Structure
Connectogram showing average connections and cortical measures of 110 normal, right-handed males, aged 25-36.
Connectograms are graphical representations of connectomics, the field of study dedicated to mapping and interpreting all of the white matter fiber connections in the human brain. These circular graphs based on diffusion MRI data utilize graph theory to demonstrate the white matter connections and cortical characteristics for single structures, single subjects, or populations.
The connectogram, as a graphical representation of brain connectomics, was proposed in 2012. [1]
Circular representations of connections have been used in a number of disciplines; examples include representation of aspects of epidemics, [2] geographical networks, [3] musical beats, [4] diversity in bird populations, [5] and genomic data. [6] Connectograms were also cited as a source of inspiration for the heads-up display style of Tony Stark's helmet in Iron Man 3. [7]
Connectograms are circular, with the left half depicting the left hemisphere and the right half depicting the right hemisphere. The hemispheres are further broken down into frontal lobe, insular cortex, limbic lobe, temporal lobe, parietal lobe, occipital lobe, subcortical structures, and cerebellum. At the bottom the brain stem is also represented between the two hemispheres. Within these lobes, each cortical area is labeled with an abbreviation and assigned its own color, which can be used to designate these same cortical regions in other figures, such as the parcellated brain surfaces in the adjacent image, so that the reader can find the corresponding cortical areas on a geometrically accurate surface and see exactly how disparate the connected regions may be. Inside the cortical surface ring, the concentric circles each represent different attributes of the corresponding cortical regions. In order from outermost to innermost, these metric rings represent the grey matter volume, surface area, cortical thickness, curvature, and degree of connectivity (the relative proportion of fibers initiating or terminating in the region compared to the whole brain). Inside these circles, lines connect regions that are found to be structurally connected. The relative density (number of fibers) of these connections is reflected in the opacity of the lines, so that one can easily compare various connections and their structural importance. The fractional anisotropy of each connection is reflected in its color. [1]
With the recent concerted push to map all of the human brain and its connections, [8] [9] it has become increasingly important to find ways to graphically represent the large amounts of data involved in connectomics. Most other representations of the connectome use 3 dimensions, and therefore require an interactive graphical user interface. [1] The connectogram can display 83 cortical regions within each hemisphere, and visually display which areas are structurally connected, all on a flat surface. It is therefore conveniently filed in patient records, or to display in print. The graphs were originally developed using the visualization tool called Circos. [10] [11]
On an individual level, connectograms can be used to inform the treatment of patients with neuroanatomical abnormalities. Connectograms have been used to monitor the progression of neurological recovery of patients who suffered a traumatic brain injury (TBI). [12] They have also been applied to famous patient Phineas Gage, to estimate damage to his neural network (as well as the damage at the cortical level—the primary focus of earlier studies on Gage). [13]
Connectograms can represent the averages of cortical metrics (grey matter volume, surface area, cortical thickness, curvature, and degree of connectivity), as well as tractography data, such as the average densities and fractional anisotropy of the connections, across populations of any size. This allows for visual and statistical comparison between groups such as males and females, [14] differing age cohorts, or healthy controls and patients. Some versions have been used to analyze how partitioned networks are in patient populations [15] or the relative balance between inter- and intra-hemispheric connections. [16]
There are many possibilities for which measures are included in the rings of a connectogram. Irimia and Van Horn (2012) have published connectograms which examine the correlative relationships between regions and uses the figures to compare the approaches of graph theory and connectomics. [17] Some have been published without the inner circles of cortical metrics. [18] Others include additional measures relating to neural networks, [19] which can be added as additional rings to the inside to show metrics of graph theory, as in the extended connectogram here:
| Acronym | Region in connectogram |
|---|---|
| ACgG/S | Anterior part of the cingulate gyrus and sulcus |
| ACirInS | Anterior segment of the circular sulcus of the insula |
| ALSHorp | Horizontal ramus of the anterior segment of the lateral sulcus (or fissure) |
| ALSVerp | Vertical ramus of the anterior segment of the lateral sulcus (or fissure) |
| AngG | Angular gyrus |
| AOcS | Anterior occipital sulcus and preoccipital notch (temporo-occipital incisure) |
| ATrCoS | Anterior transverse collateral sulcus |
| CcS | Calcarine sulcus |
| CgSMarp | Marginal branch (or part) of the cingulate sulcus |
| CoS/LinS | Medial occipito-temporal sulcus (collateral sulcus) and lingual sulcus |
| CS | Central sulcus (Rolando’s fissure) |
| Cun | Cuneus |
| FMarG/S | Fronto-marginal gyrus (of Wernicke) and sulcus |
| FuG | Lateral occipito-temporal gyrus (fusiform gyrus) |
| HG | Heschl’s gyrus (anterior transverse temporal gyrus) |
| InfCirInS | Inferior segment of the circular sulcus of the insula |
| InfFGOpp | Opercular part of the inferior frontal gyrus |
| InfFGOrp | Orbital part of the inferior frontal gyrus |
| InfFGTrip | Triangular part of the inferior frontal gyrus |
| InfFS | Inferior frontal sulcus |
| InfOcG/S | Inferior occipital gyrus and sulcus |
| InfPrCS | Inferior part of the precentral sulcus |
| IntPS/TrPS | Intraparietal sulcus (interparietal sulcus) and transverse parietal sulci |
| InfTG | Inferior temporal gyrus |
| InfTS | Inferior temporal sulcus |
| JS | Sulcus intermedius primus (of Jensen) |
| LinG | Lingual gyrus, lingual part of the medial occipito-temporal gyrus |
| LOcTS | Lateral occipito-temporal sulcus |
| LoInG/CInS | Long insular gyrus and central insular sulcus |
| LOrS | Lateral orbital sulcus |
| MACgG/S | Middle-anterior part of the cingulate gyrus and sulcus |
| MedOrS | Medial orbital sulcus (olfactory sulcus) |
| MFG | Middle frontal gyrus |
| MFS | Middle frontal sulcus |
| MOcG | Middle occipital gyrus, lateral occipital gyrus |
| MOcS/LuS | Middle occipital sulcus and lunatus sulcus |
| MPosCgG/S | Middle-posterior part of the cingulate gyrus and sulcus |
| MTG | Middle temporal gyrus |
| OcPo | Occipital pole |
| OrG | Orbital gyri |
| OrS | Orbital sulci (H-shaped sulci) |
| PaCL/S | Paracentral lobule and sulcus |
| PaHipG | Parahippocampal gyrus, parahippocampal part of the medial occipito-temporal gyrus |
| PerCaS | Pericallosal sulcus (S of corpus callosum) |
| POcS | Parieto-occipital sulcus (or fissure) |
| PoPl | Polar plane of the superior temporal gyrus |
| PosCG | Postcentral gyrus |
| PosCS | Postcentral sulcus |
| PosDCgG | Posterior-dorsal part of the cingulate gyrus |
| PosLS | Posterior ramus (or segment) of the lateral sulcus (or fissure) |
| PosTrCoS | Posterior transverse collateral sulcus |
| PosVCgG | Posterior-ventral part of the cingulate gyrus (isthmus of the cingulate gyrus) |
| PrCG | Precentral gyrus |
| PrCun | Precuneus |
| RG | Straight gyrus (gyrus rectus) |
| SbCaG | Subcallosal area, subcallosal gyrus |
| SbCG/S | Subcentral gyrus (central operculum) and sulci |
| SbOrS | Suborbital sulcus (sulcus rostrales, supraorbital sulcus) |
| SbPS | Subparietal sulcus |
| ShoInG | Short insular gyri |
| SuMarG | Supramarginal gyrus |
| SupCirInS | Superior segment of the circular sulcus of the insula |
| SupFG | Superior frontal gyrus |
| SupFS | Superior frontal sulcus |
| SupOcG | Superior occipital gyrus |
| SupPrCS | Superior part of the precentral sulcus |
| SupOcS/TrOcS | Superior occipital sulcus and transverse occipital sulcus |
| SupPL | Superior parietal lobule |
| SupTGLp | Lateral aspect of the superior temporal gyrus |
| SupTS | Superior temporal sulcus |
| TPl | Temporal plane of the superior temporal gyrus |
| TPo | Temporal pole |
| TrFPoG/S | Transverse frontopolar gyri and sulci |
| TrTS | Transverse temporal sulcus |
| Amg | Amygdala |
| CaN | Caudate nucleus |
| Hip | Hippocampus |
| NAcc | Nucleus accumbens |
| Pal | Pallidum |
| Pu | Putamen |
| Tha | Thalamus |
| CeB | Cerebellum |
| BStem | Brain stem |
The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting of allocortex. It is separated into two cortices, by the longitudinal fissure that divides the cerebrum into the left and right cerebral hemispheres. The two hemispheres are joined beneath the cortex by the corpus callosum. The cerebral cortex is the largest site of neural integration in the central nervous system. It plays a key role in attention, perception, awareness, thought, memory, language, and consciousness. The cerebral cortex is part of the brain responsible for cognition.
The development of the nervous system, or neural development (neurodevelopment), refers to the processes that generate, shape, and reshape the nervous system of animals, from the earliest stages of embryonic development to adulthood. The field of neural development draws on both neuroscience and developmental biology to describe and provide insight into the cellular and molecular mechanisms by which complex nervous systems develop, from nematodes and fruit flies to mammals.
The claustrum is a thin sheet of neurons and supporting glial cells, that connects to the cerebral cortex and subcortical regions including the amygdala, hippocampus and thalamus of the brain. It is located between the insula laterally and the putamen medially, separated by the extreme and external capsules respectively. Blood to the claustrum is supplied by the middle cerebral artery. It is considered to be the most densely connected structure in the brain, and thus hypothesized to allow for the integration of various cortical inputs such as vision, sound and touch, into one experience. Other hypotheses suggest that the claustrum plays a role in salience processing, to direct attention towards the most behaviorally relevant stimuli amongst the background noise. The claustrum is difficult to study given the limited number of individuals with claustral lesions and the poor resolution of neuroimaging.
The angular gyrus is a region of the brain lying mainly in the posteroinferior region of the parietal lobe, occupying the posterior part of the inferior parietal lobule. It represents the Brodmann area 39.
In psycholinguistics, language processing refers to the way humans use words to communicate ideas and feelings, and how such communications are processed and understood. Language processing is considered to be a uniquely human ability that is not produced with the same grammatical understanding or systematicity in even human's closest primate relatives.
Brodmann area 22 is a Brodmann's area that is cytoarchitecturally located in the posterior superior temporal gyrus of the brain. In the left cerebral hemisphere, it is one portion of Wernicke's area. The left hemisphere BA22 helps with generation and understanding of individual words. On the right side of the brain, BA22 helps to discriminate pitch and sound intensity, both of which are necessary to perceive melody and prosody. Wernicke's area is active in processing language and consists of the left Brodmann area 22 and Brodmann area 40, the supramarginal gyrus.
Brain mapping is a set of neuroscience techniques predicated on the mapping of (biological) quantities or properties onto spatial representations of the brain resulting in maps.
The posterior cingulate cortex (PCC) is the caudal part of the cingulate cortex, located posterior to the anterior cingulate cortex. This is the upper part of the "limbic lobe". The cingulate cortex is made up of an area around the midline of the brain. Surrounding areas include the retrosplenial cortex and the precuneus.
The uncinate fasciculus is a white matter association tract in the human brain that connects parts of the limbic system such as the temporal pole, anterior parahippocampus, and amygdala in the temporal lobe with inferior portions of the frontal lobe such as the orbitofrontal cortex. Its function is unknown though it is affected in several psychiatric conditions. It is one of the last white matter tracts to mature in the human brain.
A connectome is a comprehensive map of neural connections in the brain, and may be thought of as its "wiring diagram". An organism's nervous system is made up of neurons which communicate through synapses. A connectome is constructed by tracing the neuron in a nervous system and mapping where neurons are connected through synapses.
In human neuroanatomy, brain asymmetry can refer to at least two quite distinct findings:
Connectomics is the production and study of connectomes: comprehensive maps of connections within an organism's nervous system. More generally, it can be thought of as the study of neuronal wiring diagrams with a focus on how structural connectivity, individual synapses, cellular morphology, and cellular ultrastructure contribute to the make up of a network. The nervous system is a network made of billions of connections and these connections are responsible for our thoughts, emotions, actions, memories, function and dysfunction. Therefore, the study of connectomics aims to advance our understanding of mental health and cognition by understanding how cells in the nervous system are connected and communicate. Because these structures are extremely complex, methods within this field use a high-throughput application of functional and structural neural imaging, most commonly magnetic resonance imaging (MRI), electron microscopy, and histological techniques in order to increase the speed, efficiency, and resolution of these nervous system maps. To date, tens of large scale datasets have been collected spanning the nervous system including the various areas of cortex, cerebellum, the retina, the peripheral nervous system and neuromuscular junctions.
The Human Connectome Project (HCP) is a five-year project sponsored by sixteen components of the National Institutes of Health, split between two consortia of research institutions. The project was launched in July 2009 as the first of three Grand Challenges of the NIH's Blueprint for Neuroscience Research. On September 15, 2010, the NIH announced that it would award two grants: $30 million over five years to a consortium led by Washington University in St. Louis and the University of Minnesota, with strong contributions from University of Oxford (FMRIB) and $8.5 million over three years to a consortium led by Harvard University, Massachusetts General Hospital and the University of California Los Angeles.
Resting state fMRI is a method of functional magnetic resonance imaging (fMRI) that is used in brain mapping to evaluate regional interactions that occur in a resting or task-negative state, when an explicit task is not being performed. A number of resting-state brain networks have been identified, one of which is the default mode network. These brain networks are observed through changes in blood flow in the brain which creates what is referred to as a blood-oxygen-level dependent (BOLD) signal that can be measured using fMRI.
The Drosophila connectome has been completed for the (female) adult fruit fly Drosophila melanogaster in 2023, and for the larval stage earlier in 2023, and it contains 127,978 neurons, and 3,016 neurons for the larval brain. A connectome, i.e. "neuronal wiring diagram", lists all connections (synapses) between neurons; those two connectomes are available for larvae and adults, and the brain, i.e. the connectome enlarges enormously from larva to adult stage. So the synapse count is available for adults and larvae, and for the larvae it's the much lower number of roughly 548,000. The connectome is the most complex full one yet mapped, before mapped for only three other simpler organisms, first the C. elegans. The connectomes have been obtained by the methods of neural circuit reconstruction; Many of the 76 compartments of the Drosophila brain had connectomes available before the publication of the full connectome.
Connectome: How the Brain's Wiring Makes Us Who We Are (2012) is a book by Sebastian Seung. It introduces basic concepts in neuroscience and then elaborates on the field of connectomics, i.e., how to scan, decode, compare, and understand patterns in brain connectivity. The book concludes with musings on cryonics and mind uploading. It was selected by The Wall Street Journal as Top Ten Nonfiction of 2012.
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