Steven L. Cohen

The effects of frequency of encouragement on performance during maximal exercise testing

The aim of this study was to determine the effects of frequency of verbal encouragement during maximal exercise testing. Twenty-eight participants (12 males, 16 females) aged 20.9 - 1.5 years (mean - s ) performed a maximal exercise test ( V O 2max ) on a treadmill without any verbal encouragement. The participants were matched according to their pre-test V O 2max and placed into either a control group or one of three experimental groups. They performed a second exercise test (post-test) 1 week later. During the second test, the control group received no verbal encouragement; the 20 s (20E), 60 s (60E) and 180 s (180E) encouragement groups received verbal encouragement every 20, 60 and 180 s, respectively, beginning with stage 3 of the exercise test. Relative V O 2max , exercise time, blood lactate concentration, respiratory exchange ratio (RER) and ratings of perceived exertion (RPE) were not significantly different from the first test to the second test for the control group without verbal encouragement and the 180E group that received infrequent encouragement. Post-test values were significantly higher than pre-test values for the 20E and 60E groups. The post-test values of the 20E group were significantly higher than their pre-test values for relative V O 2max ( P ≪ 0.001), exercise time ( P ≪ 0.0001), blood lactate concentr . ation ( P ≪ 0.05), RER ( P ≪ 0.01) and RPE ( P ≪ 0.0001); this was also the case for the 60E group for relative V O 2max ( P ≪ 0.01), blood lactate concentration ( P ≪ 0.05), RER ( P ≪ 0.05) and RPE ( P ≪ 0.05). The results suggest that frequent verbal encouragement (every 20 s and 60 s in the present study) leads to significantly greater maximum effort in a treadmill test than when no encouragement is given or when the encouragement is infrequent (i.e. every 180 s).

Cholecystokinin-octapeptide effects on conditioned-avoidance behavior, stereotypy and catalepsy

The effect of peripherally administered cholecystokinin-octapeptide (CCK8) was tested on signaled-avoidance behavior, apomorphine-induced stereotypy, and catalepsy. Rats were trained to avoid shock in a signaled shuttle-box avoidance task, and then given CCK8, tetragastrin, or haloperidol. CCK8 (20-3840 micrograms/kg i.p.) reduced avoidance in a dose-dependent manner. The impairment at maximal dose levels was approximately 25% from its predrug level compared to 50% with haloperidol (100 micrograms/kg i.p.). Combined injection of CCK8 (320 micrograms/kg i.p.) and haloperidol (75 micrograms/kg i.p.) reduced avoidance significantly more than either drug alone. The effects of CCK8 were relatively brief in that active avoidance was impaired if CCK8 was injected up to 15 min before the avoidance test. CCK8 also facilitated the extinction of avoidance. Tetragastrin (177 micrograms/kg i.p.), which elicits gastrointestinal effects resembling CCK8, did not affect avoidance. In addition, CCK8 diminished apomorphine-induced stereotypy up to 5 min after CCK8 injection. CCK8 (20-1280 micrograms/kg i.p. and s.c.) failed to produce catalepsy in vertical grip tests. These data suggest that peripherally administered CCK8 has sedative and certain neuroleptic-like effects on behavior.

Tolerance to the anti-avoidance properties of cholecystokinin-octapeptide

Previous investigations have suggested a neuroleptic-like action of cholecystokinin-octapeptide (CCK8) on conditioned-avoidance behavior. This study was initiated to test tolerance to this effect. Rats were trained to avoid electric shock in a shuttle box under a free-operant (Sidman) avoidance paradigm. Each shuttle response postponed a 0.2 sec, 1 mA shock for 20 sec. If the rat failed to respond, shock was delivered every 5 sec until a response occurred. After avoidance training, half of the rats received two daily injections of CCK8 (0.320 mg/kg, IP) and half received saline for 7 days. Rats were then tested on the Sidman avoidance 1 min after receiving CCK8 (0.640 mg/kg, IP) or saline. CCK8 depressed avoidance responding if rats received saline for 7 days prior to the test. Rats pretreated with CCK8 for 7 days were not significantly affected by CCK8 during the avoidance test. Thus, repeated injections of CCK8 result in tolerance to its anti-avoidance properties.

Septal lesions and the reinforcer-omission effect

Abstract Five rats with septal lesions and five control rats were trained under alternating fixed-interval (FI) 75 sec schedules of reinforcement in a double-lever operant chamber. Completion of an FI on the left lever produced food and initiated the next FI on the right lever; completion of the FI on the right lever produced food and began another FI on the left lever; ect. After 25 sessions under alternating schedules, rats were tested for the omission-effect. During a test session food was omitted after completion of some of the FI schedules on the left lever, and response rate on the right lever was measured. Septal and control rats exhibited increases in response rate after food omission. During the first 30 sec of the FI, septal rats showed a greater increase in rate than controls. No differences between groups were observed in the latter part of the interval. The data suggest that septal lesions enhance the omission (frustration) — effect.

EMG Biofeedback: The Effects of CRF, FR, VR, FI, and VI Schedules of Reinforcement on the Acquisition and Extinction of Increases in Forearm Muscle Tension

Biofeedback was used to increase forearm-muscle tension. Feedback was delivered under continuous reinforcement (CRF), variable interval (VI), fixed interval (FI), variable ratio (VR), and fixed ratio (FR) schedules of reinforcement when college students increased their muscle tension (electromyograph, EMG) above a high threshold. There were three daily sessions of feedback, and Session 3 was immediately followed by a session without feedback (extinction). The CRF schedule resulted in the highest EMG, closely followed by the FR and VR schedules, and the lowest EMG scores were produced by the FI and VI schedules. Similarly, the CRF schedule resulted in the greatest amount of time-above-threshold and the VI and FI schedules produced the lowest time-above-threshold. The highest response rates were generated by the FR schedule, followed by the VR schedule. The CRF schedule produced relatively low response rates, comparable to the rates under the VI and FI schedules. Some of the data are consistent with the partial-reinforcement-extinction effect. The present data suggest that different schedules of feedback should be considered in muscle-strengthening contexts such as during the rehabilitation of muscles following brain damage or peripheral nervous-system injury.

Response strength in open and closed economies

Abstract Response strength was measured in open and closed economies using tests of resistance to change. In Experiment 1, responses were reinforced under fixed ratio schedules of reinforcement that ranged from 40 to 240. Rats in the open economy responded during a 45-min session and were immediately fed supplemental food in their home cage. Rats in the closed economy received all of their food by responding in an extended session. At each fixed ratio value, responding was disrupted by response-independent food and extinction, and response strength was indexed by the degree of response suppression relative to baseline. Response rate in the closed economy was higher than in the open economy, but no consistent difference in response strength was found. Experiment 2 was a replication of Experiment 1 using two open economy groups. One group was maintained at 80% free-feeding body weight for the entire experiment, and the other group was maintained at 90% under fixed ratio 40, 85% under fixed ratio 80, 75% under fixed ratio 160, and 70% under fixed ratio 240. Response suppression from free food and extinction was the same for both groups, suggesting that increased food deprivation under larger fixed ratios observed in Experiment 1 did not contribute to the results of that experiment. The data suggest that the ability to respond at relatively high rates under very large fixed ratio schedules of reinforcement in a closed economy does not reflect greater response strength as measured by the resistance-to-change paradigm.

A comparison of peripheral and central effects of CCK8 on water-reinforced operant responding

Systemic administration of cholecystokinin-octapeptide (CCK8) suppresses operant responding in water deprived rats, but it is unclear whether this effect is centrally or peripherally mediated. Rats were trained to press a lever for water in an operant conditioning chamber under a variable-interval schedule of reinforcement. After response rate stabilized injections were administered, and response suppression was measured by comparing injection response rate to baseline rate. Intracerebroventricular injections of CCK8 reduced lever pressing at relatively high doses (20 and 50 micrograms/rat). But in a direct comparison, the same dose of CCK8 (20 micrograms/rat) given intraperitoneally reduced responding significantly more than when given into the lateral ventricle. The suppressive effects of CCK8 (30 and 300 micrograms/kg i.p.) were significantly reduced by complete abdominal vagotomy. The effects of CCK8 (30 micrograms/kg i.p.) were blocked by pretreatment with the specific competitive CCK8 antagonist dibutyryl cyclic GMP (70 and 140 mg/kg i.p.), but not by the acetylcholine antagonist atropine (0.1 to 10 mg/kg i.p.). These data suggest that suppression by CCK8 of operant lever pressing in water-deprived rats is primarily mediated by vagal afferent fibers.

Minimized tolerance to the suppressive effects of CCK8 on operant responding

This study was designed to determine if tolerance to cholecystokinin octapeptide (CCK8) could be prevented or minimized by spacing injections, and if an appetitive operant conditioning paradigm provides a sensitive baseline to test the effects of CCK8. Male Sprague-Dawley rats were trained to press a lever for water according to a fixed-interval 60-sec schedule of reinforcement. After response rate stabilized, rats were given a series of CCK8 (0.04 mg/kg, ip) injections spaced several days apart. The first injection of CCK8 produced complete response suppression during the 30-min test session, while later injections produced partial or complete suppression. Thus, tolerance to CCK8, as measured by operant response rate, may be minimized if injections are appropriately spaced.

Comparisons of Sample Stimuli in Delayed Symbolic Matching-to-Sample: Some Results and Implications

The relationship between properties of sample stimuli and matching accuracy was examined in four delayed symbolic matching-to-sample problems with pigeons. A peck on the center key of a three-key chamber presented one of two samples. Following one sample a response on the red side key was correct, and following the other sample a response on the green key was correct. In the first problem the temporal properties of a stimulus served as a sample. The correct side key response depended upon whether a yellow sample was “short” (.5 sec) or “long” (4 sec). The second problem compared food and blackout samples, and the third problem compared color and form samples. The fourth problem combined stimulus type and duration by examining.3- and 3-sec color and form samples. The main results were that (a) these sample stimuli produced retention curves that resembled those reported in previous research, and (b) no differences in matching accuracy were observed between.5 and 4-sec stimulus-duration samples, food and blackout, and color and form samples. These data can best be described by the rule statement “If sample A is presented, then peck one side key” and “If sample A is not presented, then peck the other side key.” This analysis suggests that some matching problems may be solved by considering the presence and absence of only one of the two sample types, and that the characteristics of the other sample become irrelevant.

The effects of septal lesions on second-order schedules.

Seven Long-Evans albino rats with septal lesions and five control rats were trained on a fixed-interval 60-sec schedule of reinforcement for 25 sessions, followed by a second-order schedule of reinforcement. The second-order schedule consisted of a fixed-interval 60-sec component maintained by a variable-interval 180-sec schedule. Each fixed interval completed before the variable-interval schedule was satisfied produced a 0.3- or 8-sec brief stimulus, while each fixed interval completed after the variable-interval schedule was satisfied produced a brief stimulus that terminated with food. Septal and control rats exhibited the same response rates and patterning on the simple fixed-interval 60-sec schedule. Under the second-order schedule septal rats had the highest response rate under the 0.3-sec stimulus, and the best temporal patterning with the 8-sec stimulus. The data suggest that animals with septal lesions can inhibit responding as well as controls but tend to respond at a higher rate when inhibitory constraints are removed.