Oscillatory activity in ventrolateral thalamus of patients with Parkinson's disease

Abstract

Objective To explore the neuronal oscillatory activity in the ventrolateral thalamus (the ventral oral posterior nucleus,Vop/the ventral intermediate nucleus,Vim) in relation to parkinsonian motor signs.Methods 23 patients (M:20,F:3 ; mean age:60.6-± 8.2 years,mean duration of disease:6.6± 3.4 years) with Parkinson's disease (PD) who underwent thalamotomy were studied.Their mean Hoehn & Yahr score was 2.2 ± 0.4,and the unified Parkinson's disease rating scale (UPDRS Ⅲ)during OFFstate was 42.4 ± 12.1.The average L-dopa daily dose was 551.7 ± 219.5 mg.Microelectrode records in Vop/Vim and electromyography (EMG) on contralateral limbs to surgery were simultaneously performed.Single unit analysis,interspike interval (ISI) was used to study neuronal firing rate and pattern.Power spectral analysis was carried out to evaluate neuronal oscillation.Coherence analysis was used to study neuronal activity in relation to limb EMG.Clinical outcome was calculated by (presurgery-postsurgery/presurgery) × 100.Results 190 neurons were identified.Power spectral analysis showed that 60％ (n =114) neurons had oscillatory activity.Of those oscillatory neurons,78％ (n =89) neurons had tremor frequency band (3.0 ～ 7.5 Hz) (TFB).Oscillation showing as same frequency as tremor (P ＜0.05) ; 22％ (n =25) neurons had β frequency band(8 ～ 30 Hz) (βFB) oscillation.Further analysis showed that majority of neurons with TFB oscillation localized in Vim,while majority of neurons with βFB oscillations localized in Vop (t =2.048,P ＜ 0.05).In addition,it was found that the mean firing rate of oscillatory neurons in Vop was significantly lower than those neurons in Vim (24.3 ±9.9 Hz vs 28.5 ± 12.4 Hz,t =1.988,P ＜ 0.05).UPDRS revealed that clinical improvement was 89.7％ for tremor,48.4％ for rigidity and 38.1％ for bradykinesia respectively.Conclusions The data support that neuronal oscillations in the Vop/Vim are involved in parkinsonian symptoms.Neurons with TFB oscillation high densely distributed in the Vim indicate that the Vim is the best target for tremor.Since neurons with βFB oscillation are associated with bradykinesia,and the Vop is presumed pallidal relay nucleus.It is likely that the Vop is effective for parkinsonian bradykinesia/rigidity. Key words: Parkinson' s disease; Ventral thalamic nuclei; Microelectrodes; Neurons ; Oscillation