A multidisciplinary team co-led by researchers at the University of Pennsylvania has developed a new high-resolution, flexible, EEG electrode array for recording neural activity from the surface of the cerebral cortex 
without having to use penetrating electrodes. An article on the work has just been published in Nature Neuroscience describing the fabrication and in-vivo testing of the microelectronic device.
The 10mm x 9mm device consists of 720 silicon nanomembrane transistors in a 360-channel array. A significant advantage of the foldable array is that it can be deployed in areas that are physically inaccessible to conventional rigid electrode arrays such as inside sulci, fissures or between the cortical hemispheres. The new device also allows for a high spatial and temporal resolution using a minimal number of wires and may be easily scaled to clinical sizes (80mm x 80mm).
In addition to furthering our understanding of neurological disorders, the researchers expect that the arrays may also be perfected for use in neuroprostheses, pacemakers, ablative devices and neuromuscular stimulators in the future.
Abstract in Nature Neuroscience: Flexible, foldable, actively multiplexed, high-density electrode array for mapping brain activity in vivo