All About HD – EEG Part 1

HD-EEG stands for High Density Electroencephalogram. ‘Electro’ is easy enough to understand, it refers to electricity.  ‘Encephalo’ refers to the brain.  As for ‘gram’, this ending means that it is drawn (before computers, the EEG was on paper) or recorded (as it is now, by being saved to a computer’s hard disk).  So by ‘EEG’ what we mean is ‘electric-brain-drawing’.  However, we are not really drawing a picture of the brain – we are drawing a picture of the activity of the brain.  Electroencephalogram and electroencephalography are long words and it’s easy to get caught up in trying to pronounce it, so we simply refer to it as EEG.

Now, the ‘HD’ stands for ‘High Density’. This refers to the fact that unlike a conventional EEG which covers the head with 18-24 electrodes, High Density EEG has 128 ‘electrodes’ for a high-resolution picture of brain activity. That ‘electrode’ part can be unsettling, but it ought not to be. At CNNH (and most everywhere else), no electricity is used in the equipment that gets placed on the head.  The sensing part of the equipment, the  ‘electrodes’, passively pick up the activity of your brain, much like a camera does with light when someone takes a picture of you.  You could call a camera a ‘light –camera’ because it senses light.  Similarly, you can think of an electrode as an ‘electric –camera’ because it senses electricity.  Our HD-EEG electrodes are simply a wire connected to a tiny plastic disc, with a wet sponge attached to the end. 

With HD-EEG, there is NO scraping of the scalp, NO shaving of hair or any of the discomforts experienced with conventional EEG testing. Even our most sensitive patients wear the HD-EEG nets without the need for sedation. The sponge simply rests on the head and is wetted with a mixture of slightly salty water and a little baby shampoo. We need to use water on the little sponges because water helps focus the brain signals so that they can be carried across the sponge to the wire. For best results from your HD-EEG, don’t use hair products before you come in as they could interfere with the signals from your brain. Also, as I mentioned, we use the wet sponge to focus the signal.  So, if you come in with your hair wet – it won’t work!  So no hair products, and make sure you hair is dry.  Then you are good to go!