In Reply We thank de Castro dos Santos et al for their letter and their interest in our article. They question whether current spread to the optic tract may account for the decrease in the reported severity of visual hallucinations. The optic tract lies inferomedial to the globus pallidus internus. Deep brain stimulation (DBS) that spreads to the optic tract causes patients to experience visual perceptions commonly referred to as “flash.” None of the patients in our study reported this phenomenon either at 20-Hz or 130-Hz test stimulation. This was not a surprise to us, given that the postoperative verification of electrode position on an immediate stereotactic magnetic resonance image with the frame still on the head confirmed that all electrodes were precisely placed, straddling the nucleus basalis of Meynert (NBM) and globus pallidus internus, far lateral to the location of the optic tract (Figure). Therefore the outcomes reported cannot be attributed to a current spread to the optic tract.
Foltynie T, Jahanshahi M, Hariz M. Association of Optic Pathways and Brain Structure With Deep Brain Stimulation of the Nucleus Basalis of Meynert for Parkinson Disease Dementia—Reply. JAMA Neurol. 2018;75(7):896–897. doi:10.1001/jamaneurol.2018.1069
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