Beta band oscillations in the motor thalamus are modulated by visuomotor coordination in essential tremor patients.

Introduction: Beta oscillations in sensorimotor structures contribute to the planning, sequencing, and stopping of movements, functions that are typically associated with the role of the basal ganglia. The presence of beta oscillations (13-30 Hz) in the cerebellar zone of the thalamus (the ventral intermediate nucleus - Vim) indicates that this rhythm may also be involved in cerebellar functions such as motor learning and visuomotor adaptation. Methods: To investigate the possible role of Vim beta oscillations in visuomotor coordination, we recorded local field potential (LFP) and multiunit activity from the Vim of essential tremor (ET) patients during neurosurgery for the implantation of deep brain stimulation (DBS) electrodes. Using a computer, patients performed a visuomotor adaptation task that required coordinating center-out movements with incongruent visual feedback imposed by inversion of the computer display. Results: The results show that, in ET, Vim beta oscillations of the LFP were lower during the incongruent center-out task than during the congruent orientation. Vim firing rates increased significantly during periods of low beta power, particularly on approach to the peripheral target. In contrast, beta power in the subthalamic nucleus of Parkinson's disease (PD) patients did not differ significantly between the incongruent and the congruent orientation of the center-out task. Discussion: The findings support the hypothesis that beta oscillations of the Vim are modulated by novel visuomotor tasks. The inverse relationship between the power of Vim-LFP beta oscillations and Vim firing rates suggest that the suppression of beta oscillations may facilitate information throughput to the thalamocortical circuit by modulation of Vim firing rates.

Top-down control of human motor thalamic neuronal activity during the auditory oddball task.

The neurophysiology of selective attention in visual and auditory systems has been studied in animal models but not with single unit recordings in human. Here, we recorded neuronal activity in the ventral intermediate nucleus as well as the ventral oral anterior, and posterior nuclei of the motor thalamus in 25 patients with parkinsonian (n = 6) and non-parkinsonian tremors (n = 19) prior to insertion of deep brain stimulation electrodes while they performed an auditory oddball task. In this task, patients were requested to attend and count the randomly occurring odd or "deviant" tones, ignore the frequent standard tones and report the number of deviant tones at trial completion. The neuronal firing rate decreased compared to baseline during the oddball task. Inhibition was specific to auditory attention as incorrect counting or wrist flicking to the deviant tones did not produce such inhibition. Local field potential analysis showed beta (13-35 Hz) desynchronization in response to deviant tones. Parkinson's disease patients off medications had more beta power than the essential tremor group but less neuronal modulation of beta power to the attended tones, suggesting that dopamine modulates thalamic beta oscillations for selective attention. The current study demonstrated that ascending information to the motor thalamus can be suppressed during auditory attending tasks, providing indirect evidence for the searchlight hypothesis in humans. These results taken together implicate the ventral intermediate nucleus in non-motor cognitive functions, which has implications for the brain circuitry for attention and the pathophysiology of Parkinson's disease.

Single unit and beta oscillatory activities in subthalamic nucleus are modulated during visual choice preference.

Parkinson's disease is a neurodegenerative disease affecting the supply of dopamine to basal ganglia nuclei, leading to pathological beta band (13-35 Hz) oscillations in the subthalamic nucleus (STN). STN and beta activity are recognized in motoric functions but their role in cognitive functions remains elusive. We examined single unit and beta local field potential (LFP) activity in the STN during a visual choice preference task in PD patients (n = 12) undergoing deep brain stimulation surgery. Patients viewed 2 of 5 possible animal picture-pairs and were instructed to choose their favorite ("fav") picture by clicking the left or right mouse key. A block of trials consisted of 50-75 picture-pair presentations. Single unit histograms and LFP spectrograms were aligned to picture presentation and point of decision for pairs that included the fav and non-fav pictures, respectively. A total of 58 neurons from 26 blocks of trials were analyzed. Thirty of 58 neurons showed a selective change in spiking activity 0.20-0.65 s to fav picture presentation, which preceded the shortest recorded reaction time (=0.7 s), and 17/58 neurons showed no significant response in our task. Beta LFP significantly desynchronized in response to fav but not non-fav pictures in all trials, and in 14/26 blocks of trials, the desynchronization was followed by a "beta burst" and ramp-up to baseline activity. Neurons with choice preference responses were found throughout the dorsoventral extent of the STN. STN single units and beta activity are modulated during visual choice preference, and this suggests a role for STN beta activity in cognitive processing.

Beta oscillatory neurons in the motor thalamus of movement disorder and pain patients.

Excessive beta oscillations (15-25Hz) in the basal ganglia have been linked to the akineto-rigid symptoms of Parkinson's disease (PD) although it remains unclear whether the underlying mechanism is causative or associative. While a number of studies have reported beta activity in the subthalamic nucleus and globus pallidus internus, relatively little is known about the beta rhythm of the motor thalamus and its relation to movement disorders. To test whether thalamic beta oscillations are related to parkinsonian symptoms, we examined the spectral properties of neuronal activity in the ventral thalamic nuclei of five Parkinson's disease patients (two female, age range 50-72years) and compared them to five essential tremor (three female, aged 41-75) and four central pain patients (one female, aged 38-60). Spike and local field potential recordings were obtained during microelectrode-guided localization of thalamic nuclei prior to the implantation of deep brain stimulating electrodes. A total of 118 movement-related neurons in the region of the ventral intermediate nucleus (Vim) were analyzed across all patient groups. Eighty of these neurons (68%) displayed significant oscillatory firing in the beta range with the limbs at rest. In contrast, only 5.7% of the ventral oral posterior (Vop) (χ(2) test, p<0.05) and only 7.2% of the ventral caudal (Vc) neurons fired rhythmically at beta frequency (χ(2) test, p<0.05). Beta power was significantly decreased during limb movements (ANOVA, p<0.05) and was inversely related to tremor-frequency power during tremor epochs in ET and PD (r(2)=0.44). Comparison between patient groups showed that Vim beta power was significantly higher in ET patients versus pain and PD groups (ANOVA, p<0.05). The findings suggest that beta oscillations are found predominantly in Vim and are involved in movement but are not enhanced in tremor-dominant Parkinson's patients.