Interference Microscopy under Double-Wavelet Analysis: A New Approach to Studying Cell Dynamics

This Letter combines a novel experimental approach to the study of intracellular processes with a newly developed technique for multimode time-series analysis. Experiments are performed on isolated pond snail (Lymnaea stagnalis) neurons. Local variations in the cellular refractive index as detected by laser interference microscopy are related to the processes in the cell. A wavelet analysis shows the presence of several identifiable modes in the membrane and intracellular dynamics, and a double-wavelet analysis reveals nonlinear interactions between the regulatory processes in the form of mutual frequency and amplitude modulations.

Figure 1

(a) Optic photograph of an isolated pond snail neuron. (b) Phase height relief of the same neuron with $x$ and $y$ representing geometrical size (bar indicates $10\mu \mathrm{m}$) and $z$ phase height (bar is 200 nm). The phase height relief was obtained with a laser beam of wavelength $\lambda =532\mathrm{nm}$.

Figure 2

Power spectra calculated via the wavelet technique for (a) the low and (b) high frequency bands, respectively.

Figure 3

Typical dynamics of all local maxima of the energy density for (a) the low and (b) high frequency ranges reveals variations of rhythmic behavior in time.

Figure 4

Distribution of depth and modulation frequency for 1 and 2–4 Hz rhythmic components in the cases of (a) frequency and (b) amplitude modulation. (c) Typical normalized spectrum of the modulation process.

Figure 5

Distribution of depth and modulation frequency for 11 and 17 Hz rhythmic components in the cases of (a) frequency and (b) amplitude modulation. (c) Typical normalized spectrum of the modulation process.