If medication is no longer sufficient in alleviating restricted mobility in the advanced stage of Parkinson’s disease, one alternative is deep brain stimulation, also known as a “brain pacemaker.” An electrical pulse emitter is implanted within the brain, such as in the subthalamic nucleus, which is functionally part of the basal ganglia system. Against this backdrop, and with the aim of investigating whether and how stimulation of a certain region of the brain can have a positive impact on ambulatory ability and provide patients with a higher quality of life, researchers at Ruhr University Bochum and Philipps-Universität Marburg trialed an optogenetics technique. According to Wolfgang Kruse, from the Department of General Zoology and Neurobiology at Ruhr University Bochum, the exact mechanisms that lead to the observed relief of symptoms with deep brain stimulation in the basal ganglia are not currently fully understood. The researchers had previously shown, in studies on rats, that stimulation of the inferior colliculus, chiefly known for processing auditory input, can be used to overcome mobility restrictions. “There are indications that stimulation of this region of the brain leads to activation of the mesencephalic locomotor region, or MLR,” said Melo-Thomas. Parkinson’s disease affects the basal ganglia but does not affect the colliculus inferior. However, the research group discovered that its stimulation activates alternative motor pathways and can improve patients’ mobility. The current study offered further investigation of this activating influence of the inferior colliculus on the MLR. In the work, the researchers ensured that light reached nerve cells via implanted optical fibers. Their approach allowed the researchers to activate or inhibit the cells specifically. According to Wolfgang Kruse, from the Department of General Zoology and Neurobiology at Ruhr University Bochum, this tactic was therefore much more precise than electrical stimulation, which always affects the area around the cells as the target(s). The researchers then documented the effect of the stimulation with electrophysiological measurements of neuronal activity in the target structures using a multi-electrode system. Parallel measurement with up to four electrodes is also highly efficient, allowing minimization of the number of animals used. Optogenetic stimulation in the inferior colliculus predominantly triggered the expected increase in neuronal activity within it. “Simultaneous measurements in the deeper MLR region showed increased activity in the majority of cells, although nearly one quarter of the cells were inhibited by the additional activity in the inferior colliculus,” said Kruse. The activation of individual nerve cells occurred with an average delay of 4.7 ms, indicating a functional synaptic interconnection between the inferior colliculus and MLR. The research was published in Scientific Reports (www.doi.org/10.1038/s41598-025-96995-4).
