25

and antagonists are useful tools in the (subklassification of

the adrenoceptors involved in regulation of somato-autonomic

reactions; (2) alpha2-adrenoceptors play a critical role in the

regulation of the autonomic nervous system.

FORCE PERCEPTION AT LONG-TERM EXPOSURE TO

VIBRATION

N. Draganova and L. Svrakova

Institute of Hygiene and Occupational Health, Sofia, Bulgaria

Matching force magnitude was studied in two groups of

subjects with long-term exposure to vibration - 23 operators

working on vibrating hand instruments and 25 patients with

vibration disease. The maximum voluntary handgrip contrac-

tion (MVC) was measured and the individual reference force

(RF)= 50% of MVC was calculated. After training in RF

reproduction with visual feedback, the subjects were asked to

match it with the same nad. MVC (N), accuracy of RF

reproduction (in 5%) and mean time for onset of matching

force (Tmf) were traced. The results obtained showed signifi-

cantly lower MVC values for both groups, the reproduced

force in the first group being 20% lower than RF, while in the

second group it was 7% higher. Tmf in the second group was

greater (P 0.05) than in the first group. The data obtained

can be interpreted as supporting the hypothesis of central

mediation of force perception. The changes in the subjects

with vibration disease were most probably due to damage of

the peripheral sensory system.

EFFECTS OF SMOKING ON THE HABITUATION OF

THE ELECTRODERMAL ORIENTING RESPONSE

Gunnar Edman and Daisy Schalling

Department of Psychology and Psychiatry, Karolinska Insti-

tute, Sweden

Electrodermal (ED) responses were recorded during the pre-

sentation of 21 moderately intense (1000 Hz, 90 dB) tones in

three smoking conditions: smoking before, during and after

the tone stimulation. Differential effects of smoking on the

ED measures was also studied by administering personality.

anxiety proneness and extraversion-impulsivity scales, and smoking habit questionnaires. ED response habituation was

measured as the number of trials to a response criterion of

three successive nonresponses and the number of inversions

of response amplitude in the stimulus sequence. Smoking

before and during tone stimulation accelerated the habitua- tion rate. Significant effects of smoking were also found on

amplitude (lower) and recovery time of the first response (shorter). None of the smoking effects was related to either

personality or smoking habits. Possible interpretations of the

results were discussed and interpreted on the basis of

Sokolov’s model of the habituation process.

EFFECTS OF BARORECEPTORS ON THE BRAIN AND

HYPERTENSION

Thomas Elbert, Harald Rau, Barry Dworkin * Clin. & Physiol. Psychology, University. Tubingen, Germany

and * The Hershey Medical School, Hershey, PA, U.S.A.

The general goal of our project is to determine how changes

in blood pressure modulate events in the brain and behavior.

Of the several methods for stimulation of the baroreceptors in

humans, the pressure regulated neck chamber produces a

reliable physiological effect and is sufficiently non-invasive to

permit behavioral studies. One problem. however, was to

arrange a convincing. psychologically equivalent ‘placebo’

condition. Application of a brief external suction burst during

systole enhances the pulse amplitude through addition with

the intravascular pressure peak; whereas exactly the same

brief burst applied later. in diastole. reduces the pulse ampli- tude. To the subject unaware of the phase relationship of

changes in cuff pressure to the cardiac cycle. the two condi-

tions are perceptually indistinguishable, but as our data show.

the cardiovascular consequences are quite different.

We have investigated EEG-parameters and the organism’s

behavioural avoidance of aversive stimulation. Results show

that stimulation of baroreceptors induces an inhibitory re-

sponse in cortical regions, associated with attenuation of

stress and pain responses. Under natural conditions the pri-

mary stimulus for the baroreceptors is an increase in blood

pressure. Assuming carotid activity actually attenuates pain,

this could be a mechanism through which hypertensive re-

sponses are reinforced.

In line with Dworkin (19X8) activation of the baroreceptor

reflex arc, by its central nervous inhibitory effects leads to

reduced aversiveness. This response acts as a reinforcing

stimulus which rewards and strengthens further enhance-

ments in blood pressure. A number of factors. behavioral and

genetic, interact to specify the extent to which the proposed

mechanism constitutes a risk factor for hypertension in any given individual.

Supported by the Deutsche Forschungsgemeinschaft (El

101/3).

UNILATERAL STIMULATION OF CAROTID SINUS

BARORECEPTORS

Th. Elbert, M. Tafil-Klawe *, H. Rau and W. Lutzenberger

Clin. & Physiol. Psychology, University. Tubingen, Germany

and * Dept. of Physiology. Medical Academy, Warsaw, Poland

Effects of unilateral baroreceptor modulation on brain struc-

tures were investigated by measuring event-related potentials in response to activation and the inactivation of baroreceptors

located in either the right or the left carotid sinus.