Until recently, neurobiologists have used computers for simulation, data collection,
and data analysis, but not to interact directly with nerve tissue in live, behaving
animals. 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 in microelectromechanical systems (MEMS), CMOS electronics, and embedded
computer systems will finally let us link computer circuitry to neural cells in
live animals and, in particular, to reidentifiable cells with specific, known
neural functions. The key components of such a brain-computer system include neural
probes, analog electronics, and a miniature microcomputer. Researchers developing
neural probes such as sub- micron MEMS probes, microclamps, microprobe arrays,
and similar structures can now penetrate and make electrical contact with nerve
cells with out causing significant or long-term damage to probes or cells.
Researchers developing analog electronics such as low-power amplifiers and analog-to-digital
converters can now integrate these devices with micro- controllers on a single
low-power CMOS die. Further, researchers developing embedded computer systems
can now incorporate all the core circuitry of a modern computer on a single silicon
chip that can run on miniscule power from a tiny watch battery. In short, engineers
have all the pieces they need to build truly autonomous implantable computer systems.
Until now, high signal-to-noise recording as well as digital processing of real-time
neuronal signals have been possible only in constrained laboratory experiments.
By combining MEMS probes with analog electronics and modern CMOS computing into
self-contained, implantable microsystems, implantable computers will free neuroscientists
from the lab bench. Neurons and neuronal networks decide, remember, modulate,
and control an animal's every sensation, thought, movement, and act. The intimate
details of this network, including the dynamic properties of individual neurons
and neuron populations, give a nervous system the power to control a wide array
of behavioral functions.
The goal of understanding
these details motivates many workers in modern neurobiology. To make significant
progress, these neurobiologists need methods for recording the activity of single
neurons or neuron assemblies, for long timescales, at high fidelity, in animals
that can interact freely with their sensory world and express normal behavioral
responses.