How to avoid cable spaghetti – our tips and tricks to nicely setup your actiCAP snap cap

Since its release in 2006, the actiCAP active electrodes technology has been highly appreciated by the research community and is nowadays widely used in high impact research all over the world. Being able to record high quality data with minimal setup time significantly improves the experiences of participants and researchers alike, and the possibility to exchange single faulty electrodes in-house and independently from the manufacturer means research can be back up and running as soon as possible.

The second generation of the actiCAP slim/snap electrode system brought further improvements to different elements of the solution while maintaining its original flexible design:  stand-alone bundles of 32 electrodes which can be manually inserted in dedicated numbered holders fixed within the cap fabric. These actiCAP slim electrode bundles can therefore be moved between caps and eventually removed from the fabric completely for easy and thorough cleaning and drying. Under this concept, you may acquire multiple cap fabrics of different sizes, shapes, layouts, and only the required number of sets of electrodes, thus maximizing funding and resources.

This also means that the electrode leadwires are not fixed directly to the cap as they would be in other cap systems (see Figure 1 for different examples). Instead, an actiCAP snap cap offers you complete flexibility to arrange the actiCAP slim electrode leadwires in the way that best suits each individual application. However, setting up an actiCAP snap cap in a tidy fashion is not a trivial task!

Figure 1: Examples of cap solutions that have leadwires fixed directly to the fabric. From left to right: BrainCap Standard, BrainCap MR, LiveCap (all gel-based passive electrode cap systems), and actiCAP slim (gel-based active electrode cap system).

Proper cable management is an important practice for several reasons, especially when working with high density caps. Therefore, together with our colleagues from EASYCAP we would like to share our many years of experience in cap preparation, and gather our recommended best practices and tips in a step-by-step guide that you can use in your daily experimental routines and procedures.

As previously mentioned, there are several reasons, both practical and aesthetic, why preparing a nice and neat cap will be helpful.

One reason is that your application of choice may in fact depend on a specific arrangement of the actiCAP electrode leadwires. For example, in TMS-EEG studies, the orientation of electrode cables relative to the stimulation coil has an impact on TMS artifacts picked up in the EEG signal, so you may want to route the leadwires in the direction that minimizes these artifacts (Sekiguchi et al, 2009). In ecologically valid and mobile investigations, you may instead want to stabilize the leadwires to reduce artifacts caused by free body movements. Furthermore, if you would like to perform source localization and are using the CapTrak to detect the exact locations of the electrodes on the scalp, you would aim for a tidy cable arrangement so that all the LEDs in the electrode housings are not concealed by overlapping or messy leadwire spaghetti and can be correctly detected by the scanning system.

Tidy preparation of an actiCAP snap cap will also help you to minimise set up time because you will not need to fiddle with lots of loose electrode leadwires. For example, if you are running a cognitive study with visual stimuli presented on a screen, you would aim to keep leadwires out of the field of vision, thus more towards the back and over the shoulders of the participants. A cap that has been prepared following this fashion from the beginning will only need to be put on the head of the participant and impedance checking can start immediately with no additional fuss. This will also make removing electrodes for cleaning much faster.

Being mindful of how you are setting up your actiCAP cap will also help you take good care of it in the long run. Preparing the cap in a way that electrode leadwires do not cross each other too much will prevent unintentional damages and ensure longevity of the equipment.

Finally, having neatly arranged cables with a minimum of cable spaghetti will be much more pleasing to look at, adding to the professional appearance of your lab!

Let’s start with the basics!

If you have already worked with an actiCAP electrode system (classic and/or slim) you will know that each electrode has a specific number from 1 to 32, indicated by a label on the head of the electrode (also called its physical channel). Moreover, in an actiCAP snap cap each holder is also labelled with a number from 1 to 32, which removes the guesswork when inserting each electrode into the respective correct holder.

You will surely also know that each electrode-holder pair is associated to its corresponding channel location via a dedicated layout file. Since our standard cap layouts are designed according to the international 10-20, 10-10 or 10-5 system, electrodes are evenly distributed across the whole scalp, regardless of the number of available channels (Jasper, 1958). This means that a 32-channel cap already provides full-head coverage and increasing channel numbers will add more density – perfect for higher spatial resolution and advanced methods like source analysis. For every standalone 32-channel bundle of actiCAP slim electrodes in use, from 32 up to 160, an actiCAP snap cap will have a dedicated colour-coded and numbered group of 32 holders, as you can see in Figure 2.

Figure 2: An example of actiCAP snap cap 160 channels (left), and the list of colours used for each group of 32 holders up to 160 channels (right).

Now something that you may not have noticed before: did you know that the electrode channel numbers are assigned in a horseshoe shape? Each set of 32 coloured holders on a standard actiCAP snap cap is arranged as indicated in Figure 3 below (Top panel). The reason for this is due to the actiCAP slim electrode bundles, which are divided into 4 sets of strands-of-8-leadwires (Figure 3, Bottom panel). As you can see, each consecutive set of 8 electrodes/holders of each colour group are located within the same quadrant of a standard actiCAP snap cap. This allows electrodes to be mounted within their respective holders without their leadwires crossing over hemispheres or over each other.

Figure 3: Top panel: the horseshoe principle visually represented for a 32-channel cap (on the left) and a 128-channel cap (on the right). The four little arrows represent the locations where the strands of electrodes are meant to be threaded through Velcro straps and leave the cap. Bottom panel: example of 2 strands-of-8-leadwires that are part of one actiCAP slim electrode bundle.

To summarize, actiCAP snap caps are designed to facilitate good cable management and ease your preparation procedures ahead of the experiments. This has been achieved by arranging the colour-coded and numbered snap holders in a horseshoe shape around the cap, allowing each subset of 8-leadwire electrode bundles within each standalone 32-electrode bundle to occupy their own quadrant, regardless of overall channel density. Furthermore, Velcro straps at the sides – which can be easily opened and closed – are designed to hold the cable braids of each quadrant in a tidy fashion. This logical and practical structure encourages a simple preparation process that you may follow when preparing your actiCAP snap cap.

With the basics explained, we will now walk you through the steps that we usually follow when setting up an actiCAP snap cap. Since higher channel counts are the most likely to fall into a spaghetti style, we will prepare a 128-channel actiCAP snap cap in this example. However, all the steps we use and tips we provide can be translated into your own setup, whether you use 32, 64, 96 or 160 channels.

You can watch a tutorial video and then read through each step right below!

We usually prepare an actiCAP snap cap following its color-coded map, thus starting with the first standalone 32-slim-electrode bundle in the green holders, followed by the second bundle in the yellow holders, and so on (see Figure 4). Instead of inserting electrodes into the cap randomly, we make sure to insert electrodes in their respective colour-coded holders consecutively, following the built-in horseshoe structure of the holders’ numbers, starting with electrode number 1 and finishing with electrode number 32. In this way, we know that all electrodes have been inserted with minimal overlapping cables, and it is easier to tell if any adjustment is needed (see Step 6 below).

Figure 4 – from left to right: Examples of a 32-channel, 64-channel, 96-channel, and 128-channel setup on an actiCAP snap cap with actiCAP slim electrodes.

Figure 7: Adjusting the free length of each electrode with the cable guides is important to allow enough room to adjust on the head of the participant (left). Pulling the cables too much (middle) or leaving them too loose (right) should be both avoided.

Due to the nature of the horseshoe design, inserting electrodes in our 128-channel cap involves re-visiting previously populated quadrants with new electrodes in neighbouring holder locations. This means that the more we populate our actiCAP snap cap, the more ongoing adjustments might be needed.

For example, the leadwires of electrodes located in the lower part of the cap can be re-routed on top of the leadwires of higher electrodes since this will keep them fixed and stable (see the Before vs. After effect in Figure 9).

In such cases, it may be helpful to insert the electrodes you are currently working on first, then remove and re-arrange the neighbouring electrodes whose leadwires could be re-arranged (e.g., placed on top if in a lower position). This can be repeated with as many electrodes as needed. The important point is that finding the right arrangement of cables can involve re-inserting or re-orienting already prepared electrodes, so don’t hesitate to adjust them on the fly!

Figure 9: Re-routing cables while populating the cap can be done repeatedly when needed. Cables of electrodes located higher on the caps can be routed under the leadwires of electrodes in lower locations. In the Before picture, the cable of electrode #3 in the yellow holder lays on top of the housing of electrode #2 in the yellow holder. Re-routing the latter on top of the former allows you to keep the cable stable and avoid covering the LED light within the electrode housing.

actiCAP snap caps and actiCAP slim electrodes are designed with the researcher’s ease of use in mind, allowing you to get on with your research with minimal fuss and without inconvenient cable spaghetti.

With this article we hope we have given you some useful tips and guidelines on how to setup your actiCAP slim/snap system in a straightforward and neat way.

If you would like to re-watch the video tutorial and view more tutorials on our solutions, subscribe to our YouTube channel. Make sure to also check out further tips & tricks newsletter articles as well as the Support & Resources section on our website.