Motor Sequence Learning in the Brain: The Long and Short of It.

Motor sequence learning involves predictive processing that results in the anticipation of each component of a sequence of actions. In smooth pursuit, this predictive processing is required to decrease tracking errors between the eye and the stimulus. Current models for motor sequence learning suggest parallel mechanisms in the brain for acquiring sequences of differing complexity. We examined this model by comparing shorter versus longer sequences of pursuit eye movements during fMRI. In this way we were able to identify overlapping and distinct brain areas involved in simple versus more complex oculomotor learning. Participants revealed predictive pursuit eye movements from the second presentation of the stimulus in both short and long sequences. Brain imaging results indicated activation of parallel brain areas for the different sequence lengths that consisted of the Inferior Occipital Gyrus and the Cingulate as areas in common. In addition, distinct activation was found in more working memory related brain regions for the shorter sequences (e.g. the middle frontal cortex and dorsolateral prefrontal cortex), and higher activation in the frontal eye fields, supplementary motor cortex and motor cortex for the longer sequences, independent on the number of repetitions. These findings provide new evidence that there are parallel brain areas that involve working memory circuitry for short sequences, and more motoric areas when the sequence is longer and more cognitively demanding. Additionally, our findings are the first to show that the parallel brain regions involved in sequence learning in pursuit are independent of the number of repetitions, but contingent on sequence complexity.

Identifying the causal mechanisms of the quiet eye.

Scientists who have examined the gaze strategies employed by athletes have determined that longer quiet eye (QE) durations (QED) are characteristic of skilled compared to less-skilled performers. However, the cognitive mechanisms of the QE and, specifically, how the QED affects performance are not yet fully understood. We review research that has examined the functional mechanism underlying QE and discuss the neural networks that may be involved. We also highlight the limitations surrounding QE measurement and its definition and propose future research directions to address these shortcomings. Investigations into the behavioural and neural mechanisms of QE will aid the understanding of the perceptual and cognitive processes underlying expert performance and the factors that change as expertise develops.

The contribution of the right supra-marginal gyrus to sequence learning in eye movements.

We investigated the role of the human right Supra-Marginal Gyrus (SMG) in the generation of learned eye movement sequences. Using MRI-guided transcranial magnetic stimulation (TMS) we disrupted neural activity in the SMG whilst human observers performed saccadic eye movements to multiple presentations of either predictable or random target sequences. For the predictable sequences we observed shorter saccadic latencies from the second presentation of the sequence. However, these anticipatory improvements in performance were significantly reduced when TMS was delivered to the right SMG during the inter-trial retention periods. No deficits were induced when TMS was delivered concurrently with the onset of the target visual stimuli. For the random version of the task, neither delivery of TMS to the SMG during the inter-trial period nor during the presentation of the target visual stimuli produced any deficit in performance that was significantly different from the no-TMS or control conditions. These findings demonstrate that neural activity within the right SMG is causally linked to the ability to perform short latency predictive saccades resulting from sequence learning. We conclude that neural activity in rSMG constitutes an instruction set with spatial and temporal directives that are retained and subsequently released for predictive motor planning and responses.

The brain uses efference copy information to optimise spatial memory.

Does a motor response to a target improve the subsequent recall of the target position or can we simply use peripheral position information to guide an accurate response? We suggest that a motor plan of the hand can be enhanced with actual motor and efference copy feedback (GoGo trials), which is absent in the passive observation of a stimulus (NoGo trials). To investigate this effect during eye and hand coordination movements, we presented stimuli in two formats (memory guided or visually guided) under three modality conditions (eyes only, hands only (with eyes fixated), or eyes and hand together). We found that during coordinated movements, both the eye and hand response times were facilitated when efference feedback of the movement was provided. Furthermore, both eye and hand movements to remembered locations were significantly more accurate in the GoGo than in the NoGo trial types. These results reveal that an efference copy of a motor plan enhances memory for a location that is not only observed in eye movements, but also translated downstream into a hand movement. These results have significant implications on how we plan, code and guide behavioural responses, and how we can optimise accuracy and timing to a given target.

Fragmentation of carbohydrate anomeric alkoxy radicals. synthesis of polyhydroxy piperidines and pyrrolidines related to carbohydrates.

Imino sugars of the piperidine and pyrrolidine types can be specifically obtained when protected 5-amino-5-deoxyfuranopentoses, 5-amino-5-deoxyfuranohexoses, 6-amino-6-deoxyfuranohexoses, and 6-amino-6-deoxypyranohexoses undergo a tandem alkoxy radical beta-fragmentation-intramolecular cyclization reaction. The reaction is promoted by the system: iodosylbenzene-iodine under mild conditions. The tert-butoxycarbonyl, benzyloxycarbonyl, and diphenylphosphinoyl radicals have been studied as amino-protecting groups. Using this methodology, polyhydroxylated pyrrolidines of the D-erythrofuranoses 34 and 35, D-threofuranose 36, L-xylofuranose 42, and D-arabinofuranose 43 series and polyhydroxylated piperidines of the D-arabinopyranose type 37 and 38 were obtained.

Leptin concentrations do not predict weight gain: the Mexico City Diabetes Study.

BACKGROUND: Leptin, a hormone which is produced by adipose tissue, has been shown to inhibit food intake and increase energy expenditure. In humans, leptin levels are correlated with body fat. In addition, leptin levels decline in subjects who lose weight. Yet few data exist on whether leptin levels predict weight change, except for a recent report suggesting that low leptin levels predict weight gain in very obese middle-aged Pima Indians. METHODS: We have examined the association between baseline leptin levels and subsequent weight gain over 3.25 y in 180 non-diabetic participants in the Mexico City Diabetes Study. RESULTS: At baseline, the correlation between leptin levels and body mass index (BMI) was 0.712 in men and 0.691 in women (both P < 0.001). Subjects were matched on age (+/- 2 y), gender and BMI (+/- 2 kg/m2) at baseline. Baseline BMI was 25.3 kg/m2 in men and 27.2 kg/m2 in women. Baseline leptin levels (ng/ml) did not predict weight gain in either men (weight gainers: 4.3; weight stable: 5.8; and weight losers: 5.2) or women (weight gainers: 17.4; weight stable: 17.7; and weight losers: 17.4). CONCLUSIONS: We conclude that baseline leptin levels did not predict weight change in moderately obese individuals.

A note on the isolation of psychrotrophic coliform organisms from faecal-polluted environments.

The Simmons citrate salicin (SCS) medium was developed for the enrichment and isolation of presumptive psychrotrophic coliforms from polluted environments. The selectivity and resolution of the medium were tested with pure and mixed laboratory cultures. A procedure for the isolation of psychrotrophic coliforms from polluted environments using a lactose-bile broth and SCS medium is presented.

[Isolated ventricular inversion associated with complete atrioventricular septal defect with total anomalous pulmonary venous drainage]. / Inversión ventricular aislada asociada a defecto completo del septo atrioventricular con drenaje venoso pulmonar anómalo total.

Based upon the description of the clinico-pathological characteristic of a case with isolated ventricular inversion plus other cardiac malformations, the clinical, diagnostic and embryo-pathological implications of this entity are reviewed.

Seasonal variations of pollution indicators in a wildfowl reserve (Doñana National Park, Spain).

Pollution indicators in Doñana National Park show a cyclic seasonal pattern with maximum level in the autumn and minimum in the spring. While faecal streptococci proved to be the best indicator micro-organisms in this type of salty, alkaline environment, total coliforms gave an overestimation of pollution because of the presence of hydroteluric coliforms.