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Biomedical subjects

Georg Dirnberger

Publications and source records attributed to Georg Dirnberger.

7 recordsLinked to original sources
PubMed2006

The substantia nigra pars compacta and temporal processing.

The basal ganglia and cerebellum are considered to play a role in timing, although their differential roles in timing remain unclear. It has been proposed that the timing of short milliseconds-range intervals involves the cerebellum, whereas longer seconds-range intervals engage the basal ganglia (Ivry, 1996). We tested this hypothesis using positron emission tomography to measure regional cerebral blood flow in eight right-handed males during estimation and reproduction of long and short intervals. Subjects performed three tasks: (1) reproduction of a short 500 ms interval, (2) reproduction of a long 2 s interval, and (3) a control simple reaction time (RT) task. We compared the two time reproduction tasks with the control RT task to investigate activity associated with temporal processing once additional cognitive, motor, or sensory processing was controlled. We found foci in the left substantia nigra and the left lateral premotor cortex to be significantly more activated in the time reproduction tasks than the control RT task. The left caudate nucleus and right cerebellum were more active in the short relative to the long interval, whereas greater activation of the right putamen and right cerebellum occurred in the long rather than the short interval. These results suggest that the basal ganglia and the cerebellum are engaged by reproduction of both long and short intervals but play different roles. The fundamental role of the substantia nigra in temporal processing is discussed in relation to previous animal lesion studies and evidence for the modulating influence of dopamine on temporal processing.

Acoustic Stimulation↗
PubMed2006

Random number generation as an index of controlled processing.

Random number generation (RNG) is a functionally complex process that is highly controlled and therefore dependent on Baddeley's central executive. This study addresses this issue by investigating whether key predictions from this framework are compatible with empirical data. In Experiment 1, the effect of increasing task demands by increasing the rate of the paced generation was comprehensively examined. As expected, faster rates affected performance negatively because central resources were increasingly depleted. Next, the effects of participants' exposure were manipulated in Experiment 2 by providing increasing amounts of practice on the task. There was no improvement over 10 practice trials, suggesting that the high level of strategic control required by the task was constant and not amenable to any automatization gain with repeated exposure. Together, the results demonstrate that RNG performance is a highly controlled and demanding process sensitive to additional demands on central resources (Experiment 1) and is unaffected by repeated performance or practice (Experiment 2). These features render the easily administered RNG task an ideal and robust index of executive function that is highly suitable for repeated clinical use.

Adult↗
PubMed2005

Executive dysfunction in Parkinson's disease is associated with altered pallidal-frontal processing.

Executive dysfunction in Parkinson's disease is well documented, but it is still unclear whether this results from (i) prefrontal dysfunction, (ii) striatal dysfunction, or (iii) altered striatal outflow to the prefrontal cortex. To clarify this issue, we used H(2)(15)O PET to asses six nondemented and nondepressed patients with Parkinson's disease and six matched controls while they performed a task involving executive function, random number generation (RNG), and a control counting task. To assess the effect of increasing task demands, each task was performed at three rates. Both groups showed significant increase in nonrandomness of responses during RNG at faster rates, which was differentially greater for the patients at the faster rate. The controls showed significant activation of the lateral and medial prefrontal cortex and superior and medial parietal cortex during RNG relative to counting. For the same comparison, the patients did not show any activity in medial frontal structures. The controls showed significantly greater mesial frontotemporal activation during counting than RNG, whereas the patients did not show any modulation of regional cerebral blood flow (rCBF) in these areas with task. With faster rates of RNG, the controls showed rCBF increase in the right internal segment of globus pallidus (GPi) and a decrease in frontal cortex. The patients showed the opposite pattern of subcortical and frontal rCBF change with faster rates. The results suggest that executive dysfunction in Parkinson's disease is associated with a failure to modulate frontal activation with increased task demands (nature of task or rate), a deficit associated with altered rCBF in the GPi, the final basal ganglia output pathway to frontal cortex rather than any intrinsic prefrontal dysfunction.

Female↗
PubMed2004

Fatigue in a simple repetitive motor task: a combined electrophysiological and neuropsychological study.

Fatigue is one of the most common psychophysiological symptoms that interact with the control mechanisms regulating task behaviour. The cortical processes involved in preparation and feedback control of voluntary movement are associated with EEG activity time-locked to movement onset: a pre-movement Movement-Related Cortical Potential (MRCP) is followed by a post-movement potential (PMP). The aim of this study was to determine whether changes in subjective fatigue which arise in the course of a simple repetitive motor task affect cortical information processing as measured by MRCPs or PMPs. MRCPs/PMPs were recorded in 33 healthy subjects while they made 100 self-paced unilateral button presses with their left or right index finger, and then continued with the other index finger for another 100 movements. Before and after the motor tasks, subjective fatigue was assessed via questionnaire. (1) Subjects who reported a higher increase of fatigue when they had finished the motor tasks showed smaller (more negative) amplitudes of the PMP. (2) This increase of negativity was strongest during the initial part of the tasks. (3) Physical aspects of perceived fatigue had a stronger effect on PMP amplitude than cognitive aspects. Smaller amplitudes of the PMP in more fatigued subjects might be explained by reduced attention to somatosensory feedback. Adaptation of this effect may result from more automatic performance at later stages of the task when all subjects required a lower degree of attentional control. In conjunction with previous studies, effects of fatigue could be separated from habituation.

Attention↗
PubMed2004

Learning of ambiguous versus hybrid sequences by patients with Parkinson's disease.

Implicit motor learning as indexed by the serial reaction time (SRT) task has been shown to be impaired in patients with Parkinson's disease (PD). This has only been conclusively demonstrated for sequences that require learning of second-order sequential information (ambiguous sequences). This study examines implicit learning of ambiguous sequences as well as sequences which contain first-order information (hybrid sequences) in a sample of 12 early to middle stage Parkinson's disease patients and matched controls. The study used dual-task methodology in order to prevent strategic/attentional learning of second-order information. The results showed that while ambiguous sequences were not learned by either group, both patient and control groups demonstrated learning of the hybrid sequence under dual-task conditions. This suggests that first-order associations may be learned by people with Parkinson's disease, even under attentionally demanding conditions. This may be interpreted as providing evidence for a non-attentional learning mechanism which is relatively intact in Parkinson's disease.

Aged↗
PubMed2004

Habituation in a simple repetitive motor task: a study with movement-related cortical potentials.

OBJECTIVE: The movement-related cortical potential (MRCP) attenuates over the right hemisphere during the performance of a complex motor sequence. Because subjects have to learn complex sequences, earlier research has attributed this decrease of negativity to motor learning. The aims of this study were (1) to examine whether such an attenuation also occurs in the course of a repetitive motor task so simple that learning is not required, and (2) whether there are any transfer effects when subjects change from one to the other hand. METHODS: MRCPs were recorded in 33 right-handed healthy subjects. In a counterbalanced crossover design, subjects made 100 self-paced unilateral button presses with their left or right index finger, and then continued on the other side of the body for another 100 movements. Tasks were performed with the same speed during the entire experiment. RESULTS: (1) The amplitude of the MRCP attenuated over the right hemisphere in the course of the tasks irrespective of the side of movement. (2) The amplitude of the MRCP decreased across the entire scalp until a minimum level was reached at the end of the earlier sequence, and then increased slightly from this low level during the following sequence made after a switch of hand. CONCLUSIONS: The right hemisphere may predominate motor activation or attentional demands directed towards movement execution or somatosensory inputs even in very simple motor tasks. The decrease and subsequent increase of negativity during the first and second sequence, respectively, may reflect the subjects' changing arousal.

Adult↗