In this area you can edit two types of TVB connectivity objects:
- long-range connectivity and,
- local connectivity.
You can also download connectomes from the Allen Mouse Brain Connectivity Atlas.
This page is split in two columns.
The left View column contains several Long Range Connectivity visualizations:
a 3D view of the nodes and edges
2D Projections of the connectivity graph
- Left
- Right
- Top
a 3D view showing the time evolution of the connectivity matrix
The right column contains the connectivity matrix editor.
The matrix editor allows you to :
- easily edit the connectivity weights or tract lengths
- select a subset of the available nodes
- perform basic algebraic operations on that group; and
- save the new version as a new connectivity matrix.
The Connectivity datatype will be available in the Simulator area.
Hint
In the Connectivity Editor only one quadrant is displayed at a time. You can select which quadrant is shown by accessing the quadrant selector button in the upper left corner of the matrix display.
Assuming that the connectivity matrix is sorted such that the first half corresponds one single hemisphere:
You can create a smaller selection using three methods:
- Click on the Quick-select button and edit the list of node names.
- Click on the node labels in the matrix to toggle nodes.
- Use the node selection dropdown by clicking the Select Nodes button.
TVB enables you to save a new Connectivity object by clicking on .
This entity can be used later on in TheVirtualBrain Simulator.
You can save a particular selection. Click the Select Nodes button and the selection component will be shown. Enter a name for the selection and click save.
The Weights button opens a menu to perform basic algebraic operations on a group of edges. You can select multiple nodes from the current connectivity (by default all nodes are selected); thus you will end up with two sets of nodes: the set of selected nodes and the set of un-selected nodes. These two sets of nodes, determine four categories of edges:
- In –> In: are only the edges connecting the nodes of the selected set.
- In –> Out: are the edges that connect nodes in the selected set (rows) to nodes in the unselected set (columns).
- Out –> In: are the edges connecting nodes in the unselected set (rows) to nodes in the selected set (columns).
- Out –> Out: are edges connecting pair of nodes in the ‘unselected set’.
Note
Available operations are:
Click on the Apply weight change button to perform the selected operation on a group of edges.
Example: HOW TO REMOVE INTER-HEMISPHERIC CONNECTIONS
Using the Quick select remove all nodes from the right hemisphere.
Apply the changes. The selected nodes appear in green.
Save the selection to make it easier later.
Move to the third quadrant (Q3).
Then you can proceed to perform some operations on the edge values.
The four categories of edges in this particular case are:
- edges IN-IN: intrahemispheric edges from the left hemisphere.
- edges OUT-OUT: intrahemispheric edges from the right.
- edges IN-OUT: interhemispheric edges in quadrant 2 (Q2)
- edges OUT-IN: interhemispheric edges in quadrant 3 (Q3)
Select operation “Set(n)” for edges OUT-IN, set the value to 0 and then press Apply.
Repeat for edges IN-OUT .
Save your new matrix
9. Once you have your new matrix, you can launch the connectivity visualizers and check that these connections are not there any more.
Note
TVB is designed to handle connectivity matrices whose values are:
- positive real values, meaning that there is a connection, or
- zero values, meaning the absence of a connection
Warning
This connectivity visualizer allows you to see the structural information as a base model part of TVB.
The 3D semi-transparent surface around the connectivity nodes, whether it is the cortical surface or the outer-skin, is used just for giving space guidance.
You can select an individual node and right-click on it to activate the incoming or outgoing edges.
For each node you can choose a different color to apply to its edges.
A 2D representation of the connectivity matrix nodes and edges.
There are three main views (projections):
- Left sagittal view
- Transverse view
- Right sagittal view
Nodes are drawn as circles and the connections as lines. Only the selected nodes are shown.
The 3D and 2D Views can be used to visualize two ConnectivityMeasure datatypes. These measures can be the output of a BCT Analyzer. If given, they will determine the size and colors of the nodes in the views.
You can choose these connectivity measures before launching the Large Scale Connectivity visualizer, or from the brain menu (see tip below).
To display the measures in the 3D view check the Metrics details checkbox. Nodes will be displayed as colored spheres. The size of the sphere is proportional to the measure labeled Shapes Dimensions. The color comes from the current color scheme and is determined by the measure labeled Node Colors.
3D view of a connectivity measure. Node size is defined by the Indegree. Node color is defined by node strength.
To display the measures in the 2D views click the Show all button.
Nodes are draws as circles, their size proportional to the measure labeled Shapes Dimensions. Their color is determined by a threshold and the measure labeled Node Colors. Nodes with values above the threshold will be red and those whose value are below the threshold will be green.
Preview of 2D Connectivity Viewer (left lateral view). Node size is defined by the Indegree. Node color is defined by node strength, threshold is 40.
Tip
If you wish to change:
- the color threshold,
- the metrics used to define the node features,
- the colormap used in the Connectivity Matrix Editor, or
- the Connectivity entity
go to the brain menu on the top right corner
This is a three-dimensional representation of the delayed-connectivity structure (space-time) when combined with spatial separation and a finite conduction speed. The connectome consists of the weights matrix giving the strength and topology of the network and the tract lengths matrix gives the distance between pair of regions. When setting a specific conduction speed, the distances will be translated into time delays. The space-time visualizer disaggregate the weights matrix and each slice corresponds to connections that fall into a particular distance (or delay) range. The first slice is the complete weights matrix. Click on any of the subsequent slices to see the corresponding 2D matrix plot.
In this page, you can generate the spatial profile of local connectivity that will be used in surface-based simulations.
On the lower right of the browser you will have access to different functionalities by clicking on:
Create new Local Connectivity button: to generate the Local Connectivity entity.
View Local Connectivity button: to launch a 3D brain visualizer displaying the spatial profile of the newly generated entity.
Edit Local Connectivity button: to go back to the main Local Connectivity editing page.
On the right column there is a display showing different estimations of the spatial profile based on the length of :
Theoretical case: is the ideal case.
Most probable case: resolution is based on the mean length of the edges of the surface mesh.
Worst case: resolution is based on the longest edge in the surface mesh.
Best case: resolution is based on the shortest edge in the surface mesh.
and the red-dotted vertical line represents the cut-off distance.
The x-axis range is automatically set to two times the cut-off distance.
From this page you can initiate an operation which will download data from The Allen Mouse Brain Connectivity Atlas. See http://connectivity.brain-map.org
This operation needs an internet connection and it will take many minutes to complete. It will produce a Structural Connectivity in TVB format and a compatible brain Volume object.
Check the Project –> Operations page to see when the import from Allen is done. You can also find your resulted Connectivity in Project –> Data Structure area.