In this tutorial we will learn how simple intracerebral current sources can
generate complicated patterns of EEG potentials at the scalp.
We will then see how, under certain conditions, the underlying
EEG sources can be effectively localized from the scalp measurements.
However, the tutorial also aims to illustrate how the solution to
the inverse EEG problem can be easily confounded e.g. by the presence of
noisy background EEG activity.
Below you can download the slides of a presentation that deals with
the topic of this tutorial:
Please download the
and uncompress the .zip file. Then simply add directory tutorial_dipoles and all its
subdirectories to your MATLAB's path. To add a directory and all its subdirectories to
MATLAB's path you can use MATLAB's command:
where M:/mypath/tutorial_dipoles is the location where you uncompressed
the .zip file.
Note: The tutorial .zip file contains the tutorial code, the
required data files and this documentation in HTML format. You can browse
the documentation offline by opening with your web browser file
index.htm, which is found under folder tutorial_dipoles.
For convenience, all the dependencies have been included in the tutorial
.zip package so that you don't need to download them separately.
Note: The tutorial uses the 3D rendering capabilities of the OpenGL
implementation that is included with your operating system. As OpenGL
support differ slightly between operating systems there is a small chance
that some of the figures will display differently in different operating
systems. The figures shown in the tutorial have been generated in
The tutorial instructions explain just a small fraction of the
tutorial scripts' features. You can always get a more detailed help of
individual MATLAB functions using the command help followed by the
name of the relevant function. For instance, the command:
will display the help of MATLAB's built-in plot command.
The tutorial makes use of
Do not get get intimidated by the term. A class is just a user-defined data type.
MATLAB comes with lots of built-in data types. For instance double and single
are two types that can store numeric data:
x = 5;
The variable x above is now an instance (also called
an object) of class double. You can find out the classes of the variables
in your MATLAB's workspace using the command whos. The result could be
something like this:
Name Size Bytes Class Attributes
myHead 1x1 2805970 head.mri
x 1x1 8 double
y 1x1 8 double
where you can see that variable x is an object of class double and variable
myHead is an object of class head.mri. The latter is a class that we
have defined specifically for the purposes of this tutorial.
It is important to realize the difference between a class and an object.
In the example above, x and y are two different objects of the same class.
One of the great advantages of using objects with MATLAB is that it allows you
function names. For instance, if you run the
MATLAB will first check whether a specialized methodplot() has been defined
for class head.mri. If such method exists then it will run that method
instead of MATLAB's built-in function plot(). A head.mri object contains a
head model and a double object contains just numbers. Indeed, plotting such
different data types involve very different operations. Thus, it makes sense
that different versions of plot are called, depending on the class of what
you want to be plotted. Remember: the specialized version of plot() that
takes care of plotting mri.head objects is called a method of class
Imagine that you want to get some help on method plot() for objects of class
mri.head. You could try to do this:
but you will find that the help that is displayed corresponds to MATLAB's
built-in plot() instead of corresponding to method plot() of class
mri.head. Only if you read until the end of the help that is displayed you
will see a section that reads Overloaded methods and that lists several
other functions that are also called plot(), and that will be called
instead of the built-in, depending on the type of the input argument.
If you already installed the tutorial scripts you should see in that list
a link reading head.mri. If you click that link you will get the help that
you were looking for. Alternatively, you could have just used the command:
As both code and documentation has been made from scratch for the
year 2011 course, it is likely that you will find bugs and typos.
Please report those to email@example.com so that I can fix them.
I would also appreciate any feedback (positive or negative) on the tutorial contents
so that I can improve it.