A Positron Emission Tomography Study of Voluntarily and Electrically Contracted Human Quadriceps

peer reviewe

SPICE aided analysis of UPS vector control

The possibility is studied of UPS (uninterruptible power supply) control based on the voltage vector referred to a rotating reference frame with velocity corresponding to voltage pulsation and on voltage pulsation itself. To verify the feasibility of the control strategy, a SPICE-aided simulation is reported. The numerical results show that, with asymmetrical load, a pulsation ripple is present owing to the nonsinusoidal voltage waveforms. Nevertheless, the computer harmonic distortion values are acceptable

Exploring the unity and diversity of the neural substrates of executive functioning

peer reviewedPrevious studies exploring the neural substrates of executive functioning used task-specific analyses, which might not be the most appropriate approach due to the difficulty of precisely isolating executive functions. Consequently, the aim of this study was to use positron emission tomography (PET) to reexamine by conjunction and interaction paradigms the cerebral areas associated with three executive processes (updating, shifting, and inhibition). Three conjunction analyses allowed us to isolate the cerebral areas common to tasks selected to tap into the same executive process. A global conjunction analysis demonstrated that foci of activation common to all tasks were observed in the right intraparietal sulcus, the left superior parietal gyrus, and at a lower statistical threshold, the left lateral prefrontal cortex. These regions thus seem to play a general role in executive functioning. The right intraparietal sulcus seems to play a role in selective attention to relevant stimuli and in suppression of irrelevant information. The left superior parietal region is involved in amodal switching/integration processes. One hypothesis regarding the functional role of the lateral prefrontal cortex is that monitoring and temporal organization of cognitive processes are necessary to carry out ongoing tasks. Finally, interaction analyses showed that specific prefrontal cerebral areas were associated with each executive process. The results of this neuro-imaging study are in agreement with cognitive studies demonstrating that executive functioning is characterized by both unity and diversity of processes

Processing of contextual information during an implicit probabilistic sequence task: left ventrolateral prefrontal cortex involvement

info:eu-repo/semantics/nonPublishe

.Human Brain Mapping 10:179-194(2000). Striatum Forever, Despite Sequence Learning Variability: A Random Effect Analysis of PET Data

Abstract: This PET study is concemed with the what, where, and how of implicit sequence leaming. In contrast with previous studies imaging the serial reaction time (SRT) task, the sequence of successive locations was determined by a probabilistic finite-state grammar. The implicit acquisition of statistical relationships between serially ordered elements (i.e., what) was studied scan by scan, aiming to evidence the brain areas (i.e., where) specifically involved in the implicit processing of this core component of sequential higher-order knowledge. As behavioural results demonstrate between- and within-subjects variability in the implicit acquisition of sequential knowledge through practice, functional PET data were modelled using a random-effect model analysis (i.e., how) to account for both sources of behavioural variability.First, two mean condition images were created per subject depending on the presence or not of implicit sequential knowledge at the time of each of the 12 scans. Next, direct comparison of these mean condition images provided the brain areas involved in sequential knowledge processing. Using this approach, we have shown that the striatum is involved in more than simple pairwise associations and that it has the capacity to process higher-order knowledge. We suggest that the striatum is not only involved in the implicit automatization of serial information through prefrontal cortex-caudate nucleus networks, but also that it plays a significant role for the selection of the most appropriate responses in the context created by both the current and previous stimuli, thus contributing to better efficiency and faster response preparation in the SRT task. Hum. Brain Mapping 10:179-194,2000. @ 2000 Wiley-Liss, Inc