamo-cortical neurons, etc.). Table 1 outlines the feasibility and non-feasibility of obtaining some critical quantitative anatomical data of the minicolumn that is relevant for connectomics and models.


The anatomical problem posed by brain complexity and size: a potential solution.

DeFelipe J - Front Neuroanat (2015)

Axonal arborizations of cortico-cortical cells in monkey sensory-motor cortex. These neurons were labeled after small extracellular injections of horseradish peroxidase into a stratum of corticocortical axons situated in the white matter immediately deep to area 3b (asterisks). (A) Retrogradely labeled corticocortical cell with soma (arrow) in area 1, a minor collateral to area 3b, dense boutonal clusters in areas 1 and 2, and major collaterals apparently continuing on toward area 5. (B) Retrogradely labeled corticocortical cells with somata (arrows) in areas 3b and 3a and focused concentrations of boutons in each area. The boutonal plots were produced from high-magnification drawings of the full collateral ramifications. Each dot indicates one bouton. Bar, 500 μm. Taken from DeFelipe et al. (1986).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
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Figure 7: Axonal arborizations of cortico-cortical cells in monkey sensory-motor cortex. These neurons were labeled after small extracellular injections of horseradish peroxidase into a stratum of corticocortical axons situated in the white matter immediately deep to area 3b (asterisks). (A) Retrogradely labeled corticocortical cell with soma (arrow) in area 1, a minor collateral to area 3b, dense boutonal clusters in areas 1 and 2, and major collaterals apparently continuing on toward area 5. (B) Retrogradely labeled corticocortical cells with somata (arrows) in areas 3b and 3a and focused concentrations of boutons in each area. The boutonal plots were produced from high-magnification drawings of the full collateral ramifications. Each dot indicates one bouton. Bar, 500 μm. Taken from DeFelipe et al. (1986).
Mentions: If we were to follow the extrinsic axons entering the minicolumn that establish synapses with postsynaptic elements of the minicolumn, like motor thalamocortical axons in the rat (Kuramoto et al., 2009) for instance, we would have to face a similar difficulty due to the complexity and widespread axonal arborizations of these neurons (Figure 6). This problem would be even greater if we were to follow an extrinsic axon originating in the basal forebrain. For example, the studies of Wu et al. (2014)—using genetically-directed sparse labeling to examine the full morphologies of individual basal forebrain cholinergic neurons in the mouse—have shown that individual arbors innervate multiple cortical columns, and have >1000 branch points and total axon lengths of up to 50 cm. These authors have also estimated that basal forebrain cholinergic neurons in humans have a mean axon length of ~100 meters. Furthermore, the axons of most cortical neurons (i.e., pyramidal cells) give rise to local axonal arborizations (near the cell body of origin) but the number of axonal synaptic boutons is relatively low (in the order of a few hundreds; see e.g., DeFelipe et al., 1986; Figure 7). Thus, the majority of other synapses within the minicolumn are of extrinsic origin (i.e., axon terminals coming from neurons with a distant origin, like cortico-cortical neurons, thalamo-cortical neurons, etc.). Table 1 outlines the feasibility and non-feasibility of obtaining some critical quantitative anatomical data of the minicolumn that is relevant for connectomics and models.

Bottom Line: Over the years the field of neuroanatomy has evolved considerably but unraveling the extraordinary structural and functional complexity of the brain seems to be an unattainable goal, partly due to the fact that it is only possible to obtain an imprecise connection matrix of the brain.The reasons why reaching such a goal appears almost impossible to date is discussed here, together with suggestions of how we could overcome this anatomical problem by establishing new methodologies to study the brain and by promoting interdisciplinary collaboration.Generating a realistic computational model seems to be the solution rather than attempting to fully reconstruct the whole brain or a particular brain region.

View Article: PubMed Central - PubMed

Affiliation: Laboratorio Cajal de Circuitos Corticales (Centro de Tecnología Biomédica: UPM), Instituto Cajal (CSIC) and CIBERNED Madrid, Spain.

ABSTRACT
Over the years the field of neuroanatomy has evolved considerably but unraveling the extraordinary structural and functional complexity of the brain seems to be an unattainable goal, partly due to the fact that it is only possible to obtain an imprecise connection matrix of the brain. The reasons why reaching such a goal appears almost impossible to date is discussed here, together with suggestions of how we could overcome this anatomical problem by establishing new methodologies to study the brain and by promoting interdisciplinary collaboration. Generating a realistic computational model seems to be the solution rather than attempting to fully reconstruct the whole brain or a particular brain region.

No MeSH data available.


Related in: MedlinePlus