Jaideep Mavoori

Long-term motor cortex plasticity induced by an electronic neural implant

It has been proposed that the efficacy of neuronal connections is strengthened when there is a persistent causal relationship between presynaptic and postsynaptic activity. Such activity-dependent plasticity may underlie the reorganization of cortical representations during learning, although direct in vivo evidence is lacking. Here we show that stable reorganization of motor output can be induced by an artificial connection between two sites in the motor cortex of freely behaving primates. An autonomously operating electronic implant used action potentials recorded on one electrode to trigger electrical stimuli delivered at another location. Over one or more days of continuous operation, the output evoked from the recording site shifted to resemble the output from the corresponding stimulation site, in a manner consistent with the potentiation of synaptic connections between the artificially synchronized populations of neurons. Changes persisted in some cases for more than one week, whereas the output from sites not incorporated in the connection was unaffected. This method for inducing functional reorganization in vivo by using physiologically derived stimulus trains may have practical application in neurorehabilitation after injury.

An autonomous implantable computer for neural recording and stimulation in unrestrained primates

To perform neurobiological experiments on freely behaving primates, we have developed a miniature battery-powered implantable computer capable of recording and stimulating through chronic electrodes in the cortex. The device has: (1) an analog front end with a four-pole bandpass filter (500 Hz-5 kHz), programmable gain and offset nulling; (2) an analog-to-digital converter to sample the data at 11.7 ksps; (3) a programmable microcontroller to discriminate spikes in real time and perform computations; (4) a stimulator to deliver biphasic current pulses of up to 100 muA with variable pulse width and frequency; (5) a 4 Mbit non-volatile memory to store biological data; (6) a 57.6 kbps infrared data link for wireless communications with a hand-held or desktop computer. The device is enclosed in a 5.5 cm x 5 cm x 3 cm titanium casing on the monkeys head along with a 3.3 V lithium battery and an array of cortical electrodes. In in vivo tests, the device was able to record stable cell discharge continuously for time periods of a week or more. After downloading the parameters for recording, stimulation, discrimination, and other computations, the device is capable of operating autonomously, delivering stimuli to one electrode triggered by spikes recorded at a separate site.

The neurochip BCI: towards a neural prosthesis for upper limb function

The Neurochip BCI is an autonomously operating interface between an implanted computer chip and recording and stimulating electrodes in the nervous system. By converting neural activity recorded in one brain area into electrical stimuli delivered to another site, the Neurochip BCI could form the basis for a simple, direct neural prosthetic. In tests with normal, unrestrained monkeys, the Neurochip continuously recorded activity of single neurons in primary motor cortex for several weeks at a time. Cortical activity was correlated with simultaneously-recorded electromyogram (EMG) activity from arm muscles during free behavior. In separate experiments with anesthetized monkeys, we found that microstimulation of the cervical spinal cord evoked movements of the arm and hand, often involving multiple muscles synergies. These observations suggest that spinal microstimulation controlled by cortical neurons could help compensate for damaged corticospinal projections.

Computer electronics meet animal brains

Although digital computers and nerve tissue both use voltage waveforms to transmit and process information, engineers and neurobiologists have yet to cohesively link the electronic signaling of digital computers with the electronic signaling of nerve tissue in freely behaving animals. Recent advances will finally let us link computer circuitry to neural cells in live animals and, in particular, to reidentifiable cells with specific, known neural functions. By enabling neuroscientists to better understand the neural basis of behavior, these devices may someday lead to neural prosthetics, hardware-based human-computer interfaces, and artificial systems that incorporate principles of biological intelligence.

A miniature implantable computer for functional electrical stimulation and recording of neuromuscular activity

We present details of an implantable computer (neurochip) that we are using for functional electrical stimulation (FES) and recording in freely behaving animals. The neurochip has on-board computational capability to discriminate spikes in real-time on two channels and deliver corresponding stimuli. We are using this neurochip for stimulus-response experiments to study neuromuscular dynamics in flying insects. These experiments explore problems in biological motor control and in autonomous computing. Methods and lessons learned from these studies have applications in neural prosthetics.