Effects of attentional load on auditory scene analysis

The effects of attention on the neural processes underlying auditory scene analysis were investigated through the manipulation of auditory task load. Participants were asked to focus their attention on tuned and mistuned stimuli presented to one ear and to ignore similar stimuli presented to the other ear. For both tuned and mistuned sounds, long (standard) and shorter (deviant) duration stimuli were presented in both ears. Auditory task load was manipulated by varying task instructions. In the easier condition, participants were asked to press a button for deviant sounds (target) at the attended location, irrespective of tuning. In the harder condition, participants were further asked to identify whether the targets were tuned or mistuned. Participants were faster in detecting targets defined by duration only than by both duration and tuning. At the unattended location, deviant stimuli generated a mismatch negativity wave at frontocentral sites whose amplitude decreased with increasing task demand. In comparison, standard mistuned stimuli generated an object-related negativity at central sites whose amplitude was not affected by task difficulty. These results show that the processing of sound sequences is differentially affected by attentional load than is the processing of sounds that occur simultaneously (i.e., sequential vs. simultaneous grouping processes), and that they each recruit distinct neural networks.     

Does mental simulation of following a path improve navigation performance without vision?

We recorded the paths of subjects who walked along a memorized hexagonal route without vision, and studied the impact of previous mental simulation of this activity on how well the path could be reproduced from memory. We compared two kinds of mental simulation to actual physical practice, rest, or simple memorization of the path. The results indicated that mental simulation led to better reproduction of the global shape of a path than rest, and in fact mental simulation was as effective as actual physical practice. However, this result occurred only for 'simple shapes' when the lengths of the sides of the path were kept constant. Nevertheless, this level of performance was not reached when the complexity of the shape was increased by altering the lengths of sides, even when keeping constant the angles between consecutive sides. This finding indicates that the internal representation of space depends on geometric properties of the environment in which the subjects operate. Mental simulation appears to affect both a map-like and route-like representation of the environment.     

Perceptual learning modulates sensory evoked response during vowel segregation

With practice, people become better at discriminating two similar stimuli, such as two sounds. The neural mechanisms that underlie this type of learning have been of interest to researchers investigating neural plasticity associated with learning and recovery of function following stroke. We utilized event related potentials (ERP) to study the neural substrates underlying auditory discrimination learning. Stimuli were five steady-state American English vowels. On each trial, participants were presented with a pair of vowels created by summing together the digital waveforms of two different vowels. Listeners were instructed to identify both vowels in the pair. ERPs were recorded during two sessions separated by 1 week. Half of the participants practised the discrimination task during the intervening week while the other half served as controls and did not receive any training. Trained listeners showed greater improvement in accuracy than untrained participants. In both groups, vowels generated N1 and P2 waves at the fronto-central and temporal scalp regions. The behavioral effects of training were paralleled by decreased N1 and P2 latencies as well as enhanced P2 amplitude in the trained compared with untrained listeners. The effects of training on sensory evoked responses are consistent with the proposal that perceptual learning is associated with changes in sensory cortices.     

Subthalamic deep brain stimulation does not induce striatal dopamine release in Parkinson's disease

Deep brain stimulation of the subthalamic nucleus (STN) is an increasingly prevalent treatment for advanced Parkinson's disease (PD). Its main mechanism of action is thought to be a reduction in the inhibitory outflow from basal ganglia to cerebral cortex. However, recent animal experiments have led to the suggestion that high frequency stimulation of the STN also acts by promoting dopamine release. We tested this hypothesis by performing [11C]raclopride PET on and off stimulation in six patients with PD and implanted STN stimulators. There was no difference in tracer binding in the striatum between the two testing conditions. We conclude that high frequency stimulation of the STN does not act by increasing dopamine release.     

The French stroke program

The French healthcare system is organised according to a political, geographical and demographic framework. In France today, less than 20 hospitals have dedicated intensive care units for acute stroke patients. In the 1999 national survey, 94% of stroke patients were admitted to public hospitals, 35% were treated in neurological wards and 4% had access to an intensive care stroke unit. To improve the quality of care and resource utilisation, a national plan for stroke will be implemented at regional level during the next five-year plan. After a long period of status quo, many positive actions for stroke care have been initiated within a couple of years, based on the evidence of more effective stroke treatments, such as thrombolysis and the specialist care provided by stroke units.     

Association of gephyrin with synaptic and extrasynaptic GABAA receptors varies during development in cultured hippocampal neurons

Several studies have reported extrasynaptic clusters of GABAA receptors in hippocampal neurons. Yet their functional relevance as well as their evolution in relation with gephyrin during synaptogenesis remain unknown. We have analyzed the expression pattern of the main proteins of the GABAergic synapses during synaptogenesis in cultured hippocampal neurons. We found that GABAergic terminals, characterized by VIAAT and GAD-65 expression, differentiated 3 to 7 days after the glutamatergic endings. At the postsynaptic side, the GABAAR- beta3 subunit was first diffuse and then clustered when GABAergic terminals differentiated and gephyrin formed large clusters. Colocalization of these proteins was high and increased with development. At later stages, GABAAR beta3 clusters colocalized with gephyrin at synaptic but also at extrasynaptic sites. GABAAR gamma2 subunits were directly expressed as clusters which were first extrasynaptic and not associated with gephyrin. Subsequently, the GABAAR gamma2 subunits associated with gephyrin at synaptic and/or extrasynaptic sites. Our data indicate that formation of GABAAR gamma2 subunit clusters is gephyrin independent.     

The construct validity of the client questionnaire of the Wisconsin Quality of Life Index--a cross-validation study

The Wisconsin Quality of Life Index (W-QLI, Becker, Diamond and Sainfort, 1993) consists of eight scales: satisfaction with life domains, occupational activities, symptoms, physical health, social relations/support, finances, psychological wellbeing, and activities of daily living. The W-QLI has been modified to fit the characteristics of the Canadian population, the universal Canadian health system, and community and social services in Canada and the modified form was named CaW-QLI (Diaz, Mercier, Hachey, Caron, and Boyer, 1999). This study will verify the empirical basis of these theoretical dimensions by applying a cross-validation procedure on two samples, most of whose subjects have a serious mental illness. Confirmatory factor analyses and exploratory factor analyses using the principal component extraction technique with varimax rotation were applied. With the exception of the occupational activities domain, the remaining scales were correctly identified by the factor analyses on each sample. The occupational activities scale should be developed by additional items for representing this scale, which is too brief, and two other items should be revised in order to improve the quality of the instrument.     

Executive function differences in multiple system atrophy and Parkinson's disease

The aim of the present study was to assess executive function in patients with multiple system atrophy (MSA) and Parkinson's disease (PD) looking for specific differences and considering motor disability and disease duration. Performance of 11 MSA patients was compared to that of 12 healthy controls and two groups of 12 PD patients, one matched with respect to the severity of motor symptoms and the other with respect to disease duration. Compared to healthy controls, MSA and PD patients both presented executive dysfunction but, in MSA, the impairment was more severe and diffuse. This study suggests that despite the evidence of some differences in executive function in MSA and PD, the contribution of standard neuropsychological examination to the differential diagnosis of both syndromes remains still limited.     

Behavioural changes after an acute stress: stressor and test types influences

Behavioural consequences of different acute stressors (30 min of restraint, 20 min of forced swim stress, 15 min of inescapable footshocks) applied at the beginning of the active period were assessed in using two behavioural tests: a 20 min light extinction test 24 h after the stressor exposure in order to explore the psychomotor ability and a 10 min open field session within the dark period 48 h after the stressor exposure to estimate the emotional status and the locomotor activity of the rat. Different behavioural responses were observed depending on the nature of the applied stressor. In the light extinction test, the footshock-stressed rats developed a very low activity independent on light conditions whereas the rats submitted to forced swim and restraint exhibited an activity level depending on the strain. Moreover, restrained rats had a higher transient activity than forced swim rats under light condition. In the open field test, none of the stressed rats did develop differences in behaviour. The efficacy of a 24 h recovery period on the behavioural response to an acute stressor exposure depends on the intensity of the applied stressor and the behavioural demands.