Decoding human swallowing via electroencephalography: a state-of-the-art review

Swallowing and swallowing disorders have garnered continuing interest over the past several decades. Electroencephalography (EEG) is an inexpensive and non-invasive procedure with very high temporal resolution which enables analysis of short and fast swallowing events, as well as an analysis of the organizational and behavioral aspects of cortical motor preparation, swallowing execution and swallowing regulation. EEG is a powerful technique which can be used alone or in combination with other techniques for monitoring swallowing, detection of swallowing motor imagery for diagnostic or biofeedback purposes, or to modulate and measure the effects of swallowing rehabilitation. This paper provides a review of the existing literature which has deployed EEG in the investigation of oropharyngeal swallowing, smell, taste and texture related to swallowing, cortical pre-motor activation in swallowing, and swallowing motor imagery detection. Furthermore, this paper provides a brief review of the different modalities of brain imaging techniques used to study swallowing brain activities, as well as the EEG components of interest for studies on swallowing and on swallowing motor imagery. Lastly, this paper provides directions for future swallowing investigations using EEG.

Multivariate spectral analysis for identifying the brain activations during olfactory perception

Olfactory perception is a complex phenomenon associated with other processes such as cognition and emotion. Due to this complexity, there are still open issues and challenges regarding olfactory psychophysiology. One challenge concerns the investigation of the hedonic dimension of olfaction, and how it affects the power of the brain oscillations. Although there are some EEG studies exploring the changes in the power of the brain oscillations during olfactory perception, they use simple power spectral analysis techniques and vary much in terms of the reported findings. To reduce this variability, we propose the use of multivariate spectral analysis, to reveal only the frequency patterns of the EEG signals that contribute the most to olfactory perception. The goal is to investigate how these frequency patterns are affected by hedonically different odors throughout the cortex.

Effect on electroencephalogram of chewing flavored gum

The objective of the present study was to evaluate the effect on the electroencephalogram (EEG) of a chewing gum with and without our prepared new flavor. Electroencephalograms were obtained after the following three tests: chewing pure gumbase with sucrose (standard gumbase), chewing flavored standard gum and the inhalation of flavored aromatic oil. As the control, we used the pre-stimulus control EEG record without a stimulus. We examined the relationship between the pre-stimulus control record and the post-stimulus record using the changes of power in four bands. Chewing the standard gumbase led to an increase in the alpha wave and a decrease in the beta wave. Chewing the flavored standard gum and inhaling the flavored aromatic oil each increased the alpha and beta waves. In addition, chewing the flavored standard gum led to a change in the ratio of theta wave in the frontal area. The difference in the theta, alpha and beta bands in chewing gum with and without the added flavor suggested that the flavor as well as chewing could induce concentration with a harmonious high arousal state in brain function.

Olfactory event-related potentials and aging: normative data

Unlike the clinical usages of evoked potentials (e.g. brain stem auditory evoked potentials for the assessment of auditory function), normative data for the olfactory event-related potential (OERP) have been unavailable. The principal objective was to establish normative data across the human life span for OERPs with a given set of parameters. Participants were 140 persons from seven age groups (16-19, 20-29, 30-39, 40-49, 50-59, 60-69 and 70-79 years of age), with equal numbers of males and females, screened for nasal health and dementia. The odor stimulus was amyl acetate, presented at nasal temperature in a humidified airstream delivered by an air-dilution olfactometer at a constant flow rate, using a 60-s inter-stimulus interval. OERPs were recorded at Fz, Cz, and Pz electrode sites, amplified and averaged over trials. Amplitudes of the N1/P2 and P3 and latencies of the P2 and P3 were analyzed. Processing speed decreased at a constant rate over decades for the sensory (P2 latency) as well as cognitive (P3 latency) components. Decline in amplitude over decades was also apparent. Normative data will be useful in research on olfactory function and in clinical assessment of olfactory functional status.

Normal aging and odor intensity effects on the olfactory event-related potential

Olfactory event-related potentials (OERPs) were recorded in 14 young and 14 older adults, with odor strength of isoamyl acetate manipulated to assess olfactory stimulus intensity. Young participants produced significantly larger N1/P2, N2/P3 amplitudes and shorter N1, P2 and N2 latencies than older participants. Medium- and high-odor concentrations elicited significantly shorter P2 and N2 latencies than the lowest concentration for both age groups. Odor concentration appears to affect the speed of olfactory stimulus information processing regardless of age.

Effects of three principal constituents in chewing gum on electroencephalographic activity

The effects of three principal constituents (sugar, spearmint, and gumbase) in chewing gum on EEG findings in 20 normal subjects were investigated. After they chewed the gumbase, theta activity decreased significantly at Fp2, O1, T3, T4, F4, P3, and Pz; alpha activity increased significantly at O1 and decreased significantly at Fpl, and beta activity increased significantly at Fpl, Fp2, O1, T3, T4, P3 and Pz. After they inhaled the spearmint, alpha activity decreased significantly at 02, F3, P4, and Fz, and beta increased significantly at 02, F3, P4, and Fz. The mean frequency of the alpha band was significantly higher than after 1 min at rest without inhalation. After the subjects chewed the gumbase with sucrose, theta activity increased at Fp2 and Fz; alpha activity increased significantly at T3; and beta activity decreased significantly at Fpl, Fp2, F4, P3, P4, Fz, and Pz. The mean frequency of the alpha band was significantly lower than after 1 min at rest without it at almost all the positions. These results suggest that the gumbase with sucrose induced relaxed concentration effects while inhalation of spearmint induced arousal effects. The chewing of gumbase showed arousal tendency.

Human electroencephalographic (EEG) response to olfactory stimulation: two experiments using the aroma of food

The present studies sought to examine the effect of olfactory stimulation on human Central Nervous System activity. In the first experiment (n = 21), EEG response to the 'synthetic' odours of chocolate, spearmint, almond, strawberry, vegetable, garlic and onion, and cumin or no odour was recorded from 19 electrodes (F3, F4, F7, F8, Fz, T3, T4, T5, T6, P3, P4, Pz, O1, O2, C3, C4, Cz) in all EEG frequencies (delta, theta, alpha, beta1 and beta2). Exposure to the odour of chocolate was associated with significant reductions in theta activity when compared with the odours of almond and cumin, with a trend towards significance when compared with no-odour control. Exposure to the odour of spearmint was associated with a significant reduction in EEG theta when compared with the no-odour control. No significant effects were observed in other frequencies. In a second experiment (n = 15), EEG response to the odours of real foods (chocolate, baked beans, rotting pork) and two controls (no odour and hot water) was recorded as in Experiment 1. The odour of chocolate was associated with significantly less theta activity than was any other stimulus. It is hypothesised that the alterations in theta reflect shifts in attention or cognitive load during olfactory perception, with a reduction in theta indicating a reduced level of attention.

EEG, ERPs and food consumption

Baseline electroencephalographic (EEG) and auditory event-related brain potentials (ERPs) were assessed in subjects before and after consuming food and under eyes open and closed recording conditions in an attempt to replicate and extend previous food--ERP effects. Subjects were assessed the morning after fasting from the previous night, before and after eating a standard lunch. Delta- band EEG spectral power decreased and theta- and early alpha-band frequency increased after food consumption. However, in contrast to previous reports, P300 amplitude was unaffected by food consumption and peak latency increased. The strength of the correlational association between background EEG activity and P300 measures decreased for the delta- and theta- bands, but increased for the early and late alpha- bands. The findings suggest that food consumption affects general arousal, rather than specific cognitive EEG or ERP factors and are discussed with respect to previous EEG-ERP findings on food intake.