The first version of Staalhemel was based on a general, averaged measurement of alpha wave levels. In 2010 I’m investigating with researcher Lindsay Brown from Holst Centre in Eindhoven how we can interpret the discrete measurements of the eight individual electrodes on the headset. The electrode positions are named FP1, FP2, F7, F8, C3, C4, O1 and O2.
FP1 covers Brodmann area 10 on the front left side of the frontal lobe. This is part of the prefrontal cortex, that highly developed part of the brain which sets us apart from other mammals since it is responsible for the execution of cognitive tasks. Complex behaviours and simultaneous mental activities need a kind of working memory that keeps track of running tasks in either pending states or executive states. For most cognitive functions information needs to be retrieved after completion of another task. The prefrontal cortex co-ordinates all of this mental traffic and shows clear elevation in beta levels when performing calculative tasks, logical puzzles or other intellectual questions. FP2 covers the right side of the prefrontal cortex.
F7 and F8 cover parts of the frontal cortex. The frontal cortex is involved in integrating sensory information with data retrieval from memory locations. This way new sensory information can be compared with earlier perceptions. Area 45 – which is one part of Broca’s area, a brain centre dedicated to language production – at position F8 is also believed to recover semantic information and to evaluate that information in the light of the current context.
C3 and C4 are located on top of the primary somatosensory cortex, in the parietal part of the cortex. This is a clearly defined strip on top of the brain responsible for processing touch and sensation as well as keeping track of the location of your body parts (proprioception).
The two electrodes at the back of the headset, O1 and O2 for the occipital area of the cortex, cover the secondary visual cortex which is processing information relating to visual association. Cells are tuned to simple properties such as orientation, spatial frequency, and color. Depending on the exact positioning of the headset – which is likely to be slightly different per individual – they might also track the primary visual cortex from which the information is forwarded to the secondary visual cortex. Primary cortex here corresponds to Brodmann area 17 and the secondary to area 18. The connectivity between primary and secondary cortices is important for visual memory.
Table to check which Brodmann area corresponds to which electrode position
conversation experiment 1
On the picture above you see graphs of alpha wave levels (relaxation) and beta wave levels (focus) from all electrodes on the headset. You see left and right for alpha and then left and right for beta on each row. See my previous post on brain functions to understand the positions on the scalp from which these recordings were taken. Basically the order from top to bottom reflects the orientation from front of head to back of head. This experiment consisted of making a phone call and have a conversation while registering my brain waves.
On the plotting of data from the left prefrontal electrode you clearly see a decrease in alpha wave values corresponding with a block of sustained peak values in beta (blue circles). This is quite an extreme example in the recording of cognitive concentration to perform the task of conversing, formulating questions and answering to the other party’s questions. The alpha waves show a majority of values under 10%, whereas the peak values in beta show values over 30% (percentages are measured differently for beta than for alpha but in my plotting all percentages are scaled respectively to a range between 1 and 10). Alpha values for the right prefrontal area are inconclusive with values centering around an average. The beta values for the same area however (top right window), are very significant in a totally different way from peaking at maximum. In this window you see how a repetitive pattern of sustained identical values is established. This pattern also shows when the test subject is writing or reading e-mail. This type of block iteration can be monitored on several windows and can be considered significant for the occurrence of an event, which in this case means the act of getting information – while talking on the phone to my wife – about how my daughter is doing in daycare.
Another striking data profile is found on the occipital electrodes at the back of the head where the visual cortex resides (green circles). Again alpha is decimated, especially on the right channel, and simultaneously the beta window shows sustained peaks (and a lot of separate peaks on the left side). The orange circle shows you there’s a difference between left and right vision, since peaks start with a different timing. At present I don’t have enough test results to make conclusions as to why beta values for visual processing are elevated here.