1. Introduction

In the sensory system, a stimulant likely activates stimulant-specific subsets of neurons with a stimulant-specific response profile through the sensory pathway from the sensory organ to the primary sensory cortex, resulting in identical sensory perception of the stimulant. At different stages of this neuronal information processing, the redundancy in sensory information changes by summing or subtracting overlapping signals from cognate and noncognate receptors for common and unique elements. The sensory systems generate oscillatory activities between related cortical regions and the thalamus, except in the olfactory system. The olfactory system generates oscillatory activities in the first and second olfactory centers, the olfactory bulb, and the anterior piriform cortex (aPC). It is significantly more difficult to quantify the degree of similarity or difference in these transient oscillatory responses compared to stationary oscillatory activities. We previously developed a wavelet correlation analysis that is phasetolerant for transient oscillatory responses and demonstrated a stimulus dependency of the odor-evoked oscillatory brain waves (oscillatory local field potentials, osci-LFPs) in the aPC output layer and an experience dependency in the input layer [1]. These results suggest that the redundancy in the neural representation of olfactory information may change in the aPC.

condition of no inputs from the nonolfactory sensory systems (Figure 1) [1, 5]. Oscillatory brain waves initiate during the 1-s odor presentation before the peak of the receptor potential, the electro-olfactogram (EOG) (the lowest trace in Figure 1) [1]. A pair of quite different odors, lavender essential oil (Lav), and a mixture of three fatty acids—mc4 + mc6 + mc8 (mc468) were selected as plant- and animal-related odors, respectively. Linalool (Lina) and n-butanoic acid (mc4) were selected as the single-compound odors of Lav and mc468, respectively, with partial overlaps of the activated olfactory receptors and their respective signal pathways with their original mixtures as well as 0.1 Lav (10-fold diluted Lav). As expected, oscillatory brain waves of a pair of quite different Lav and mc468 odors look dissimilar in the initial phase but

Wavelet Correlation Analysis for Quantifying Similarities and Real-Time Estimates of Information Encoded…

http://dx.doi.org/10.5772/intechopen.74810

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Figure 1. Odor-evoked oscillatory brain waves in layer I of the anterior piriform cortex (aPC) [1]. Time courses of lowpass-filtered (0–45 Hz) oscillatory brain waves and the receptor potential (electro-olfactogram, EOG) at the centromedial or caudocentral\*\* site of the aPC in the isolated whole brain are shown for three odors (Lav, lavender essential oil as an odor from a plant; 0.1 Lav (10-fold diluted Lav); and mc468, a mixture of three fatty acids as an imitated odor from animals). Ringer solution (RN) was used as a control. The odor or RN was presented to the nose of the isolated brain for 1 or 4 s\* (only for the sixth Lav), as indicated by the horizontal bar in the in-presentation order for each odor (entire

presentation order). The responses in the 2.5-s time window\* of interest were analyzed.

are partially similar in the late phase.

Sensory systems are incorporated in higher brain functions that synergistically control animal behaviors through multiple neural systems including sensory, memory, decision, motor, or other systems. Generally, all neural systems would maintain the reliability of signal processing in identical activities of identical subsets of neurons in identical time courses through neural pathways with acceptable across-trial variability. This suggests that brain waves in identical behaviors could be, to some extent, reproduced in each brain. Small fluctuations, however, sometimes change oscillatory phases across trials, as has been observed in odor-induced oscillatory brain waves [1]. The fine temporal structures of phase-fluctuated oscillatory activities responsible for informational differences are easily lost by averaging several brain waves, even for identical information in each brain. Associations of single-trial brain waves with inbrain information have been rarely studied. Regarding mental states, the most important individual-independent frequencies of electroencephalography (EEG) are 7–12 Hz at the P1 electrode and <5 Hz at Fz for attention, 10–20 Hz at F4 for fatigue, and 4–7 Hz at Fz and 10–20 Hz at Cz for frustration, with even greater variations in frequencies observed across individuals [2]. Alpha-band oscillations (8–13 Hz) exert top-down influences on the early visual processing for attention orienting [3] and are sensitive markers in the auditory memory loading process [4]. As a test case, we applied a wavelet correlation analysis to estimate odor information in the fine temporal structures of single-trial brain waves.
