NonInvasive Methods Electroencephalography (EEG) While EEG is a great place to start in developing an exocortex…
Invasive Methods Electrocordiography (ECoG)
The biggest difficulty in developing a potential data input mechanism is it would need to be able to send fairly abstract input into the brain of the user. While TMS has been used to gain fairly specific control over the motor cortex, this area is generally not of interest for the purposes of an exocortex.
Transcranial Magnetic Stimulation (TMS) Transcranial magnetic stimulation has been successfully used to induce specific responses in the motor cortex, enough so to allow the control of one human being's hand from another's brain via input in another room.[3]
[1] Wikipedia article on Exocortex [2] Pushing the Communication Limit of a Noninvasive BCI speller [3] Researcher Controls Colleagues Motions in BCI Interface