Computational and entrainment models of circadian food-anticipatory activity: Evidence from non-24-hr feeding schedules.

Rats anticipate a daily meal, provided that meal onset intervals are within a circadian (22-31 hr) range. Food-anticipatory activity (FAA) has been interpreted as evidence for a food-entrained circadian pacemaker or for a computational process that uses stored representations of pacemaker phase. The models make different predictions concerning the symmetry and history dependence of the circadian limits to FAA. To test those predictions, rats were entrained to 24-hr light-dark and feeding cycles and then exposed to feeding cycles of 21, 22, 25, 26, or 27 hr. Rats showed strong FAA to feeding cycles ≥24 hr, but not to schedules     

Ontogeny of eyeblink conditioned response timing in rats.

Eyeblink conditioned response (CR) timing was assessed in adult and infant rats. In Experiment 1, adult rats were trained with a 150-ms tone conditioned stimulus (CS) paired with a periorbital shock unconditioned stimulus (US; presented at 200- or 500-ms interstimulus intervals [ISIs]). The rats acquired CRs with 2 distinct peaks that occurred just before the US onset times. Experiments 2 and 3 examined developmental changes in CR timing in pups trained on Postnatal Days 24-26 or 32-34. Experiment 3 used a delay conditioning procedure in which the tone CS continued throughout the ISIs. Pups of both ages exhibited robust conditioning. However, there were age-related increases in the percentage of double-peaked CRs and in CR timing precision. Ontogenetic changes in eyeblink CR timing may be related to developmental changes in cerebellar cortical or hippocampal function. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Long- and short-term regulation of feeding patterns in the rat.

Analysis of feeding patterns in 3 experiments with a total of 22 male hooded Long-Evans and 4 Wistar rats showed that the amount of food eaten in relatively long intervals (24–72 hrs) was correlated with mean meal size but was essentially uncorrelated with meal frequency. Similarly, the regulatory adjustment in daily food intake occurring in response to changes in environmental temperature was found to be the result of an adjustment in mean meal size, with no change in meal frequency. In contrast, the amount of food eaten in relatively short intervals (3–22 hrs) was more highly correlated with meal frequency than with mean meal size, and a reliable correlation between meal size and the postmeal interval was obtained. The meal size/postmeal interval regression equation predicted the long-term relation between mean meal size and the amount of food eaten. Results indicate that meal frequency is controlled largely by short-term regulatory signals and that some of these signals affect meal size directly. (44 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Performance of four seed-caching corvid species in the radial-arm maze analog.

Four seed-caching corvid species were tested in an open-room analog of the radial-arm maze. During Experiment 1, the species more dependent on stored food, Clark's nutcrackers (Nucifraga columbiana) and pinyon jays (Gymnorhinus cyanocephalus), acquired the task more quickly and to higher accuracy levels than either scrub jays (Aphelocoma coerulescens) or Mexican jays (A. ultramarina). During Experiment 2, performance after retention intervals was tested. When intervals of 30–210 min were tested in ascending order, species differences observed during acquisition were again obtained. However, when intervals of 5–300 min were tested in random order, the species differed only at shorter intervals. During Experiment 3, only nutcrackers gave any indication of performing above chance after a 24-hr retention interval. Results support the hypothesis of species differences in spatial information processing that correlate with dependence on stored food. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of administering cocaine at the same versus varying times of day on circadian activity patterns and sensitization in rats.

The effects of different schedules of cocaine administration on circadian activity patterns and locomotor sensitization were studied. Rats received intraperitoneal injections of either saline or 20 mg/kg cocaine at either 24- or 33-hr intervals for 8 cycles (development). After a 2-day withdrawal, they were given a cocaine challenge in a novel environment. Rats given cocaine at 24-hr intervals were hypoactive 4 to 9 hr postinjection during development and, during cocaine challenge, showed sensitization of locomotor activity. Rats given cocaine at 33-hr intervals did not show these effects. On the 33-hr-period schedule, activity was enhanced beginning 24 hr after drug receipt. Different intermittent schedules of cocaine receipt may alter the vulnerability to cocaine, and altered vulnerability may be more likely when a subsequent cocaine injection interacts with a distal state of sensitivity produced by a prior injection. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stimulus and temporal cues in classical conditioning.

In 2 experiments, separate groups of rats were given stimulus conditioning, temporal conditioning, untreated control and (in Experiment 2) learned irrelevance control procedures followed by a compound with both stimulus and temporal cues. Stimulus conditioning consisted of a random 15-s duration conditioned stimulus (CS) followed by food; temporal conditioning consisted of food–food intervals of fixed 90 s (Experiment 1) or fixed 75?+?random 15 s (Experiment 2). The stimulus group abruptly increased responding after CS onset, and the temporal group gradually increased responding over the food–food interval. When the food–food interval was fixed 90 s, the temporal cue exerted stronger control in the compound, whereas when the food–food interval was fixed 75?+?random 15 s, the stimulus cue exerted stronger control. The strength of conditioning, temporal gradients of responding, and cue competition effects appear to reflect simultaneous timing of multiple intervals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal search as a function of the variability of interfood intervals.

We attempted to determine whether timing theories developed primarily to explain performance in fixed-interval reinforcement schedules are also applicable to variable intervals. Groups of rats were trained in lever boxes on peak procedures with a 30-, 45-, or 6O-s interval, or a 30- to 6O-s uniform distribution (Experiment 1); a 60-s fixed and 1- to 121-s uniform distribution between and within animals (Experiment 2); and a procedure in which the interval between food and next available food gradually changed from a fixed 60 s to a uniform distribution between 0 and 120 s (Experiment 3). In uniform interval schedules rats made lever responses at particular times since food, as measured by the distribution of food-food intervals, the distribution of postreinforcement pauses, and the mean response rate as a function of time since food. Qualitative features of this performance are described by a multiple-oscillator connectionist theory of timing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Precision and accuracy in the reproduction of simple tone sequences.

In four experiments we investigated the precision and accuracy with which amateur musicians are able to reproduce sequences of tones varied only temporally, so as to have tone and rest durations constant over sequences, and the tempo varied over the musically meaningful range of 5–0.5 tones per second. Experiments 1 and 2 supported the hypothesis of attentional bias toward having the attack moments, rather than the departure moments, precisely timed. Experiment 3 corroborated the hypothesis that inaccurate timing of short interattack intervals is manifested in a lengthening of rests, rather than tones, as a result of larger motor activity during the reproduction of rests. Experiment 4 gave some support to the hypothesis that the shortening of long interattack intervals is due to mnemonic constraints affecting the rests rather than the tones. Both theoretical and practical consequences of the various findings, particularly with respect to timing in musical performance, are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The timing of food availability affects growth in chicks

Three experiments challenged the ability of domestic chicks to grow normally by differentially restricting when and for how long food was available. In Experiments 1 and 2, food was available for six 1-hr, three 2-hr, two 3-hr, or one 6-hr (a.m., p.m.) periods/day over the first 3 posthatch weeks. Control groups received continuous access to food. In Experiment 3, different amounts of light surrounded the 6-hr feeding period. In Experiments 2 and 3, chicks composed their own diets from separate sources high in protein or carbohydrate. Except for the single 6-hr meal preceding dark, large meals at other times of day impaired growth--primarily because chicks consumed insufficient dietary protein and ate less earlier in the light phase. We conclude that both the amount eaten and the proportion of the diet consumed as protein at given times of the day are phylogenetically acquired strategies that fit the omnivorous, diurnal chicken to its niche, independent of its momentary requirements, and appear early in development.     

Abdominal vagotomy disrupts food-related drinking in the rat.

In 2 experiments with a total of 41 Sprague-Dawley albino rats, Ss with complete subdiaphragmatic bilateral transection of the abdominal vagus (Vgx-C) showed disordered food-related drinking when drinking water in temporal association with a meal of dry food after 5-hr food deprivation and when drinking water in association with a liquid meal after 24-hr food deprivation. The Vgx-C Ss drank after significantly longer latencies and drank significantly less water in 1 hr than did sham-vagotomized (Sham) Ss after eating the same size meal (solid or liquid). Ss with incomplete vagal transection (Vgx-I) ate and drank like Shams. Water intake of Sham and Vgx-I Ss correlated positively with the meal size of solid food, but the water intake of Vgx-C Ss did not. The failure of Vgx-C Ss to drink water normally when food was ingested was not due to failure of a food stimulus to reach the intestine, because Vgx-C and Sham Ss emptied equivalent volumes of liquid food from the stomach into the intestine within 10 min of food entering the stomach. Results indicate that the abdominal vagus is an important neurological substrate for food-related drinking in the rat. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mechanisms for enhanced feeding in the cold in rats.

The effect of environmental cold upon feeding, food-motivated behavior, and gastric clearance of food was studied in 36 female Sherman rats in 4 experiments. Ss ate liquid diet in either a 5 or 22Deg. C ambient temperature (T-sub(a)) following (a) 24-hr food deprivation at T)a) of either 5 or 22Deg. C or (b) 0- or 48-hr food deprivation at T-sub(a) 22Deg. C. Ss ate more at 5 than at 22Deg. C regardless of the ambient temperature during deprivation. Ss increased feeding in the cold by increasing meal frequency but not meal size. Cold (5Deg. C) also enhanced the urge to eat. Ss barpressed for food more often in the cold on a VI 30-sec schedule when gastric clearance of food was prevented by a pyloric noose and when food cleared from the stomach normally. Quinine adulteration of food suppressed food intake only in the 22Deg. C. Cold (5Deg. C) enhanced gastric clearance of liquid food within 20 min of ingestion. Results support the view that the peripheral sensation of cold is an adequate stimulus for feeding and that cold T-sub(a) can stimulate feeding directly by increasing the urge to eat and indirectly, secondary to increased gastric clearance. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Circadian rhythmic fractal scaling of heart rate variability in health and coronary artery disease

BACKGROUND: In clinical cardiology, heart rate variability is a putative index of autonomic cardiovascular function. Signs of reduced vagal activity are not only associated with an enhanced risk of sudden cardiac death, but such impaired heart rate variability became a new predictor of sudden cardiac death and other mortality in patients with a variety of diseased states. HYPOTHESIS: It is postulated (1) that the time structure (chronome) of heart rate variability in clinical health includes a circadian rhythm and deterministic chaos, the latter gauged by the correlation dimensions of RR intervals; and (2) that this chronome is altered in patients with coronary artery disease (CAD). METHODS: From 24-h Holter records of 11 healthy controls and 10 patients with CAD, 500-s sections around 02:00, 06:00, 10:00, 14:00, 18:00 and 22:00 hours were analyzed for smoothed RR intervals sampled at 4 Hz. Correlation integrals were estimated for embedding dimensions from 1 to 20 with a 1.0-s time lag, using an algorithm modified from Grassberger and Procaccia. The Wilcoxon signed-rank test compares circadian end points assessed by cosinor between the CAD patients and age-matched controls. RESULTS: A circadian rhythm characterizes the correlation dimension of healthy subjects peaking during the night (p < 0.005). Patients with CAD have a lowered correlation dimension (p < 0.05) and an altered circadian variation which requires the consideration of an approximately 12-h (circasemidian) component. CONCLUSION: The results demonstrate the sensitivity of circadian rhythms for the detection of disease. A partial 24- to 12-h (circadian-to-circasemidian) frequency multiplication (or partial variance transposition) in CAD of the correlation dimension, apart from being a potential clue to the etiology of the disease, adds a new feature to a chronocardiology combining, with the fractal scaling, an assessment of circadian and circasemidian components as measures of predictable variability to be tested for use in diagnosis, prognosis, and as putative guides to treatment timing.     

Relations between feeding and sleep patterns in the rat.

A concomitant analysis of sleep and feeding patterns in 11 male Wistar rats was carried out over 8 days, using continuous EEG recording. The proportion of slow-wave sleep and paradoxical sleep within an intermeal interval was constant and varied only in relation to the time of the day. During the dark period only, there were significant correlations between meal size and amount of time spent in both stages of sleep in the following intermeal interval. These correlations were even stronger between meal size and sleep duration in the intermeal interval that followed the next meal. Circadian variations in satiety ratios (i.e., units of subsequent intermeal interval and sleep per units of food ingested) and in deprivation ratios (i.e., units of feeding per units of prior intermeal interval and sleep) suggest that division of 24-hr data into 3 8-hr periods rather than 2 12-hr periods reveals distinct correlations between meal size and pre- and postmeal sleep and might reflect more accurately the underlying metabolic events. (34 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learning about deprivation intensity stimuli.

Rats demonstrated that they can use deprivation-produced stimuli as discriminative signals for shock in three experiments that used observation of freezing behavior as the index of learning. In Experiment 1, one group was shocked under 24-hr, but not under 0-hr food deprivation. Another group received the reversed discrimination. Both groups froze more under their shocked than under their nonshocked deprivation level. Furthermore, freezing was greatest under a given deprivation level for the group shocked under that level. Behavior was shown to be a function of this learning during subsequent testing under other deprivation levels. In Experiment 2, rats discriminated between deprivation intensities approximating those encountered under free-feeding conditions, and behavior under other deprivation levels also depended on this learning. Experiment 3, using 6- and 23-hr food deprivation, showed that discriminative responding occurred in the absence of cues arising from the recent memory of food in the home cage. Generalization of discriminative control to cues produced by intubation of a high calorie load and to injection of insulin (Experiment 3{a}) provided evidence that animals learned about the interoceptive stimulus consequences of their deprivation states. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interval timing accuracy and scalar timing in C57BL/6 mice.

In many species, interval timing behavior is accurate—appropriate estimated durations—and scalar—errors vary linearly with estimated durations. Whereas accuracy has been previously examined, scalar timing has not been clearly demonstrated in house mice (Mus musculus), raising concerns about mouse models of human disease. The authors estimated timing accuracy and precision in C57BL/6 mice, the most used background strain for genetic models of human disease, in a peak-interval procedure with multiple intervals. Both when timing 2 intervals (Experiment 1) or 3 intervals (Experiment 2), C57BL/6 mice demonstrated varying degrees of timing accuracy. An important finding was that, both at the individual and group levels, their precision varied linearly with the subjective estimated duration. Further evidence for scalar timing was obtained using an intraclass correlation statistic. This is the first report of consistent, reliable scalar timing in a sizable sample of house mice, thus validating the peak-interval procedure as a valuable technique, the intraclass correlation statistic as a powerful test of the scalar property, and the C57BL/6 strain as a suitable background for behavioral investigations of genetically engineered mice modeling disorders of interval timing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The circadian variation of urinary N-acetyl-beta-D-glucosaminidase and gamma-glutamyl transpeptidase in clinically healthy cats

The circadian variation of urinary N-acetyl-beta-D-glucosaminidase (NAG, EC 3.2.1.30) and gamma-glutamyl transpeptidase (gamma-GTP, EC 2.3.2.2) was evaluated in cats. Urine and blood were collected at 4-hr intervals from adult cats (3 males, 9 females) weighing between 2.6 and 5.0 kg. There was no circadian variation in the urine volume, creatinine clearance, creatinine excretion, NAG excretion or gamma-GTP excretion. The average NAG and gamma-GTP indices in the 4-hr urine were similar to those for the 24-hr urine. However, the variance for the 4-hr urine samples was higher than that of 24-hr urine. In conclusion, although 4-hr urine samples can be used to estimate 24-hr urinary enzyme excretion, short-term spot urine samples may cause increased variation in the enzyme index.     

When to start explicit counting in a time-intervals discrimination task: A critical point in the timing process of humans.

Four interval discrimination experiments were conducted to determine the interval length at which explicit counting becomes a useful strategy. Experiment 1 showed that for intervals lasting about 1 s, there was no advantage to counting regardless of the counting strategy adopted. Experiment 2 showed that for 2.5-s intervals, performance was much better with an explicit-counting strategy. To study the functional relationship between variability and duration in the counting versus no-counting conditions, variability was estimated for base durations lasting 0.7–1.9 s in Experiment 3. This experiment showed that the generalized form of Weber's law applied well to data in the no-counting condition. Experiment 4 showed that variability remained the same for durations lasting 1.3–1.9 s when an explicit-counting strategy was adopted. Taken together, the experiments showed that it becomes useful to count explicitly when intervals are longer than 1.18 s. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of chronic intrahypothalamic infusion of insulin on food intake and diurnal meal patterning in the rat.

In Experiment 1, rats were chronically infused with insulin (2.7, 27, or 270 ng/hr) or 0.9% saline into the ventromedial (VMH), medial perifornical (PF), or lateral (LH) hypothalamus. VMH infusions of insulin caused a significant, dose-dependent decrease in food intake and body weight; PF infusion of insulin was less effective, but significant; whereas LH infusions of insulin were ineffective. In Experiment 2, rats were chronically infused with insulin (0.54 ng/hr) or 0.9% saline into the VMH, paraventricular (PVN), or posterior (PN) hypothalamic nucleus. Subjects that received VMH or PN infusions of insulin failed to regain weight lost as a result of surgery even 2 weeks after infusion; subjects that received PVN infusions of insulin regained their preoperative weights faster than did controls. All of the groups that received insulin significantly increased their daytime food intake during the infusion period and decreased their night food intake slightly; 24-hr food intake remained unchanged. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal Learning in Random Control Procedures.

Experiments 1 and 2 delivered conditioned stimuli (CSs) at random times and unconditioned stimuli (USs) at either fixed (Experiment 1) or random (Experiment 2) intervals. In Experiment 3, CS duration was manipulated, and US deliveries occurred at random during the background. In all 3 experiments, the mean rate of responding (head entries into the food cup) in the background was determined by the mean US-US interval, and the mean rate during the CS was a linear combination of responding controlled by the mean US-US and mean CS onset-US intervals; the pattern of responding in time was determined by the interval distribution form (fixed or random). An event-based timing account, Packet theory, provided an explanation of the results. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perception and production of temporal intervals across a range of durations: Evidence for a common timing mechanism.

Study participants performed time perception and production tasks over a set of 4 intervals ranging from 325 to 550 ms. In 3 experiments, variability on both the production and perception tasks was found to be linearly related to the square of the target intervals. If the perception and production of short temporal intervals use a common timing mechanism, the slopes of the functions for the 2 tasks should be identical. The results of Experiment 1 failed to support this prediction. However, when the 2 tasks were made more similar by providing a single (Experiment 2) or multiple (Experiment 3) presentations of the target interval per judgment or production, the perception and production functions were nearly identical. The results suggest that temporal judgments and productions are based on an integrated internal representation of the target interval rather than reference to an internal oscillatory process. (PsycINFO Database Record (c) 2010 APA, all rights reserved)