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PubMed2000

HMO penetration and the geographic mobility of practicing physicians.

In this study, we assessed the influence of changes in health maintenance organization (HMO) penetration on the probability that established patient care physicians relocated their practices or left patient care altogether. For physicians who relocated their practices, we also assessed the impact of HMO penetration on their destination choices. We found that larger increases in HMO penetration decreased the probability that medical/surgical specialists in early career stayed in patient care in the same market, but had no impact on generalists, hospital-based specialists, or mid career medical/surgical specialists. We also found that physicians who relocated their practices were much more likely to choose destination markets with the same level of HMO penetration or lower HMO penetration compared with their origin markets than they were to choose destination markets with higher HMO penetration. The largely negligible impact of changes in HMO penetration on established physicians' decisions to relocate their practices or leave patient care is consistent with high relocation and switching costs. Relocating physicians' attraction to destination markets with the same level of HMO penetration as their origin markets suggests that, while physicians' styles of medical practice may adapt to changes in market conditions, learning new practice styles is costly.

Career Mobility↗
PubMed2000

Maternal corticosterone during lactation permanently affects brain corticosteroid receptors, stress response and behaviour in rat progeny.

The long-term consequences of a physiological-range increase of maternal corticosterone during lactation were investigated on the 15-month-old progeny. The offspring of rats drinking water supplemented with corticosterone (200 microgram/ml of corticosterone hemisuccinate) from day 1 postpartum to weaning exhibited: (i) better performance in a conditioned learning test; (ii) reduction of fearfulness in two conflict situations; (iii) lower stress-induced corticosterone secretion and (iv) higher number of corticosteroid receptors in the hippocampus. The results of this study show that the effects of maternal physiological-range hypercorticosteronemia during lactation are lifelong. Moreover, these data suggest that corticosteroids, secreted during neonatal life, may constitute a factor directing the neurobiological development of the infant. In line with this hypothesis, glucocorticoid-induced early events have consequences on the behavioral and physiological status of adulthood. These consequences may be either "beneficial" or "detrimental" depending on the plasma levels of corticosterone induced by the early life occurrences, as well as on the kind of the stimulus and the developmental stage at which the neonate experiences the event. The present study demonstrates that, when the increase of corticosterone in infancy is moderate, the adult rats show reduced anxiety, improved learning and a better coping strategy to deal with stressful situations.

Analysis of Variance↗
PubMed2002

Judging meaning improves function in the aging brain.

Important new evidence suggests that under-recruitment of frontal cortex under intentional learning conditions in older adults can be repaired when older subjects are instructed to focus on meaning. However, the tendency for older subjects to activate both hemispheres when young adults recruit only one was not reversible. These findings provide important insights with respect to plasticity and compensation in the aging brain.

Journal Article↗
PubMed1995

Neuropsychological evidence for frontostriatal dysfunction in schizophrenia.

Schizophrenics and controls were compared on a computerized test of attentional set-shifting which provides a componential analysis of the Wisconsin Card Sort Test and has previously been shown to be sensitive to frontal lobe dysfunction and Parkinson's disease. The main test was of extra-dimensional shifting where subjects are required to shift response to an alternative perceptual dimension. In one condition, termed 'perseveration', subjects are required to shift to a novel dimension and ignore the previously relevant one. In the other condition, termed 'learned irrelevance', subjects are required to shift to the previously irrelevant dimension and ignore a novel one. Chronic medicated schizophrenics (N = 32) show a highly significant impairment on the perseveration but not the learned irrelevance condition, as compared to normal age and IQ matched controls (N = 24). This was true even of a subgroup of patients with preserved IQ. The impairments in attentional set-shifting failed to correlate with patients' scores on the Mini-Mental State Examination (mean; S.D. 26.8; 1.8) or with scores on a test of recognition memory. These results provide evidence for a specific deficit in a set-shifting test of executive function and support a hypothesis of frontostriatal dysfunction in schizophrenia.

Adult↗
PubMed1990

The role of parental input in the development of a morphological system.

In order to isolate the properties of language whose development can withstand wide variations in learning conditions, we have observed children who have not had access to any conventional linguistic input but who have otherwise experienced normal social environments. The children we study are deaf with hearing losses so severe that they cannot naturally acquire spoken language, and whose hearing parents have chosen not to expose them to a sign language. In previous work, we demonstrated that, despite their lack of conventional linguistic input, the children developed spontaneous gesture systems which were structured at the level of the sentence, with regularities identifiable ACROSS gestures in a sentence, akin to syntactic structure. The present study was undertaken to determine whether one of these deaf children's gesture systems was structured at a second level, the level of the gesture-that is, were there regularities WITHIN a gesture, akin to morphologic structure? We have found that (1) the deaf child's gestures could be characterized by a paradigm of handshape and motion combinations which formed a matrix for virtually all of his spontaneous gestures, and (2) the deaf child's gesture system was considerably more complex than the model provided by his hearing mother. These data emphasize the child's contribution to structural regularity at the intra-word level, and suggest that such structure is a resilient property of language.

Child, Preschool↗
PubMed1997

Direct and indirect stimulus-frequency effects in recognition.

Subsequent recognition of stimuli perceived in a given situation was studied in relation to stimulus familiarity as determined by frequency in observers' prior experience. To distinguish direct and indirect frequency effects, on the basis of selective memory retrieval and selective attention during learning, respectively, rigorous controls were imposed on stimulus rehearsability and learning conditions. As predicted by a global memory model, both hits and false alarms on recognition tests increased as a function of prior frequency in a concordant pattern that indicates a direct effect, in contrast with the usual indirect effect of varying normative word frequency. Understanding the role of experiential stimulus frequency in recognition may further the interpretation of research in such paradigms as eyewitness testimony.

Adult↗
PubMed1991

Fimbria-fornix transections disrupt the ontogeny of delayed alternation but not position discrimination in the rat.

In Experiment 1, Long-Evans rat pups received fimbria-fornix transections or sham surgery on Postnatal Day 10 (PND10) and were then trained on PND23 to perform either a discrete-trials delayed alternation (DA) or a simple position discrimination (PD) task in a T maze. Rat pups in both surgical conditions learned the PD task within five 12-trial blocks of training. However, only sham-operated pups learned the DA task. In Experiment 2, performance of DA emerged between PND19 and PND27 in sham-operated pups but failed entirely to develop in pups with early lesions. In Experiment 3, fornix-transected pups that were given extended DA training (132 trials) on PND23-PND24 showed some improvement in performance but remained impaired in relation to sham-operated controls. These findings implicate the limbic system in the postnatal development of DA but not PD and suggest that dual-process theories of memory may be relevant to the psychobiology of cognitive development.

Animals↗
PubMed2005

Learning about sex: conditioning of partner preference: theoretical comment on Coria-Avila et Al. (2005).

Sexual partner preference in female rats has been difficult to establish experimentally because the vaginocervical stimulation the female receives during the preference test can be rewarding or aversive depending on the context. G. A. Coria-Avila, A. J. Ouimet, P. Pacheco, J. Manzo, and J. G. Pfaus (2005) reported that female rats can be conditioned to show partner preference for a male that is scented with a sexually neutral odor if they are mated repeatedly with that male in a paced mating test. These results suggest that establishment of a partner preference depends on rewarding characteristics of the vaginocervical stimulation the female receives during an initial mating and that selection of a sexual partner can be determined by olfactory stimuli associated with that stimulation. These results are discussed within the context of the appetitive-consummatory construct of sexual behavior and the evolutionary significance of conditioned partner preference.

Animals↗
PubMed1994

Memory for pictures and sounds: independence of auditory and visual codes.

Three experiments examined the mnemonic independence of auditory and visual nonverbal stimuli in free recall. Stimulus lists consisted of (1) pictures, (2) the corresponding environmental sounds, or (3) picture-sound pairs. In Experiment 1, free recall was tested under three learning conditions: standard intentional, intentional with a rehearsal-inhibiting distracter task, or incidental with the distracter task. In all three groups, recall was best for the picture-sound items. In addition, recall for the picture-sound stimuli appeared to be additive relative to pictures or sounds alone when the distracter task was used. Experiment 2 included two additional groups: In one, two copies of the same picture were shown simultaneously; in the other, two different pictures of the same concept were shown. There was no difference in recall among any of the picture groups; in contrast, recall in the picture-sound condition was greater than recall in either single-modality condition. However, doubling the exposure time in a third experiment resulted in additively higher recall for repeated pictures with different exemplars than ones with identical exemplars. The results are discussed in terms of dual coding theory and alternative conceptions of the memory trace.

Auditory Perception↗
PubMed2003

Tumour-cell invasion and migration: diversity and escape mechanisms.

Cancer cells possess a broad spectrum of migration and invasion mechanisms. These include both individual and collective cell-migration strategies. Cancer therapeutics that are designed to target adhesion receptors or proteases have not proven to be effective in slowing tumour progression in clinical trials--this might be due to the fact that cancer cells can modify their migration mechanisms in response to different conditions. Learning more about the cellular and molecular basis of these different migration/invasion programmes will help us to understand how cancer cells disseminate and lead to new treatment strategies.

Animals↗
PubMed1998

Functional anatomy of musical processing in listeners with absolute pitch and relative pitch.

We used both structural and functional brain imaging techniques to investigate the neural basis of absolute pitch (AP), a specialized skill present in some musicians. By using positron emission tomography, we measured cerebral blood flow during the presentation of musical tones to AP possessors and to control musicians without AP. Listening to musical tones resulted in similar patterns of increased cerebral blood flow in auditory cortical areas in both groups, as expected. The AP group also demonstrated activation of the left posterior dorsolateral frontal cortex, an area thought to be related to learning conditional associations. However, a similar pattern of left dorsolateral frontal activity was also observed in non-AP subjects when they made relative pitch judgments of intervals, such as minor or major. Conversely, activity within the right inferior frontal cortex was observed in control but not in AP subjects during the interval-judgment task, suggesting that AP possessors need not access working memory mechanisms in this task. MRI measures of cortical volume indicated a larger left planum temporale in the AP group, which correlated with performance on an pitch-naming task. Our findings suggest that AP may not be associated with a unique pattern of cerebral activity but rather may depend on the recruitment of a specialized network involved in the retrieval and manipulation of verbal-tonal associations.

Adult↗
PubMed1978

Intrinsic feedback, interpolation, and the closed-loop theory.

The amount of experience of a target location, or its surrounding locations, was manipulated to test Adams' (1971) prediction that the perceptual trace (stored perception of the correct response) is based on repeated sensations of the correct response. Sixteen learning trials, each followed by knowledge of results, on a linear-positioning task were permitted for all subjects. Each learning trial required movement to an adjustable physical stop. In learning condition without target experience, movements never terminated in a zone within which the target was interpolated. Other groups experienced movements terminating at the target point. The strength of the perceptual trace was inferred from the ability to move to the target during 20 test trials with the stop removed and without knowledge of the results. Slow movements could be made to a novel location equally as well as to a repeatedly practiced location.

Journal Article↗
PubMed1986

Development of the motor memory trace and control program.

A theoretical explanation of the development of the memory trace constrained to fit into a computer analog requires a coded reference "image" of the intended motor act, a tentative control program (memory trace) based on mobilizing and coordinating various pre-established motor-control subroutines, and an afferent neural description of the act as actually performed. The afferent information is non-consciously compared with the reference image, and the resulting discrepancy used to modify the control program so as to reproduce the reference image more exactly on the next attempt. The discrepancy consists of the sum of two types of differences, between image and program (present during learning) and the error difference between program and performance. The trial-by-trial discrepancies cumulate in the memory trace, so that during both learning and postlearning practice the error component results in a within-individual odd-even trial correlation. This constitutes a mechanism for a remoteness effect in the inter-trial correlation matrix generated in a group of individuals during post-learning as well as learning conditions. Fifty-one individuals performed 50 trials on a simple arm movement task; 35 of these (the learners) showed individual systematic improvement during the first 20 trials but no improvement during the last 24; 16 (the non-learners) failed to improve with practice. Separate correlational analyses (both within- and inter-individual) of the two groups resulted in a variety of patterns that were predicted a priori in the learners by the theory, as did the 49 learners of another sample of 51 who performed a more complicated arm movement task. Also, as predicted, the non-learners failed to produce organized correlation patterns.

Journal Article↗
PubMed2006

Important components of a short-term family group programme. From the Danish National Multicenter Schizophrenia Project.

Clinicians from three psychiatric departments have established family groups as a specific intervention for the relatives of patients with first-episode psychosis. The intervention manual is combining the psychoeducational model with psychodynamic understanding and principles. The aim of this study was to identify the special elements of the programme that were the most important to the relatives. A questionnaire was developed for the participants of the groups in order to establish their satisfaction concerning 1) The actual knowledge received; 2) improvement in ability to cooperate with the therapeutic system and other public institutions; 3) the possibility of sharing thoughts, feelings and problems; and 4) dealing with feelings of guilt and shame and the possibility of altering the relationship with the mentally ill relative. Thirty-five relatives of 26 patients filled in the questionnaire consisting of 15 specific items. More than 95% of the relatives appreciated the gained knowledge about schizophrenia as well as the possibility of sharing thoughts and feelings with others. Two specific elements had the highest rating as important factors for the learning condition: 1) to listen to others with similar problems and 2) the group leaders' attitude towards patients and relatives.

Adult↗
PubMed1988

'Frontal' cognitive function in patients with Parkinson's disease 'on' and 'off' levodopa.

A wide range of cognitive impairments can be observed in patients with Parkinson's disease. A close parallel exists between these deficits and those found following damage to prefrontal cortex. Anatomical evidence is reviewed which reveals a complex pattern of neuronal circuits connecting the frontal cortex and basal ganglia. All these circuits are in some way dependent upon dopamine, suggesting that changes in the levels of dopamine stimulation may alter performance on 'frontal' tests. To test this hypothesis, a group of patients with Parkinson's disease were assessed both on and off levodopa treatment, on a range of tests selected from the human and animal experimental literature as being sensitive to disruption of prefrontal cortex. A variable pattern of results was obtained. On one test, a measure of verbal fluency, patients were impaired, compared with normal controls, only when off levodopa. On two measures, associative conditional learning and subject-ordered pointing, patients were impaired only when on levodopa, while on the final measures, the Wisconsin Card Sorting Test, patients were impaired both on and off levodopa. Two mechanisms are discussed to explain these results, one based on the effects of dopamine depletion, and the other based on the adverse effects of dopamine overstimulation. The results suggest that different areas of prefrontal cortex are involved in the tasks employed, and that functional levels of dopamine in separate areas of cortex and caudate may differ crucially in Parkinson's disease.

Aged↗