Brightness Discrimination Research Articles

明るさ識別と刺激呈示持続時間

明るさ識別と刺激呈示持続時間

Discrimination learning requiring different memory components in rats: age and neurochemical comparisons.

The performances of young (8-9 months) and aged (22-24 months) male ACI rats were compared in a T-maze requiring two discriminations, each of which placed different demands on memory processing. A spatial discrimination in the stem of the T-maze required long-term reference memory; a discrete-trial, alternation discrimination in the arms of the T-maze required working memory. Following acquisition training in one maze, rats were also trained in a second maze at a different location in the room. The correct response in the stem of this maze was opposite to that in the first maze. In two experiments with slightly different pretraining procedures, similar results demonstrated that aged rats made more errors in all phases of maze training than did their young counterparts. The results suggest that all components of memory processing were affected equivalently because the age-related impairment was not selectively greater in any component of the task. In a third experiment, aged rats were unimpaired in the ability to perform in a T-maze task involving a brightness discrimination with intramaze cues. This result suggests that the age-related impairment in the two-component T-maze task was restricted to the cognitive demands of the task. Neurochemical analyses were performed to determine whether regional neurotransmitter synthetic enzyme activities could be used to identify neurochemical systems associated with performance in these tasks and with any age-related impairments observed. Choline acetyltransferase and glutamic acid decarboxylase were assayed as markers for cholinergic and GABAergic systems, respectively, in the hippocampi and the following cortical regions: frontal, sensorimotor, auditory, cingulate, occipital, and pyriform-perirhinal. A slight (8%) but significant age-related decline was observed in the activity of glutamic acid decarboxylase but not of choline acetyltransferase. Although the correlation between maze performance and regional enzyme activities generally supported several previous observations, the only significant correlation to emerge was between working memory performance and glutamic acid decarboxylase activity in the cingulate cortex.

Recovery of function after brain damage: On withdrawals from the memory bank

The present research addressed the question of whether any change between the conditions of original preoperative learning and postoperative recovery would interfere with the availability and retrieval of the spared memories. The procedure was to train rats initially on a brightness discrimination for appetitive rewards and then postoperatively reinstate the appetitive motivation but require that the animals recover the brightness habit, or its reversal, to escape/avoid footshock. The postoperative availability of the spared memories of the preoperative learning was quantified by the occurrence of impaired postoperative reversal training. The results indicated that simply reinstating the preoperative motivation state is insufficient to allow the animal access to the preoperative memories. However, if the preoperative motivation state is reinstated and the animal is also provided rewards appropriate to that motivation, then the addition of another motivation and rewards will not prevent the retrieval of spared preoperative memories.

The effect of devascularization of the visual cortex on visual function in the rabbit

The role of the visual cortex in brightness and pattern vision was re-examined in the rabbit. Animals were trained on both a brightness and a horizontal-vertical striation discrimination. Bilateral removal of the dura mater overlying the entire visual cortex produced no impairments in either brightness or pattern vision. When the visual cortex was devascularized by removal of the pia mater bilaterally, total loss of pattern vision was found with no impairment of brightness discrimination ability. The significance of the finding that the effects of slowly developing degenerative lesions are the same as those of surgical ablation was discussed.

Temporal brightness enhancement: studies of individual differences.

We have previously identified categorical individual differences in the occurrence of temporal brightness enhancement (TBE) by using a simultaneous brightness discrimination paradigm (Bowen & Markell, 1980).TBE is a nonmonotonic relation between brightness and pulse duration, pulses of intermediate duration (75–125 msec) can appear brighter than longer or shorter pulses of the same luminance. Three classes of observers can be defined based on whether they perceive TBE under one of two conditions of temporal asynchrony between a short test pulse and a longer (500 msec) comparison pulse:simultaneous onset of the pulses orsimultaneous offset. Type A observers show TBE for both asynchrony conditions; Type B observers show the effect for simultaneous offset but not simultaneous onset; Type C observers do not show TBE for either asynchrony. In the present study, we show that Type A and Type C observers maintain a constant brightness-duration relation as the asynchrony between test and comparison pulses is varied from simultaneous onset to simultaneous offset. Type B observers show a gradual shift in the brightness-duration relation as asynchrony changes. In a separate experiment, we find that practice has little effect on Type A and Type B observers but that Type C observers may change in classification to Types A and B over as few as five experimental sessions. The hypothesis that individual differences are due to differential “weighting” of chromatic (sustained) and achromatic (transient) visual channels is discussed.

Complex visual discrimination of tradimensional patterns in rats: Progressive learning improves discriminative and recognition capacities

The purpose of these experiments was to evaluate the rat's discriminative capacities when facing tridimensional patterns. The behavioral approach involved 3 steps: (1) After establishing a brightness discrimination in a Y-maze (S + = dark, S - = bright), tridimensional objects were introduced into the goal boxes. (2) Brightness differences were gradually attenuated during the course of the fading procedure and correct responding to the tridimensional patterns was obtained. (3) This procedure had a second fading phase where configurational differences between these patterns were progressively reduced. All animals trained with this method of successive approximations learned the discrimination to a 90% criterion; whereas control animals, given the same complex discrimination without any shaping procedure, failed to learn. These experiments show that success or failure in the acquisition of a visual task is specific to the training method used. Our fading procedure produced complex discrimination behavior.

Effect of apomorphine on retention of a brightness discrimination in dopamine supersensitive rats

Apomorphine is known to improve the retention performance of a brightness discrimination task after post-training intrahippocampal application to rats. The present study shows that the retention performance of dopamine supersensitive rats was improved by a low dose of apomorphine which was still ineffective in control animals. Dopamine supersensitivity by itself had no effect on acquisition and retention parameters of brightness discrimination. The result further supports the assumption that dopamine receptors in rat hippocampus can modulate the formation of memory.

Perinatal linoleate deprivation impairs learning and memory in adult rats

Rats receiving polyunsaturated fatty acid (PUFA) deficient diets during the perinatal period showed in adult age undisturbed acquisition of a footshock motivated brightness discrimination task, but a significant impairment of retention. The same effects on retention were obtained in rats receiving the PUFA deficient diet in adulthood, when the behavioral parameters were investigated at the end of the dietary treatment.

Phencyclidine-like behavioral effects of 2-methyl-3,3-diphenyl-3-propanolamine (2-MDP)

2-Methyl-3,3-diphenyl-3-propanolamine (2-MDP) produced effects in animals similar to those produced by the dissociative anesthetics such as phencyclidine (PCP). Specifically, it shared the discriminative stimulus properties of PCP in rats trained to discriminate PCP (1 mg/kg) from saline; at higher doses, it disrupted brightness discrimination and stimulated locomotor activities in rats trained to avoid shocks in an automated Y-maze; and it produced surgical anesthesia when injected IV to rhesus monkeys. These pharmacological activities were observed only with the levo-isomer of 2-MDP. The dextro-isomer was either inactive or produced opposite effects, depending on the tests. Among several related diphenylpropylamines, 2-MDP represents the optimal structure for potency of PCP-like effects since changes in the amino, 2-methyl and 3-hydroxy groups reduced the potencies of the PCP-like discriminative properties.

Improvements in visual performance following a pulsed field of light: a test of the equivalent-background principle.

The offset of a pulsed conditioning field of light has recently been shown to produce enhancements of temporal resolution and brightness discrimination. These enhancements are similar to those that are due to imposing a high level of light adaptation on the visual system. Here we analyze whether there is a true equivalence of adaptive state between some level of steady light adaptation and the offset of a conditioning field. The enhancements of visual function at field offset were replicated by using a suprathreshold two-pulse discrimination task and a task requiring detection of an incremental probe stimulus superimposed upon a suprathreshold pulse. These effects are shown to be qualitatively but not quantitatively similar to those produced by an equivalent background selected on the basis of its ability to raise threshold to the same degree as field offset. We conclude that the equivalent-background principle cannot be supported for our measures of foveal visual function.

Influence of MSH and corticosterone on stimulus control over an operant response

Several previous papers have indicated that MSH/ACTH-like neuropeptides facilitate the reversal of brightness discrimination in a runway task. The present experiment was undertaken to explore the development during both acquisition and reversal of stimulus control over an operant response. Male albino adult rats were treated daily with either 10 μg of MSH, 500 μg of corticosterone or a placebo in a double blind procedure during the establishment of an on-light control over availability of reinforcement. Having completed this regime the conditions were reversed so that reinforcement was present only when the chamber-light was off. The results indicated that treatment with MSH during acquisition produced a significant decrease in % correct responses compared to animals treated with either the placebo or corticosterone with neither of these latter groups differing from the other. During the reversal phase of training there was a trend for both MSH and corticosterone to lower % correct responses. The discussion focuses on other literature which has shown opposite effects of corticosterone on aversive and appetitively motivated tasks.

Recovery of function after brain damage: Differences in aged rats?

Age at the time of brain injury is generally considered an important determinant in recovery of function. The implication is that older individuals show less recovery. Existing data challenge this common notion, but suggest differential effects of brain damage in aged subjects. To assess these differences old rats were trained on a two-choice brightness discrimination, subjected to visual decortication, and retrained with nonreversed or reversed reinforcement contingencies. A significant reversal impairment established that sparing of function in aged rats was similar to that in adult rats. However, a significant reversal X brightness interaction suggested that the progress of recovery of function in aged rats is influenced not only by what is spared but also by whether the expression of what is spared is consistent with or antagonistic to competing innate response biases.

Visual discrimination after bilateral removal of the visual cortex in the rabbit

Rabbits were trained on a brightness and a vertical vs horizontal discrimination. After bilateral removal of the visual cortex the threshold of brightness discrimination was significantly higher. In addition, there was a severe impairment of striated pattern discrimination.

Changes in activities if fucokinase and fucosyltransferase in rat hippocampus after acquisition of a brightness discrimination reaction

Activities of enzymes involved in utilization of the glycoprotein precursor L-fucose (fucokinase and fucosyltransferase) were studied in rat hippocampal tissue after acquisition of a brightness discrimination reaction. Fucokinase activity was increased immediately after training, while fucosyltrabsferase revealed decreased values. However, 7 hr after training fucokinase activity showed normal values, while fucosyltransferase activity rose in trained animals over active and passive controls. The results are discussed in the light of a regulatory role that fucokinase and fucosyltransferase may play in fucose utilization under altered functional conditions.

Posterolateral hypothalamic and midbrain central gray lesions impair visual and spatial reversal learning: Further additions to the “general learning system” of the rodent brain

It has been assumed that the components of the rodent’s “general learning system” (a group of brain structures essential for normal acquisition of a wide range of laboratory tasks) can roughly be identified by determining which lesion placements within the rat brain will lead to defective acquisition of a spatial discrimination habit and its reversal as well as a brightness discrimination habit and its reversal. The results of this experiment suggest that the regions of the posterolateral hypothalamus and mesencephalic central gray, but not the regions of the nucleus accumbens, septofornix, medial supraoptic area, or ventromedial hypothalamus, qualify as components of the general learning system.

Memory retention in old rats: improvement by orotic acid.

The effect of methylglucamine orotate (MGO) on learning and memory was investigated in 24-month-old rats using brightness discrimination in a Y-chamber and active avoidance in a shuttle box. In both learning procedures, an improvement of memory retention following 5-day MGO treatment (225 mg/kg per day) was observed. The retention of untreated old animals was significantly lower compared to 8-week-old rats. MGO treatment resulted in a significant improvement of retention in old rats, which nearly compensated for their memory deficit.

Acquisition of brightness discrimination in the rat is impaired by opiates with psychotomimetic properties

The acquisition of shock avoidance behavior by rats was studied in an automated Y-maze which incorporates a simultaneous brightness discrimination paradigm. When administered prior to each of 5 consecutive daily sessions, two opiate derivatives with psychotomimetic properties, cyclazocine and N-allylnormetazocine, impaired the acquisition of brightness discrimination at doses which also increased movements between trials. These effects were similar to those produced by phencyclidine, ketamine, and a high dose of d-amphetamine. Pretreatment with morphine, pentazocine and scopolamine at motor stimulant doses before each training session did not affect acquisition of brightness discrimination. Nalorphine, naltrexone, and chlorpromazine also had no effect on brightness discrimination, even at motor depressant doses. Whereas the motor stimulation produced by morphine or pentazocine was blocked by naltrexone, the motor stimulation and discrimination disruption produced by cyclazocine or N-allylnormetazocine were only incompletely antagonized by naltrexone. The results demonstrate similarities between psychotomimetic opiates and phencyclidine-like compounds and may reflect the sensory or cognitive disturbance produced by these drugs in man.

Intact selective attention in rats with lesions of the dorsal noradrenergic bundle.

Mason's hypothesis (1980) was tested that lesions of the dorsal noradrenergic bundle (DNB), which induce depletion of forebrain noradrenaline, alter performance of discrimination tasks because they retard habituation to naturally attractive, but instrumentally irrelevant, stimuli. In Experiment 1, groups of rats with either vehicle or 6-hydroxydopamine injections into the DNB were assigned to five different discrimination tasks in a cross-maze with black and white goal arms. The tasks were acquisition and reversal of position, visual, or turn discrimination, and acquisition of visual or turn discrimination followed by a shift to the alternative discrimination. In spite of evidence that the rats preferred to attend more to the visual stimuli of the goal arms than to directions of turns, lesions of the DNB did not impair acquisition and reversal of turn discrimination with visual stimuli irrelevant, and did not facilitate performance of turn-to-visual shift. In fact, the lesions did not alter performance of any tasks. In Experiment 2, control and noradrenaline-depleted rats were trained in a task of light-dark discrimination followed by shift to position discrimination in a Y-maze. At the onset of training, the rats of both groups reliably avoided the bright goal arm and responded to the dark goal arm, thus demonstrating predominant attention for the relevant brightness stimuli rather than the irrelevant position stimuli. The DNB lesions impaired acquisition of brightness discrimination only when the positive stimulus was the illuminated goal arm, and they did not alter shift performance. These results do not support the hypothesis at test. On the other hand, they indicate that DNB lesions in the rat can impair habituation of light avoidance.

A comparison of lateral peristriate and striate neocortical ablations in the rat

The effects of striate, lateral peristriate and sham ablations upon the postoperative reacquisition of visual discriminations were studied in two experiments. The results of Experiment 1 indicated that lesions restricted to the lateral peristriate neocortex rendered the rat incapable of resolving an oblique stripe discrimination. Seven of the 9 rats with striate ablations were unable to form the discrimination. The histological findings indicated that the deficit following lateral peristriate injury was not due to interruption of the geniculostriate system. However, the behavioral impairment in destriate rats corresponded to the degree of unintentional injury in lateral peristriate neocortex, but not medial peristriate tissue. In Experiment 2, the effects of these lesions were studied upon the postoperative reacquisition of either a non-reversal or reversal of a preoperatively acquired brightness discrimination. Animals with striate damage demonstrated considerable savings on the non-reversed brightness discrimination, and they acquired the reversal at a rate equal to that seen in animals with sham ablations. Rats with peristriate ablations showed no savings on the non-reversed brightness habit, and they required more extensive training than both the striate and sham groups on the reversal. These findings suggest that the frequently reported loss of a preoperative brightness habit following large posterior neocortex ablations is due to damage in the lateral peristriate neocortex rather than damage of the geniculostriate system. These results, taken with other literature, suggest an important role of the lateral peristriate neocortex in visuospatial sensory function.

Apomorphine and glycoprotein synthesis during consolidation

The dopamine agonist, apomorphine, was injected intrahippocampally immediately after acquisition of a brightness discrimination task, which was motivated by footshock in rats. This led to an increase in the incorporation of L-fucose into total proteins which were measured in the hippocampus 7–9 hours later. In behavioral experiments, the same application improved the retention of a learned task. A possible linkage between increased glycoprotein synthesis and improvement of the retention of a new learned behavior due to the action of apomorphine is discussed.