Chapter 61 Effects of deep brain stimulation for treatment of Parkinson's disease

Abstract

Publisher Summary Deep brain stimulation provides an attractive alternative to surgical ablation because the electrodes can be introduced without significant tissue injury. Moreover, the stimulation parameters can be adjusted and bilateral procedures can be performed with minimal morbidity. Currently, the ventral intermediate nucleus (VIM) of the thalamus, internal globus pallidus (GPi), and subthalamic nucleus (STN) are main targets for deep brain stimulation (DBS) procedures for Parkinson's disease (PD). VIM stimulation has been demonstrated to improve tremor in double-blinded studies in PD patients and in patients with essential tremor. Both GPi and STN stimulation improve parkinsonian symptoms, but there are significant differences. GPi stimulation produces effects that are similar to GPi pallidotomy— that is, marked improvement of l -dihydroxyphenylalanine (DOPA) induced dyskinesia, moderate improvement of akinesia, rigidity and tremor, and ability to tolerate the same or higher doses of l -DOPA. STN stimulation produces marked improvement in akinesia, rigidity, and tremor and allows reduction in l -DOPA dosage, leading to the improvement of l -DOPA induced dyskinesia. The other effects of GPi and STN are also discussed in the chapter. This chapter discusses of the effects of GPi stimulation on motor threshold and motor evoked potentials (MEP) recruitment and on cortical inhibition and facilitation. Motor threshold is related to neuronal membrane excitability and likely reflects the excitability of a central core region of neurons in the motor cortex. MEP recruitment tests neurons that are less excitable or further away from the central core region. GPi stimulation can directly activate the corticospinal tract under some circumstances. Dopaminergic drugs lengthen the silent period (SP) in normal subjects and PD patients. SP in PD patients with the stimulator turned off is related to the relatively high doses of dopaminergic medications used to treat their advanced PD. The shortening of the SP, with GPi stimulation, may be related to the reduction of dyskinesia and anti l -DOPA effects of ventral GPi stimulation.