g.tec provides a new lecture about Evoked Potentials

The Lecture Evoked Potentials explains the recording and analysis of auditory steady-state responses (ASSRs) and brainstem auditory evoked potentials (BAEP). Both EPs are important in clinical Electroencephalography.

The main objectives of the Lecture are to

• Configure the auditory stimulator correctly for EPs
• Record and analyze ASSRs
• Record and analyze BAEPs
• Perform step-by-step the off-line analysis
• Run analysis batches to generate the EPs

ASSRs

Auditory steady-state responses (ASSRs) are used for objective audiometry. ASSRs can be used to estimate the hearing threshold in infants or to evaluate hearing aids. ASSRs are recorded with a special auditory stimulation which consists of a carrier frequency that is modulated with a lower frequency. The carrier frequency can be e.g. 500 Hz with a modulation frequency of 80 Hz.

The EEG data and a trigger impulse coming from the auditory stimulation device are recorded with a Simulink model. The Simulink model visualizes the EEG data, the trigger signal, saves the data and performs a real-time analysis of the ASSR signal.

The Spectrum Scope shows on-line the spectral information of the EEG to allow effective high quality recordings. In the Figure below a 90 Hz modulation frequency was used for the auditory stimulation and therefore the 90 Hz and the harmonic peak at 180 Hz appear in the spectrum.

BAEP

For the recording of BAEPs an auditory stimulator and a biosignal acquisition device are needed. The BAEP is generated with short-lasting auditory impulses generated by a sound board. The Simulink model receives trigger signals from the sound board and performs EEG averaging around each trigger to increase the signal to noise ratio. BAEPS are short-lasting components and appear within 10 ms after the trigger. Therefore the sampling frequency must be high enough to record these short lasting events.

A Simulink model is also used for the EEG and trigger signal acquisition and analysis. The Vector Scope performs on-line the BAEP calculation and therefore the quality of the recording can be investigated during acquisition.

g.BSanalyze can be used to calculate the BAEP in off-line mode after the recording. The image below displays the BAEP signal for odd (green) and even (blue) trials which is often used as quality measure in EP recordings. The two EPs should match as much as possible.

In total the Lecture contains 10 different task to learn the acquisition and analysis of EPs. It takes about 4-5 hours to perform the tasks.