Temporal context and conditional associative learning

<p>Abstract</p> <p>Background</p> <p>We investigated how temporal context affects the learning of arbitrary visuo-motor associations. Human observers viewed highly distinguishable, fractal objects and learned to choose for each object the one motor response (of four) that was rewarded. Some objects were consistently preceded by specific other objects, while other objects lacked this task-irrelevant but predictive context.</p> <p>Results</p> <p>The results of five experiments showed that predictive context consistently and significantly accelerated associative learning. A simple model of reinforcement learning, in which three successive objects informed response selection, reproduced our behavioral results.</p> <p>Conclusions</p> <p>Our results imply that not just the representation of a current event, but also the representations of past events, are reinforced during conditional associative learning. In addition, these findings are broadly consistent with the prediction of attractor network models of associative learning and their prophecy of a persistent representation of past objects.</p

Hypoxia and hypoxia inducible factor-1α are required for normal endometrial repair during menstruation

About a quarter of pre-menopausal women will suffer from heavy menstrual bleeding in their lives. Here, Maybin and colleagues show hypoxia and subsequent activation of HIF-1α during menses are required for normal endometrial repair, and identify pharmacological stabilisation of HIF-1α as a potential therapeutic strategy for this debilitating condition

Motor Skill Learning, Retention, and Control Deficits in Parkinson's Disease

Parkinson's disease, which affects the basal ganglia, is known to lead to various impairments of motor control. Since the basal ganglia have also been shown to be involved in learning processes, motor learning has frequently been investigated in this group of patients. However, results are still inconsistent, mainly due to skill levels and time scales of testing. To bridge across the time scale problem, the present study examined de novo skill learning over a long series of practice sessions that comprised early and late learning stages as well as retention. 19 non-demented, medicated, mild to moderate patients with Parkinson's disease and 19 healthy age and gender matched participants practiced a novel throwing task over five days in a virtual environment where timing of release was a critical element. Six patients and seven control participants came to an additional long-term retention testing after seven to nine months. Changes in task performance were analyzed by a method that differentiates between three components of motor learning prominent in different stages of learning: Tolerance, Noise and Covariation. In addition, kinematic analysis related the influence of skill levels as affected by the specific motor control deficits in Parkinson patients to the process of learning. As a result, patients showed similar learning in early and late stages compared to the control subjects. Differences occurred in short-term retention tests; patients' performance constantly decreased after breaks arising from poorer release timing. However, patients were able to overcome the initial timing problems within the course of each practice session and could further improve their throwing performance. Thus, results demonstrate the intact ability to learn a novel motor skill in non-demented, medicated patients with Parkinson's disease and indicate confounding effects of motor control deficits on retention performance

fMRI Supports the Sensorimotor Theory of Motor Resonance

The neural mechanisms mediating the activation of the motor system during action observation, also known as motor resonance, are of major interest to the field of motor control. It has been proposed that motor resonance develops in infants through Hebbian plasticity of pathways connecting sensory and motor regions that fire simultaneously during imitation or self movement observation. A fundamental problem when testing this theory in adults is that most experimental paradigms involve actions that have been overpracticed throughout life. Here, we directly tested the sensorimotor theory of motor resonance by creating new visuomotor representations using abstract stimuli (motor symbols) and identifying the neural networks recruited through fMRI. We predicted that the network recruited during action observation and execution would overlap with that recruited during observation of new motor symbols. Our results indicate that a network consisting of premotor and posterior parietal cortex, the supplementary motor area, the inferior frontal gyrus and cerebellum was activated both by new motor symbols and by direct observation of the corresponding action. This tight spatial overlap underscores the importance of sensorimotor learning for motor resonance and further indicates that the physical characteristics of the perceived stimulus are irrelevant to the evoked response in the observer

Automated operant assessments of Huntington's Disease mouse models

Huntington’s disease (HD) presents clinically with a triad of motor, cognitive, and psychiatric symptoms. Cognitive symptoms often occur early within the disease progression, prior to the onset of motor symptoms, and they are significantly burdensome to people who are affected by HD. In order to determine the suitability of mouse models of HD in recapitulating the human condition, these models must be behaviorally tested and characterized. Operant behavioral testing offers an automated and objective method of behaviorally profiling motor, cognitive, and psychiatric dysfunction in HD mice. Furthermore, operant testing can also be employed to determine any behavioral changes observed after any associated interventions or experimental therapeutics. We here present an overview of the most commonly used operant behavioral tests to dissociate motor, cognitive, and psychiatric aspects of mouse models of HD

The effect of systemic d-amphetamine on motor versus motivational processes in the rat

This study examined the effects of systemic amphetamine in rats performing a reaction time task in which motivation and motor readiness were independently varied. Visual cues indicated the number of trials (one, two or three) needed before reinforcement was made available (i.e., reward cost). Lower reward cost was reflected in both a greater proportion of correctly completed trials and faster reaction times. Reaction times were also shorter as a function of increasing time from start of trial to the onset of the imperative stimulus (foreperiod), reflecting motor readiness or temporal probability summation. It was found that increasing dose of amphetamine resulted in faster reaction times, but the manner in which reaction time was speeded more closely resembled that of motor readiness than it did the speeding due to increasing motivation. Furthermore, the effects on performance of amphetamine and motivational condition were found to be entirely independent: there was no evidence to suggest that amphetamine enhanced, or disrupted, the expectation of forthcoming work or the response vigor which this engenders. It is concluded that systemic amphetamine does not act simply to amplify a natural reward signal. By contrast, amphetamine was found to enhance the effect of foreperiod, suggestive of a mechanism for the psychomotor stimulating effects of amphetamine.</p

The effect of excitotoxic lesions of the pedunculopontine tegmental nucleus in rats: an examination of the perception of reward strength measured by responding on a progressive ratio schedule of reinforcement.

The pedunculopontine tegmental nucleus has connections with sites in both dorsal and ventral striatum, and a number of studies have suggested that it has a role in reward-related behaviour. The present experiment aimed to investigate the perception of reward in pedunculopontine tegmental nucleus-lesioned rats responding for food under a progressive ratio schedule, which measures willingness to work for a given reward. Rats were trained on a progressive ratio-5 schedule for food reward, then given ibotenic acid or sham lesions of the pedunculopontine tegmental nucleus. Their performance under this schedule was examined again following recovery from surgery.Compared with sham-lesioned rats, those with lesions of the pedunculopontine tegmental nucleus showed significantly reduced breaking points and significantly longer post-reinforcement pauses. However, there was no difference between the groups in their latency to collect food pellets once earned, suggesting that pedunculopontine tegmental nucleus excitotoxin and sham-lesioned rats were equally motivated by the presence of food. Excitotoxin-lesioned rats made significantly more responses on the control lever and more entries to the food hopper as progressive ratio increment increased, but did not differ from controls when the schedule requirement was low. These results are interpreted as indicating no global loss of motivation, since lesioned rats performed normally at low schedule requirements, and were as fast as controls to collect pellets. But as the schedule requirement increased, excitotoxin-lesioned rats showed reductions in responding on the active lever (that is, a reduction in breaking point) and an increase in inappropriate responses towards the food hopper and the control lever.We consider these data to indicate that the behavioural deficits in pedunculopontine-lesioned rats arise not from a sensory or hedonic change, but from alteration in the control of motor output. (C) 2002 IBRO. Published by Elsevier Science Ltd. All rights reserved.</p