Intracerebral Radio Stimulation

and Recording in

Completely Free Patients


José M. R. Delgado, M.D., et al.[1]


In Psychotechnology: Electronic Control of Mind and Behavior, edited by Robert L. Schwitzgebel and Ralph K. Schwitzgebel, Chapter 15, New York: Holt, Rinehart and Winston, 1973. Reprinted from The Journal of Nervous and Mental Disease, 1968, Oct.; 147(4): 329-40



Diagnosis and treatment of focal brain dysfunction associated with behavioral abnormalities are complex tasks which require more effective exploratory techniques. Intracerebral electrodes, electrocorticographical studies, and subsequent discrete neurosurgery have given the epileptologist and stereotaxic surgeon new possibilities for clinical investigation which as yet have been applied to only a small percentage of the patients suffering from neurological disorders including temporal-lobe epilepsy and related episodic behavior problems. In these therapeutic studies, recordings and stimulations of any chosen cerebral structure can be performed over a period of days or weeks, and neuronal sites identified as triggers for abnormal electrical patterns associated with behavioral disturbances can be destroyed by electrolysis or resection. Unfortunately, in some patients episodic behavior disorders may be more disabling than their epileptic seizures, and focal lesions may improve one syndrome without modifying the other. Furthermore, recording and stimulation are usually performed under conditions which qualify their usefulness, because the patients’ mobility is limited by connecting leads, and their behavior is likewise altered by the stressful and artificial environment of the recording room.

During the last few years, methodology has been developed to stimulate and record the electrical activity of the brain in completely unrestrained monkeys and chimpanzees (Delgado, 1967; Delgado & Mir, in press). This procedure should be of considerable clinical interest because it permits exploration of the brain for unlimited periods in patients without disturbing their rest or normal spontaneous activities. This paper reports instrumentation used and clinical application in four patients with psychomotor epilepsy in whom electrodes had been implanted in the temporal lobes. To our knowledge, this is the first clinical use of intracerebral radio stimulation and recording in man.



METHODS


Implantation of Electrodes

Electrodes were constructed and stereotaxically implanted according to methods previously described (Mark & Ervin, 1969). The electrode assemblies, which were connected to a McPherson skull plug, consisted of a plastic styled, 1.2mm in diameter, with 15 stainless steel 3mm wide contacts attached at 3mm intervals, plus one thermistor and three other contacts at the tip. Using a McPherson Type 2 stereotaxic machine (Mark & Ervin, 1969), electrode assemblies were implanted bilaterally into the anterior medial amygdala of each patient.


Radio Stimulation

This system consists of two instruments: (1) the RF transmitter that measures 30cm x 25cm x 15cm and includes the circuitry for controlling the repetition rate, duration, and amplitude (intensity) of the stimulating pulse. The repetition rate may be varied in steps between 10 and 200Hz and the duration between 0.1 and 1.5msec. Single pulses may also be generated. Intensity control is accomplished by varying the frequency of the three subcarrier oscillators that operate in the 100 to 500 kHz frequency range. A 100mHz oscillator is turned on and off by the pulse train from the subcarrier oscillators. The duration of this pulse train is determined by the pulse-duration switch. These bursts of 100mHz RF energy are received by (2) the receiver-stimulator which is carried by the subject, measures 3.7cm x 3.0cm x 1.4cm, and weighs 20g. The solid-state circuitry is encapsulated in epoxy resin which provides it with very good mechanical strength and makes it waterproof. Space for the 7-volt Mercury battery is included in the size mentioned above. After RF detection, the resulting subcarrier frequency is demodulated into an amplitude. This amplitude controls the current intensity of the stimulation pulse by means of a constant current transistor in the output circuit of the receiver. This method makes the pulse intensity independent of biological impedance changes over a wide range. Under average stimulation conditions, the battery life is approximately one week. Operating range is up to 100ft. Three channels of stimulation are available. The pulse intensity of each channel can be controlled individually from the transmitter. The pulse duration and repetition rate are the same for all three channels.


Electroencephalographic (EEG) Telemetry

A miniature FM-FM amplifier-transmitter combination and a telemetry receiver are used for this purpose. (1) The transmitting circuitry, carried by the subject, consists of an EEG amplifier with a gain of 100, input impedance of 2 megohms, frequency response from 2 to 200Hz, and a voltage-controlled oscillator (VCO) for each channel. The VCO operates in one of the frequency bands assigned for subcarrier oscillators by the IRIG standards. In these studies, a three-channel system was used which operated on IRIG channels (Delgado & Hamlin, 1962; Delgado & Mir, in press; Fonberg and Delgado, 1961). The outputs of all three subcarrier oscillators were summed and connected to the single RF transmitter module. The miniaturized RF transmitter operates at 216mHz and its range is 50 to 200 ft, depending on the environment. The size of the three-channel unit, including the battery, is 4.5cm x 4.5cm x 1.5cm, and it weighs 50g. The signals from the depth electrodes are received by the amplifier. The output signal of the amplifier controls the frequency of the subcarrier oscillator, and the oscillator output in turn controls the frequency of the transmitter. (2) After amplification of the received signal from the transmitter has been demodulated, the composite subcarrier signals are connected to the inputs of the three discriminators, which then separate and demodulate their respective subcarriers to obtain the telemetered analogue information. In the instrumentation used in this instance, a 100µV signal at the input of the EEG amplifier resulted in a 1-volt output from the corresponding discriminator in the receiver.

The analogue output signals from the receiver were connected to the inputs of an EEG recorder and a magnetic tape recorder. A microphone was also mounted in the room with the subjects and conversation was recorded along with the EEG on magnetic tape.


Stimoceiver

The integration of the three-channel units for radio stimulation and EEG telemetry constitutes the stimoceiver (stimulator and EEG receiver). Several tests were conducted to ensure proper electronic and biological operation, as explained later. The complete instrument, which weighs only 70g, can easily be taped onto the patient’s head bandage (Figure 1). During part of her treatment, one patient wore a wig which covered her stimoceiver and all evidence of instrumentation.


Additional Equipment

Conversations with the patients were taperecorded and synchronized with the EEG recordings and the moments of stimulation. During interviews with the first two patients, time-lapse photography was used to record possible changes in facial expression or behavior, according to a method employed for studies in monkey colonies (Delgado, 1964).


Physical Location of the Studies

The first two patients were under treatment at the Boston General Hospital, and radio stimulations and recordings were performed in a curtained, shielded, 12 x 12 ft room in which the patients could walk around or remain seated. The other two cases were studied in their customary quarters within a closed psychiatric ward at Massachusetts General Hospital, and they could move freely around their bedrooms, bathroom, sittingroom, or diningroom. Nurses and other patients were present during some of the recording and stimulation sessions, as seen in Figure 1.