Dark Preference Research Articles

Behavioural conflict in two strains of rat: Home cage preference versus dark preference

When confronted with a novel situation rats show a tendency either to stay in a dark place or to retreat to a familiar place, if available. To produce a conflict between these two tendencies the rat's home cage was connected by a runway to a dark but unfamiliar compartment. Three groups of rats were tested in this apparatus with different levels of illumination in the home cage. Tryon Maze Bright rats showed a strong preference for the home cage which was independent of the illumination level. This preference was also found in Wistar rats. With a very high level of illumination in the home cage, however, Wistar rats showed a preference for the home cage only in the first few trials or a series of repeated trials. In later trials they spent more time in the dark part of the apparatus. The results were regarded as an indication that in a novel situation rats primarily search for a familiar place. When such a place is available they tolerate aversive stimulation present in this place.

Reliability and sources of control of preference for signaled shock

Five experiments investigated the reliability of, and a possible explanation for, the preference for signaled shock (PSS) phenomenon, in which animals show a preference for signaled over unsignaled, unmodifiable shock. Experiment 1 demonstrated the generality of our previous PSS shuttlebox data. In an attempt to explain some of the studies in which a failure to obtain a PSS has been reported, Experiments 2 and 3 found that under certain conditions the PSS effect could be overridden by an innate preference for dark; however, the series of experiments in toto speaks clearly for the robustness of the phenomenon. Consistent with the recently proposed “crossover consequence hypothesis,” Experiments also revealed that shuttling behavior during manifestations of PSS is not randomly distributed in time. However, Experiments 4 and 5 found that PSS could not generally be attributed to an interaction between the acquired aversiveness of the signal and the spatially asymmetrical probability of shuttling being punished, as proposed by this hypothesis.

Escape versus exploratory activity: An interpretation of rats' behaviour in the open field and a light-dark preference test

To test the assumption that dark preference in rats can serve as a measure of emotionality, dark preference was compared with ambulation and defacation in the open field. One group of 80-days-old male rats was handled for seven days; another group remained undisturbed. All animals were tested on each of five successive days in both a light-dark preference situation and an open field. Handled rats ambulated more in the field and stayed less time in the dark than non-handled ones. Significant negative correlations were found for the different days between open field ambulation and dark preference. Correlations between dark preference and open field defacation were positive except on day one. From the first to the second trial dark preference increased in both groups while open field ambulation decreased. The results were considered to support the hypothesis of dark preference as a measure of emotionality. In a second study an investigation was made as to whether high initial activity in a new situation is brought about by exploration or by an escape tendency. Again one group of male albino rats was handled. During testing, half of the handled and half of the non-handled rats had the chance of escaping from the open field into the adjacent home cage. From there the animals had the possibility of re-entering the field. The second half of each group had to stay in the field. These latter animals showed a remarkable decrease in ambulation from the first to the second trial. Rats which had access to their home cages seldom re-entered the field in the first trial. In later trials, however, ambulation in the field increased. Non-handled rats needed more trials before they started investigating the field. It was concluded that this result gives more support to an explanation of initial activity in terms of escape behaviour.

The influence of adult handling and social isolation on dark preference in albino rats

Social isolation and adult handling are supposed to alter emotionality in rats. In order to investigate the hypothesis that dark preference in albino rats is dependent on their emotional level, one group of male, 60-day-old Wistar rats was housed in pairs, another group was housed individually, bothfor 30 days. After this period one half of each group was handled for 7 days. The animals were tested on several consecutive days in a light-dark choice situation. Handled animals stayed significantly less time in the dark than non-handled ones. Isolation on the other hand, increased time spent in the dark. Groups not only differed in the mean times they stayed in the dark, but also showed different forms of curves over the days. These results could be replicated in a second experiment. Data seem to support the hypothesis of dark preference as an emotional response.

Activity and dark preference responses of albino and hooded rats receiving MSH

Albino rats preferred a dark to a dimly lit alley significantly more than did hooded rats. Injections of melanocyte-stimulating hormone (MSH) did not change overall preference or activity levels for either strain. However, albino rats receiving MSH during the first three days spent more time in the dark than those receiving MSH during the last three days, whereas hooded rats were not affected by the order in which the hormone was given. The results caution against hormonal studies with albino rats in which light may act as an aversive stimulus. The findings suggest that MSH may intensify inherent emotional reactions to novel and aversive stimuli.

Synthetic rat scotophobin induces dark avoidance in mice.

Two independent research groups replicate alteration of dark preference to dark avoidance by mice injected with synthetic scotophobin, a pentadecapeptide.

A period of time-out from flickering light as a sensory reinforcer

A period of cessation of flickering light (darkness and light for 0.5 sec. intervals) was made contingent on the bar pressing of hooded rats. The cessation period consisted of either continuous darkness or continuous light, for 1.5, 3.0 or 6.0 sec. Cessation of flicker was reinforcing only if the “time-out” period was continuous darkness. The notion that a discrepancy from any kind of stimulus adaptation level, with equal discrepancies being equally rewarding, is not entirely supported by the results. The direction of change is important in determining the effectiveness of a sensory change as a reinforcer. The results of a separate phase of the experiment demonstrated that this finding can not be accounted for by a greater preference for darkness versus flickering light than for continuous light versus flickering light. No preferences were exhibited.

Effects of dark preference on attention to the positive cue in posterior neodecorticated albino rats

Transfer of attention to the relevant stimulus dimensions of a successive brightness discrimination was assessed by the “acquired distinctiveness of cues” method in posterior neodecorticated rats. Attention to the relevant cue was retarded when Ss responded trophically toward the dark in a simultaneous brightness problem. Dark preference was negatively correlated with effective performance of a subsequent successive problem.

Preference and sensory factors in brightness discrimination learning of posterior neodecorticated albino rats

Albino rats preferred the dark areas in a free choice situation, and preference was enhanced at high differential brightness levels. Posterior neodecortication did not reduce dark preference significantly, as it does in hooded rats. Learning was retarded when ablated albinos were forced to approach a high intensity light in the T-maze apparatus. With low illumination, sensory and preference factors were balanced so that scores of light- and dark-positive rats were nearly identical.

Chemical transfer of learned fear: Failure to replicate Ungar

Thirty naive male Sprague-Dawley rats were used as donors and were randomly divided into three groups of 10. One group was shocked only in the black box, according to Ungar’s paradigm. The second group received shock equally in the white and black boxes, to control for the possible activating effects of shock, regardless of where administered. The third group was a control group that received handling only, with no shock. The prepared brain extracts were injected into recipient mice, prescreened to eliminate those showing no dark preference. There was no evidence of a reliable differential avoidance of the dark box by any treatment group. Activity measures also failed to differentiate the three groups. Further, the difficulty of obtaining mice with a dark preference was discussed.

Oxygen Preference in the Spring Cavefish, Chologaster agassizi

Chologaster agassizi exhibits a preference for high over low oxygenated water; however, the cavefish does not discriminate between oxygen concentrations of 2 mg/l or less, whether the two concentrations are relatively high or low. The tolerance point for oxygen preference appears to be near 6 mg/l with higher concentrations giving no observable preference. The stimulus to avoid light is more pronounced than the stimulus to select against low oxygen conditions. The reactions of the cavefish to oxygen conditions appear to be attributed to the fish sensing the unfavorable nature of the water and searching for a more desirable area. Included among the intrinsic factors involved in the migration of Chologaster from the cave to the epigean environment may be the preference for dark and high oxygen conditions.

Visual behavior of the Mongolian gerbil (Meriones unguiculatus)

The Mongolian gerbil, Meriones unguiculatus, appears to be deficient in depth perception. Whereas C57BL/6J mice show a predominance of shallow responses on a visual cliff (e.g., 100% of initial responses is to the shallow side), gerbils show random behavior (e.g., 56% of initial responses is to the shallow side). Gerbils are not blind, however, as they show a strong preference for darkness when allowed a choice, and their circadian activity cycle can be readily entrained with the light cycle.

ILLUMINATION PREFERENCE OF ALBINO RATS IN A CLOSED HEXAGONAL MAZE.

Ss were allowed to choose among 6 illumination conditions by altering their location in a maze. For a choice among 0 (darkness), 1, 2, 4, 8, and 16 ft.-candles in Exp. 1, preference decreased with increasing intensities. Ss tested during the dark portion of their cycle showed a stronger preference for darkness than Ss tested during the lighted portion of their cycle. In Exp. 2, preference for 0, .01, .1, 1.0, 10.0, and 25.0 ft.-candles was again inversely related to intensity, except that there was no difference between preference for darkness and .01 ft.-candles.

Effects of lesions in central nervous visual structures on light aversion of rats.

The effects were investigated of bilateral lesions in three central nervous visual structures, a) superior colliculus, b) lateral geniculate body, and c) striate cortex, on the light aversion (or dark preference) of rats. While both normal and brain-operated animals displayed an aversion to crossing into the bright alleys of the test apparatus, the manifest aversion to light was reduced in all three brain-operated groups. The decreased light aversion was accompanied in all groups by increased locomotor activity. The reduction in light aversion appeared to depend on the relative size of the lesion rather than on the specific central nervous visual structure destroyed.