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Biomedical subjects

R M Church

Publications and source records attributed to R M Church.

At least 37 records · Page 2Linked to original sources
PubMed1987

Nucleus basalis magnocellularis and medial septal area lesions differentially impair temporal memory.

Functional dissociations between the medial septal area (MSA) and the nucleus basalis magnocellularis (NBM) were examined using the concepts and experimental procedures developed by scalar timing theory. Rats were tested in variations of a signalled discrete-trial peak-interval schedule of reinforcement in which the response rate functions identified the time when the rats expected reinforcement. The variations assessed aspects of both reference and working memory for information obtained from prior trials and from the current trial. A double dissociation was found in reference memory. Rats with NBM lesions, like those with frontal cortex (FC) lesions, remembered the time of reinforcement as having occurred later than it actually did; rats with MSA lesions, like those with fimbria-fornix (FF) lesions, remembered the time of reinforcement as having occurred earlier than it did. A single dissociation was found in working memory. MSA lesions and FF lesions impaired working memory, while NBM and FC lesions had no effect on it. These data begin to identify the brain mechanisms underlying temporal memory; they indicate that the frontal and hippocampal systems are both involved, but in complementary ways; and they provide information that helps specify more clearly the functions of the frontal and hippocampal systems.

Animals↗
PubMed1986

Arginine vasopressin innoculates against age-related increases in sodium-dependent high affinity choline uptake and discrepancies in the content of temporal memory.

Systemic injections of arginine vasopressin (AVP, 0.08 pressor units/kg i.p.) to mature rats (10-13 months) trained on a positively reinforced timing task prevented the age-related discrepancies in the content of temporal memory and the increases in sodium-dependent high affinity choline uptake (SDHCU) in the frontal cortex observed in control rats when the rats became aged (27-30 months). AVP administration had no effect on muscarinic receptor density as measured by [3H]quinuclidinyl benzilate (QNB) binding or on choline acetyltransferase (ChAT) levels in either the hippocampus or the frontal cortex.

Aging↗
PubMed1985

Temporal integration in duration and number discrimination.

Temporal integration in duration and number discrimination by rats was investigated with the use of a psychophysical choice procedure. A response on one lever ("short" response) following a 1-s white-noise signal was followed by food reinforcement, and a response on the other lever ("long" response) following a 2-s white-noise signal was also followed by food reinforcement. Either response following a signal of one of five intermediate durations was unreinforced. This led to a psychophysical function in which the probability of a long response was related to signal duration in an ogival manner. On 2 test days, a white-noise signal with 5, 6, 7, 8, or 10 segments of either 0.5-s on and 0.5-s off or 1-s on and 1-s off was presented, and a choice response following these signals was unreinforced. The probability of a long response was the same function of a segmented signal and a continuous signal if each segment was considered equivalent to 200 ms. A quantitative fit of a scalar estimation theory suggested that the latencies to initiate temporal integration and to terminate the process are both about 200 ms, and that the same internal accumulation process can be used for counting and timing.

Animals↗
PubMed1984

Hippocampus, time, and memory.

Five experiments were conducted to determine the effects of hippocampal damage on timing and the memory for temporal events. In Experiments 1-3, rats were trained to discriminate between auditory signals that differed in both duration (2 or 8 s) and rate (2 or 16 cycles/s). Half of the rats were trained to discriminate duration, and half were trained to discriminate rate. After rats acquired the relevant discrimination, signals with intermediate durations and rates were presented to obtain psychophysical functions that related signal duration and/or rate to response choice. Rats then received either lesions of the fimbria-fornix or control operations. Postoperatively, the accuracy of duration and rate discriminations as measured by the difference limen (DL) was unaffected by the lesion, but the point of subjective equality (PSE) was shifted to a shorter duration and a slower rate by the lesion in Experiment 1. Both rats with lesions and rats with control operations showed cross-modal transfer of duration and rate from the auditory signals used in training to visual signals used in testing in Experiment 2. A 5-s delay was imposed between the end of a signal and the opportunity to respond in Experiment 3. The delay served as a retention interval for the rats trained in the rate discrimination, and the rats with fimbria-fornix lesions were selectively impaired by the addition of the delay as measured by an increase in the DL. The delay did not serve as a retention interval for rats trained in the duration discrimination because they were able to continue timing through the delay. A peak procedure was employed in Experiment 4. The maximum response rate of control rats was approximately at the time of scheduled reinforcement (20 s), but the maximum response rate of rats with fimbria-fornix lesions was reliably earlier than the time of scheduled reinforcement. When a 5-s gap was imposed in the signal, control rats summed the signal durations before and after the gap, whereas rats with fimbria-fornix lesions showed no retention of the signal duration prior to the gap. Experiment 5 continued the testing of the rats used in Experiments 1-4 and showed that rats with lesions had an impairment in a test of spatial working memory in an eight-arm radial maze. Taken together, these results demonstrate that a fimbria-fornix lesion interferes with temporal and spatial working memory, reduces the remembered time of reinforcement stored in reference memory, and has no effect on the animal's sensitivity to stimulus duration.

Animals↗
PubMed1984

Properties of the internal clock.

Evidence has been cited for the following properties of the parts of the psychological process used for timing intervals: The pacemaker has a mean rate that can be varied by drugs, diet, and stress. The switch has a latency to operate and it can be operated in various modes, such as run, stop, and reset. The accumulator times up, in absolute, arithmetic units. Working memory can be reset on command or, after lesions have been created in the fimbria fornix, when there is a gap in a signal. The transformation from the accumulator to reference memory is done with a multiplicative constant that is affected by drugs, lesions, and individual differences. The comparator uses a ratio between the value in the accumulator (or working memory) and reference memory. Finally, there must be multiple switch-accumulator modules to handle simultaneous temporal processing; and the psychological timing process may be used on some occasions and not on others.

Animals↗
PubMed1984

Simultaneous temporal processing.

Seven experiments assessed the ability of rats to process temporal information from two internal clocks simultaneously and independently. In the first six experiments a light stimulus signalled an overall interval between the beginning of a trial and the availability of food reinforcement (e.g., a 50-s fixed interval). During the overall interval a sound stimulus was used to signal shorter intervals that divided the overall interval into equal segments. When there was a fixed temporal relation between the final segment signal and the availability of reinforcement, there was a double-scallop pattern of responding throughout the segmented overall interval; the function relating response rate to time during segment intervals was similar to the function relating response rate to time in unsegmented overall intervals; a change in response rate occurred at the time that a normally presented segment signal was omitted. Taken together, the results indicate that rats timed the overall interval and the segment intervals simultaneously and independently without interference. In Experiment 7 a light stimulus was used on some trials, and a sound stimulus was used on other trials to signal a discrete-trial 50-s peak procedure. When these two signals were presented in compound, there was a leftward shift of the response function, which suggests that rats timed both signals simultaneously. For all of the experiments a scalar timing model with specific stimulus integration rules is used to explain the results. The stimulus integration rule used in the first six experiments, in which there were two signals for the same reinforcement, was to respond if both the segment and the overall interval had exceeded a response threshold. The stimulus integration rule used in Experiment 7, in which there were two signals for different reinforcements, was to respond if the response threshold for either interval had been exceeded.

Animals↗
PubMed1984

Two-step acquisition: modification of an internal clock's criterion.

Ten rats were trained on a discrete-trial peak procedure in which food, if available, occurred following the first response after a signal had been present for 10 s. Ten other rats were trained on the same procedure with a 20-s criterion. When the time of reinforcement was changed (10 to 20 s or 20 to 10 s), subjects adjusted their temporal criterion in two abrupt steps. During the intermediate state of the three-step function, rats used a temporal criterion that was near the geometric mean of the initial and terminal times of reinforcement. The conclusion is that the intermediate transition state reflects an internal structure in the animal's information processing system not readily accounted for by stimulus-response models of behavior.

Animals↗
PubMed1983

The differential effects of haloperidol and methamphetamine on time estimation in the rat.

Forty rats were trained to make a left lever response if a signal (white noise) was 2.5s and to make a right lever response if the signal was 6.3s. When seven intermediate signal durations, to which responses were not reinforced, were randomly interspersed the probability of a right-lever ('long') response increased as a function of signal duration. Methamphetamine shifted this psychometric function leftward and decreased its slope: haloperidol also decreased the slope but shifted the function rightward. A combination of haloperidol and methamphetamine led to a function similar to the saline control function. The leftward shift probably reflects an increase in the speed of an internal clock, and the rightward shift probably reflects a decrease in its speed. Since methamphetamine releases several catecholamines, including dopamine, and haloperidol blocks dopamine receptors, it is plausible that the horizontal location of the psychometric function (the speed of the clock) is related to the effective level of dopamine.

Animals↗
PubMed1983

A mode control model of counting and timing processes.

The similarity of animal counting and timing processes was demonstrated in four experiments that used a psychophysical choice procedure. In Experiment 1, rats initially learned a discrimination between a two-cycle auditory signal of 2-sec duration and an eight-cycle auditory signal of 8-sec duration. For the number discrimination test, the number of cycles was varied, and the signal duration was held constant at an intermediate value. For the duration discrimination test, the signal duration was varied, and the number of cycles was held constant at an intermediate value. Rats were equally sensitive to a 4:1 ratio of counts (with duration controlled) and a 4:1 ratio of times (with number controlled). The point of subjective equality for the psychophysical functions that related response classification to signal value was near the geometric mean of the extreme values for both number and duration discriminations. Experiment 2 demonstrated that 1.5 mg/kg of methamphetamine administered intraperitoneally shifted the psychophysical functions for both number and duration leftward by approximately 10%. Experiment 3 demonstrated that the magnitude of cross-modal transfer from auditory signals to cutaneous signals was similar for number and duration. In Experiment 4 the mapping of number onto duration demonstrated that a count was approximately equal to 200 msec. The psychophysical functions for number and duration were fit with a scalar expectancy model with the same parameter values for each attribute. The conclusion was that the same internal mechanism is used for counting and timing. This mechanism can be used in several modes: the "event" mode for counting or the "run" and the "stop" modes for timing.

Animals↗
PubMed1982

Temporal generalization.

Responses of 26 rats were reinforced following a signal of a certain duration, but not following signals of shorter or longer durations. This led to a positive temporal generalization gradient with a maximum at the reinforced duration in six experiments. Spacing of the nonreinforced signals did not influence the gradient, but the location of the maximum and breadth of the gradient increased with the duration of the reinforced signal. Reduction of reinforcement, either by partial reinforcement or reduction in the probability of a positive signal, led to a decrease in the height of the generalization gradient. There were large, reliable individual differences in the height and breadth of the generalization gradient. When the conditions of reinforcement were reversed (responses reinforced following all signals longer or shorter than a single nonreinforced duration), eight additional rats had a negative generalization gradient with a minimum at a signal duration shorter than the single nonreinforced duration. A scalar timing theory is described that provided a quantitative fit of the data. This theory involved a clock that times in linear units with an accurate mean and a negligible variance, a distribution of memory times that is normally distributed with an accurate mean and a scalar standard deviation, and a rule to respond if the clock is "close enough" to a sample of the memory time distribution. This decision is based on a ratio of the discrepancy between the clock time and the remembered time, to the remembered time. When this ratio is below a (variable) threshold, subjects respond. When three timing parameters--coefficient of variation of the memory time, the mean and the standard deviation of the threshold--were set at their median values, a theory with two free parameters accounted for 96% of the variance. The two parameters reflect the probability of attention to time and the probability of a response given inattention. These parameters were not influenced by stimulus manipulations but were affected by manipulations of reinforcement rate and by individual differences.

Animals↗
PubMed1981

Methamphetamine and time estimation.

Three experiments were conducted to determine the effect of methamphetamine on the performance of rats in two timing tasks. When food sometimes followed the first response after T sec of a signal, the response rate increased to a peak near T sec and then declined. Methamphetamine decreased the time of the peak (Experiments 1 and 2). When one response (called a "short response") was reinforced following a short signal and a different response (a "long response") was reinforced following a long signal (where the short and long signals were 1 and 4, 2 and 8, or 4 and 16 sec), the probability of a long response increased as a function of signal duration. The point of indifference (50% long response) occurred near the geometric mean of the extreme durations, and methamphetamine decreased the point of indifference by about 10%. These results suggest that methamphetamine increases the speed of an internal clock used by rats in time discrimination tasks.

Animals↗
PubMed1981

Time left: linear versus logarithmic subjective time.

In two experiments, subjects were given a choice between a standard fixed interval to reinforcement and the time left to reinforcement in an elapsing comparison interval. In Experiment 1, rats were trained to respond on a comparison 60-sec fixed-interval schedule on one lever and a standard 30-sec fixed-interval schedule on a second lever. Then combined trials were given that began with the entry of the comparison 60-sec lever, followed by the standard 30-sec lever after 15, 30, or 45 sec. Rats preferred to respond on the standard lever when it entered early (at 15 sec), they preferred to respond on the comparison lever when the standard entered late (at 45 sec), and they were approximately indifferent between the two levers when the standard entered halfway through the comparison interval so that the remaining time to food was equal on both levers. In Experiment 2, pigeons were trained to choose between the time left to food in an elapsing comparison interval (C sec long) and a standard fixed interval one half as long (S = C/2) in a concurrent-chains paradigm. Birds came to choose the standard early and the comparison late in the trial interval. The indifference point was linearly related to the midpoint of the elapsing C interval at a variety of S,C pairs. The results of both experiments are consistent with a Scalar Timing theory in which subjective time is linear in real time and memory variance is scalar, and they are inconsistent with a logarithmic time scale.

Animals↗
PubMed1980

An explanation of the language of a chimpanzee.

The language barrier of the chimpanzee Lana, previously described by Rumbaugh (1977), can be simulated by a computer model in which the animal selects, depending upon context, one of six stock sentences with fixed and variable elements.

Animal Communication↗
PubMed1978

Time-allocation matching between punishing situations.

In the presence and absence of white noise, response-independent aversive events were delivered to rats according to several variable-time electric-shock schedules. The animals could switch from the noise component to the no-noise component and vice versa by making a single lever-press response. If the schedule in one component was not in operation when the animal was in the other component, the proportion of time allocated to one component equalled or matched the proportion of obtained punishers in the other component. If both schedules were always in operation, minimizing tended to occur: the animals allocated almost all of their time to the component having the lower shock rate. An analysis of these results, in terms of the expected time until an aversive event, is presented.

Journal Article↗
PubMed1977

Bisection of temporal intervals.

Eight rats were trained to make one response if a signal was shorter than a criterion duration and a different response if the signal was longer than the criterion. When exposed to intermediate durations, the rats bisected the interval at the geometric mean and the difference limen divided by the geometric mean was a constant. The rats learned new temporal discriminations more easily when the response maintained its relative, rather than its absolute, meaning. These data were interpreted in terms of a model of an internal clock that included a clock, a criterion, and a response rule.

Animals↗
PubMed1976

Duration discrimination by rats.

A psychophysical procedure was used to determine the difference limen for the duration of a signal that ranged from .5 to 8.0 sec. The accuracy of three rats in keeping track of the duration was assumed to be limited by three factors: (a) inattention to the signal on some trials, (b) variability in starting to time the duration when the signal begins (and/or in stopping to time the duration when the signal ends), and (c) factors related to signal duration itself. A generalized Weber model provided a better approximation to the growth in the difference limen as a function of signal than a generalized Counter model.

Animals↗