Dynamics of Nasal Chemesthesis

摘要

Dynamics, or how stimulation occurs over time, influences the somatosensory impactof volatile chemicals. Within an experimental session, sensation waxes with steadypresentation over seconds to minutes, may reach a plateau, and then may fade. Long-term occupational exposure can desensitize the trigeminal system. Short- and long-term dynamics might be mediated by different mechanisms. For brief intranasal ex-posures (i.e., up to about 10 seconds), studies have systematically manipulated bothtime (duration of exposure) and concentration to maintain a fixed perceived intensityor a fixed level of detection. A simple mass integration model describes the trade-offbetween concentration and time quite well: a fixed-ratio increase in duration com-pensates for a fixed-ratio decrease in concentration. However, for most compounds,more than a two-fold increase in duration are required to compensate for cutting con-centration in half. For example, for ethanol, an increase in duration of about six-foldare required. For such compounds that display highly imperfect integration, a fixednumber of molecules might have a much greater sensory impact when presented over0.2 seconds than over 0.5 seconds. Nasal chemesthesis may be temporally sluggishcompared to olfaction, but fine-grained dynamics still matter. Time—intensity ratingsof nasal irritation from dynamic stimuli also support this conclusion. Although integra-tion is generally imperfect, compounds vary widely in how far they fall short of perfecttime—concentration trading. Current studies use a structure—activity approach to deter-mine how molecular parameters correlate with how well a compound integrates overtime.