IEEE TRANSACTIONS ON NEURAL SYSTEMS AND REHABILITATION ENGINEERING, VOL. 12, NO. 3, SEPTEMBER 2004 339
Computer Control Using Human Intracortical
Local Field Potentials
Philip R. Kennedy, Member, IEEE, M. Todd Kirby, Melody M. Moore, Member, IEEE, Brandon King, and
Adon Mallory
Abstract—We describe the use of human cortical control sig-
nals to operate two assistive technology tools—a virtual keyboard
speller and a computer-simulated digit. The cortical signals used
for control are local field potentials recorded through an implanted
neurotrophic electrode. In this system, the patients’ cortical signals
are transmitted wirelessly to a receiver and translated by computer
software into either a computer cursor movement (for the virtual
keyboard) or flexion of a cyber digit on a virtual hand. This re-
port focuses on the progress of two subjects toward effective use
of their “virtual” neuro-prosthetic devices to meet their assistive
technology needs.
Index Terms—Amyotrophic lateral sclerosis (ALS), cyber digit,
local field potentials (LFP), locked-in syndrome, mitochondrial
myopathy, neurotrophic electrode, virtual keyboard.
I. INTRODUCTION
ENABLING cortical control of computers and other assis-tive technology devices is a long-term aim of neural pros-
thetic researchers [1], [2]. For people suffering from “locked-in”
syndrome (i.e. cognitively intact but completely paralyzed), cor-
tical control of the external environment could restore a means
of communication via moving a computer cursor [3].
Cortical signals have the potential to provide control of assis-
tive technology devices such as wheelchairs, or even to operate
prosthetics which could restore movement of a paralyzed limb.
These cortical signals can consist of either fast transients (FTs,
such as action potentials) or local field potentials (LFPs). The
transition from computer cursor control to control of a paralyzed
limb is a large step. We report here on some intermediate steps
toward this goal with two locked-in subjects, JR and TT. Using
LFP cortical neural signals recorded through an implanted neu-
rotrophic electrode, JR and TT demonstrated control of a key-
board cursor and a computer-simulated digit (cyber digit). This
paper addresses the adequacy of LFPs for such control using an
approach based on a voltage threshold of the LFP along with
multiple feedback loops. We also discuss the question of how
many signals are needed to control a paralyzed limb.
Manuscript received Feburary 15, 2002; revised January 15, 2004. This work
was supported in part by the National Institute of Neurological Disorders and
Stroke, National Institutes of Health, under Grant 2R44NS36913-02.
P. R. Kennedy and A. Mallory are with the Neural Signals, Inc., Atlanta, GA
30340 USA.
M. T. Kirby was with the Neural Signals, Inc., Atlanta, GA 30340 USA and
is now with Respironics, Inc., Murrysville, PA 15668-8550 USA.
M. M. Moore is with the GSU BrainLab, Computer Information Systems
Department, Georgia State University, Atlanta, GA 30303-4015 USA (e-mail:
melody@gsu.edu).
B. King was with the Neural Signals, Inc., Atlanta, GA 30340 USA and is
now with Abbott Laboratories, Abbott Park, IL 60071 USA.
Digital Object Identifier 10.1109/TNSRE.2004.834629
Fig. 1. (a) Neurotrophic electrode consists of two insulated wires inside a
miniature glass cone. Myelinated axons grow up into the cone under influence
of neurotrophic factors and make contact with the wires. Implanted electronics
include a board-mounted FM transmitter and amplifier and two coils—one to
broadcast the neural signals out via the implanted FM transmitter and a second
coil to power the implanted electronics via an externally placed power induction
coil. (b) X-ray of the implanted electronics in patient JR illustrate the implanted
coils (dotted lines with arrows) for power. Similar but smaller implanted coils
on the circuit boards are used for signal transmission in the 30–40-MHz range.
II. METHODS
The neurotrophic electrode consists of two insulated wires in-
side a miniature glass cone [Fig. 1(a)]. Myelinated axons grow
inside the cone under the influence of proprietary trophic factors
placed inside the cone before cortical implantation [4]. Fig. 1(b)
shows an X-ray of the electronics implanted in patient JR. Power
for the devices is provided by a power induction system via in-
duction loops cemented in place on the skull. Induction coils
1534-4320/04$20.00 © 2004 IEEE