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Module 1: The Inverse Problem & EEG Localization

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The Inverse Problem & EEG Localization - Lesson Summary

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EGG data can be used to pin the area in the brain responsible for producing a signal. In engineering, physics, or applied mathematics, modeling involves predicting the effect or results for a set of known parameters. This is known as forward modeling, or the forward problem. With EEG signals, you get the results, but you need to model to find where the signal originated from. This is called an inverse problem. When solving an inverse problem, EEG data is used to infer which brain areas caused the signals. Unlike in a forward problem, the inverse problem has no unique solution. Multiple (in theory infinite) set of parameters might explain the same measurement data. Therefore, typically, neurophysiologists constrain possible solutions using prior knowledge from neuroanatomy and neurophysiology.
The Source Model: A source model tells us the three-dimensional position of dipoles on the cortical surface. This is also sometimes referred to as source space. It is assumed that EEG signals are generated by sources that can be approximated as dipoles.
The Head Model: Helps us to understand how the electrical currents will flow from the sources, through the head and to the EEG electrode on the scalp.
The head model in constructed from an MRI image , but it has a different 3D coordinate system than an EEG, therefore, it is necessary to align the EEG electrode locations to the subjects MRI in a common coordinate system.
Different computer software can be used for source modeling, such as BESA, LORETA, and CARTOOL.
Brain-computer interfaces are devices or systems which respond to the neural processes in the brain that generate or modify movement. It is a technology based on the acquisition of brain waves which are then processed by a computer to execute commands.
What are the goals of BCI?• To enable people with damaged neural pathways to control their environment via reanimation of paralyzed limbs, or the control of robotic devices. • The commercialization of BCI systems for medical and non-medical applications.• Expanding the senses, such as touching infra-red signals.
Neural Signals is developing technology to restore speech to disabled people. A brain implant in the speech area of the brain, the Broca’s, will transmit signals to a computer which will transmit them to a speaker.
NASA has researched a system that reads electrical signals from the nerves in the mount and throat area, rather than from the brain, and they have been able to mentally type the word “NASA” into a search engine.
Cyberkinetics Neurotechnology Systems is a neural interface system allowing disabled people to control a wheelchair, robotic prosthesis or computer cursor.
Japanese researchers and the software company Emotive have developed a brain-to-computer interface that allows users to control their avatar in an online world, for example, Second Life or World of Warcraft.