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.
Circular representations of connections have been used in a number of disciplines; examples include representation of aspects of epidemics,[1] geographical networks,[2] musical beats,[3] diversity in bird populations,[4] and genomic data.[5] Connectograms were also cited as a source of inspiration for the heads-up display style of Tony Stark's helmet in Iron Man 3.[6]
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.[7]
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. 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 |