Ove Franzén

Perception of pulpal pain as a function of intradental nerve activity

&NA; The purpose of the present investigation was to find neurophysiological correlates of pain perception. The magnitude and time course of perceived pain was successfully related to the neural discharge evoked by rapid cooling of the tooth surface in 6 dental patients whose lower incisors were to be extracted for prosthodontic reasons. Two cavities were prepared on the facial surface of human lower incisors. The cavities were deepened using hand driven instruments until the pulp was visible through a thin layer of dentin. A metal tube was placed in contact with amalgam on each cavity bottom and fixed in place by composite filling material. The tubes were connected to standard equipment for electrophysiological recordings by a flexible circuit. The magnitude of perceived pain was assessed by a cross‐modality matching to finger span in combination with sensory verbal pain descriptors and magnitude estimation. The striking agreement between the integrated nerve activity, probably of the A&dgr; type and pain perception, is of great importance from the methodological point of view since it strongly argues in favor of the appropriateness of the techniques applied here to elucidate the neural substrate of some types of nociception and also to evaluate various means of relieving such pain.

Apparent contrast as a function of modulation depth and spatial frequency: A comparison between perceptual and electrophysiological measures

Abstract The contrast sensitivity function describing the interrelated contrast and spatial response characteristics of the visual system was determined for sine-wave gratings. Three spatial frequencies were then selected for psychophysical scaling of apparent contrast using an intermodal matching technique. The perceptual contrast curves were to a fair approximation power functions of the physical contrast of the striped target. Power transformations as a function of spatial fequency were observed, i.e. with decreasing sensitivity the exponents of the apparent contrast functions increased. A reanalysis of evoked response data published by Campbell and Maffei confirmed these observations.

Vibrotactile frequency discrimination

Thresholds for vibrotactile discrimination of pulse interval were determined for pulse frequencies between 1 and 384 Hz. The results point to a temporal resolution significantly more accurate than that demonstrated in earlier studies. Although touch as a vibratory sensor is in general much inferior to audition, the present results show a striking resemblance to those obtained on auditory pitch. The neurophysiological implications for the tactile as well as for the auditory system are discussed.

Dental Pain Evoked by Hydrostatic Pressures Applied to Exposed Dentin in Man: A Test of the Hydrodynamic Theory of Dentin Sensitivity

The hydrodynamic theory of dentin sensitivity holds that pain is evoked by stimuli producing minute shifts in tubule fluid. In human volunteers hydrostatic pressures were applied to prepared dentinal cavities. The subjects reported the magnitude and quality of their sensations of pain by means of an intermodal matching technique in combination with verbal descriptors. No pain could be elicited when the smear layer was present. After removal of this layer, pressure stimuli of either direction evoked sharp pain. Rapid changes in pressure induced higher pain intensities than slow changes, indicating that the dental A-delta system is dynamic and gradient dependent. These results provide support for the hydrodynamic theory of dentin sensitivity and also lend credence to the notion that the movement of fluid across dentin induces a selective activation of the A-delta nerves in healthy pulps which is highly correlated with a sensation of sharp and/or shooting pain.

Peripheral Coding Mechanisms of Touch Velocity

In November 1925 Adrian and Zotterman managed for the first time to record electrical impulses set up in a single fiber originating in a mechanoreceptive end-organ and thereby provide direct evidence for the basic principle that the conduction in sensory nerves is an all-or-none event. They found, furthermore, in a subsequent study that the mechanoreceptors could be dichotomized into rapidly and slowly adapting categories on the basis of the adaptive properties (Adrian and Zotterman, 1926).

The intensive aspect of information processing in the intradental A-delta system in man—a psychophysiological analysis of sharp dental pain

The tooth pulp has many attractive features for the study of peripheral pain mechanisms because of its rich innervation, its unique distribution of nerve fibers and its general disposition to give rise to pain upon stimulation. An experimental model has been developed for simultaneous recordings of intradental multi-unit A-delta nerve activity and the subjective intensity and quality of pain evoked by tooth pulp stimulation in conscious, alert humans. The only teeth to be considered for this kind of investigations are those having such a periodontal condition that they have to be extracted. The nerve activity was recorded from two electrodes placed in the dentin on the labial tooth surface, one at the level of the most incisal part of the pulp, and the other as far apically as possible. Brief cold stimulation was produced by using evaporating ethyl chloride administered between the recording electrodes. The magnitude of perceived pain was estimated by means of an intermodal matching technique (finger span) in combination with verbal descriptors. Of three response criteria selected--average response amplitude, peak amplitude and area under the response curve (integral)--for describing the relationship between intradental nerve activity and sharp, shooting pain, the integral yielded the highest mean correlation coefficient.

TACTILE INTENSITY FUNCTIONS IN PATIENTS WITH SUTURED PERIPHERAL NERVE

Publisher Summary This chapter discusses tactile intensity functions in patients with sutured peripheral nerve. Four male patients at the age of 19 to 22 who had sustained median-nerve injury at the wrist of their right arm took part in some experiments described in the chapter. They had their nerves sutured by a surgeon four to eight years prior to the investigation. The distal pad of the index or middle finger of the patients right and left hand was perpendicularly stimulated by a piston of 2 mm diameter mounted on a Bruel and Kjaer vibrator. The probe protruded through a small hole in a flat wooden plate that supported the hand. Half-wave sinusoids of 10 ms duration from a Wavetek generator (Model 112) actuated the minishaker. The stimulation was sensed as a distinct tap on the skin that increased in subjective magnitude with increasing intensity. It was observed that on the affected side, the sensation was different. The stimuli were felt like pulses through the finger. The subjects reported a distortion of sensation.

Effects of Systemic Morphine on Monkeys and Man: Generalized Suppression of Behavior and Preferential Inhibition of Pain Elicited by Unmyelinated Nociceptors

After years of extensive usage, morphine is still regarded as the most powerful pharmacological tool for control of pain. Despite this long record of success in the clinics, it is clear that morphine is not an analgesic, in that pain is not obliterated at systemic dosages that leave respiration intact in man (Javert and Hardy, 1951). Clinical patients report that pain can be elicited in the presence of morphine. Also, the effects of morphine on psychophysical ratings of phasically elicited pain are subtle in comparison with subjective estimates of clinical effectiveness (Beecher, 1957). This disparity of clinical and experimental findings has led to a number of hypotheses concerning the primary actions of morphine: (a) Morphine has been claimed to be an anxiolytic, and its action has been likened to the effects of frontal lobotomy, which is said to attenuate the emotional reactions to pain without disturbing the primary sensations of pain (Freeman and Watts, 1948).

Quantitative judgements and matching of subjective speed of apparent laser speckle flow induced by refractive defocus

The speed of laser speckles induced by refractive defocus was determined by means of the direct method of free magnitude estimation in combination with sensory verbal descriptors. Physical measures of angular velocities were obtained by matching a similar pattern under the viewers control to the laser speckles for equal subjective velocity. Theoretical speckle speed was calculated from geometrical formulae proposed by Charman [7]. The velocity percept of apparent speckle motion was a monotonic function of the refractive power of the positive lenses added to the observers eye, although it exhibited a tendency of levelling off at the greatest strength. The magnitude estimates of this motion percept were highly correlated with corresponding subjective judgements of the angular velocity of the real motion of the matched pattern. Theoretical velocity plotted against empirically obtained values of velocity through matching yielded a product moment correlation coefficient of 0.98 and a regression coefficient of 0.94 indicating a high internal and external validity of these measurements as well as the usefulness of speckle speed as a cue for voluntary changes of the crystalline lens of the eye.

Precision and Ambiguity in Coding Vibrotactile Information

In diagnosing a disease palpation and percussion carried out by the hand depends among other things, on its great vibrotactile sensibility (pallaethesia). Helen Keller has also witnessed about the importance of somesthesis:…“ I perceive countless vibrations. By placing my hand on a person’s lips and throat, I gain an idea of many specific vibrations…”.