Abstract—Deep Brain Stimulation or DBS is a surgical treatment for Parkinson’s Disease with three stimulation parameters: frequency, pulse width, and voltage. The parameters should be selected appropriately to achieve effective treatment. This selection now, performs clinically. The aim of this research is to study chaotic behavior of recorded tremor of patients under DBS in order to present a computational method to recognize stimulation optimum voltage. We obtained some chaotic features of tremor signal, and discovered embedding space of it has an attractor, and its largest Lyapunov exponent is positive, which show tremor signal has chaotic behavior, also we found out, in optimal voltage, entropy and embedding space variance of tremor signal have minimum values in comparison with other voltages. These differences can help neurologists recognize optimal voltage numerically, which leads to reduce patients' role and discomfort in optimizing stimulation parameters and to do treatment with high accuracy. Keywords—Chaos, Deep Brain Stimulation, Parkinson’s Disease, Stimulation Parameters, tremor. I. INTRODUCTION ARKINSON'S disease is the most common movement disorder which is seen in old people [1]. It is assumed by most neurologists that the reduction of dopamine neurotransmitter at some parts of Basal Ganglia causes this disease [2]. Tremor is the most important symptom of this disease, and results in a rhythmic oscillation with a frequency of 4-6 Hz [3]. Usually prescribed Levodopa, a combination of dopamine, is the first treatment for this disease [4]. When it releases neurotransmitter in the brain, the patients' symptoms improve. Unfortunately, brain cells become resistant to this substance by passing the time, and treatment stops. Consequently, DBS becomes the second method in Parkinson's disease treatment [3]. DBS is electrode placement in some area of the brain depending on patients' symptoms, and high frequency electrical stimulation by a pulse generator located under the Clavicle bone [5]. M. Sadeghi is with the Islamic Azad University of Iran science and research branch, biomedical engineering faculty (corresponding author to provide phone: 00989125464711; fax:00982144440505; e-mail: mhrzd.sadeghi@ gmail.com). A.H. Jafari is with the Tehran University Medical Sciences of Iran (e-mail: h_jafari@tums.ac.ir). In 1980s, DBS was being used in some new parts of Basal Ganglia. Grenoble group for the first time applied high frequency stimulation in ventralis intermedius nucleus of the thalamus for tremor treatment [6]. After a while other disorders like epilepsy, depression, and obsession were treated by this method [7]-[8]-[9]. Stimulation parameters are frequency, pulse width and voltage [10]-[11]. There is not any accurate procedure for the optimizing these parameters and regulating them. Now, this operation is performed by trial and error method, which leads to high cost, patient’s inconvenience and time wasting problems. The characteristics of these parameters are degree of freedom, unknown effects and complicated responses [12]. Mechanism of DBS with high frequency is still unknown, but there are some hypotheses to respond. Assuming that Parkinsonian tremor is abnormal oscillation in some regions of the brain, DBS might act to block or interfere with the transmission of oscillatory activity to the motor neurons, or DBS acts to desynchronize these oscillators. Another hypothesis is that DBS might lead to a change in system parameters, and this in turn would lead to a Hopf bifurcation in the dynamics so that the abnormal limit cycle associated with the tremor would be destabilized. This change in system parameters could be related to a gradual change in network properties generating the tremor [13]-[14]-[15]. The aim of this research is to obtain some chaotic features from patients' clinical data whom were under DBS treatment. For every patient chaotic features of tremor in optimal voltages were evaluated and compared with those of other voltages. These features are: embedding space, embedding dimension, correlation dimension, largest Lyapunov exponent, entropy and variance of embedding space along with x, and y axes. II. APPROPRIATE SELECTION OF STIMULATION PARAMETERS Electrical stimulation parameters comprise frequency, pulse width and voltage that are regulated by a pulse generator placed under the Clavicle bone [5]-[10]-[11]. In order to obtain satisfactory clinical results, optimal parameters hove to S.M.P. Firoozabadi is with the Tarbiat Modarres University of Iran and the Islamic Azad University of Iran science and research branch (e-mail: purmir@modares.ac.ir). A Chaotic Study on Tremor Behavior of Parkinsonian Patients under Deep Brain Stimulation M. Sadeghi, A.H. Jafari, and S.M.P. Firoozabadi P World Academy of Science, Engineering and Technology International Journal of Medical and Health Sciences Vol:5, No:2, 2011 78 International Scholarly and Scientific Research & Innovation 5(2) 2011 scholar.waset.org/1307-6892/15274 International Science Index, Medical and Health Sciences Vol:5, No:2, 2011 waset.org/Publication/15274