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Abstract: Enhanced oscillatory local field potential (LFP) activities over a broad frequency range (5–30 Hz) have been consistently reported from the basal ganglia in patients with Parkinson''s disease (PD) and in animal models of this disease. Here we test the hypothesis that these activities may have different functional connotations according to their frequency, by seeking a relatively differentiated distribution within the different functional territories of the subthalamic nucleus (STN). To this end we made intra-operative microelectrode recordings of LFP activities within the STN of 8 PD patients undergoing functional neurosurgery. A significantly larger beta (13–30 Hz) power was found in the dorsolateral part of STN, which is related to motor cortical areas, compared to the ventral (associative/limbic) part of STN. This specific topography was not observed for low frequency activity (5–12 Hz). Our data suggest that the relative distribution of oscillatory activity within the STN of patients with PD may differ according to frequency and confirm previously reported findings that beta activity may provide a functional marker for the ‘motor’ STN in functional neurosurgery. [Copyright &y& Elsevier]

Abstract: Depth recordings in patients with Parkinson''s disease (PD) have demonstrated oscillatory activity in the gamma frequency (60–100 Hz) band in local field potentials (LFPs) recorded from the region of the subthalamic nucleus (STN). Although this activity has been hypothesised to contribute to movement preparation, it is unclear to what extent these LFP oscillations arise in the STN and are synchronous with local neuronal discharge. We therefore recorded LFPs and neuronal activity from microelectrodes inserted into the STN in PD patients during functional neurosurgery. Eight sides in seven patients out of 15 sides in 12 patients were identified that had peaks in the gamma band in spectra of LFPs. As microelectrodes descended towards STN, there was a pronounced increase in gamma frequency band LFP activity 1 mm above the line joining the anterior and posterior commissures and 2 mm above the microelectrode defined dorsal border of the STN. Gamma activity dropped again 3 mm below the microelectrode defined dorsal border of the STN. Spike-triggered averages of LFP activity suggested that the discharges of neurons in this region were locked to gamma oscillations in the LFP. Gamma band oscillations in the LFP are therefore likely to represent synchronous activity in populations of neurons in the upper STN and bordering zona incerta of patients with PD. [Copyright &y& Elsevier]

Abstract: Depth recordings in patients with Parkinson''s disease (PD) have demonstrated prominent oscillatory activity in the beta frequency (13–35 Hz) band in local field potentials (LFPs) recorded from the region of the subthalamic nucleus (STN). Although this activity has been hypothesized to contribute to bradykinesia, it is unclear to what extent the LFP oscillations arise in the STN and are synchronous with local neuronal discharge. We therefore recorded both LFPs and multi-neuronal activity from microelectrodes inserted into STN in six PD patients (8 sides) during functional neurosurgery. As microelectrodes passed from above STN into STN, there was a pronounced increase in beta frequency band LFP activity. Furthermore, spike-triggered averages of LFP activity suggested that the discharges of neurons in STN were locked to beta oscillations in the LFP. The LFP is therefore likely to represent synchronous activity in populations of neurons in the STN of patients with PD. [Copyright &y& Elsevier]

Abstract: Pallidal recordings of local field potentials (LFPs) in patients with dystonia have demonstrated semi-oscillatory activity over 3–12 Hz. Although this activity has been hypothesized to contribute to dystonia, it is unclear to what extent these LFP oscillations arise in the globus pallidus interna (GPi) and are synchronous with local neuronal discharge. We therefore recorded LFPs and neuronal activity from microelectrodes inserted into the pallidum on nine sides in six awake patients with primary dystonia during functional neurosurgery. Mean normalized LFP power over 3–12 Hz was higher in GPi than globus pallidus externa. Spike triggered averages were computed, and 11 exhibited significant features in the 3–12 Hz band, indicating that the discharges of local neurons were locked to 3–12 Hz oscillations in the LFP. All but two of these STAs were in GPi. We conclude that pallidal oscillations at 3–12 Hz are maximal in GPi, the surgical target, in patients with dystonia and that they can be synchronized to activity in local neurons. This lends support to a pathophysiological relationship between LFP activity at 3–12 Hz and dystonia. [Copyright &y& Elsevier]

Abstract: Local field potential (LFP) gamma (55–95 Hz) activity has been recorded in the vicinity of the subthalamic nucleus with both microelectrodes and macroelectrodes in patients with Parkinson''s disease undergoing functional neurosurgery. Although this activity increases with movement its functional significance remains unknown. We hypothesised that elevations in local gamma activity might be associated with an increase in the capacity of individual spike trains to code information. Changes in the median firing frequency, entropy and baud were determined during spontaneous variations in the level of simultaneously recorded LFP gamma activity in a sample of 31 neurons. The latter were recorded from the zona incerta (n =5) and subthalamic nucleus (n =26) in 10 parkinsonian patients. Although 19% of neurons showed a decrease in firing rate, overall there was a net increase in spike frequency and baud of 18.0±5.5% and 16.9±5.3%, when periods of high gamma were compared to periods of low gamma LFP activity. In contrast, entropy dropped by only 0.8±0.2% across the sampled neuronal population during periods of high gamma. All net changes were significant. We conclude that overall there was a net elevation in firing rate and potential information coding capacity, assessed in terms of baud, amongst neurons during periods of elevated gamma LFP activity in the subthalamic region. [Copyright &y& Elsevier]