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Biomedical subjects

Peter Brown

Publications and source records attributed to Peter Brown.

94 records · Page 6Linked to original sources
PubMed2002

Defective cortical drive to muscle in Parkinson's disease and its improvement with levodopa.

We recorded whole-scalp magnetoencephalographic (MEG) signals simultaneously with surface electromyographic (EMG) activity from eight patients with Parkinson's disease after withdrawal and reinstatement of treatment with levodopa. Variations were seen in the coherence between the forearm extensor EMG and the MEG signal originating near or in the hand region of the primary motor cortex. As a group, the parkinsonian patients withdrawn from levodopa showed a reduction in the coherence at 15-30 Hz and 35-60 Hz, and a further three untreated patients had abnormally strong MEG-EMG coherence at 5-12 Hz compared with when medicated or with eight healthy age-matched control subjects. We conclude that the basal ganglia have a specific effect on the temporal organization of motor cortical activity during voluntary tonic contraction. Abnormalities in this aspect of basal ganglia function may directly contribute to bradykinesia and weakness in Parkinson's disease.

Adult↗
PubMed2002

Movement-related changes in synchronization in the human basal ganglia.

There is a wealth of data suggesting that behavioural events are reflected in the basal ganglia through phasic changes in the discharge of individual neurones. Here we investigate whether events are also reflected in momentary changes in the degree of synchronization between neuronal elements. We simultaneously recorded local potentials (LPs) from the subthalamic nucleus (STN) and/or ipsilateral globus pallidus interna (GPi) or scalp EEG during voluntary movements of a hand-held joystick in six awake patients following neurosurgery for Parkinson's disease. Without medication the power within the STN and the coherence between the STN and the GPi were dominated by activity with a frequency of <30 Hz. This coupling was attenuated by movement. In the presence of exogenous dopaminergic stimulation, power within the STN and coherence between the STN and the GPi was dominated by activity at 70-85 Hz, which increased with movement. The movement-related changes in coherence between the STN and EEG showed a similar pattern of pharmacological dependence, as seen subcortically. Movement-related frequency-specific changes in synchronization occur in the basal ganglia and extend to involve subcortico-cortical motor loops. The dynamic organization of activities in the frequency domain might provide a means for temporal co-ordination within and across different processing streams in the basal ganglia. This organization is critically dependent on the level of dopaminergic activity.

Adult↗
PubMed2002

Dopamine-dependent changes in the functional connectivity between basal ganglia and cerebral cortex in humans.

We test the hypothesis that interaction between the human basal ganglia and cerebral cortex involves activity in multiple functional circuits characterized by their frequency of oscillation, phase characteristics, dopamine dependency and topography. To this end we took recordings from macroelectrodes (MEs) inserted into the subthalamic nucleus (STN) in eight awake patients following functional neurosurgery for Parkinson's disease. An EEG was also recorded, as were the signals from MEs in the globus pallidus interna (GPi) in two of the cases. Coherence between EEG and ME potentials was apparent in three major frequency bands, 2-10 Hz, 10-30 Hz and 70-85 Hz. These rhythmic activities differed in their cortical topography, although coherence was always strongest over the midline. Coherence between EEG and ME potentials in the 70-85 Hz band was only recorded in patients treated with levodopa. Cortical activity phase led that in the basal ganglia in those oscillatory activities with frequencies <30 Hz. In contrast, STN and GPi phase led cortex in the 70-85 Hz band. The temporal differences in the way in which cortical activity led or lagged behind that in STN/GPi were similar, around 20 ms, regardless of the overall direction of information flow and frequency band. We conclude that the basal ganglia may receive multiple cortical inputs at frequencies <30 Hz and, in the presence of dopaminergic activity, produce a high frequency drive back to the cerebral cortex, in particular the supplementary motor area (SMA).

Adult↗