Hemoencephalography is a form of biofeedback that employs fNIRS infra red LEDs to project light through the skull into the brain. The light is then reflected back to detectors & reveals the blood flow to the brain surface.
This is most commonly used on the prefrontal cortex where working memory is localized. Research reveals that the strength of links between the prefrontal cortex and other brain structures are an indicator of intelligence http://news.wustl.edu/news/Pages/24068.aspx
Control of thought and behavior is fundamental to human intelligence. Evidence suggests a frontoparietal brain network implements such cognitive control across diverse contexts. We identify a mechanism—global connectivity—by which components of this network might coordinate control of other networks. A lateral prefrontal cortex (LPFC) region's activity was found to predict performance in a high control demand working memory task and also to exhibit high global connectivity. Critically, global connectivity in this LPFC region, involving connections both within and outside the frontoparietal network, showed a highly selective relationship with individual differences in fluid intelligence. These findings suggest LPFC is a global hub with a brainwide influence that facilitates the ability to implement control processes central to human intelligence.
As HEG is non electrical and even less invasive than TDCs there is no interference between the two modalities if used at the same time.
By combining HEG biofeedback and TDCs one should be able to generate a more significant progression with working memory training. Both Working Memory and prefrontal cortex biofeedback are linked to cognitive enhancement and increases in IQ.
HEG devices are very easy to construct simply consisting of an array of infra red LEDs with the correct bandwidth to be responsive to blood cells. The software is more challenging for non programmers but I am a JAVA developer & electronics engineer so I am comfortable with the project.
The data is processed and interfaced with biofeedback software.
Last year I researched fNIRS and found a site showing how to make a device in some detail especially how to make the head set from silicone, sensors & LED's. Unfortunately a search of my HDD has failed to come up with the link. Really such a device is easy to construct with optical fibres running to the the signal processing box .http://felixchenier.com/lib/exe/fetch.php?media=research:pdf:a_new_brain_imaging_device_based_on_fnirs.pdf Discusses some of the hardware.
As a final observation if we look at the Drexel page outling areas of fNIRS research http://www.biomed.drexel.edu/fnir/CONQUER/fNIR_Research.html we can see that there is a strong overlap with TDCs research of most interest math ability and general cognitive enhancement.