Biomedical subjects

M A Flaten

Publications and source records attributed to M A Flaten.

17 recordsLinked to original sources

PubMed2001

Effects of caffeine, caffeine-associated stimuli, and caffeine-related information on physiological and psychological arousal.

RATIONALE: To test the classical conditioning and expectancy theories of placebo effects. OBJECTIVE: Two experiments investigated whether administration of caffeine-associated stimuli elicited conditioned arousal, and whether information that a drink contained or did not contain caffeine modulated arousal. METHOD: Experiment 1 (n=21) used a 2 Caffeine (0 and 2 mg/kg) x 2 Solution (Coffee, Juice) x 2 Information (Told caffeine, Told not-caffeine) within-subjects design. Experiment 2 (n=48) used a 2 Solution (Coffee, Orange juice) x 3 Information (Told caffeine, Told not-caffeine, No information) between-subjects design. Indexes of arousal were skin conductance responses and levels, startle eyeblink reflexes, cardiovascular measures, and the Bond and Lader 1974 mood scale. RESULTS: Caffeine-associated stimuli increased alertness, contentedness and skin conductance levels, and information that the drink contained caffeine decreased calmness in Experiment 1. However, unexpected information about the caffeine content of the drink, and the order of the conditions, could have masked some effects of the experimental manipulations. Experiment 2 followed up this hypothesis. The results showed a conditioned increase in startle eyeblink reflexes, and that caffeine-associated stimuli together with information that the drink contained caffeine increased contentedness. CONCLUSIONS: Caffeine-associated stimuli increased arousal, and information about the content of the drink modulated arousal in the direction indicated by the information. Thus, both the classical conditioning and expectancy theories of placebo effects received support, and placebo effects were strongest when both conditioned responses and expectancy-based responses acted in the same direction.

Adult↗

PubMed2001

Medial prefrontal lesions attenuate conditioned reflex facilitation but do not affect prepulse modification of the eyeblink reflex in rabbits.

Conditioned reflex facilitation occurs when the amplitude of the eyeblink (EB) unconditioned reflex (UR) is increased as a result of prior pavlovian conditioning. Prepulse modification of the EB reflex is produced by preceding the unconditioned stimulus (US) by a brief low-level neutral stimulus. This study examined both conditioned EB facilitation and prepulse modification in rabbits with either medial prefrontal (mPFC) lesions or sham lesions. Conditioned reflex facilitation was assessed by comparing EB UR amplitude prior to and after pavlovian EB conditioning. Animals that received CS/US paired presentations showed evidence of conditioned reflex facilitation, but animals with unpaired training did not. However, this increase in EB UR magnitude in the paired groups was smaller in animals with mPFC lesions, compared to those with sham lesions. In two subsequent experiments different groups of sham and lesion animals received an intense burst of white noise preceded by tones with different interstimulus interval durations to assess prepulse modification. Unlike conditioned facilitation, prepulse modification was unaffected by mPFC lesions.

Acoustic Stimulation↗

PubMed2001

Assessment of visual acuity in relation to central nervous system activation in children with mental retardation.

Assessment of visual acuity was combined with observations of behavioral state indicating CNS activation in 24 individuals with mental retardation. Visual acuity was assessed by presentations of Teller Acuity Cards on two occasions. Behavioral state was classified along a scale with four categories during visual acuity testing. Results showed good test-retest reliability for the Teller Acuity Cards. Six participants had different behavioral state scores on the two test occasions, but displayed similar visual acuity on both tests. No participant rated as "drowsy" displayed responses on the acuity test. Results indicate that forced-choice preferential-looking technique can be used to test visual acuity in this population unless the participant is drowsy.

Adolescent↗

PubMed1999

Caffeine-associated stimuli elicit conditioned responses: an experimental model of the placebo effect.

RATIONALE: A neutral stimulus repeatedly paired with administration of a drug may elicit a conditioned response. This process, termed pharmacological classical conditioning, may be important in the understanding of placebo effects. OBJECTIVE: The unconditioned response to caffeine is increased physiological and psychological arousal. The present study investigated whether stimuli associated with the use of caffeine, i.e. the smell and taste of coffee, elicited a conditioned increase in arousal. It was also investigated whether conditioned arousal modulated the unconditioned arousal induced by caffeine. METHODS: Twenty subjects who drank at least two cups of coffee per day were exposed to four conditions in a within-subjects design, where the subjects received coffee or orange juice crossed with placebo or 2 mg/kg caffeine. Dependent variables were skin conductance responses and startle reflexes to 85 dB noise bursts, skin conductance levels, blood pressure, heart rate, and subjective measures of arousal. RESULTS: Both caffeine (caffeinated juice) and caffeine-associated stimuli (decaffeinated coffee) increased subjective and physiological arousal. When caffeine and caffeine-associated stimuli were presented together (caffeinated coffee), a non-significant tendency towards an additive effect of the conditioned arousal on the unconditioned arousal to caffeine was seen in some dependent variables. CONCLUSIONS: Presentation of caffeine-associated stimuli to caffeine-users elicited conditioned responses similar to the unconditioned drug response. Thus, presentation of caffeine-associated stimuli could be used as an experimental model of placebo effects.

Adolescent↗

PubMed1999

Caffeine and prepulse inhibition of the acoustic startle reflex.

RATIONALE: A stimulus presented immediately prior to a startle reflex-eliciting stimulus inhibits the startle reflex. This is termed prepulse inhibition (PPI) and is postulated to index automatic and controlled attentional processing of the prepulse. OBJECTIVE: Two experiments investigated the effect of 0, 2, and 4 mg/kg oral caffeine on PPI of the acoustic startle eyeblink reflex across stimulus onset asynchronies (SOAs) ranging from 30 to 420 ms. In experiment 1, acoustic prepulses were used and automatic attention was investigated, whereas in experiment 2, acoustic and tactile prepulses were used and automatic and controlled attention was investigated. Controlled attention was investigated by instructing the subjects to attend to one stimulus (attended stimulus) and not to another stimulus (non-attended stimulus). METHODS: Caffeine was administrated to human subjects in within-subjects designs (n = 24 and n = 18). Startle reflexes to 100 dB noise were recorded by electromyography. A mood scale and readings of blood pressure indexed arousal. RESULTS: Caffeine increased the indexes of arousal. There were, however, no significant main effects of caffeine on startle, nor did caffeine significantly interact with any other variable. Attended acoustic prepulses increased PPI at the 120 ms and longer SOAs. Caffeine 4 mg/kg abolished this difference between attended and non-attended stimuli. Attended tactile prepulses facilitated startle at short SOAs, and caffeine reduced facilitation of startle by tactile prepulses. CONCLUSIONS: Caffeine did not facilitate automatic attention. Caffeine 4 mg/kg abolished the effect of controlled attention on PPI. Facilitation of startle by attended acoustic prepulses is best explained by facilitation of motoneurons in the facial nucleus.

Acoustic Stimulation↗

PubMed1998

Caffeine-induced arousal modulates somatomotor and autonomic differential classical conditioning in humans.

Two experiments (n = 48 and n = 45) investigated the effects of caffeine-induced arousal on differential classical conditioning of eyeblink (experiment 1) and autonomic (experiment 2) responses. Three groups of human subjects received double-blind administration of 0, 2, and 4 mg/kg oral caffeine (groups 0, 2, and 4, respectively). Twenty minutes after caffeine administration, a differential classical conditioning procedure was in effect. Physiological and subjective arousal was assessed by readings of blood pressure, skin conductance level, and a questionnaire, administered before caffeine administration, and after the conditioning procedure. The results showed increased indexes of physiological arousal in groups 2 and 4. In experiment 1, differential classical eyeblink conditioning was observed in groups 0 and 4, whereas no differential conditioning was seen in group 2. In experiment 2, differential classical conditioning was seen in group 0, whereas caffeine-induced arousal masked acquisition of conditioned skin conductance responses in group 4. This group displayed increased resistance to extinction compared to the other groups. Group 2, which had an intermediate level of arousal, did not display differential conditioning in either experiment. Taken together, the results indicate that small increases in arousal may be detrimental to learning, and larger increases in arousal may reverse this effect.

Adult↗

PubMed1998

Effects of caffeine and caffeine-associated stimuli on the human startle eyeblink reflex.

An experiment was performed (n = 19) that investigated the effect of caffeine and expectancy of caffeine on the eyeblink component of the startle reflex. Nineteen habitual caffeine users received caffeinated coffee, caffeinated juice, decaffeinated coffee, or decaffeinated juice in four sessions spaced 1 week apart. Twenty-five to 30 min after ingestion of the liquid, 30 acoustic startle stimuli were presented. The results showed that caffeine increased startle eyeblink amplitude. Startle reflex onset latency was significantly longer in the decaffeinated coffee condition than in the other three conditions. This may have been due to the activation of a compensatory slowing of the reflex by the anticipation of caffeine, a slowing that was then overridden by caffeine speeding the response.

Acoustic Stimulation↗

PubMed1998

A parametric study of the separate contributions of the tactile and acoustic components of airpuffs to the blink reflex.

Airpuffs are often used as blink reflex eliciting stimuli, but the airpuff makes an abrupt noise when it leaves the tube. The present study investigated the effects of the tactile and acoustic components of airpuffs on the blink reflex in 18 human subjects. Subjects received airpuffs to the temple at 10.3, 20.7 and 31.0 kPa in a within-subjects design. The airpuff-associated noise was attenuated (Airpuff + Attenuated noise) or airpuffs were presented without noise-attenuation (Airpuff+ Unattenuated noise) in two conditions. In the third condition, the airpuff was directed away from the temple to eliminate the tactile component of the airpuff (Noise alone). Reflexes were larger, more probable and faster to the Airpuff+ Unattenuated noise compared to the Airpuff+ Attenuated noise. This indicates that there is an excitatory influence from the acoustic component of the airpuff. The findings suggest that researchers should reduce the acoustic component of airpuffs in studies that use airpuffs as reflex eliciting stimuli.

Adult↗

PubMed1993

Startle reflex facilitation as a function of classical eyeblink conditioning in humans.

I investigated whether classical eyeblink conditioning increases the activating effect of the conditional stimulus (CS) on the relevant alpha motoneuron pool in the facial nucleus. The activating effect was measured by the reflex modification method, where startle reflexes, sharing the facial nerve motor pathway with conditional and unconditional eyeblink reflexes, were elicited in the presence of reinforced and nonreinforced CSs (CS+ and CS-). To reduce influences of conditional arousal on startle, a weak airpuff to the eye was used as unconditional stimulus and relatively short stimulus onset asynchronies (SOAs) of 300 and 600 ms were used in three startle tests presented while conditioning was in progress. Two groups (N = 72) received 100% or 0% reinforcement (Groups 100 and 0) of a tone CS+. The CS- was not reinforced. Three startle tests, consisting of acoustic startle probes presented alone and after CS+ and CS- onset, were conducted early, middle, and late in conditioning. Results showed increased startle reflex facilitation after CS+ onset in the late startle test in Group 100, indicating that startle increased as a function of classical conditioning. Although reflex facilitation at the 300-ms SOA in Group 100 is consistent with the hypothesis that CS presentations activated motoneurons in the facial nucleus, the present study cannot itself definitively support this hypothesis. Reflex facilitation at the 600-ms SOA in Group 100 could be influenced by conditional arousal.

Adolescent↗

PubMed1991

Aversive and compensatory classical conditioning with diazepam as conditional stimulus.

The purpose of the first experiment was to investigate whether diazepam could acquire anxiogenic properties by signalling an aversive event. Rats were trained in an operant chamber in the pentylenetetrazol (PTZ) model of anxiety. Thereafter the animals were divided into groups that received classical diazepam conditioning (Group 1), and conditioning of diazepam + tone (Group 2). In the test phase diazepam was injected prior to placement in the operant chamber. Group 2 selected the PTZ-appropriate lever more often than the other groups, indicating that the tone induced anxiety, and diazepam did not. Tones and shock may therefore be more easily associated than diazepam and shock. The second experiment investigated this. Rats were trained the same way as in the first experiment. Thereafter the experimental group received injections of a small dose of diazepam prior to a second injection of a large dose of diazepam. The hypothesis was that a compensatory anxiogenic conditional response to diazepam's anxiolytic effect should be elicited by the small dose. There were no differences between the groups in lever selection, indicating that a compensatory anxiogenic response was not elicited.

Animals↗

PubMed1990

Effects of habituation and classical conditioning on reflex modification.

Reflex modification is the inhibition or facilitation of a reflex by a stimulus (S1) occurring prior to a reflex-eliciting stimulus (S2). Two experiments were conducted that investigated the effects of habituation of the orienting response (OR) and classical conditioning on reflex modification of skin conductance responses (SCRs). During the first phase of Expt. 1 two groups (Group S1 and the Control group) received pre-presentations of S1 (200 Hz). Another group (Group S3) received pre-presentations of a different tone (S3, 3000 Hz). During the second phase, Groups S1 and S3 received pairings of S1 with S2 (white noise), whereas the Control group received pairings of S2 with S1. The predictions were: if the OR to S1 produces reflex modification of the response to S2, then Group S1 and the Control group will display larger SCRs on the first trial of the second phase of the experiment compared to Group S3, in which the OR to S1 will produce reflex modification. However, if conditioned diminution of the unconditioned response (UR) elicited by S1 produces reflex modification of the response to S2, then there should be no initial differences between the groups in the second phase of the experiment. The results showed that SCRs in Group S1 were significantly larger in the second phase compared to Group S3. This result favors an OR explanation of reflex modification. In Expt. 2, the effect of conditioned diminution of the UR on reflex modification was further investigated.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗

PubMed1990

Reflex modification in the electrodermal system: conceptual and methodological issues.

Reflex modification (RM) is the inhibition or facilitation of a reflex response by a stimulus (S1) occurring prior to a reflex-eliciting stimulus (S2). The present experiment investigated two issues: (1) whether RM may be confounded by orienting generated by changes in the experimental procedure, or habituation generated by repeated stimulus presentations; (2) whether the strength of RM is influenced by repeated pairing of S1 and S2, that is, classical conditioning. Two groups of subjects were given two series of stimulus presentations. Group A received first 10 S2-alone presentations, before 10 S1-S2 presentations. Group B received the stimuli in reversed order, that is, first 10 S1-S2 presentations, and then 10 S2-alone presentations. This design permits a comparison of unconfounded with confounded RM, as well as assessment of influences of learning. The results showed RM to be influenced by orienting caused by changes in the experimental procedure. The strength of RM tended to be gradually reduced as a function of the number of S1-S2 pairing, indicating that the orienting response to S1 habituated across trials. It is concluded that RM may be useful in the objective investigation of more complex cognitive processes.

Adult↗

PubMed1989

An IBM-PC and Commodore 64 microcomputer-based system for elicitation and recording of eyeblink reflexes.

The eyeblink reflex is well suited for the study of habituation, sensitization, reflex modification and classical conditioning in humans. A microcomputer-based system for elicitation and recording of the eyeblink reflex is described. The system consists of three functional units: (1) an air-pressure bottle and pressure-reducing valves for delivery of air puffs to the eye in order to elicit the eyeblink reflex, and a CBM 64 computer for presentations of auditory stimuli in conjunction with air puffs; (2) a pair of light-emitting diodes and photocells placed in a pair of goggles placed on the subject for detection of eyeblinks; (3) an IBM-compatible personal computer, equipped with the ASYSTANT + software for eyeblink data acquisition and overall control of experiment and parameters. The system is presently in use in our laboratory, and technical details about the system can be obtained by writing to the first author.

Acoustic Stimulation↗

PubMed1989

Hemispheric differences in recognition of facial expressions: a VHF-study of negative, positive, and neutral emotions.

The present study was concerned with a tachistoscopic investigation of asymmetry of recognition of different facial emotional expressions. Twenty-eight subjects had nine different drawings of facial expressions (either positive, negative, or neutral in emotional content) presented either to the left or right visual half-field. Recognition of the correct face was made for each stimulus-presentation. The results showed overall better recognition for presentations in the left half-field (LVF) (i.e., right hemisphere) compared to right half-field (RVF) (i.e., left hemisphere) presentations. Furthermore, while all three emotional categories were recognized about equally well in the right half-field, positive emotional expressions were significantly better than the neutral and negative categories when presented to the left half-field. The results are discussed in relation to previous findings of cerebral asymmetry in processing of emotional facial expressions.

Adult↗

PubMedDate not supplied

Effects of auditory frequency-shifts on zero and below-zero SCR habituation.

The purpose of the present experiment was to test a procedure for the measurement of effects of zero- and below-zero habituation (BZH) on responding to frequency shifts in auditory stimuli. The present procedure avoided some of the drawbacks of other procedures, that is, long duration, ambiguity in the definition of BZH, and inadequate control procedures. Two groups received 18 stimulus presentations each; group 1 received first a tone of 1000 Hz 12 times, then 1400 Hz (test stimulus 1) 3 times, and 1850 Hz (test stimulus 2) 3 times. Group 2 received the same stimuli, but 3, 12, and 3 times, respectively. The procedure had the advantages of short duration of the experiment, zero habituation and BZH were operationally defined (as 3 and 12 stimulus presentations, respectively), and there were adequate control conditions since a control group that did not receive stimulus change on the relevant trial was employed. The results showed no effects of stimulus shifts on responding to the test stimuli. Group 2 responded significantly less than group 1 across trials, though, and this may be explained by an inhibitory process elicited by changes in weak stimulation during the habituation process.

Adult↗

PubMedDate not supplied

Conditioned-reflex facilitation in young and older adults.

Young (18-30 years) and elderly (63-88 years) human subjects received 70 trials of single-cue classical eyeblink conditioning (paired group), or 70 explicitly unpaired presentations of the tone conditioned stimulus (CS) and airpuff unconditioned stimulus (unpaired group). Before and after conditioning, reflex-eliciting white noise and corneal airpuff stimuli were presented alone or paired with the CS to investigate the effects of conditioning on eyeblink reflex amplitude. The results showed increased conditioned responses in the paired group compared to the unpaired group for the young but not the elderly subjects. There was, however, evidence of conditioned facilitation of noise-elicited reflexes in both young and elderly subjects. These data indicate that conditioned facilitation of the startle reflex may be a sensitive indicator of classical conditioning processes in human subjects.

Acoustic Stimulation↗

PubMedDate not supplied

Drug-related information generates placebo and nocebo responses that modify the drug response.

OBJECTIVE: Administration of the muscle relaxant carisoprodol and placebo was crossed with information that was agonistic or antagonistic to the effect of carisoprodol. It was investigated whether information alone induced physiological and psychological responses, and whether information modified the response to the drug. METHODS: Half of the subjects received capsules containing 525 mg carisoprodol together with information that the drug acted in a specific way (Groups Relaxant/C, Stimulant/C, and No Information/C). The other half of the subjects received lactose (Groups Relaxant/L, Stimulant/L, and No Information/L). Dependent variables were blink reflexes and skin conductance responses, subjective measures of tension and sleepiness, and serum carisoprodol and meprobamate concentrations. Recordings were made between 15 and 130 minutes after administration of the capsules. RESULTS: The Stimulant/L group reported more tension compared with the other two groups, and carisoprodol increased tension even more in the Stimulant/C group. The Relaxant/C group displayed higher levels of carisoprodol serum concentration compared with the other groups that received carisoprodol. CONCLUSIONS: Reported tension was modulated in the direction suggested by the stimulant information. The effect of carisoprodol on tension was also modulated by stimulant information. Increased carisoprodol absorption in the group that received relaxant information could be a mechanism in the placebo response.

Adolescent↗