Time-frequency analysis of gustatory event related potentials (gERP) in taste disorders.

In taste disorders, the key to a correct diagnosis and an adequate treatment is an objective assessment. Compared to psychophysical tests, EEG-derived gustatory event-related potentials (gERP) could be used as a less biased measure. However, the responses identified using conventional time-domain averaging show a low signal-to-noise ratio. This study included 44 patients with dysgeusia and 59 healthy participants, who underwent a comprehensive clinical examination of gustatory function. gERPs were recorded in response to stimulation with two concentrations of salty solutions, which were applied with a high precision gustometer. Group differences were examined using gERP analyzed in the canonical time domain and with Time-Frequency Analyses (TFA). Dysgeusic patients showed significantly lower scores for gustatory chemical and electrical stimuli. gERPs failed to show significant differences in amplitudes or latencies between groups. However, TFA showed that gustatory activations were characterized by a stronger power in controls than in patients in the low frequencies (0.1-4 Hz), and a higher desynchronization in the alpha-band (8-12 Hz). Hence, gERPs reflect the altered taste sensation in patients with dysgeusia. TFA appears to enhance the signal-to-noise ratio commonly present when using conventional time-domain averaging, and might be of assistance for the diagnosis of dysgeusia.

The Pitfalls and Perspectives of Assessing Olfactory Function via Optical Brain Imaging.

Olfaction is critical for maintaining daily life activities. It is crucial to measure olfactory performance for the diagnosis and treatment of certain neurodegenerative diseases. Moreover, impairments and a lack of quality in the olfactory system may indicate the early diagnosis of some diseases such as Parkinson's. In this context, there are several imaging methods available for evaluating olfactory function. In addition to the conventional methods used in measuring the brain's responsiveness to olfactory stimuli, this article presents a systematic review of the current applicability of optical brain imaging (i.e., functional near-infrared spectroscopy) in the evaluation of olfactory function. A database literature search was conducted in PubMed, Scopus, the Web of Science, and ScienceDirect. This review excluded animal studies, clinical studies, pathology- or neurodegenerative disease-related studies, newborn-related studies, cross-modal- and dual-task-related studies, and non-original research studies. Thus, seven studies were examined to discuss the pitfalls and perspectives of the use of optical brain imaging under olfactory stimulation. As for this conclusion, they can be used to evaluate olfactory performance in healthy individuals through the interpretation of hemodynamic changes. Further studies are needed to standardize the applicability of these optical imaging techniques.

The Influence of Acute Sprint Interval Training on the Cognitive Performance of Male Basketball Players: An Investigation of Expertise-Related Differences.

Highly developed cognitive abilities are an important prerequisite for reaching elite athletic levels. This study aimed to investigate the effect of an acute sprint interval training (SIT) session on the cognitive performance of amateur and elite players. Eighteen amateur and ten elite male basketball players were included in this study. They were asked to perform an acute SIT consisting of the Wingate Test (i.e., four bouts of 30 s all-out sprints) on a cycle ergometer, interspersed with 4 min of active recovery. Before and after the acute SIT, three cognitive tests (i.e., Change Detection Test, Timewall Test, Mackworth Clock Test) were performed. Exercise-induced changes in cognitive performance and between-group differences were analyzed. We did not observe significant between-group differences in the performance of any cognitive test at the pretest, but elite basketball players outperformed the amateur players in specific measures of the Change Detection Test and Timewall Test after the acute SIT (p < 0.05). In addition, for the Clock Test, only the elite basketball players' performance improved from pre- to posttest. The current study's findings suggest that male elite basketball players, compared to amateur basketball players, can preserve their cognitive performance after an acute bout of SIT.

The Effects of Virtual Reality Nonphysical Mental Training on Balance Skills and Functional Near-Infrared Spectroscopy Activity in Healthy Adults.

CONTEXT: Athletic skills such as balance are considered physical skills. However, these skills may not just improve by physical training, but also by mental training. The purpose of this study was to investigate the effects of mental training programs on balance skills and hemodynamic responses of the prefrontal cortex. DESIGN: Randomized controlled trial. METHODS: Fifty-seven healthy adults (28 females, 29 males), aged between 18-25 years, participated in this study. Participants were randomly assigned to 3 groups: virtual reality mental training (VRMT) group, conventional mental training (CMT) group, and control group. The training program included action observation and motor imagery practices with balance exercise videos. The VRMT group trained with a VR head-mounted display, while the CMT group trained with a non-immersive computer screen, for 30 minutes, 3 days per week for 4 weeks. At baseline and after 4 weeks of training, balance was investigated with stabilometry and Star Excursion Balance Test (SEBT). Balance tests were performed with simultaneous functional near-infrared spectroscopy (fNIRS) imaging to measure prefrontal cortex oxygenation. RESULTS: For the stabilometry test, at least 1 variable improved significantly in both VRMT and CMT groups but not in the control group. For SEBT, composite reach distance significantly increased in both VRMT and CMT groups but significantly decreased in the control group. For separate directional scores, reach distance was significantly increased in both mental training groups for nondominant leg posterolateral and posteromedial directions, and dominant leg posterolateral direction, while nondominant posteromedial score was significantly increased only in the VRMT group. Between-group comparisons showed that dominant leg posteromedial and posterolateral score improvements were significantly higher than control group for both mental training groups, while nondominant leg improvements were significantly higher than control group only for the VRMT group. The fNIRS oxyhemoglobin levels were not significantly changed during stabilometry tests. However, oxyhemoglobin levels significantly reduced only in the control group during SEBT. CONCLUSIONS: Our findings suggest that both mental training interventions can significantly improve balance test results. Additionally, VRMT may have some advantages over CMT. These findings are promising for the use of mental training in prevention and rehabilitation for special populations such as athletes and older adults.

Hemodynamic changes in athletes' brains: is there any adaptation?

This study compared the hemodynamic changes in the prefrontal cortex during sprint interval training (SIT) and recovery periods in sedentary and athletes. SIT was performed on a cycling ergometer on 12 male athletes and 9 sedentary participants. A functional near-infrared spectroscopy (fNIRS) device was used to record the hemodynamic changes of the prefrontal cortex throughout the protocol. The oxyhemoglobin (Oxy-Hb) levels in the prefrontal cortex were increased significantly, and the power outputs were decreased in repetitive Wingate anaerobic tests (WAnTs) in Sedentary and Athletes group (p < 0.001). In addition, the Sedentary group had higher Oxy-Hb values (p < 0.001). However, the recovery times decreased significantly after all WAnTs (p < 0.05). Despite the increased fatigue, athletes performed better with less Oxy-Hb than the sedentary participants. Also, the recovery of the Oxy-Hb values in the prefrontal region was faster in athletes. These results may highlight a possible brain adaptation in athletes.

Electrophysiological Recordings from the Olfactory Epithelium and Human Brain in Response to Stimulation with HLA Related Peptides.

In many species, social communication and mate choice are influenced by olfactory cues associated with the major histocompatibility complex (MHC). It has been reported that humans also respond to olfactory signals related to the human MHC-equivalent, the Human Leucocyte Antigen (HLA)-System, and exhibit an olfactory-mediated preference for potential mating partners with a dissimilar, disassortative, HLA-type compared to their own. The aim of this study was to investigate whether HLA-associated peptides, presented as volatile cues, elicit neuronal responses at the receptors in the human olfactory epithelium and can be consciously perceived. To this end the discrimination ability for peptides was tested in a 3-alternative forced choice model. Furthermore electro-olfactograms of the olfactory epithelium and EEG-derived chemosensory event related potentials were recorded using precisely controlled olfactometric stimulation with peptides and control odors. Based on responses from 52 young, healthy participants the peptides could not be discriminated and the electrophysiological signals provided no evidence for a specific response to the peptides which was in contrast to the control odors. In conclusion, within the current setup the results suggest that HLA-associated peptides do not produce specific olfactory activation in humans.

Central Nervous System Processing of Floral Odor and Mother's Milk Odor in Infants.

Newborns have a functioning sense of smell at birth, which appears to be highly significant for feeding and bonding. Still, little is known about the cerebral odor processing in this age group. Studies of olfactory function relied mostly on behavioral, autonomic, and facial responses of infants. The aim of the present study was to investigate central odor processing in infants focusing on electroencephalography (EEG)-derived responses to biologically significant odors, namely a food and a non-food odor. A total of 21 term-born, healthy infants participated (11 boys and 10 girls; age range 2-9 months, mean 5.3 ± 2.2 months). Odor stimuli were presented using a computer-controlled olfactometer. Breast milk was used as food odor. Farnesol was presented as a non-food odor. In addition, odorless air was used as a control stimulus. Each stimulus was presented 30 times for 1 s with an interstimulus interval of 20 s. EEG was recorded from 9 electrodes and analyzed in the frequency domain. EEG amplitudes in the delta frequency band differed significantly after presentation of food (breast milk) odor in comparison to the control condition and the non-food odor (farnesol). These changes were observed at the frontal recording positions. The present study indicates that central odor processing differs between a food and a non-food odor in infants. Results are interpreted in terms of focused attention towards a physiologically relevant odor (breast milk), suggesting that olfactory stimuli are of specific significance in this age group.

Sleep Is a Refreshing Process: An fNIRS Study.

Sleep is a very critical process that constitutes up to one third of daytime of a healthy adult. It is known to be an active period where body and brain is refreshed for the next day. It is both part of a larger cycle, i.e., circadian rhythm, and has subcsycles in it, i.e., sleep stages. Although hemodynamics of these stages have been investigated especially in the last two decades, there are still points in the hemodynamics to be illuminated especially in terms of refreshment. This study aims to investigate refreshing property of sleep in terms of sleep stages using functional near-infrared spectroscopy (fNIRS) for measuring prefrontal cortex (PFC) hemodynamics. Nine healthy subjects slept in sleep laboratories, monitored by polysomnography and fNIRS before, during, and after night sleep. REM stage had lower oxyhemoglobin (HbO) and total hemoglobin (HbT) than the other sleep stages and wakefulness. Deoxyhemoglobin (HbR) did not differ between any stages. All sleep stages and wakefulness stage at the end of the sleep had higher HbO and lower HbR than the beginning of the sleep. HbT levels did not differ between the beginning and the end of the sleep for any stages. During REM sleep, PFC seems to get lower blood supply, possibly due to increased demand in other brain regions. Regardless of the stage, PFC has higher oxygenation toward the end of sleep, indicating refreshment. Overall, our brain seems to be on duty during sleep throughout the night for "cleaning" and "refreshing" itself. Hemodynamic changes from the beginning to end of sleep might be the indicator of this work. Thus, accordingly REM stage seems to be at a central point for this work.

Deaf adolescents have bigger responses for somatosensory and visual stimulations.

The functions of the sensory systems on disabled people have been one of the most investigated topics in brain research. In these studies, mostly visual stimuli had been employed while investigating the deaf participants. Limited number of electrophysiological studies revealed better visual sensory processing in deaf participants. On the other hand, studies deploying tactile stimuli especially used either electrical or painful stimulus or they focused the psychophysical assessments of thresholds associated with tactile stimuli. The present study tried to evaluate electrophysiological brain responses in deaf and control group with a unimodal study design including both the visual and non-painful tactile stimuli, and to reveal the possible changes in brain plasticity within modality basis. Thirteen congenitally deaf adolescents (mean: 14.61 ±â€¯1.06 years; 7 girls) and 10 adolescents with normal hearing (16.6 ±â€¯2.72 years; 4 girls) were recruited for the study. Somatosensory evoked potentials (SEP) and visual evoked potentials (VEP) were separately delivered to the participants and in order to maintain neutrality among sessions they were presented in random order while the electroencephalography (EEG) recordings were taken. Brain responses to non-painful tactile and visual stimuli were measured for N1, P2, and N2 components. All amplitudes of deaf group were significantly larger than all amplitudes of control group in SEP session whereas in VEP session only P2 and N2 amplitudes of deaf group were statistically larger. In addition, the latency of N1 component in VEP session was significantly earlier in deaf group. These findings suggest early cortical excitability, less neuronal capacity usage and also more efficient sensory processing in deaf group.

Auditory brain oscillatory responses in drug-naïve patients with Parkinson's disease.

Parkinson's Disease (PD) is a common neurodegenerative disorder affecting the function of dopaminergic cells in basal ganglia. Besides the motor symptoms, tremor, and dysfunction of sensory systems. In the literature, there was limited studies which investigates the basic sensorial processing in PD. Therefore, we aimed to establish the sensorial processing of simple auditory stimulations in naïve PD comparing to healthy controls (HC) via delta, theta, and alpha brain oscillatory responses. 12 naïve PD and 12 HC participated to the study. Brain responses recorded via the 64-channel electroencephalography (EEG) system in an electromagnetically and acoustically isolated room. The auditory stimuli (1500 Hz, 60 dB SPL, 500 ms) were delivered to the subjects via a headphone. The inter-stimulus interval was ranged between 2.5-4.5 s. The peak-to-peak maximum amplitudes were measured in the delta, theta and alpha frequency bands on 11 electrodes (including the frontal, central and parietal areas) for the statistical analysis in which one-way ANOVA test was employed for the comparisons between PD and HC. For the delta oscillatory responses, PD group has bigger amplitudes in frontal, central and parietal areas in comparison with HC. For the theta and alpha oscillatory responses, PD group has bigger amplitudes in parietal areas in comparison with HC. As a result, amplitudes of brain oscillatory responses in PD group were significantly bigger than the HC. In this context, decreased inhibitory mechanisms of cortical auditory processing due to the dysfunction of the dopaminergic activity may lead the increased evoked responses in PD group.

Brain asymmetry in directing attention during dichotic listening test: An fNIRS study.

In a classical dichotic listening paradigm, besides auditory brain asymmetry, cognitive functions such as attention and conflict resolution play a major role. The aim of this study is to reveal the possible haemodynamic mechanisms of higher attentional performance in prefrontal cortex during dichotic listening test. Twenty-six healthy participants underwent a dichotic listening task in three sessions; non-forced attention, attention focused to right ear, and attention focused to left ear. In each session, haemodynamic activity of prefrontal brain area was recorded using functional near-infrared spectroscopy (fNIRS). Effects of focused attention and performance level of the task on oxy-, deoxy-, and total haemoglobin levels were investigated. Oxy- and total haemoglobin levels in right prefrontal regions during forced-right and forced-left sessions were significantly higher than levels of the non-forced session. This might be an indicator of inhibition and orienting attentional functions of right inferior frontal gyrus. High performers had significantly higher deoxyhaemoglobin levels in the forced-left session compared to the non-forced session, while low performers' deoxyhaemoglobin levels did not differ among these sessions. Observing this difference only in the forced-left session but not in the forced-right session might suggest conflict resolution in top-down and bottom-up processes during the forced-left session for right-handed participants.

The impact of musical experience on neural sound encoding performance.

In this study, 64-channel single trial auditory brain oscillations (STABO) have been firstly analyzed by using complexity metrics to observe the effect of musical experience on brain functions. Experimental data was recorded from eyes-opened volunteers during listening the musical chords by piano. Complexity estimation methods were compared to each other for classification of groups (professional musicians and non-musicians) by using both classifiers (support vector machine (SVM), Naive Bayes (NB)) and statistical tests (one-way ANOVA) with respect to electrode locations. Permutation entropy (PermEn) is found to be the best metric (p ≪ 0.0001, 98.37% and 98.41% accuracies for tonal and atonal ensembles) at fronto-temporal regions which are responsible for cognitive task evaluation and perception of sound. PermEn also provides the meaningful results at the whole cortex (p ≪ 0.0001, 99.81% accuracy for both tonal and atonal ensembles) through SVM with Radial Basis kernels superior to Gaussians. Almost the similar performance is also obtained for temporal features. Although, performance improvements are observed for spectral methods with NB, the considerable better results are obtained with SVM. The results indicate that musical stimuli cause pattern variations instead of spectral variations on STABO due to relatively higher neuronal activities around auditory cortex. In conclusion, temporal regions produce response to auditory stimuli, while frontal area integrates the auditory task at the same time. As well, the parietal cortex produces neural information according to the degree of attention generated by environmental changes such as atonal stimuli. It can be clearly stated that musical experience enhances the neural encoding performance of sound tonality at mostly fronto-temporal regions.

Electro-olfactogram Responses Before and After Aversive Olfactory Conditioning in Humans.

The aim of the present study was to investigate whether repetitive aversive odor conditioning induced changes at the level of the peripheral olfactory system in humans. A total of 51 volunteers participated. A pair of indistinguishable odor enantiomers [(+)-rose oxide and (-)-rose oxide] were used as stimuli. During the pre-conditioning, participants' ability to discriminate between the two odors was assessed using a three-alternative, forced-choice discrimination test. In addition, electro-olfactograms (EOG) from the olfactory epithelium were recorded. Participants underwent three conditioning sessions on consecutive days. The experimental group received an electrical stimulus to the forearm only following (+)-rose oxide presentation, whereas its enantiomer sibling was never paired with the aversive stimulus; the control group did not receive any electrical stimulation. During the post-conditioning session, their ability to discriminate the two enantiomers was assessed again using the discrimination test and EOG recordings were obtained similarly to the pre-conditioning session. Results showed significant differences in the peripheral electrophysiological responses between the conditioned and the unconditioned stimulus, demonstrating contextually induced changes at the level of the first neuron in the olfactory system.

Indistinguishable odour enantiomers: Differences between peripheral and central-nervous electrophysiological responses.

The ability of humans to discriminate enantiomeric odour pairs is substance -specific. Current literature suggests that psychophysical discrimination of odour enantiomers mainly depends on the peripheral processing at the level of the olfactory sensory neurons (OSN). To study the influence of central processing in discrimination, we investigated differences in the electrophysiological responses to psychophysically indistinguishable (+)- and (-)- rose oxide enantiomers at peripheral and central-nervous levels in humans. We recorded the electro-olfactogram (EOG) from the olfactory epithelium and the EEG-derived olfactory event-related potentials (OERP). Results from a psychophysical three alternative forced choice test indicated indistinguishability of the two odour enantiomers. In a total of 19 young participants EOG could be recorded in 74 and OERP in 95% of subjects. Significantly different EOG amplitudes and latencies were recorded in response to the 2 stimuli. However, no such differences in amplitude or latency emerged for the OERP. In conclusion, although the pair of enantiomer could be discriminated at a peripheral level this did not lead to a central-nervous/cognitive differentiation of the two stimuli.

Acute Supramaximal Exercise Increases the Brain Oxygenation in Relation to Cognitive Workload.

Single bout of exercise can improve the performance on cognitive tasks. However, cognitive responses may be controversial due to different type, intensity, and duration of exercise. In addition, the mechanism of the effect of acute exercise on brain is still unclear. This study was aimed to investigate the effects of supramaximal exercise on cognitive tasks by means of brain oxygenation monitoring. The brain oxygenation of Prefrontal cortex (PFC) was measured on 35 healthy male volunteers via functional near infrared spectroscopy (fNIRS) system. Subjects performed 2-Back test before and after the supramaximal exercise wingate anerobic test (WAnT) lasting 30-s on cycle ergometer. The PFC oxygenation change evaluation revealed that PFC oxygenation rise during post-exercise 2-Back task was considerably higher than those in pre-exercise 2-Back task. In order to describe the relationship between oxygenation change and exercise performance, subjects were divided into two groups as high performers (HP) and low performers (LP) according to their peak power values (PP) obtained from the supramaximal test. The oxy-hemoglobin (oxy-Hb) values were compared between pre- and post-exercise conditions within subjects and also between subjects according to peak power. When performers were compared, in the HP group, the oxy-Hb values in post-exercise 2-Back test were significantly higher than those in pre-exercise 2-Back test. HP had significantly higher post-exercise oxy-Hb change (Δ) than those of LP. In addition, PP of the total group were significantly correlated with Δoxy-Hb.The key findings of the present study revealed that acute supramaximal exercise has an impact on the brain oxygenation during a cognitive task. Also, the higher the anerobic PP describes the larger the oxy-Hb response in post-exercise cognitive task. The current study also demonstrated a significant correlation between peak power (exercise load) and post-exercise hemodynamic responses (oxy-, deoxy- and total-Hb). The magnitude of this impact might be related with the physical performance capacities of the individuals. This can become a valuable parameter for future studies on human factor.

Assessing Olfactory Function in Parkinson's Disease via Entropy Analysis of Chemosensory Event Related Potentials.

The relationship between Parkinson's disease (PD) and olfactory dysfunction has been investigated via psychophysical and electrophysiological assessments. Despite the increasing number of electrophysiological studies focusing on olfactory function, there are still some limitations to observe the chemosensory event-related potentials (CSERP), which are electrophysiological responses of the brain to olfactory and trigeminal stimulations, because of the low sensitivity (low signal-to-noise ratio). Recent studies attempted to establish new techniques to increase the sensitivity for evaluating the CSERP and brain responsiveness. We aimed to inspect CSERP via entropy analysis in assessing chemosensory related brain responses that has been used for the first time. Twelve newly diagnosed and non-medicated PD patients and 12 healthy subjects participated in the study. Psychophysical and electrophysiological evaluation of olfaction were assessed via Sniffin' Sticks Test (SST) and entropy analysis on CSERP in three time windows. The scores of odor threshold, odor identification and total scores of SST were lower (hyposmic) in PD patients compared to healthy subjects. Electrophysiological assessments revealed a significant change in entropy among time windows for olfactory stimulation with phenyl ethyl alcohol and trigeminal stimulation with carbon dioxide (both p < 0.05) in healthy subjects but not in PD patients. Entropy findings indicate that the brain operates in ordered state among healthy subjects in response to olfactory/trigeminal stimuli, whereas the PD patients displayed a chaotic pattern. This pattern in the PD patients suggests the lack of proper smell function. It should be studied if this pattern can be used as a biomarker for PD.

Olfactory dysfunction in children with Kallmann syndrome: relation of smell tests with brain magnetic resonance imaging.

OBJECTIVE: Kallmann syndrome (KS) is a genetic disorder with the distinctive features of hyposmia or anosmia and hypogonadotropic hypogonadism. Though hyposmia/anosmia can be evaluated by both objective and subjective smell tests, there is no study comparing these two methods in KS. The aim of the present case series was to discuss the results of objective and subjective smell tests and compare them to volumetric magnetic resonance imaging (MRI). METHODS: A total of six adolescent males (aged between 14-18 years) with KS were examined by objective and subjective olfactometry to test smell function and by specific MRI sequences to measure the olfactory bulbs. RESULTS: The objective smell test showed anosmia in all six of the patients. However, the subjective test revealed anosmia in five patients and hyposmia in one patient. Brain MRI showed olfactory bulb aplasia in all six cases. CONCLUSION: MRI provides robust evaluation of the olfactory bulb volume. Our data show excellent compatibility between the results obtained via objective olfactometry and those obtained by measuring olfactory bulb volume as determined by MRI and therefore demonstrate that objective olfactometry remains a highly reliable test. Furthermore, although the number of subjects studied was small, these data also suggest that cheaper and more easily available subjective tests could be used in preference to the more expensive as well as labor-intensive and time-consuming objective smell tests. In the event of doubts as to the validity of the subjective tests, the objective olfactometry tests can confirm the diagnosis. The bulb volumetric MRI may be also used in difficult cases.