Fig 1.
Schematics and exemplar view of the brain-to-brain interface (BBI) system.
On the left panels, the EEG-based BCI procedure is shown, including the placement of EEG electrodes over the motor cortices. Upon the presentation of the left/right target on a computer display, the sender’s motor imagery of the left/right hand modulates the EEG signal through the reduction of the mu rhythm in each hemisphere (i.e., illustration given in the C3 and C4 EEG location), and moves the computer cursor (appeared as a ball) through BCI signal processing. When the cursor reaches its target, the computer generates a trigger signal that is transmitted to the receiving location (~30 km away) through the internet (via TCP/IP protocol), whereby the FUS-based CBI (illustrated on the right panels) stimulates either the left or right SI. The right panel illustrates implementation of two FUS transducers that independently stimulate left/right SI of the receiving individuals. The stimulation of the SI elicits tactile sensation of the contralateral hand area, and the receiver was instructed to signal the hand where she/he felt the elicited tactile sensations.
Fig 2.
Flow charts of the visual displays used for the brain-computer interface (BCI) task trials.
(A) The timing diagram of BCI test sessions used for setting the BCI parameters. (B) The timing diagram used for BCI experiment session for decoding the motor intention during the BBI implementation.
Fig 3.
Schematics for the FUS-mediated CBI system in BBI communication.
(A) Left panel: a rendering of the FUS setup for the CBI segment. The left and right SI were independently targeted by two single-element 210 kHz FUS transducers where the locations of FUS foci were tracked by using the optical trackers (‘tracker 1’ and ‘tracker 2’) in reference to the head (tracked via ‘helmet tracker’). Each tracker having four infrared-reflective markers was recognized by a motion capture camera. The gap between the transducer and the scalp was filled with a soft compressible hydrogel for the acoustic coupling. FUS transducers were actuated by separate sets of computer-controlled driving circuits. Right panel: The acoustic intensity mapping of the FUS transducer. The FWHM of the intensity profile is demarcated by red dotted lines. (B) Illustration of the FUS actuations triggered by the transmitted signals from the BCI segment with the following acoustic parameters: SD = 500 ms; ISI, inter-stimulation-interval, = 7 s; TBD = 1 ms; PRF = 500 Hz; Isppa = 35.0 W/cm2. (C and D) Exemplar views of the FUS targeting to the bilateral SI as guided by individual-specific neuroimage data. The sonication target is indicated as the intersection of the green orthogonal crosshairs shown in the triplanar views (i.e., axial, sagittal, and coronal slices), while the thick yellow line (connecting green and red dots as intended entry to target points) and green line represent the orientation of the planned and guided sonication beam paths, respectively. In the lower right panel of 3D rendered view, the four colored dots show the locations of anatomical markers used for the spatial co-registration between the subject and the neuroimage data. ‘R’ and ‘L’ denote right and left, respectively.
Table 1.
Accuracy and processing time of the BCI segment, CBI segment, and overall BBI communication for three sessions.
Fig 4.
Exemplar view of CBI segment responses during a BBI session.
FUS-mediated CBI segment exemplar capture screen of the BCI-originated trigger signals, which includes the elicited responses from the CBI segments.
Table 2.
Performance of the BCI segment, CBI segments, and overall BBI sessions.
Fig 5.
Performance of the six subject pairs for the implemented brain-to-brain interface (BBI).
The ROC curves from the six subject pairs were shown in terms of EEG-based BCI task (left column), FUS-mediated CBI task (middle column), and overall BBI communication (right column). The rows indicate three multiple sessions (rows: session #1 to #3). Each BCI/CBI subject or BBI pair was labeled 1–6 around the data point circles.