Parietofrontal network upregulation after motor stroke.

Objective: Motor recovery after stroke shows a high inter-subject variability. The brain's potential to form new connections determines individual levels of recovery of motor function. Most of our daily activities require visuomotor integration, which engages parietal areas. Compared to the frontal motor system, less is known about the parietal motor system's reconfiguration related to stroke recovery. Here, we tested if functional connectivity among parietal and frontal motor areas undergoes plastic changes after stroke and assessed the behavioral relevance for motor function after stroke. Methods: We investigated stroke lesion-induced changes in functional connectivity by measuring high-density electroencephalography (EEG) and assessing task-related changes in coherence during a visually guided grip task with the paretic hand in 30 chronic stroke patients with variable motor deficits and 19 healthy control subjects. Quantitative changes in task-related coherence in sensorimotor rhythms were compared to the residual motor deficit. Results: Parietofrontal coupling was significantly stronger in patients compared to controls. Whereas motor network coupling generally increased during the task in both groups, the task-related coherence between the parietal and primary motor cortex in the stroke lesioned hemisphere showed increased connectivity across a broad range of sensorimotor rhythms. Particularly the parietofrontal task-induced coupling pattern was significantly and positively related to residual impairment in the Nine-Hole Peg Test performance and grip force. Interpretation: These results demonstrate that parietofrontal motor system integration during visually guided movements is stronger in the stroke-lesioned brain. The correlation with the residual motor deficit could either indicate an unspecific marker of motor network damage or it might indicate that upregulated parietofrontal connectivity has some impact on post-stroke motor function.

The control of complex finger movements by directional information flow between mesial frontocentral areas and the primary motor cortex.

Complex movements require the interplay of local activation and interareal communication of sensorimotor brain regions. This is reflected in a decrease of task-related spectral power over the sensorimotor cortices and an increase in functional connectivity predominantly in the upper alpha band in the electroencephalogram (EEG). In the present study, directionality of information flow was investigated using EEG recordings to gain better understanding about the network architecture underlying the performance of complex sequential finger movements. This was assessed by means of Granger causality-derived directed transfer function (DTF). As DTF measures the influence one signal exerts on another based on a time lag between them, it allows implications to be drawn on causal relationships. To reveal causal connections between brain regions that are specifically modulated by task complexity, we contrasted the performance of right-handed sequential finger movements of different complexities (simple, scale, complex) that were either pre-learned (memorized) or novel instructed. A complexity-dependent increase in information flow from mesial frontocentral to the left motor cortex and, less pronounced, also to the right motor cortex specifically in the upper alpha range was found. Effective coupling during sequences of high complexity was larger for memorized sequences compared with novel sequences (P = 0.0037). These findings further support the role of mesial frontocentral areas in directing the primary motor cortex in the process of orchestrating complex movements and in particular learned sequences.

Differential behavioral and physiological effects of anodal transcranial direct current stimulation in healthy adults of younger and older age.

Changes in γ-aminobutyric acid (GABA) mediated synaptic transmission have been associated with age-related motor and cognitive functional decline. Since anodal transcranial direct current stimulation (atDCS) has been suggested to target cortical GABAergic inhibitory interneurons, its potential for the treatment of deficient inhibitory activity and functional decline is being increasingly discussed. Therefore, after-effects of a single session of atDCS on resting-state and event-related short-interval intracortical inhibition (SICI) as evaluated with double-pulse TMS and dexterous manual performance were examined using a sham-controlled cross-over design in a sample of older and younger participants. The atDCS effect on resting-state inhibition differed in direction, magnitude, and timing, i.e., late relative release of inhibition in the younger and early relative increase in inhibition in the older. More pronounced release of event-related inhibition after atDCS was exclusively seen in the older. Event-related modulation of inhibition prior to stimulation predicted the magnitude of atDCS-induced effects on resting-state inhibition. Specifically, older participants with high modulatory capacity showed a disinhibitory effect comparable to the younger. Beneficial effects on behavior were mainly seen in the older and in tasks requiring higher dexterity, no clear association with physiological changes was found. Differential effects of atDCS on SICI, discussed to reflect GABAergic inhibition at the level of the primary motor cortex, might be distinct in older and younger participants depending on the functional integrity of the underlying neural network. Older participants with preserved modulatory capacity, i.e., a physiologically "young" motor network, were more likely to show a disinhibitory effect of atDCS. These results favor individually tailored application of tDCS with respect to specific target groups.

Concurrent outbreaks of Salmonella Typhimurium in South Australia.

The Communicable Disease Control Branch of the South Australian Health Commission received 45 laboratory notifications of Salmonella between 23 December 1996 and 17 January 1997. A rapid screening test, undertaken by the Institute of Medical and Veterinary Sciences, Adelaide, was the first indication that this was more than one outbreak, prompting the establishment of separate investigations. Three Salmonella Typhimurium (S. Typhimurium) phage types were subsequently identified. Investigations are continuing into an outbreak of S. Typhimurium phage type (PT) 64, while investigations failed to identify any association between four cases of PT 44. As of 12 February 1997, 71 notifications had been confirmed as S. Typhimurium PT 135. Epidemiological investigations found this outbreak was associated with consumption of bread rolls with a meat filling distributed through local Asian grocery stores from a home-based manufacturer. The product was voluntarily withdrawn and there have been no new cases of PT 135.

Epidemiological characteristics of Legionella infection in South Australia: implications for disease control.

About one third of adults surveyed in South Australia have shown evidence of past silent infection with Legionella pneumophila serogroup 1. However, the annual notification rate for symptomatic disease is only about 0.5 per 100,000 residents in non-epidemic years. The male to female ratio is 2.5 to one and approximately 50% of the cases are at least 60 years of age. Cases have presented more in summer and in the metropolitan areas. Twenty cases of Legionnaires' disease occurred during the summer of 1985-86. A cooling tower was held to be the principal source with aerosols being dispersed up to three kilometers away during an atmospheric thermal inversion. A subsequent outbreak of 22 L. longbeachae serogroup 1 infections had no marked geographic clustering. The outbreak commenced in spring and cases were distinguished as active gardeners. L. longbeachae was found in garden soil and it is hypothesised that this soil inhabitant can become aerosolised and inhaled during gardening. The potential for primary prevention of Legionnaires' disease is discussed in relation to water-handling equipment and the need for early precautionary treatment of all community-acquired pneumonia as suspect Legionnaires' disease is emphasised.