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Biomedical subjects

J J Ayres

Publications and source records attributed to J J Ayres.

At least 19 recordsLinked to original sources
PubMed2001

Treatments that weaken Pavlovian conditioned fear and thwart its renewal in rats: implications for treating human phobias.

In experiments using a total of 144 albino rat subjects, the authors assessed the ability of fear-weakening treatments to prevent fear renewal (relapse). Conditioned suppression of operant behavior served as the measure of fear in an A-B-A (acquisition-treatment-test) renewal paradigm. In Experiment 1, 100 nonreinforced exposures to a feared cue during treatment (extinction) did not reduce fear renewal relative to 20 exposures. In Experiment 2, explicitly unpaired (EU) treatments thwarted both renewal and reacquisition. In Experiment 3, conditioned inhibition (CI) and differential conditioning (DC) treatments weakened renewal and resisted both reacquisition and a form of reinstatement. In Experiment 4, EU, DC, and CI treatments all thwarted renewal. Evidence suggested that the ability of the treatments to do so reflected the combined effects of transfer of extinction across treatment and test contexts and habituation to the unconditioned stimulus.

Animals↗
PubMed1999

Blocked and overshadowed stimuli are weakened in their ability to serve as blockers and second-order reinforcers in Pavlovian fear conditioning.

The ability of a blocked or overshadowed conditioned stimulus (CS) to serve as (a) blocker or (b) a 2nd-order reinforcer in Pavlovian fear conditioning was tested in 152 albino rats. CS-evoked suppression of barpressing for food was the index of conditioned fear. Experiments 1 and 2 showed that an overshadowed CS was weakened in its ability to serve as a blocker. In Experiment 2, a blocked CS was similarly weakened. Experiment 3 showed that an overshadowed and blocked CS was weakened in its ability to serve as a 2nd-order reinforcer. Experiments 4 and 5 failed to restore the blocking ability of blocked (Experiment 4) or overshadowed (Experiment 5) CSs by extinguishing the CSs that had blocked or overshadowed them. Results favor a learning-deficit view of blocking and overshadowing.

Animals↗
PubMed1997

Converging evidence for one-trial context fear conditioning with an immediate shock: importance of shock potency.

In a sample of 208 Holtzman-descended albino rats, we found evidence with 4 measures of conditioning (freezing, defecation, side crossing, and nose crossing) that a single 2-s, 1.0-mA immediate shock could condition fear to a context (Experiments 1, 2, and 4). When we reduced the shock intensity to 0.5 mA, we obtained a complete immediate-shock conditioning deficit according to all measures in Experiment 3 and to all but the defecation measure in Experiment 4. Results suggest two conclusions: (a) Differences in shock potency between laboratories may help explain discrepant findings about whether immediate shock supports contextual conditioning; (b) theories of contextual conditioning need a mechanism that permits that conditioning to result from immediate shock.

Animals↗
PubMed1996

Conditioned stimulus determinants of conditioned response form in Pavlovian fear conditioning.

Four experiments using barpress conditioned suppression in rats found that tone evoked more freezing (immobility) than did light. Still, tone and light appeared to have similar conditioned value as assessed by suppression in Experiments 1, 2, and 3, and by blocking, second-order conditioning, and overconditioning assays in Experiments 1, 2, and 3, respectively. Experiment 4 arranged for tone to evoke less suppression than light but more freezing. Results suggest that in fear conditioning, the nature of the conditioned stimulus affects the form of conditioned responding (strong vs. weak freezing). This conclusion extends one drawn by P. C. Holland (1977) on the basis of his work in appetitive conditioning.

Animals↗
PubMed1994

A deficit in one-trial context fear conditioning is not due to opioid analgesia.

Rats given a foot shock immediately after placement in a box subsequently freeze (immobility) much less in that box than rats given the same shock 2 min after placement. A possible explanation of this result is that these two procedures might induce different levels of opioid analgesia at the time of shock. Opioids might be present immediately after handling, transporting, and exposure to a new situation, but absent 2 min later. Two experiments examined this possibility by giving the opioid antagonist naloxone before conditioning (Experiment 1) or before conditioning and testing (Experiment 2). There was no effect of naloxone relative to saline controls. The results do not support the analgesia hypothesis. Experiment 2 precludes a stage-dependent learning account of the results.

Analgesia↗
PubMed1993

Extending continuous versus discontinuous conditioned stimuli before versus after unconditioned stimuli.

Conditioned suppression was used with rats to study the effects of extending conditioned stimuli (CSs) before versus after the delivery of unconditioned stimuli. These extensions are termed B and A extensions, respectively. Within-group designs were used to compare the effects of extending CSs when 2-min parts of those CSs were separated by temporal gaps of 6 min versus a separation of no gap. The results were as follows: (a) B extensions weakened conditioning more than did A extensions, with or without gaps; (b) under some conditions, this asymmetrical effect persisted with extended training; (c) gaps between 2-min parts of a B extension had no detectable effect; and (d) under some parameter values, gaps between 2-min parts of an A extension weakened conditioning significantly. These results are better predicted by the Sometimes Opponent-Process model (SOP; A. R. Wagner, 1981) than by the Rescorla-Wagner-Frey-Sears real-time model (J. J. B. Ayres, M. Albert, & J. C. Bombace, 1987).

Animals↗
PubMed1992

One-trial backward excitatory fear conditioning transfers across contexts.

One path to human phobia may be one-trial backward fear conditioning. Human phobias transfer readily across contexts. However, animal studies of one-trial backward fear conditioning have yet to demonstrate such transfer. The present study sought to do so. It used a lick-suppression procedure with 84 naive male albino rats. Two conditioning contexts, designated O and V, were crossed factorially with two test contexts, O and V. Within each cell of the factorial design, rats received in the conditioning context either a single 12 sec tone backward paired with a single 4 sec 1 mA shock or the same tone explicitly unpaired with shock. Fear of context and fear of tone were subsequently assessed in terms of the suppression of licking that they evoked. Test results suggested that (1) the rats discriminated between contexts O and V, and (2) despite such discrimination, one-trial backward fear conditioning transferred across the two contexts. The results enhance the plausibility of one-trial backward fear conditioning as a source of human phobia.

Animals↗
PubMed1987

Effect of naloxone on conditioned suppression in rats.

Painful stimuli are known to engage an endorphin analgesic system that can be reversed by the opiate antagonist, naloxone. Naloxone, then, should increase the effectiveness of aversive unconditioned stimuli (USs) in Pavlovian fear conditioning. Consistent with this hypothesis, naloxone administered during the acquisition of conditioned suppression in rats enhanced posttrial suppression and preconditioned stimulus (pre-CS; context-controlled) suppression. Furthermore, it enhanced CS-elicited suppression during extinction when administered during acquisition but not when administered only during extinction. Thus naloxone does not enhance an already existing fear nor enhance the memory of previous conditioning; instead, it enhances the conditioning of fear presumably by making the aversive US more painful.

Animals↗
PubMed1985

Conditioned suppression tests of the context-blocking hypothesis: testing in the absence of the preconditioned context.

Two experiments are reported that use rats in a conditioned suppression situation. The experiments, designed to remove confounds that have complicated interpretations of prior research, tested the context-blocking hypothesis, the proposition that static apparatus cues or conditioning contexts can block conditioning to discrete conditioned stimuli (CSs). Experiment 1, like previous work, tested for conditioning to the target CS in the same context that had been preconditioned and in which target conditioning had occurred; the experiment demonstrated a context-blocking like effect. Experiment 2 tested for conditioning not only in the preconditioned context but also in a nonpreconditioned context. Evidence for context blocking appeared similar in the two test situations. This suggests that conditioned contexts block the acquisition of associative strength by discrete CSs at the time of target conditioning (e.g., Rescorla & Wagner, 1972) and not through performance factors at the time of testing (e.g., Gibbon & Balsam, 1981).

Animals↗
PubMed1979

Physiologic effects on adult men of circuit strength training and jogging.

The purpose of this study was to determine the effects of 8 weeks of circuit strength training (CST) followed by 8 weeks of jogging and then 8 weeks, of CST or jogging. During the final 8 weeks, the subjects were randomly assigned to either CST or jogging groups. The subjects (n=16, x age = 29 yrs) exercised 3 days/week. The strength training involved 2 circuits of reciprocal exercises using isokinetic devices with 10 to 15 repetitions/set and 30 seconds of rest between sets. The subjects jogged 3 miles/day during the jogging program. After the initial 8 weeks of CST, significant changes were found in treadmill performance time, maximum oxygen uptake (VO2max), maximum pulmonary ventilation (VEmax), body fat, total skinfold fat, fat weight, lean weight, isotonic bench and leg press, and isokinetic slow speed, fast speed, and power endurance measures. The jogging program elicited significantly greater changes in treadmill performance time and VO2max. Further reductions were found in total skinfolds and waist girth during the jogging program. Leg strength was maintained during jogging but upper body strength was reduced significantly. Physiologic levels were maintained during the final 8 weeks and showed no differences between the CST and jogging groups.

Adult↗
PubMed1978

A comparison of body fat determined by underwater weighing and volume displacement.

Two hydrostatic techniques, underwater weighing and water displacement, were used to determine body fat for 67 volunteer men between 25 and 61 yr of age (-/x=41 yr). All tests were administered in random order in the morning on the same day while subjects were in the postabsorptive state. Test-retest reliabilities for the underwater weighing and water displacement techniques were 0.995 and 0.96, respectively. The correlation between the two hydrostatic techniques was r=0.96. The mean percent fat determined by underwater weighing (-/x=20.1 +/- 6.4) and water displacement (-/x=19.4 +/- 6.1) were significantly different (t=28.16; df=65; P less than 0.001). These analyses showed that both techniques were reliable in measuring percent body fat, but produced slight systematic differences. Regression equations were provided to adjust for the difference.

Adipose Tissue↗
PubMed1978

The effect of circuit weight training on strength, cardiorespiratory function, and body composition of adult men.

The purpose of this study was to determine the changes elicited by circuit weight training (CWT) and running (RN) programs conducted 3 days/week for 20 weeks. Subjects were randomly assigned to one of three groups: CWT (n = 11); RN (n = 16); and control (n = 14). CWT consisted of 10 exercises performed in 2 sets of 15 reps with 20 to 25 sec rest between exercises. CWT workout time decreased from 30 min to 23 min; exercise heart rate (HR) increased from 79% to 84% max; average weight increased from 42% to 56% of max 1 RM strength and total weight increased 81% (1506 to 2720 lbs/workout). The RN group exercised at 85% max HR for 23 to 27 min/workout. Multivariate and step-down analyses showed the CWT group to be significantly different from the control group at the end of 20 weeks in leg press strength, fat weight, and Vo2 max (1/min). The RN group was significantly different from the CWT group in Vo2 max and treadmill time. Univariate analyses revealed no differences between the CWT and control groups in Vo2 max expressed as ml/kg LBW.min but did show a significant superiority of the RN group over the other two groups in this variable. It was concluded that the CWT program was most specific in improving strength and changing body composition and produced only a small aerobic effect as measured on the treadmill running test.

Adult↗
PubMed1976

A comparative analysis of four protocols for maximal treadmill stress testing.

The purpose of this investigation was to compare the results from four commonly used maximal treadmill stress tests: Balke, Bruce, Ellestad, and a continuous multistage running protocol. The results compared serial and maximal heart rate, metabolic demands, and ECG determinations. Fifty-one healthy men, 35 to 55 years of age, volunteered for this study and were dichotomized into trained and untrained subjects. Regression analyses showed all the tests to correlate highly. No significant differences were found between tests at maximum for V02, heart rate, and blood pressure, except for V02 for the Balke as compared to the running protocol (39 vs. 41 ml./Kg-min). The Balke protocol showed lower values at maximum in VE and RP than the other three tests as well as the most gradual rate of progression in MET cost (0.5 METS per minute). The increase for the Bruce and Ellestad tests was from 1 to 1.5 METS per minute, and a rapid initial increase (9 METS in the first 3 minutes) made the running test undesirable as a screening method. Although serial plots of heart rate and MET costs were similar to those previously reported for different population samples, the present data further refined these values. Finally, a nomograph comparing treadmill time and V02, max. for the Balke, Bruce, and Ellestad tests was developed from these data.

Adult↗
PubMed1974

Some factors involved in the comparison of response systems: acquisition, extinction, and transfer of head-poke and lever-press Sidman avoidance.

Head poking, a suggested natural escape reaction to shock for the rat, was compared to lever pressing in a Sidman avoidance study. Both responses could be emitted at any time, but only one was effective in a given session. Acquisition and extinction of the two responses were compared under both signalled and unsignalled avoidance. Then, a test for transfer was conducted in which acquisition conditions were re-instated, but the effectiveness of the responses was reversed. Three differences between responses were noted: (a) head poking was superior in reducing shock rates under signalled conditions; (b) head poking was more resistant to extinction, especially under signalled conditions; (c) under unsignalled conditions, animals were unable to learn to head poke if they had previously learned to lever press. Findings a and c were pursued in later experiments. Finding a depended on the location of the warning signal with respect to the response system. When the lever press required approach to the warning signal, the head poke was superior. But when the head poke required approach to the warning signal, the two responses were equally effective. Finding c depended on the absence of feedback for head poke during transfer. Two conclusions are offered: first, the two responses appear to obey the same laws when their topographical differences are taken into account. Second, response feedback appears to be more critical in transfer than in original acquisition.

Acoustic Stimulation↗
PubMed1971

Suppression of operant vs consummatory behavior.

The magnitude and variability of conditioned suppression of bar pressing and dipper licking were compared. In two steady-state experiments, suppression of bar pressing was more profound and more stable from day to day. The two measures of suppression were uncorrelated as indexed by Pearson product-moment correlation coefficients computed for adjacent trials. Correlations within measures (internal consistency) were somewhat higher for the bar-press system except when a high proportion of rats completely suppressed on one of the correlated trials. In a transient state experiment in which possible adventitious punishment of both response systems was eliminated, suppression of bar pressing was again more profound and considerably slower to extinguish.

Animals↗