Research methods

At the premises of University of Helsinki we have several electroencephalography (EEG) laboratories with shielded rooms, trans-cranial magnetic stimulator integrated with EEG (TMS/EEG), and mobile recording units which can be used outside the laboratories. Also eye tracking and signals of autonomic nervous system can be measured in combination with EEG. Outside the institute, we have access to 3T fMRI and MEG located in the Helsinki metropolitan area.

Our laboratories have been built to serve many projects and users. The stimulus systems have been optimized and measured to meet high requirements e.g. in temporal accuracy. In case of tech-related questions, please contact the laboratory engineer.

 

EEG is a functional brain research technique that records electric activity caused by neural activity. EEG is often recorded to study ERPs (see below). EEG is typically measured with electrodes attached to the scalp. EEG offers a good temporal resolution, but exact sources of brain activity are challenging to interpret. It is a safe, cost-effective and easy method that is in heavy clinical and scientific use around the world, even in studies of newborn infants.

We use the following EEG devices:

BrainProducts BrainAmp DC
BrainProducts QuickAmp
BrainProducts LiveAmp
BioSemi ActiveTwo
NeuroScan Synamps 2

 

 

ERPs are electric responses recorded from the brain, and they are calculated from the EEG signal. ERPs are event-related, i.e., they depict the brains activity in response to an internal or external stimulus, for example a repeating sound. In a typical ERP experiment, EEG is recorded and at the same time, the participant hears sounds, sees pictures or performs a given task.

In measuring ERPs it is important to have an extremely controlled set of stimuli. Usually the external stimuli are auditory, visual, or both and they are repeated rapidly in a sequence. These stimuli can be delivered by using specialized hardware and software which are optimized to maintain high temporal accuracy. For presenting stimuli we mainly use Presentation (Neurobehavioral Systems) and Psychtoolbox.

MMN is an ERP response with negative polarity, calculated by subtracting the ERP to frequently occurring standard stimuli from the ERP to occasionally occurring deviant stimuli in a so-called oddball paradigm. It reflects pre-attentive processing of expectation violations and can reflect differences in long-term experience, e.g., it can be modified with language learning or music training. MMN was first introduced by Risto Näätänen and colleagues in CBRU in 1978, and is currently studied extensively around the world. Because MMN elicitation is pre-attentive, it can be measured already in prenatal and neonatal age.

In TMS, an electric current (induced by magnetic pulse) is used to stimulate neural tissue. With suitable stimulation parameters it is possible to either inhibit or excite neural function. When combined with EEG, functional connections between brain areas can be investigated. TMS enables even determining causal connections between brain and behaviour.

We use the navigated TMS device by Nexstim.

Eye-tracker is a camera based device which is able to track the pupil and its movements relative to the head. With an eye-tracker the point of gaze, micro movements of the eyes, and changes in pupil size can be measured.

We are currently using Eyelink 1000 Plus eye tracker by SR Research.

With ANS recording devices, one can collect signals reflecting the activity of the autonomic nervous system, which is influenced by, for example, emotional states. ANS measures include the heart rate (and its variability), skin conductance, bodily temperature, and the tonus of (facial) muscles.

Genetic analysis can be done to identify inherited disorders or abnormalities. The whole or selected parts of the human genome can be examined by looking at the sequence of DNA (Deoxyribonucleic acid) bases. The DNA is normally extracted from blood or saliva.

MEG is a functional neuroimaging technique, which enables us to measure the magnetic activity fields caused by of the brain’s neural activity. Magnetic currents occur naturally in the human brain, because of the synchronized activity of cortical neurons during information processing during rest and cognitive tasks. MEG has a very high temporal resolution and a fairly good spatial resolution.

We are using a MEG system by Elekta Neuromag which is located in Biomag.

fMRI belongs to hemodynamic measures. The ratio of oxygenated and deoxygenated hemoglobin is measured. It has a very high spatial resolution and enables the investigations of even deep brain structures, but its temporal resolution is relatively poor.

The 3T MRI scanner is located at AMI centre in Espoo.

ABRs are ERP responses recorded only from the auditory brainstem, an early sound processing structure located above where the brain connects with the spinal cord. It uses fewer electrodes and can be recorded from adults as well as infants and sleeping people. The ABR waveforms are comprised of several components from about 5ms to 40ms after a stimulus. They are very reliable and typically reflect stimulus properties and physiological processing limits of the system but have recently been used to show subcortical plasticity reflecting musical and language experience.