Abstract
Chronic dopamine depletion in Parkinson's disease leads to progressive motor and cognitive impairment, which is associated with the emergence of characteristic patterns of synchronous oscillatory activity within cortico-basal-ganglia circuits. Deep brain stimulation of the subthalamic nucleus is an effective treatment for Parkinson's disease, but its influence on synchronous activity in cortico-basal-ganglia loops remains to be fully characterized. Here, we demonstrate that deep brain stimulation selectively suppresses certain spatially and spectrally segregated resting state subthalamic nucleus-cortical networks. To this end we used a validated and novel approach for performing simultaneous recordings of the subthalamic nucleus and cortex using magnetoencephalography (during concurrent subthalamic nucleus deep brain stimulation). Our results highlight that clinically effective subthalamic nucleus deep brain stimulation suppresses synchrony locally within the subthalamic nucleus in the low beta oscillatory range and furthermore that the degree of this suppression correlates with clinical motor improvement. Moreover, deep brain stimulation relatively selectively suppressed synchronization of activity between the subthalamic nucleus and mesial premotor regions, including the supplementary motor areas. These mesial premotor regions were predominantly coupled to the subthalamic nucleus in the high beta frequency range, but the degree of deep brain stimulation-associated suppression in their coupling to the subthalamic nucleus was not found to correlate with motor improvement. Beta band coupling between the subthalamic nucleus and lateral motor areas was not influenced by deep brain stimulation. Motor cortical coupling with subthalamic nucleus predominantly involved driving of the subthalamic nucleus, with those drives in the higher beta frequency band having much shorter net delays to subthalamic nucleus than those in the lower beta band. These observations raise the possibility that cortical connectivity with the subthalamic nucleus in the high and low beta bands may reflect coupling mediated predominantly by the hyperdirect and indirect pathways to subthalamic nucleus, respectively, and that subthalamic nucleus deep brain stimulation predominantly suppresses the former. Yet only the change in strength of local subthalamic nucleus oscillations correlates with the degree of improvement during deep brain stimulation, compatible with the current view that a strengthened hyperdirect pathway is a prerequisite for locally generated beta activity but that it is the severity of the latter that may determine or index motor impairment.
Highlights
Parkinson’s disease is a common disorder, influencing movement and cognition, and is characterized by the progressive degeneration of nigrostriatal dopaminergic neurons
At rest, there are spectral peaks centred at $7 Hz, $15 Hz and $30 Hz. These approximately correspond to the alpha, low beta and high beta frequency bands, respectively, these bands have been previously defined according to cortical reactivity and do not precisely match with subcortical spectral reactivities
deep brain stimulation (DBS) resulted in a significant suppression of activity in the stimulated subthalamic nucleus (STN) over 11–14 Hz, which for simplicity we will consider within the low beta frequency band
Summary
Parkinson’s disease is a common disorder, influencing movement and cognition, and is characterized by the progressive degeneration of nigrostriatal dopaminergic neurons. Previous studies in rodent and primate models, and in patients with Parkinson’s disease, have implicated excessive oscillatory synchrony, in the beta band (13– 30 Hz) as an important pathological feature emerging in the dopamine depleted state. Both the administration of the dopamine precursor levodopa and high frequency DBS of the STN, lead to a suppression of resting beta synchrony (Brown et al, 2001; Eusebio et al, 2011; Whitmer et al, 2012). Several studies have shown correlations between the extent of beta activity suppression by the dopamine prodrug levodopa and clinical improvements in motor performance (Kuhn et al, 2006b, 2009; Weinberger et al, 2006; Ray et al, 2008)
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