Table 1.

Summary and comparison of some notable BBCIs built so far.

BBCI	Input & Output	Decoding & Encoding	Achievements	Limitations
O’Doherty et al., 2011	Spikes from monkey M1 cortex & intracortical microstimulation in S1 cortex	Unscented Kalman filter & Biphasic pulse trains of different frequencies	Simultaneous brain-controlled cursor and artificial tactile feedback in monkeys	Artificial tactile feedback limited to reward/no reward information
Flesher et al., 2016	Spikes from human M1 cortex & intracortical microstimulation in S1 cortex	Velocity-based linear decoder & linear encoding of torque to pulse train amplitude	Simultaneous brain-controlled prosthetic hand & force feedback in humans	Simple force matching task with only two levels (gentle or firm)
Moritz et al., 2008	Spikes from monkey M1 cortex & functional electrical stimulation of muscles	Volitional control of firing rate of single neuron & linear encoder	Direct brain control of paralyzed muscles to restore wrist movement in monkeys	Simple flexion and extension movements of the wrist only, muscle fatigue with prolonged use
Bouton et al., 2016	Multiunit activity from hand area of human M1 cortex & functional electrical stimulation of paralyzed forearm muscles	Support vector machines for classifying 1 of 6 wrist/hand motions & previously calibrated stimulation for each motion	Direct brain control of forearm muscles for hand/wrist control in paralyzed human	Decoder based on classification of 6 fixed motions, muscle fatigue with prolonged use
Ajiboye et al., 2017	Spikes and high frequency power in hand area of human M1 cortex & functional electrical stimulation of paralyzed arm muscles	Linear decoder & percent activation of stimulation patterns associated with hand, wrist or elbow movements	Direct brain control of arm muscles for multi-joint movements and point-to-point target acquisitions in paralyzed human	Percent activation of fixed stimulation patterns, muscle fatigue with prolonged use
Capogrosso et al., 2016	Multiunit activity from leg area of monkey M1 cortex & epidural electrical stimulation of the lumbar spinal cord	Linear discriminant analysis to predict foot strike/foot off & activation of spinal hotspots for extension/flexion	Direct brain control of the spinal cord for restoring locomotion in paralyzed monkeys	Simple two state decoder and encoder models, viability for restoration of bipedal walking in humans yet to be demonstrated
Delgado, 1969	Local field potentials in monkey amygdala & electrical stimulation in the reticular formation	Decoder algorithm for detecting fast “spindle” waves & an electrical stimulation for each detection	First BBCI to control behavior and induce neuroplasticity in animals	Results not consistent from subject to subject, did not generalize to treating depression in humans
Deadwyler et al., 2017	Spikes from area CA3 in monkey hippocampus & electrical microstimulation in area CA1 in hippocampus	Multi-input/multioutput (MIMO) nonlinear filtering model to decode CA3 activity & encode predicted CA1 activity as biphasic electrical pulses	First demonstration of memory enhancement in a short-term memory task in a monkey	Applicability to memory restoration in Alzheimer’s or other patients unclear due to MIMO model training requirement
Jackson et al., 2006	Spikes from a region of monkey M1 cortex & intracortical microstimulation of a different region of M1	Single spike detection & biphasic electrical pulse for each spike detection	First demonstration of Hebbian plasticity induction using a BBCI in a freely behaving monkey	Single input/single output protocol, not designed for multi-input/multioutput goal-directed plasticity induction
Guggenmos et al., 2013	Spikes from rat premotor cortex & intracortical microstimulation of S1 somatosensory cortex	Single spike detection in premotor cortex & electrical pulse stimulation in S1 after 7.5 ms.	First demonstration of improved motor function after traumatic brain injury in a rat using a BBCI for plasticity induction	Single input/single output protocol, plasticity induction not geared toward optimizing behavioral or rehabilitation metrics