Current‐dependent ocular tilt reaction in deep brain stimulation of the subthalamic nucleus: Evidence for an incerto‐interstitial pathway?

Abstract

Background and purpose: The aim was to characterize a combined vestibular, ocular motor and postural syndrome induced by deep brain stimulation (DBS) of the subthalamic nucleus in a patient with Parkinson's disease. Methods: In a systematic DBS programming session, eye, head and trunk position in roll and pitch plane were documented as a function of stimulation amplitude and field direction. Repeat ocular coherence tomography was used to estimate ocular torsion. The interstitial nucleus of Cajal (INC), zona incerta (ZI) and ascending vestibular fibre tracts were segmented on magnetic resonance imaging using both individual and normative structural connectomic data. Thresholded symptom-associated volumes of tissue activated (VTA) were calculated based on documented stimulation parameters. Results: Ipsilateral ocular tilt reaction and body lateropulsion as well as contralateral torsional nystagmus were elicited by the right electrode in a current-dependent manner and subsided after DBS deactivation. With increasing currents, binocular tonic upgaze and body retropulsion were observed. Symptoms were consistent with an irritative effect on the INC. Symptom-associated VTA was found to overlap with the dorsal ZI and the ipsilateral vestibulothalamic tract, while lying rather distant to the INC proper. A ZI-to-INC 'incerto-interstitial' tract with contact to the medial-uppermost portion of the VTA could be traced. Conclusion: Unilateral stimulation of INC-related circuitry induces an ipsilateral vestibular, ocular motor and postural roll-plane syndrome, which converts into a pitch-plane syndrome when functional activation expands bilaterally. In this case, tractography points to an incerto-interstitial pathway, a tract previously only characterized in non-human primates. Directional current steering proved useful in managing this rare side effect.

Midbrain lesion-induced disconjugate gaze: a unifying circuit mechanism of ocular alignment?

“…Distinct midbrain regions have been associated with disconjugate horizontal [ 4 – 6 ] or vertical [ 1 , 2 , 7 , 8 ] eye movements. The dorsal midbrain has been implicated both in hemi-seesaw and convergence–retraction nystagmus [ 5 , 6 , 8 ].…”

Midbrain lesion-induced disconjugate gaze: A unifying circuit mechanism of ocular misalignment?

“…Lesions or stimulation within the dorsal midbrain induce unique ocular motor patterns [1][2][3][4] . This region is neuroanatomically complex, owing to its role as a nexus for numerous interconnecting pathways and nuclei, integral to controlling eye movements 5 .…”