Abstract
Optimal phase alignment between oscillatory neural circuits is hypothesized to optimize information flow and enhance system performance. This theory is known as communication-through-coherence. The basal ganglia motor circuit exhibits exaggerated oscillatory and coherent activity patterns in Parkinson's disease. Such activity patterns are linked to compromised motor system performance as evinced by bradykinesia, rigidity and tremor, suggesting that network function might actually deteriorate once a certain level of net synchrony is exceeded in the motor circuit. Here, we characterize the processes underscoring excessive synchronization and its termination. To this end, we analysed local field potential recordings from the subthalamic nucleus and globus pallidus of five patients with Parkinson's disease (four male and one female, aged 37-64 years). We observed that certain phase alignments between subthalamic nucleus and globus pallidus amplified local neural synchrony in the beta frequency band while others either suppressed it or did not induce any significant change with respect to surrogates. The increase in local beta synchrony directly correlated with how long the two nuclei locked to beta-amplifying phase alignments. Crucially, administration of the dopamine prodrug, levodopa, reduced the frequency and duration of periods during which subthalamic and pallidal populations were phase-locked to beta-amplifying alignments. Conversely ON dopamine, the total duration over which subthalamic and pallidal populations were aligned to phases that left beta-amplitude unchanged with respect to surrogates increased. Thus dopaminergic input shifted circuit dynamics from persistent periods of locking to amplifying phase alignments, associated with compromised motoric function, to more dynamic phase alignment and improved motoric function. This effect of dopamine on local circuit resonance suggests means by which novel electrical interventions might prevent resonance-related pathological circuit interactions.
Highlights
Oscillatory activity is ubiquitous in the brain and suspected of playing a key role in neural communication (Buzsaki and Draguhn, 2004)
In line with the theory, optimal phase alignment between functionally connected cortical regions predicted an increase in correlation between the two regions, with correlation being a proxy for information exchange (Womelsdorf et al, 2007)
There is a subthalamic nucleus (STN)-GP phase difference, half a cycle displaced from the above, which is associated with the lowest instantaneous beta local field potential (LFP) amplitude in the globus pallidus
Summary
Oscillatory activity is ubiquitous in the brain and suspected of playing a key role in neural communication (Buzsaki and Draguhn, 2004). The above theory of ‘communication-through-coherence’ proposes maximal effective connectivity and information exchange during optimal phase alignment. This may not equate with optimal network performance from the behavioural as opposed to information theoretic perspective. The model system consists of the basal ganglia in patients with Parkinson’s disease, a condition that, in the untreated state, is dominated by exaggerated synchronization and coherence in the basal gangliacortical circuit (Brown et al, 2001; Williams et al, 2002; Weinberger et al, 2006; Pogosyan et al, 2010; Hirschmann et al, 2011; Litvak et al, 2011). Such synchronization is diminished by dopaminergic therapy, in tandem with amelioration of motor deficit (Kuhn et al, 2006, 2009; Weinberger et al, 2006; Ray et al, 2008)
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