Circadian organization of food intake and meal patterns in the rat.
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Animals↗
Biomedical subjects
M Terman
Publications and source records attributed to M Terman.
Food availability and daily biological rhythms.
Restricted daily feeding schedules result in the partial or complete synchronization of a wide range of rhythmic biological functions in rodents. In some cases, exemplified by drinking behavior and liver tyrosine transaminase activity, this represents primarily a direct, exogenous influence of food intake. In others, synchronization is achieved by entrainment of a circadian time-keeping mechanism distinct from that which underlies free-running rhythms in these functions. This food-entrained mechanism is responsible for the timing of anticipatory increases in locomotor and lever-pressing activity immediatley prior to food delivery, and may also underlie similar anticipatory increases in body temperature, corticosterone secretion, and in the activities of some intestinal enzymes. It is suggested that such a mechanism may enable an animal to recognize and take advantage of the periodic recurrence of significant events in its biotic environment.
Animals↗
Effects of illumination level on the rat's rhythmicity of brain self-stimulation behavior.
Rhythmic patterns in the rat's brain self-stimulation behavior were analyzed across levels of illumination, including conditions of constant illumination (LL), constant darkness (DD), and light-dark cycles (LD 12:12). LD entrainment was achieved with light intensities ranging from 0.25 to 440 lux, and little or no change was found in the phase-angle difference between the dominant spectral peak and the light transitions. Under constant conditions, the circadian period (tau) increased in proportion to illumination level, with means ranging from 24.10 h (DD) to 25.90 h (LL 440 lux). tau increased linearly as a function of long I within the range of 0.25 to 30 lux, yielding a change of 0.28 h for a 10-fold increment in illumination level, a value which closely matches Aschoff's [3] preliminary estimate of delta tau/delta ILL for the rat. The circadian spectral component was influenced by several factors. (1) Re-entrainment protocol. Given a succession of LL conditions without entrainment segments in between, circadian rhythmicity was obscured at high illumination levels. (2) Duration of LL exposure. Even following an entrainment segment, long-term LL resulted in reduced power or loss of the circadian component. (3) LD vs LL. Spectral power was consistently higher under entrainment than under corresponding LL intensities, and there was a trend toward reduced power as a function of LL intensity. A wide range of ultradian spectral components was found across conditions. Under entrainment, most such components were harmonics of the circadian fundamental; under constant conditions, the frequency relationships were relatively variable.
Animals↗
Feeding schedules and the circadian organization of behavior in the rat.
Feeding and drinking behavior of rats maintained in constant light were recorded before, during and after feeding schedules with periods lying within or outside the range of circadian entrainment. Regardless of period, all schedules immediately resulted in the partial or complete synchronization of drinking behavior, but failed to entrain the free-running circadian feeding and drinking rhythms. This indicated that drinking can be passively driven by periodic access to food. However, other results suggested that a separate circadian system was entrained by feeding schedules: First, the 24-h periodicity induced by 24-h feeding schedules often continued for several days after termination of the schedules. Second, the rats showed anticipatory activity under schedules with periods within, but not outside, the circadian range of entrainment. Third, lesions of the suprachiasmatic nuclei (SCN), which resulted in the immediate elimination of free-running rhythms, did not alter the rhythmic influences of the feeding schedules. These results provide evidence for the participation of two distinct circadian systems in the control of behavior in the rat. The two systems appear to have different entrainment characteristics and separate physiological substrates.
Adrenal Cortex Hormones↗
Comparison of yes-no and latency measures of auditory intensity discrimination.
Rats discriminated auditory intensity differences of sinusoids at 3.0 kilohertz in a go/no-go signal detection procedure. Responses to the signal (hits) were reinforced with electrical brain stimulation, and misses produced a brief timeout. On intermixed noise trials, withholding of responses (correct rejections) was reinforced, and false alarms produced the time-out. In two test conditions, the signal was either the louder (100 decibels) or softer (90, 93, 96, or 99 decibels) of the pair of intensities presented within a set of trials. Each animal was first trained with signal value louder or softer, and reversed for the second condition so that the former noise value served as signal. Hits showed shorter latencies than false alarms, regardless of the relative intensity of signal and noise, and the magnitude of differentiation was proportional to signal-noise separation. Both hits and false alarms showed longer latencies as the discrimination became more difficult. Isosensitivity contours derived from the latencies showed close similarity across conditions; in comparison, the yes-no measure of detectability, d', showed greater variability. The similarity of latency differentiation across louder and softer signal conditions supports a detection model in which the observer's judgment is controlled by the distance of sensory effect from criterion on each trial, as opposed to the loudness of the tones per se.
Animals↗
Control of the rat's circadian self-stimulation rhythm by light-dark cycles.
Rats with hypothalamic and septal electrodes were maintained in continuous test environments where bar-press responses produced brief reinforcing electrical stimulations. Long-term trends in response emission were measured under continuous exposure to light, dark and 12 hr light-dark alternations. In addition, transient behavioral adjustment to sudden 180 degrees phase shifts in the light-dark schedule was studied. The ambient light condition was found to control the period and phase of the circadian rhythm of brain self-stimulation behavior, as quantified by Fourier analysis. The circadian period was greatest under constant light (up to 24.90 hr under dim illumination), and approximated 24.00 hr under constant dark. Successful nocturnal entrainment to 12 hr light-dark alternations was obtained, with the peak of the 24 hr Fourier fundamental occurring in the middle-to-late dark segments. Three to 11 days were required for re-entrainment to 180 degrees light-dark phase shifts, during which the behavioral oscillation period increased to values comparable to periods under constant light. The rate of re-entrainment appeared to be proportional to illumination intensity during light segments.
Animals↗
Control of the rat's sniffing behavior by response-independent and dependent schedules of reinforcing brain stimulation.
The rat's sniffing response occurs in continuous bursts, at approximately 5-11 Hz. In the present experiments, the analog signal from a thermo-couple probe in the nasal cavity was digitized to provide a discrete logic pulse, defining a sniff, and permitting on-line presentations of reinforcing brain stimulation contingent on momentary sniffing patterns. Schedules of reinforcer presentation included response-independent fixed interval (temporal conditioning), continuous reinforcement (CRF), and differential reinforcement of low rates (DRL 10 sec). Under temporal conditioning, bursts of sniffing were observed immediately after stimulation, and an acceleration in sniffing developed preceding stimulation. Under CFR, operant rate-intensity functions were found to be similar to traditional bar-press data. Under DRL, sniffs were effectively paced by the criterion interval, and interresponse time analyses revealed evidence of temporal discrimination. The behavioral patterns were interpreted in terms of the interplay of operant and respondent functions.
Animals↗
Phase locked loop: an application in temperature telemetry and a method for its evaluation.
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Animals↗
Latency differentiation of hits and false alarms in an operant-psychophysical test.
Rats detected the luminance difference of standard and comparison stimuli in a go/no-go procedure. A key press was reinforced by brain stimulation only when the key's luminance was 10.53 ft-L (36.01 cd/m(2)), and key presses to dimmer comparison values produced a 5-sec timeout. These asymmetrical reinforcement contingencies maximized the bias toward hits and false alarms ("yes" reports), and thus the number of latencies available for analysis. False alarm latencies exceeded hit latencies, with the magnitude of differentiation proportional to luminance difference, demonstrating stimulus control on the very occasions that errors (key presses to comparison luminances) were emitted. Overall latencies decreased when the standard-comparison luminance difference was made smaller, suggesting a reduction in observing time when the stimuli became indiscriminable.
Animals↗
Circadian rhythm of brain self-stimulation behavior.
Under constant conditions of light, sound, temperature, and humidity, rats exhibited circadian rhythmicity in rate of bar-pressing with hypothalamic and septal reinforcing brain stimulation. Variations in reinforcer magnitude aflected absolute levels of operant response emission but not the frequency of the circadian rhythm. In long sessions, the time of peak responding deviated systematically from a strict 24-hour period. Such data show marked similarity to free-running rhythms of motor activity.
Animals↗
Some temporal properties of intracranial self-stimulation.
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Animals↗
Detection of brief tones in noise by rats.
Two rats were trained to detect brief 8000-Hz tones centered in a one-third octave band of noise. The procedure was analogous to the yes-no method of human psychophysics in that one response was defined as correct and reinforced if the tone were present in the noise, and another response was correct and reinforced if the tone were absent. The percentage of correct responses was determined principally by the energy in the tone for the range of durations studied (75 to 600 msec): if the tone's duration were halved, for example, its power had to be doubled to keep the percentage of correct responses about the same. The ratio of the energy in the tone to the power per cycle of the noise needed to maintain 75% correct responses was about 36 db for one animal and 41 db for the other. Although the two responses were similar, and their consequences equal, biases in responding were sometimes observed.
Animals↗
Discrimination of auditory intensities by rats.
Rats were trained to press one of two keys when a standard intensity value of a 4.0-kHz sine tone (70 or 100 db re 2 x 10(-4) microbar) was presented from a centrally located loudspeaker. Pressing the other key was reinforced when comparison intensity values (as much as 30 db less than the standard value) were presented. The animals initiated tone presentations by breaking a light beam at the rear of the chamber. Correct choices produced brain-stimulation reinforcement, and errors produced a timeout. A procedure designed by Jenkins was used to partial out choice data under potential control of sequential cues in the stimulus series. When the standard-comparison intensity difference was varied, the rats showed similar psychometric functions despite wide differences in response bias (relative position preference). A signal detection analysis showed that response biases for individual animals remained fairly consistent during psychophysical testing. The trend of decreasing choice accuracy at small intensity differences was described by the cumulative normal probability function. The similarity of psychometric functions obtained with 70- and 100-db standards supported Weber's law. There was some evidence that response latencies were controlled by intensity differences even when choice behavior was undifferentiated.
Animals↗
Discrimination of brightness differences by rats with food or brain-stimulation reinforcement.
Rats were trained to respond to the brighter of two keys. Four animals were trained with food pellets and four with electrical brain stimulation. Each discrimination sequence was initiated when the animal broke a light beam at the rear of the chamber, turning on the key lights and starting a 30-sec reinforcement period. An initial response on the brighter key was immediately reinforced, and further responses on the brighter key were then intermittently reinforced. Any time the dimmer key was pressed, a 30-sec timeout was introduced. During timeout, no response had any programmed consequence. When the reinforcement period or the timeout ended, a new discrimination sequence could be initiated. Daily 1-hr training sessions were conducted, and after seven or eight sessions, all animals were at or near errorless performance levels. The luminance of the brighter key was then systematically reduced, in seven steps, with two 30-min test sessions at each step. Orderly psychometric functions were generated for individual animals. Initial acquisition, once position preferences were broken, was equally rapid for food and for brain-stimulation animals, and the two reinforcement procedures yielded comparable levels of brightness discriminability.
Animals↗