Abstract
Although deep brain stimulation (DBS) is a clinically effective surgical treatment for essential tremor (ET), and its neurophysiological mechanisms are not fully understood. As the motor thalamus is the most popular DBS target for ET, and it is known that the thalamic nucleus plays a key role in relaying information about the external environment to the cerebral cortex, it is important to investigate mechanisms of thalamic DBS in the context of the cerebello-thalamo-cortical neuronal network. To examine this, we measured single-unit neuronal activities in the resting state in M1 during VL thalamic DBS in harmaline-induced tremor rats and analyzed neuronal activity patterns in the thalamo-cortical circuit. Four activity patterns – including oscillatory burst, oscillatory non-burst, irregular burst, and irregular non-burst – were identified by harmaline administration; and those firing patterns were differentially affected by VL thalamic DBS, which seems to drive pathologic cortical signals to signals in normal status. As specific neuronal firing patterns like oscillation or burst are considered important for information processing, our results suggest that VL thalamic DBS may modify pathophysiologic relay information rather than simply inhibit the information transmission.
Highlights
Essential tremor (ET) is a neurological condition that causes shaking or rhythmic motion in body parts
The firing rates of oscillatory-non-burst cells were only significantly increased (p < 0.0001; p < 0.05, M1 and VL thalamus (VLT), respectively by t-test). These results indicate that the increased firing rate by harmaline injection might be driven by the increase of oscillatory-non-burst cells, which were the dominant population in the M1 and the VLT
Neuronal firing rates of the M1 were increased with harmaline administration, and this increased firing rate of the M1 was modulated by VL thalamic deep brain stimulation (DBS)
Summary
Essential tremor (ET) is a neurological condition that causes shaking or rhythmic motion in body parts. ET is characterized by a positional and/or volitional 4- to 12-Hz tremor that can affect all body parts (Marshall, 1962) and affects nearly 1% of the world’s population, increasing to 4% of those over age 40 (Müller et al, 2016). The preferred treatment for ET is pharmacology based, medications for ET may decrease in efficacy over time or not be efficacious (Chopra et al, 2013). It is estimated that pharmacological treatment can improve tremor in only 50% of patients (Lyons et al, 2003). Deep brain stimulation (DBS) becomes an alternative treatment option when medication is not effective or not tolerated in patients with disabling tremor (Zhang et al, 2010; Crowell and Shah, 2016). Ventral intermediate nucleus of the thalamus (VIM) is a well-established DBS target for ET (Deuschl and Bergman, 2002), because the VIM is a cerebellar relay nucleus in the ventrolateral (VL) part of the thalamus and is known to be involved in ET
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