The overall goal of this procedure is to assess cognitive and emotional functions of interacting brain structures through simultaneous recordings from both deep and surface neuronal sources. This method can help answer key questions in human neurophysiology. Such as, the relationship between brain activity patterns and brain function, especially regarding deep-seated, barely accessible brain areas.
The main advantage of this technique is that it uses the framework of deep brain stimulated patients to extract live information of cortical and sub-cortical structures in humans during cognitive and emotional tasks. The recording steps in this section focus on a patient with a movement disorder performing a flanker task. The analysis steps in the next section, however, focus on a patient with chronic disorder of consciousness listening to a cognitive, emotional speech paradigm.
Begin by setting up electroencephalography, or EEG equipment in the testing room. Connect the recording computer to the EEG system and start the EEG recording software. Click File, and then, New Workspace to define the workspace in the EEG recording software by specifying a sampling frequency of five kilohertz, a low cut-off and high cut-off frequency, EEG channels according to the international 10-20 system, and local field potential, or LFP channels.
Click Monitor to verify that the specified channels are now set up for recording. Next, set up the stimulus computer and check the connection to the parallel port of the EEG system. Start the stimulus software.
Click Run, to check the paradigm's functionality on the computer monitor. Ensure triggers from the stimulus computer are sent to the recording system by checking their appearance on the EEG recording software during presentation of stimuli, as well as during the subject's response. Mark the vertex of the patient's head as the midpoint between the nasion and inion by using a skin marker pen.
Then, mark the chosen EEG electrode positions, according to the 10-20 system. Clean each selected location with an isopropyl alcohol pad and abrasive paste. Then, attach the EEG surface electrodes to the scalp.
Alternatively, depending on space restrictions, a multi-channel EEG net may be used. Another high-end method to assess superficial brain activity would be be used magnetoencephalography, or MEG. Connect the percutaneous extension cable from deep brain stimulation, or DBS electrodes, to an external cable connector.
Connect each electrode provided by the external cable connector to the EEG control box, according to the EEG recording setup. Connect the EEG scalp electrodes to the EEG control box. Next, provide the patient with instructions about the flanker task.
Ensure that the patient is comfortable and instruct him to stop the experiment at any time for discomfort. Click Run on the stimulus software so that the patient is able to see the paradigm on the monitor. Perform a training session with the patient until they are comfortable with the task.
Finally, start simultaneous recording of sub-cortical LFP and cortical EEG brain activity while the patient performs the flanker task. Begin by opening the EEG analysis software. Click New, to visualize the recorded data from the emotional cognitive speech paradigm by specifying the folder paths and data's name.
Click Edit Channels, to select channels of interest. Then, click Channel Preprocessing, and then New Reference, to re-reference adjacent DBS contacts, which creates virtual bipolar context for the left and right hemispheres. Click Raw Data Inspection to screen data for physiological and equipment related artifacts with emphasis on motor jittering and equipment disturbances.
Mark segments in which artifacts are present. Next, click Data Filtering, and then IIR Filters to specify a notch filter and choose Butterworth zero phase filters by specifying low and high cut-off parameters. Click Change Sampling Rate, to down sample the recording signals to a specified frequency, and also specify the interpolation type.
Export bipolar channels of interest by clicking Export, and then Generic Data. Export data triggers by clicking Export, and then Markers. Name the files to be exported by selecting a T-X-T format.
Next, start up MAT lab and click on Set Path to add the field trip folders path. Calculate the LFP spectral power for channels of interest by first specifying, in script one, the path and name of EEG and LFP files and by running this script to generate a file with the data structure required by script two. Second, run script two after specifying spectral analysis parameters, such as spectral method, frequency, time range of interest, and baseline correction, and statistical parameters, such as type of analysis and P value.
Then, calculate coherence between sub-cortical and cortical brain signals by running script three, not before specifying segment length, overlap percentage, frequency of interests, and type of analysis. Finally, calculate cross-frequency phase amplitude coupling by running the software implementation available as a supplementary file in the reference seen here. This protocol assessed emotional cognitive functions in the thalamus during the paradigm shown here.
With stimuli of neutral non-addressing speech and familiar-addressing speech. Here, stimulus locked modulation of oscillatory activity within the central thalamus, revealed a right-sided increase of beta power within the first second when contrasting neutral addressing versus familiar-addressing conditions. Analysis of power change corresponding to the LFP two three, revealed an early beta increase within the first second, as well as a late data modulation.
Furthermore, a significant theta increase in the familiar addressing condition at four to six point five hertz, and time period two point six to two point eight seconds on the LFP two three was revealed. Once mastered, this technique can be done in one hour if it is performed properly. While attempting this procedure, it is important to remember that the spatial resolution of recordings provided by this technique is at the level of local field and EEG potentials.
After watching this video, you should have a good understanding of how to perform combined invasive and non-invasive neurophysiological recordings in humans to assess cognitive and emotional functions.
