Researchers interested in using MR-compatible game controller to design functional magnetic resonance imaging (fMRI) studies.

One major field in social neuroscience is to study human interactions and their neural correlate. Compared to electroencephalography (EEG), functional magnetic resonance imaging (fMRI) using BOLD signal has advantages of high spatial resolution and homogeneous sensitivity across the whole brain. However, the strong magnetic field in fMRI experiments poses a technical challenge in using commercial computer peripheral devices to record subjects’ responses. This challenge has been partially addressed by using devices with fiber optical interface, such as joysticks and response buttons. Alternatively, keyboard¹ and joystick² after replacing ferromagnetic components, filtering noise, or using electromagnetic shielding, have been proposed. However, these wired devices may increase the risk of RF burning and decrease the signal-to-noise ratio (SNR) because of the common-mode current along the connecting wire³.

Here, we developed a multi-purpose joystick controller with Bluetooth communication. This wireless device was first tested on a 3T MRI scanner to ensure that it causes minimal image distortion and time-domain SNR degradation. We then used these joysticks in a preliminary hyper-scanning⁴ experiment to record two subjects’ brain responses during a chess game.

Our Bluetooth multi-purpose game controller was modified from a commercial wired game controller (USB interface) with a D pad, 4 buttons, and 4 triggers. All electronic components on the circuit board were removed. A Bluetooth module (Bluefruit EZ-Key, Adafruit Industries, New York, New York) was used to receive key strokes and to transmit the signal to a dongle placed outside the MRI bore but inside the MRI shielding room. The Bluetooth dongle was connected to a computer to present fMRI stimuli and to record subject’s responses (Psychtoolbox, 3). The power of the wireless game controller was provided a lithium polymer battery (3.7 V; 280 mAh) mounted inside.

Imaging experiments were done on a 3T MRI scanner (Skyra, Siemens, Erlangen, Germany) on a saline phantom using a 32-channel head array and EPI (TR = 2 s; TE = 30 ms; Flip Angle =90°; 3.50 mm isotropic). The game controller was parametrically placed with distances to the periphery of the phantom at 0 cm (next to the phantom), 20 cm, 40 cm, and 60 cm. Images without the game controller were also acquired to check if the game controller caused image distortions. Maps of time-domain SNR were calculated by taking the ratio between the mean and the standard deviation of the time series of each image voxel in EPI over 5 minutes. Two game controllers were used by two subjects at two separate 3T MRI scanners (Tim Trio and Skyra, Siemens) to engage a chess game (Reversi). Four runs of EPI data were collected. The interaction between brains were quantified by calculating the inter-subject correlation coefficients transformed to the Z-scores.

Figure 1 shows the exterior view of our wireless game controller and its circuit. Figure 2 shows the tSNR maps. No visible distortion was observed in instantaneous phantom images with and without the game controller. We found that the tSNR was moderately reduced when the game controller was right next to the phantom. However, in cases where the distance between the game controller and the phantom is larger than 20 cm, there is no discernable tSNR difference. Figure 3 shows the inter-subject correlations of the hyper-scanning. Enabled by our game controller, two subjects successfully played the game in two MRI’s for about 12 minutes in 4 runs (min: 614 s; max: 940 s). Stronger inter-subject correlations were found at bi-hemispheric occiptotemporal lobe junctions and percuneus (Figure 3).We developed a low-cost wireless game controller for fMRI experiments. Results show that the game controller caused minimal distortion and tSNR degradation. This is likely to be explained by the fact that the operating frequency (2.4 GHz) of our Bluetooth module was far away from the Larmor frequency of MRI. Preliminary results from a two-person hyperscanning experiment successfully recorded subjects’ responses and interesting inter-subject correlated brain activity. The wireless design ensures no risk to the subject caused by the common-mode current in wired devices. The Bluetooth interface allows our game controller to be easily used in different software packages to process behavior responses and to coordinate stimuli presentation on computers with most operating systems.