233

~,~!~!~i~ • ~

~ ~~:::

:,L J; '

r

234 delivered b3 Ther~ since the inv

summation. At this level of flux per area the source is usually not suitable for stimulation which is less than 250 msec. Though, conceptually, a very large source c a n b e employed for a shorter duration, technical difficulties, mainly those of heat sinking of the source during the non-activated period, can be considerable.

and staNe electrophysiological respon time of ".he heat produced by the wires The nexl choice was application of irradiant heat by a Laser beam. 'I3.m initial expe,,iments were quite successful, and not only staNe pain sensations were obtained, but clear and stable evoked .)otenfials to the irradiant energy produced, by the Laser beam were recorded as well. The method seems t:,~,be accurate enough and proper y contrC~ed for experimentation in pain and is brietiy reported here. The Laser beam is almost parallel, as if c~.~ming from, infinite intensity in infinite distance. By focusing, tl~e collimated energy can be therefore enormous. Either a pulsed beam or a chop!~d continuous beam can be: "fiei~and v e ~ : s h m burs:~ of ener~,~ which is virtually unlfmited in intensity, ~ a p ~p i e ~ : k ~ e area of can

be vex/ed from heat to pain, depending on wavelength and intensiEr. The technique used was short exposures to a c o n t i ~ o u s oul manufactured by the Electro-Optical Industries of israel. ~ s Las infrared beam (10.6 ~m) at intensifies up 1:o 50 W. The diameter sour:e is 20 mm b'at it can. be limited further either byintroduciyag a 1 or by focusing it with a germanium lens. The intensity can be varied ~ output of the Laser beam, but this control is rather difficult and doest incremepts of sthnulafion energy. Therefore, the energy is mmfipulated the output of the ,Laser but rather by vary~ng the duration of the s~ durations necess~ary for~tudy of evoked :responses e a n b e '* ~ ....vil prop:date choppi~:g~of the confinuou~ output. Very smal!:t~si'imu . for somatosensory studies can be easily achieved by focUsiingi::2 into predetermined, discrete stimulus, a system of two s~m!tNrs wai~i to tke source of radiation a shutter of beavv ~au~e~ btadkened a', ~i

,

an

at

short

TM

TM

235 safeW shutter #6'

r

M'-------I I

Computer operated the capacitance value ,pening duration. The when the capacitor is

normally the output of the Laser without being damaged and without reflecting the radiation. This shutter serves also as a heat sink. It is driven by a solenoid activated by the discharge of a capacitor (eft Ng. 1). The dimensions of the capaci~:or were chosen so that the shutter stayed open the shortest length of time appropriate to a

vals, re(mires the-information that the shutter is open and opens the light shutter for:the predetermi~-durafiOni The location of the-stimuIus is controlled by a germanium lens which follows the line of the beam after the fast Shutter. The major proNem in the appVcation of highenergy Laser Io ~ r somatic st~mulao fiOn i s t h e safety precautions which shou!d be taken i~ :order to avoid trauma to the

236 SEi~y shutter Ir

shut

CO2 Loser

I

II

1

._,

Computer

Fig. 2. A CO2 Laser system used for cutaneous pain stimulation.

subject. Laser energy can cause net only overt burns but also discrete damage to red blood cells 4. Our system ha,, the same room with the Lase through a small hole which We have built the system in into the path of the Laser and The subject sits quietly, the r system does not result in a si for the safety of the experim~ of the eyes (since the 10.6 ~n the retina). Initial experiments with this sy~;tem showed that the sensation which accompa-

dures beside recording o f stable evoked responses:

ACKNOW

¸!i