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N. Ravi, H.R. Nagendra & Shirley Telles 

Vivekananda Kendra Yoga Research Foundation, Bangalore, India.

Abstract : The sympathetic skin response (SSR) is a measure of the electrodermal activity recorded by an endosomatic method, i.e., without using external current. It correlates with exogenous (e.g., a sound) and endogenous (e.g., a deep breath) stimuli. This paper describes the variations in the SSR waveform with varied amplifier filter settings (low cut filter settings 0.1 Hz, 0.3 Hz, and 5.0 Hz and high cut filter settings 15 HZ, 35 Hz, and 75 Hz) in 25 healthy male volunteers (aged between 20 and 40 years); under different physiological conditions (e.g., deep breathing and with successive sound stimuli). The optimal amplifier settings for psychophysiological studies using the SSR are discussed.

Introduction The sympathetic skin response (SSR) is a slow wave, generated in deep layers of the skin, resulting from reflex activation of the sudomotor sympathetic efferent fibers. This slow galvanic reflex response is known to occur following a deep breath, an unexpected or arousing stimulus [1]. Its possible clinical uses in the diagnosis of autonomic disorders in both central and peripheral neuropathies, is gaining importance. As the spontaneous response and that to endogenous stimuli is a relatively new, inadequately worked out parameter in neurological studies, the amplifier filter settings for optimal recording were evaluated in the present study. 

The component in equipment that eliminates unwanted frequencies is a filter [2]. A high frequency filter will affect the designated frequency by 20 or 30 percent and is expected to affect frequencies slower than the designated at a progressively lesser degree until there is no attenuation at all. In contrast frequencies above the designated filter will have progressively more than 20 or 30 percent attenuation so that in all cases some higher frequencies will be attenuated and be eliminated.


Fig.1 Calibration

The terms time constant and low linear frequency are used interchangeably in considering the effect on slow activity, but the number is not the same where the terms are varied. A time constant of 1 sec represents a low linear frequency filter of 0.1 Hz. It is understood that the low frequency filter attenuates rather than eliminates low frequencies.

The present study assessed the SSR in normal volunteers during baseline conditions, while breathing deeply, and when given auditory stimuli. The filter settings were varied and the optimal SSR, with respect to number of responses and maximum amplitude was determined.

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