MEG

 Magnetoencephalography (MEG) measures the minute magnetic fields generated by electric neuronal activity. It allows studying brain functions at temporal precision of milliseconds. With MEG, one can study activity time courses in single cortical areas, the spread of activity from one area to another, and interactions between brain areas. Our MEG lab is located in the Kärki building in the Mattilanniemi campus.

Research environment

Our MEG laboratory is equipped with a multitude of stimulation and monitoring devices.The research environment was built with emphasis on our core research areas, but can be accommodated according to researchers needs. Stimulation options cover most of the human senses, with many different stimulator types available. Likewise, subject responses can be collected with several alternative methods. Finally, subject’s behaviour can be monitored with many different approaches. All of these devices have been specifically manufactured or altered to suit the demanding, magnetically silent environment of the MEG laboratory. 

 

Physiological basis of MEG signal

Neuronal cells in the brain process and transfer information. When the neuronal signalling proceeds over a synapse from one neuron to another, the synaptic ion currents generate an electro-magnetic field. If there are enough simultaneously active synapses, this field is observable also outside of the head. Luckily, the often inadequately known conduction geometry of the mediating tissues is not a huge problem for MEG, because the magnetic fields pass them freely. The mediation of the electric and magnetic fields across the cranial tissues forms the basis of non-invasive studies of information processing in the human brain.

 

Measuring minute magnetic fields

The magnetic fields elicited by electric neuronal activity are extremely tiny. Therefore, special arrangements are needed to measure them. First, the MEG device is closed in a magnetically isolated chamber in order to keep out environmental magnetic noise. Then, the extra-cranial fields are measured with SQUID-based (Superconducting QUantum Interference Device) sensors, one of the few methods to observe such small signals. The sensors need to be immersed in liquid helium to work, which gives the MEG device the bulky appearance. There are altogether 306 sensors arranged all around the head, which is enough to obtain a complete picture of the neuronal magnetic fields.

 

Approaches to data analysis

The MEG recording consist of 306 channels sampled 1000 times in a second, which are the magnetic field intensities around the head. These information as such do not provide very useful information about brain activity. To obtain a clearer picture of neuronal events during the experiment, there are two principal approaches to analysis of MEG data. One option is to average the responses over a repeated event, which often is an artificial stimulus. This way, the temporal dynamics selectively associated with the event can be observed more vividly. Another option is to investigate the properties of ongoing activity, for example frequency content. By careful experimental design, it is also possible to combine these approaches. To a large extent, development in the field of MEG takes place through improvement in data analysis, including pre-processing techniques.

 

Basic research and clinical applications

Most of the research performed in the CIBR MEG belongs to one of our focus areas. An up-to-date list of ongoing projects can be found in the Projects sub-page.

Currently, most ongoing studies are related to basic or applied neuroscience from many fields of study represented in our University. We mostly study healthy young adult, but several studies with school-aged children, aged persons or diagnosed volunteers as subjects are going on as well.

The MEG method has also clinical value. The two most significant clinical applications are tracking of epilectic seizures and localization of primary sensory and motor regions before surgical operations. Novel applications for diagnostics and treatment are constantly under development.

 

 

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