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Applied to the nasal mucosa in low concentrations, nicotine vapor evokes odorous sensations (mediated by the olfactory system) whereas at higher concentrations nicotine vapor additionally produces burning and stinging sensations in the nose (mediated by the trigeminal system). The objective of this study was to determine whether intranasal stimulation with suprathreshold concentrations of S(-)-nicotine vapor causes brain activation in olfactory cortical areas or if trigeminal cortical areas are also activated. Individual olfactory detection thresholds for S(-)-nicotine were determined in 19 healthy occasional smokers using a computer-controlled air-dilution olfactometer. Functional magnetic resonance images were acquired using a 1.5T MR scanner with applications of nicotine in concentrations at or just above the individual"s olfactory detection threshold. Subjects reliably perceived the stimuli as being odorous. Accordingly, activation of brain areas known to be involved in processing of olfactory stimuli was identified. Although most of the subjects never or only rarely observed a burning or painful sensation in the nose, brain areas associated with the processing of painful stimuli were activated in all subjects. This indicates that the olfactory and trigeminal systems are activated during perception of nicotine and it is not possible to completely separate olfactory from trigeminal effects by lowering the concentration of the applied nicotine. In conclusion, even at low concentrations that do not consistently lead to painful sensations, intranasally applied nicotine activates both the olfactory and the trigeminal system.
BACKGROUND: Feedback from the body is assumed to be altered in depression. Nevertheless, empirical studies investigating this assumed relationship remain sparse. This study aimed to examine interrelations between the ability to perceive heartbeats accurately (interoceptive awareness), depressive symptoms, and anxiety in healthy participants. METHODS: A well-validated heartbeat perception task to measure interoceptive awareness together with two questionnaires indexing anxiety and depression were administered to 119 participants. RESULTS: As main results we observed a negative correlation between heartbeat perception and depression. Only when focussing on high anxiety levels this negative correlation coefficient between depression and interoception remained significant. CONCLUSIONS: Our results highlight the possible relationship between depressive symptoms and interoceptive awareness and may have further implications for theoretical models of anxiety disorders and their treatment. Further research is required to examine the potential consequences of altering interoceptive awareness in healthy subjects in relation to depression and anxiety.
Compared with visual and auditory imagery, little is known about olfactory imagery. There is evidence that respiration may be altered by both olfactory perception and olfactory imagery. In order to investigate this relationship, breathing parameters (respiratory minute volume, respiratory amplitude, and breathing rate) in human subjects during olfactory perception and olfactory imagery were investigated. Fifty-six subjects having normal olfactory function were tested. Nasal respiration was measured using a respiratory pressure sensor. Using an experimental block design, we alternately presented odors or asked the subjects to imagine a given smell. Four different pleasant odors were used: banana, rose, coffee, and lemon odor. We detected a significant increase in respiratory minute volume between olfactory perception and the baseline condition as well as between olfactory imagery and baseline condition. Additionally we found significant differences in the respiratory amplitude between imagery and baseline condition and between odor and imagery condition. Differences in the breathing rate between olfactory perception, olfactory imagery, and baseline were not statistically significant. We conclude from our results that olfactory perception and olfactory imagery both have effects on the human respiratory profile and that these effects are based on a common underlying mechanism.
On the relationship between interoceptive awareness and the attentional processing of visual stimuli
(2009)
Mental processes related to visceral activity have gained growing interest during the last few years. The following study is the first to investigate possible interactions between interoceptive awareness and measures of attentional performance. We tested the hypothesis whether interoceptive awareness is positively related to indices of selective and divided attentional performances. Using a heartbeat perception task, 29 healthy female participants were separated into two groups scoring either high or low in an interoceptive awareness task. Attentional performance was assessed by several tests including the 'd2 test of attention' and subtests from the 'TAP: Test Battery for Attentional Performance'. We observed a significantly better performance in selective and divided attention for participants with high interoceptive awareness. Our data suggests that interoceptive awareness is related to a better performance especially in tasks assessing selective and divided attention. We conclude 1) that perception of bodily states might be a crucial determinant for the processing of external, visual stimuli, 2) that the ability to perceive internal signals might be an indicator of self-focused attention, and 3) that bodily signals may use, at least in part, similar processing resources as signals from the attention system.