Hemodynamic Response of the Frontal Cortex Elicited by Intravenous Thiamine Propyldisulphide Administration

Prefrontal Responses to Odors in Individuals With Autism Spectrum Disorders: Functional NIRS Measurement Combined With a Fragrance Pulse Ejection System

Individuals with autism spectrum disorders (ASD) are impaired not only in social competencies but also in sensory perception, particularly olfaction. The olfactory ability of individuals with ASD has been examined in several psychophysical studies, but the results have been highly variable, which might be primarily due to methodological difficulties in the control of odor stimuli (e.g., the problem of lingering scents). In addition, the neural correlates of olfactory specificities in individuals with ASD remain largely unknown. To date, only one study has investigated this issue using functional magnetic resonance imaging (fMRI). The present study utilized a sophisticated method-a pulse ejection system-to present well-controlled odor stimuli to participants with ASD using an ASD-friendly application. With this advantageous system, we examined their odor detection, identification, and evaluation abilities and measured their brain activity evoked by odors using functional near-infrared spectroscopy (fNIRS). As the odor detection threshold (DT) of participants with ASD was highly variable, these participants were divided into two groups according to their DT: an ASD-Low DT group and an ASD-High DT group. Behavioral results showed that the ASD-High DT group had a significantly higher DT than the typically developing (control) group and the ASD-Low DT group, indicating their insensitivity to the tested odors. In addition, while there was no significant difference in the odor identification ability between groups, there was some discrepancy between the groups' evaluations of odor pleasantness. The brain data identified, for the first time, that neural activity in the right dorsolateral prefrontal cortex (DLPFC) was significantly weaker in the ASD-High DT group than in the control group. Moreover, the strength of activity in the right DLPFC was negatively correlated with the DT. These findings suggest that participants with ASD have impairments in the higher-order function of olfactory processing, such as olfactory working memory and/or attention.

Near-infrared spectroscopy of orbitofrontal cortex during odorant stimulation

BACKGROUND

For olfaction, several studies have reported near-infrared spectroscopy (NIRS) signal changes in the orbitofrontal cortex (OFC) during odor stimulation. However, the roles of human OFC in olfactory cognition are less well understood. This study was designed to better understand the roles of OFC for olfaction.

METHODS

Hemodynamic responses for phenyl ethyl alcohol or citral in the OFCs were measured with NIRS. After the experiment, participants were asked to describe the characteristics of the odor and to rate odor intensity and hedonic valence.

RESULTS

Statistical analysis of all participants' data showed significant changes in the concentration of total hemoglobin in the left OFC during the trial (p = 0.04). The total hemoglobin signal increased significantly in the right OFC (p = 0.0008) of the participants who successfully identified the odorant stimulus.

CONCLUSION

Our findings showed that NIRS combined with a questionnaire is a useful method for studying the functional neuroanatomy of OFC in terms of olfaction.

Effects of methylphenidate on olfaction and frontal and temporal brain oxygenation in children with ADHD

OBJECTIVE

Olfaction and attention-deficit-/hyperactivity disorder (ADHD) are mediated by dopamine metabolism and fronto-temporal functioning converging in recent findings of increased olfactory sensitivity in children with ADHD modulated by methylphenidate (MPH) and altered frontal and temporal oxygenation in adults with ADHD.

METHOD

We investigated olfactory sensitivity, discrimination, and identification (Sniffin' Sticks) in 27 children and adolescents with ADHD under chronic MPH medication and after a wash-out period of at least 14 half-lives in balanced order and 22 controls comparable for handedness, age, and intelligence. In addition, inferior frontal and temporal oxygenation was measured by means of functional near-infrared spectroscopy (fNIRS) during the presentation of 2-phenylethanol. Group differences in regard to sex distribution were statistically controlled for by analysis of covariance.

RESULTS

Patients did not differ from controls in any olfactory domain under treatment with MPH. Cessation of medication led to a significant increase in olfactory discrimination. Controls displayed typical inferior frontal and temporal brain activity in response to passive olfactory stimulation, while brain oxygenation was diminished in the patient group when assessed without medication. Under medication ADHD patients showed a trend for a normalisation of brain activity in the temporal cortex.

CONCLUSIONS

The here reported effects of MPH cessation on olfactory discrimination and frontal and temporal oxygenation along with previous findings of increased olfactory sensitivity in medication-naïve ADHD children and its normalisation under chronic MPH treatment lead to the conclusion that MPH exerts differential chronic effects vs. acute cessation effects on altered olfactory function in ADHD. These effects are most probably mediated by modulation of the dopaminergic system.

Cortical hemodynamic responses to intravenous thiamine propyldisulphide administration detected by multichannel near infrared spectroscopy (NIRS) system

Intravenous injection of thiamine propyldisulphide (TPD), which induces sensation of a garlic-like odor, has been used as a representative subjective olfactory test in Japan. However, cortical loci activated by TPD still remain unclear. We recorded cerebral hemodynamic responses (changes in Oxy-Hb concentrations) induced by TPD administration using whole-head multi-channel near infrared spectroscopy (NIRS) system based on 3D-MRIs. TPD as an odorant and saline as a control were injected from the cephalic vein in the left forearm in ten male normosmic (five young and five elderly) subjects and five dysosmic elderly patients. The all normosmic, but not dysosmic, subjects felt the garlic-like odor in the all TPD trials. There was no significant difference in hemodynamic responses between the young and elderly normosmic subjects. However, TPD injection induced significantly larger hemodynamic responses in the bilateral operculums, bilateral dorsolateral prefrontal cortices (PFC) and anteromedial PFC in the normosmic subjects, compared with saline injection. Onset latencies of these hemodynamic responses were significantly correlated with onset latencies of subjective odor sensation in the normosmic subjects. Comparison of hemodynamic responses between the normosmic and dysosmic subjects indicated a significant difference in the bilateral operculums. The results demonstrated that Oxy-Hb increases in the bilateral operculums reflected olfactory sensation induced by TPD injection. Consideration of a route for intravenous TPD to reach the olfactory mucosa suggests that these hemodynamic responses might be attributed to food-related retronasal olfactory responses to TPD.

Maternal breast milk odour induces frontal lobe activation in neonates: a NIRS study

We used near-infrared spectroscopy (NIRS) to examine differences in neonates' orbito-frontal cortical activation in response to the odours of maternal breast milk and formula milk in terms of changes in the oxygenation of cerebral blood flow. Twenty-six healthy neonates were tested in their cribs while they slept in a silent room. The neonates were exposed to each olfactory stimulus by an experimenter. NIRS monitoring was performed using optodes placed above the bilateral anterior orbito-frontal gyri. The differences in oxygenated haemoglobin (oxy-Hb) values between baseline and stimulation were defined as the change in oxy-Hb. The degrees of change were calculated by an analysis of variance (ANOVA). A 2 (stimulus: breast milk and formula milk) × 2 (probe location: right and left) ANOVA showed that the odour of maternal breast milk (right/left: M=0.28/0.48) induced a significantly (F=6.36, p<0.05) greater increase in the oxygenated blood of the orbito-frontal region than did the odour of formula milk (right/left: M=-0.03/-0.07). Differences in the intensity of odour had no significant influence on the blood oxygenation of the orbito-frontal region. Maternal breast milk odour increased oxygenated blood flow in the orbito-frontal region to a greater extent than did formula milk odour. These results suggest that neonates can distinguish between the odours of maternal breast milk versus formula.

Effects of fragrance administration on stress-induced prefrontal cortex activity and sebum secretion in the facial skin

Although fragrances have long been known to influence stress-induced psychosomatic disorders, the neurophysiological mechanism remains unclear. We evaluated the effect of fragrance on the relation between the level of sebum secretion in the facial skin and the stress-induced prefrontal cortex (PFC) activity, which regulates the activity of the hypothalamic-pituitary-adrenal axis. Employing near infrared spectroscopy, we measured hemoglobin concentration changes in the bilateral PFC during a mental arithmetic task in normal adults (n=31), and evaluated asymmetry of the PFC activity in terms of the laterality index (i.e., [(right-left)/(right+left)]) of oxyhemoglobin concentration changes (LI-oxyHb). We measured the level of sebum secretion in the facial skin before the task performance. There was a significant positive correlation between the LI-oxyHb and the level of sebum secretion (r=+0.44, p=0.01). We selected the subjects who exhibited high levels of sebum secretion and right-dominant PFC activity for the study on the fragrance effect (n=12). Administration of fragrance for four weeks significantly reduced the level of sebum (p=0.02) in the fragrance group (n=6). In addition, the LI-oxyHb decreased significantly from 0.11+/-0.07 to -0.10+/-0.18 (p=0.01), indicating that the dominant side of the stress-induced PFC activity changed from the right to left side. In contrast, neither LI-oxyHb nor the levels of sebum secretion changed significantly in the control group (n=6). These results suggest that administration of fragrance reduced the level of sebum secretion by modulating the stress-induced PFC activity. The PFC may be involved in the neurophysiological mechanism of fragrance effects on systemic response to mental stress.

Dimenhydrinate effect on cerebral oxygen status and salivary chromogranin-A during cognitive tasks

To investigate the effects of dimenhydrinate on cerebral oxygen status (COS; cerebral oxygenated hemoglobin concentration changes) and salivary chromogranin-A (CgA) during a cognitive test battery, a double-blind, placebo-controlled, randomized, crossover protocol was used to examine the effect of 50 mg of dimenhydrinate or placebo in 12 subjects. This test battery includes tests of both reaction time and fundamental cognitive ability and was used in the assessment of pilots. Poor cognitive performance was observed in the subjects taking dimenhydrinate. We used two-channel near-infrared spectroscopy to investigate the effects of dimenhydrinate on the COS. With the one exception of shifting attention task in the left forehead, no significant difference was found between dimenhydrinate and placebo during the tasks of the test battery. Under placebo treatment, on the other hand, CgA levels were significantly elevated during cognitive testing when compared with baseline. However, CgA levels were not significantly elevated above baseline following dimenhydrinate. The present study is one of the first to demonstrate that the first-generation antihistamine drugs altered the responses of salivary CgA during cognitive tasks. The changes in salivary CgA secretion, as a result of dimenhydrinate administration, may serve as a sensitive biomarker of a psychological status such as a drug-induced sedation during the performance of a cognitive test battery. Further studies, however, are required to examine the usefulness of this sensitive biomarker in investigation of psychological agents during cognitive tasks.

Functional Optical Hemodynamic Imaging of the Olfactory Cortex

OBJECTIVE

We used multichannel near-infrared spectroscopy (MNIRS) to monitor the activity of the frontal cortex as mirrored by hemodynamic responses subjected to olfactory stimulation. The aim of this study was to clarify the functional brain imaging of olfactory activity.

STUDY DESIGN

Prospective study.

METHODS

This study was conducted on eight healthy subjects aged from 22 to 39 years (4 men and 4 women; mean age, 28.8 yr). We used a 22-channel near-infrared spectroscopy device with eight light-incident fibers and seven detector fibers, each with an interoptode distance of 2.5 cm on the frontal region. Olfactory stimulation consisted of five repetitions, each lasting 5 seconds and followed by a 55 seconds rest period. Isovaleric acid was used as odor stimulation, and saline was used as a control. We measured the changes in concentrations of oxyhemoglobin [oxyHb], deoxyhemoglobin [deoxyHb], and total hemoglobin [totalHb] from prebaseline values. Furthermore, we divided the frontal cortex into four areas (right upper, left upper, right lower, left lower) and investigated the activity in each area.

RESULTS

Isovaleric acid caused changes, especially in the lower area, but saline caused no changes. [oxyHb] and [totalHb] increased after odor stimulation, but [deoxyHb] did not change. These active areas may be related to the orbitofrontal cortex, corresponding to olfactory cortices.

CONCLUSION

This study has shown that MNIRS enables evaluation of changes in hemodynamics related to brain activity by olfactory stimulation.

Smell intensity monitoring using metal oxide semiconductor odor sensors during intravenous olfaction test

The intravenous olfaction test using prosultiamine (PST) solution is simple to perform and has been used clinically in Japan. We monitored intranasal intensity of smell continuously in real time under various conditions of administration using metal oxide semiconductor odor sensors and established an optimal PST injection procedure. In this study, we found that 1) although there was fluctuation in the pattern of intensity of increase in smell in the PST original solution test, the pattern of increase in intranasal smell intensity could be stabilized by prolonging the injection time to 40 s and 2) dilution of PST with physiological saline was effective in preventing angialgia during intravenous injection. It appears that PST administration is best performed by adding 10 ml of saline to 10 mg (2 ml) of PST and injecting the resulting 12-ml solution (6x dilution) and that the best respiratory cycle for testing is once in every 2 s.