Neuronal activity in primate dorsolateral and orbital prefrontal cortex during performance of a reward preference task

An important function of the prefrontal cortex (PFC) is the control of goal-directed behaviour. This requires information as to whether actions were successful in obtaining desired outcomes such as rewards. While lesion studies implicate a particular PFC region, the orbitofrontal cortex (OFC), in reward processing, neurons encoding reward have been reported in both the OFC and the dorsolateral prefrontal cortex (DLPFC). To compare and contrast their roles, we recorded simultaneously from both areas while two rhesus monkeys (Macaca mulatta) performed a reward preference task. The monkeys had to choose between pictures associated with different amounts of a juice reward. Neuronal activity in both areas reflected the reward amount. However, neurons in the DLPFC encoded both the reward amount and the monkeys' forthcoming response, while neurons in the OFC more often encoded the reward amount alone. Further, reward selectivity arose more rapidly in the OFC than the DLPFC. These results are consistent with reward information entering the PFC via the OFC, where it is passed to the DLPFC and used to control behaviour.     

Synchrony dynamics in monkey V1 predict success in visual detection

Behavioral measures such as expectancy and attention have been associated with the strength of synchronous neural activity. On this basis, it is hypothesized that synchronous activity affects our ability to detect and recognize visual objects. To investigate the role of synchronous activity in visual perception, we studied the magnitude and precision of correlated activity, before and after stimulus presentation within the visual cortex (V1), in relation to a monkey's performance in a figure-ground discrimination task. We show that during the period of stimulus presentation a transition in synchronized activity occurs that is characterized by a reduction of the correlation peak height and width. Before stimulus onset, broad peak correlations are observed that change towards thin peak correlations after stimulus onset, due to a specific decrease of low-frequency components. The magnitude of the transition in correlated activity is larger, i.e. a stronger desynchronization occurs, when the animal perceives the stimulus correctly than when the animal fails to detect the stimulus. These results therefore show that a transition in synchronous firing is important for the detection of sensory stimuli. We hypothesize that the transition in synchrony reflects a change from loose and global neuronal interactions towards a finer temporal and spatial scale of neuronal interactions, and that such a change in neuronal interactions is required for figure-ground discrimination.     

Organization of Working Memory Processes in Monkeys: The Effects of a Dopamine Receptor Agonist

The effects of the dopamine receptor agonist agroclavin on cognitive processes associated with mechanisms of visual recognition and long-term and working (short-term) memory were studied in delayed visual differentiation and delayed spatial selection tasks in monkeys (rhesus macaques). Measurements made before and after p.o. pharmacological treatment with this agent were used to identify the p.o. dose (5 mg/kg) inducing a significant effect. The psychotropic effect of agroclavin, which induced cognitive dysfunction, was present in all the monkeys studied to one extent or another. Behavioral criteria were: the probability of correct solutions of the visual differentiation task, the probability of refusals to resolve the task, and the time taken for correct motor responses. Despite individual differences in these behavioral characteristics in monkeys, significant changes due to agroclavin were consistently evident in all animals. There was a reduction in the probability of correct solutions, due to worsening of the characteristics of short-term memory; most monkeys showed increases in the numbers of refusals to solve tasks and increases in the time for correct motor responses during these solutions. In fact, all monkeys showed no increases in the number of erroneous solutions in visual differentiation and spatial selection tasks without delays, though in most cases there were increases in the time taken for correct motor reactions and the number of refusals to solve tasks. Data were obtained indicating that the effect of agroclavin was not uniform with respect to different types of visual information. The possible structural-functional organization of processes underlying working memory is discussed on the basis of the conclusion that the behavioral characteristics studied here reflect different components of cognitive processes realized by structures with different functional properties and different locations.     

Sexual behavior in old male rhesus monkeys: Influence of familiarity and age of female partners

Old male rhesus monkeys (Macaca mulatta)whose sexual behavior had declined over a 10-year period were studied. The same ovariectomized females, comparable in age to the males (about 20 years old), served as sexual partners during the 10 years. In the first experiment the old males were paired with unfamiliar females to determine whether changing sexual partners would reverse the decline in performance that had been observed. The unfamiliar females, also about the same age as the males, were ovariectomized and treated with estradiol before pairing, as were the familiar females. Although the males contacted the unfamiliar females more often than they contacted the familiar females, there were no other differences in sexual activity. The two groups of females did not differ in their behavior toward the males. The low level of sexual performance by the males with both familiar and unfamiliar females could have been the result of decreased sexual initiative and responsiveness associated with the advanced age of the females, so a second experiment was undertaken to test this possibility. The old males were paired with two different groups of unfamiliar, intact, cycling females. One group was young (about 4 years old), the other old (about 20 years). The sexual responses of the males to both young and old females were the same. The two groups of females did not differ in their behavior toward the males.     

REGULATION OF BLOOD GLUCOSE IN PRETERM MONKEYS

Preterm rhesus monkeys who become hyperglycemic in response to a glucose infusion do so because they do not switch off endogenous glucose production.     

Postnatal maturation of the dopaminergic innervation of monkey prefrontal and motor cortices: A tyrosine hydroxylase immunohistochemical analysis

The mature functional architecture of the primate prefrontal cortex arises during a protracted period of postnatal development. Although catecholaminergic afferents arrive in the primate cortex quite early during fetal development, several lines of evidence suggest that substantial changes in the dopaminergic innervation of prefrontal cortex may occur during postnatal development. In this study, we used immunocytochemical techniques and antibodies against tyrosine hydroxylase, the rate-limiting enzyme in catecholamine biosynthesis, to examine the precise time course from birth to adulthood of the maturational changes of tyrosine hydroxylase-labeled axons in prefrontal cortical areas 9 and 46 and primary motor cortex (area 4) of rhesus monkeys. In area 9, the densities of tyrosine hydroxylase-labeled axons and varicosities in the superficial and deep cortical layers remained relatively constant during postnatal development. In contrast, marked developmental changes in innervation density occurred in the middle cortical layers. For example, in deep layer III, the density of tyrosine hydroxylase-positive varicosities was relatively low and uniform in animals under 1 month of age but then increased by a factor of three in animals 2–3 months of age. The density of labeled varicosities continued to increase, reaching a peak (sixfold greater than in the youngest animals) in aninuds 2–3 years of age before declining to stable adult levels. Similar laminar-specific patterns of change also occurred in areas 46 and 4, although regional differences were present in the magnitude and precise time course of these developmental changes. These findings demonstrate that the innervation of monkey frontal cortex by tyrosine hydroxylase-immunoreactive axons undergoes a protracted, laminar-specific pattern of change during postnatal development that continues through adolescence and into early adulthood. These developmental refinements may interact with other modifications of cortical circuitry that underlie the functional maturation of these regions. © 1995 Wiley-Liss, Inc.     

裂隙灯致视网膜损伤的眼底荧光血管造影观察

作者作国产裂隙灯对3只恒河猴双眼黄斑周围视网膜共36个部位进行随机持续光照,视网膜照度为226.8mW/cm~2。照射时间分别为30,45,60,90,105,120,150,180min。通过眼底镜,荧光血管造影对光照前及光照后即刻到2个月的视网膜变化进行观察。当持续光照达120min以上时出现视网膜损伤。光照后不同时间使视网膜损伤的眼底改变不同。作者提出,裂隙灯使用的相对安全时间阈值为98min,并提出多部位投照方法。     

Detection of fetal RhD sequence from peripheral blood of sensitized RhD-negative pregnant women

A sensitive PCR-based assay was developed to amplify fetal-derived rhesus D (RhD) sequence from peripheral blood of RhD-negative pregnant women with circulating anti-D. RhD-PCR positivity was detected in 7/22 samples from women bearing RhD-positive fetuses. despite the presence of varying levels of anti-D. Evidence is presented with suggests that rising matermal anti-D levels might reduced circulating fetal cell numbers. Further development of this assay may have implications in the clinical management of RhD-sensitized pregnancies and aid the understanding of the physiology of feto-maternal cell trafficking.     

Spatial patterns of visual cortical fast EEG during conditioned reflex in a rhesus monkey

A preliminary assay was made of the existence of time-space coherence patterns of fast EEG activity in the visual cortex of a Rhesus monkey. The primary intent of the present study was to evaluate the similarities and differences in relation to the olfactory bulb, where such coherences ave been described and have been demonstrated to be associated with behavior. Segments 1.5 s in duration were recorded simultaneously without averaging from 16 of 35 subdural electrodes fixed over the left occipital lobe in an array3.6cm× 2.8cm. Each segment was taken during the delivery of a visual conditioned stimulus (CS) and the performance of a conditioned response (CR) by a well-trained Rhesus monkey. The EEGs appeared chaotic with irregular bursts lasting 75–200 ms, resembling those in the olfactory EEG but with lower peak frequencies. Fourier spectra showed broad distributions of power resembling ‘ 1/fnoise’ with multiple peaks in the range of 20–40 Hz. Time intervals were selected where coherent activity seemed to be present at a number of electrodes. A dominant component waveform that was common to all channels was extracted by principal components analysis (PCA) of each segment. The distribution of the power of this component across the electrodes (the factor loadings) was used to describe the spatial pattern of the coherent cortical activity. Statistical analyses suggested that different patterns could be associated to the CS and the CR, as has been found in the olfactory system. These patterns remained stable over a 6 week recording interval. The patterns can be better discriminated, when the factor loadings of each channel are normalized to zero mean and unit variance, to discard a basic pattern of power distribution, which may reflect anatomical and electrode positioning factors that are related to behavioral information processing by the cortex. The wide spatial distribution of the common patterns found suggests that EEG patterns that manifest differing states of the visual cortex may also be accessible with scalp electrodes.     

Copulation,dominance, and plasma androgen levels in adult rhesus males born and reared in the laboratory

The subjects consisted of adult male rhesus macaques (N = 22) that had been born and reared in the laboratory and had failed to ejaculate in standardized tests of sexual behavior in adulthood. As infants they had been given regular but limited social experience, and as juveniles and adults they had been housed in individual cages. Saphenous vein blood (3 ml) was taken on each of 5 days; the plasma was removed and stored for later assay for testosterone (T) and dihydrotestosterone (DHT). The males were then released into a 1-acre outdoor enclosure with 8—14 adult females. Behavior was observed daily for 2 hr, and blood was taken from the males once a week for hormone assays. During the first 8 weeks, four males ejaculated, and they were removed from the enclosure. During the second 8 weeks, four additional males ejaculated, and they were also removed from the enclosure. The remaining 14 males were never observed to achieve intromission or to ejaculate during the 28 weeks in the enclosure, but 11 masturbated to ejaculation. There was no evidence that individuals with high plasma T levels were more sexually active or more dominant than males with lower T levels. Mean levels of plasma T were within the range observed in wild-born rhesus males, but the level of sexual performance was not. At the end of the 12th week, all of the females initially in the enclosure were removed and 13 different adult females were introduced. Three females became pregnant.This study is publication No. 1068 of the Oregon Regional Primate Research Center. This study was supported in part by Grant RR-00163 and HD-05969 from the National Institutes of Health, U.S. Public Health Service.