A Novel Method of Measuring Autonomic Nervous System Pupil Dynamics Using Wavelet Analysis

Abstract

This paper presents a Pupillometer that has been developed in order to detect the pupil’s variation in time in a non-invasive way. The output signal of the equipment, a Pupillogram, was analyzed using Time-Frequency Analysis with the aim of better understanding the brain signals’ activity expressed in the human eye.

The Autonomic Nervous System (ANS) is divided into the Sympathetic and Parasympathetic components and theoretically they are always competing with each other as a two oscillator model.

The goal of this project is to demonstrate that these components can be identified and their frequency bands become more evident.

It is known that the pupil contracts when the Sympathetic component of the ANS is inhibited and the pupil dilates due to the inhibition of the parasympathetic component of the ANS. Because the pupil constrictor muscle is supplied by parasympathetic fibers and the dilator by sympathetic fibers, autonomic disorders may be detected with the appliance of a light stimulus (unresponsiveness to light) or other alarm stimuli.

With the present results we show that the signal from the pupil’s variation has three major frequency bands, the first being 0.04-0.08 Hz band (LF - Low Frequency), the second being 0.10-0.70 (MF – Medium Frequency) and the third being 0.80 – 1.2 Hz band (HF - High Frequency). The MF and HF bands showed interesting results, from which we can infer a possible representation of the ANS activity.