First: select the right montage for scanning. Don’t use an average reference that contains channels with excessive artifact or contamination. If you use the machine reference (or any single electrode, e.g., Cz) make sure that the electrode is located away from the suspected area of activation or pathology (i.e., an "active" site). Not sure? Use Insight to make and save an average reference without the contaminated channels, then scan using your new average reference in SpikeDetector. (See the Clinical Application Note Tips for Long Term Monitoring for more information.)
Second: Use the Review Wizard to identify and remove any other artifact events. Here’s how:
Using the Spike List on the right side of the SpikeReview screen:
- Click on the Height column to sort the spike events by this parameter. (Scroll the event list to the right to see the Hgt column.)
- Multiple select all the outrageous values (using the SHIFT or CTRL key + mouse select) and delete them by pressing DELETE on your keyboard.
We have highlighted all of the outrageous height values in our sample file (e.g., > 500 µv—the upper threshold for any given recording can easily be found with a glance at the height-sorted event list). No surprises here—both the average trace and the P3 label in the Focus column clearly show the contribution from the bad electrode. Pressing DELETE will immediately remove this bad channel from our consideration. (Note that since we are doing this by height, any spikes detected at P3 before it became dislodged and after it was fixed will not be deleted.)
The ability to sort events by parameter enables you to remove channels individually if you like (e.g., you can remove Fp1/Fp2 without re-scanning. Don’t worry about the intermittent/unnoticed activity— the Review Wizard will separate this out for you).
- Click on the Focus column to sort by channel.
- Multiple select all the events for the channel you wish to remove and press DELETE on your keyboard.
You can also remove events during a range of time by clicking on the time column, multiple selecting the range of time and pressing DELETE on your keyboard.
Once you have deleted the obvious artifact, use the Review Wizard to cluster the remaining spikes (and delete any remaining artifact group) by selecting Tools|Cluster, or click the Cluster button on the toolbar.
If you wish to restore all of the deleted events, select Edit|Restore Deleted from the SpikeReview menu.
SpikeReview will allow you to sort events by other criteria as well, and in combination (e.g., click Focus then Time to sort events by channel and time). Click on the column’s name to sort by any of the parameters listed below. The scroll bar at the bottom of these columns can be used to bring them into view.
| Parameter |
Description |
| Time |
Detection time at the peak of the Focal Spike |
| Sign |
Scalp negative or positive |
| Perception |
Perception value assigned, from .1 (very low) to 1 (exemplar). |
| Focus |
Channel of the focal spike |
| Duration (Dur) |
Duration of focal spike in milliseconds. |
| Height (Hgt) |
Absolute uV value of the focal spike |
| Angle (Ang) |
Absolute angle in degrees of the peak of the Focal Spike |
Removing the obvious artifact in SpikeReview is one aspect of the ability to selectively adjust detection sensitivity without re-scanning the recording (you can also adjust sensitivity for lower-perception events, or take a random subset from the Tools|Filter menu in SpikeReview. For a step-by-step tour on the use of Persyst SpikeDetector as well as the other EEG Suite analysis tools, please refer to the EEG Suite Help file: (Start|Programs|Insight|EEG Suite Help).
