Wavelet decomposition of the blink re¯ex R2 component enables improved discrimination of multiple sclerosis M.S. Kumaran a , Suresh R. Devasahayam a,1, * , T. Sreedhar b a School of Biomedical Engineering, Indian Institute of Technology, Powai, Bombay 400076, India b All India Institute for Physical Medicine and Rehabilitation, Haji Ali, Bombay 400034, India Accepted 21 December 1999 Abstract Objectives: The blink re¯ex R2 component was subjected to wavelet decomposition for time feature extraction in order to classify the functional status of patients with multiple sclerosis. Methods: The blink re¯ex was recorded bilaterally with unilateral stimulation of the supra-orbital nerve in 37 normal subjects and 9 patients with multiple sclerosis (MS). The late component, R2, was subjected to time-frequency decomposition using the Daubechies-4 wavelet. Using the time-frequency coef®cients, the mean time of the R2 wave as well as the standard deviation of the R2 interval were calculated in each trial. The wavelet transform enables noise reduction by allowing selective use of frequency bands with high signal-to-noise ratio for time feature extraction; therefore automatic estimation of time parameters is robust. The distribution densities of the mean and the standard deviation of the R2 wave duration for the set of trials for each subject were computed. Results: An appreciable difference in the densities of the two parameters extracted in the wavelet domain was seen between normals and patients. This is in contrast to the onset latency of R2 which poorly discriminates MS patients from normals. Conclusion: The results suggest that the mean and standard deviation of the R2-time robustly estimated using wavelet decomposition can be used to support clinical diagnosis in tracking the functional status of patients with diseases like multiple sclerosis. q 2000 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Blink re¯ex; R2 component; Time-frequency analysis; Wavelet transform; Multiple sclerosis; R2 mean time; R2 duration 1. Introduction The blink re¯ex is a re¯ex contraction of the orbicularis oculi muscle in response to various stimuli. In normal subjects, an early component of the blink re¯ex, R1, occurs with an onset latency of about 10 ms and duration of 5 ms while a late component, R2, occurs with a latency of about 30 ms and duration of 30±60 ms (Shahani, 1970; Shahani and Young, 1972). The trigeminal nerve forms the afferent limb of the re¯ex and the facial nerve forms the efferent limb of the re¯ex. With electrical stimulation of the supraor- bital nerve the R1 component is evoked ipsilateral to the side of the stimulus whereas R2 is evoked bilaterally. The entire blink re¯ex being a myoelectric signal, is easily recorded and has good signal to noise ratio. R1 is believed to be mediated by an oligosynaptic pathway through the lateral midpons involving two or at the most 3 synapses (Aminoff, 1992; Hopf, 1994; Aramideh et al., 1997). Abnormalities of R1 can occur in various cranial nerve and brainstem diseases, wherein a delay in the onset latency or complete absence of the wave is seen (Aramideh et al., 1997). The R2 is a polysynaptic response involving the caudal medulla and apparently in¯uenced suprasegmentally by the hemispheres and the mesencephalon (Hopf, 1994; Aramideh et al., 1997). The R2 wave is not exactly repro- ducible and changes appreciably from trial to trial. Although the R2 is said to habituate, the nature and extent of habitua- tion varies widely among subjects. The complex nature of the R2 component re¯ects the complex neuronal intercon- nections responsible for its generation. This makes the R2 an attractive candidate for insight into the function and pathology of neurones in its pathway. Present clinical tech- niques for analysis of the R2 are essentially restricted to measurement of the amplitude (including peak, mean-recti- ®ed value and area), onset time and duration, and sometimes recovery studies following paired pulse stimulation (Eekhof et al., 1996). Given the polyphasic nature of the R2 and its lack of exact reproducibility, it is not surprising that these Clinical Neurophysiology 111 (2000) 810±820 CLINPH 99541 1388-2457/00/$ - see front matter q 2000 Elsevier Science Ireland Ltd. All rights reserved. PII: S1388-2457(00)00253-4 www.elsevier.com/locate/clinph * Corresponding author. Fax: 191-225-783-480. E-mail address: surdev@cc.iitb.ernet.in (S.R. Devasahayam) 1 URL: http://www.iitb.ernet.in/~sbme/faculty/srd.phtml/