Beta burst coupling across the motor circuit in Parkinson's disease.

Exaggerated activity in the beta band (13-35 Hz) is a hallmark of basal ganglia signals in patients with Parkinson's disease (PD). Beta activity however is not constantly elevated, but comes in bursts. In previous work we showed that the longer beta bursts are maintained, the more the oscillatory synchronisation within the subthalamic nucleus (STN) increases, which is posited to limit the information coding capacity of local circuits. Accordingly, a higher incidence of longer bursts correlates positively with clinical impairment, while the opposite is true for short, more physiological bursts. Here, we test the hypothesis that beta bursts not only indicate local synchronisation within the STN, but also phasic coupling across the motor network and hence entail an even greater restriction of information coding capacity in patients with PD. Local field potentials from the subthalamic nucleus and EEG over the motor cortex area were recorded in nine PD patients after temporary lead externalization after surgery for deep brain stimulation and overnight withdrawal of levodopa. Beta bursts were defined as periods exceeding the 75th percentile of signal amplitude and the coupling between bursts was considered using two distinct measurements, first the % overlapping (%OVL) as a feature of the amplitude coupling and secondly the phase synchrony index (PSI) to measure the phase coupling between regions. %OVL between STN and cortex and between the left and the right STN was higher than expected between the regions than if they had been independent. Similarly, PSI was higher during bursts as opposed to non-bursts periods. In addition, %OVL was greater for long compared to short bursts. Our results support the hypothesis that beta bursts involve long-range coupling between structures in the basal ganglia-cortical network. The impact of this is greater during long as opposed to short duration beta bursts. Accordingly, we posit that episodes of simultaneously elevated coupling across multiple structures in the basal ganglia-cortical circuit further limit information coding capacity and may have further impact upon motor impairment.

Triple-stimulation technique improves the diagnosis of chronic inflammatory demyelinating polyradiculoneuropathy.

INTRODUCTION: A difficult clinical situation occurs when a chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) patient does not fulfill any of the diagnostic criteria. Moreover, nerve conduction studies (NCS) can be consistent with axonal neuropathy and lead to misdiagnosis. METHODS: We aimed to assess the usefulness of the triple-stimulation technique (TST) for detection of proximal conduction blocks (CBs) in patients with axonal-like CIDP. Four patients with axonal-like CIDP were studied and compared with 10 typical CIDP patients. In the axonal-like group, NCS showed a decrease in compound muscle action potential amplitude without features of demyelination, but nerve biopsy showed features of demyelination in all 4. RESULTS: Twelve nerves were tested with TST, and 8 CBs were detected between the root emergence and the Erb point in the 4 patients, all of whom improved after treatment with intravenous immunoglobulin. CONCLUSION: TST can identify very proximal CBs in CIDP. The sensitivity of nerve conduction studies may be improved by TST in CIDP.