If you thought we had reached a new horizon of mass social behavior modification via electronic drugs (ie social media and the consumer surveillance apparatus), then just wait until the smells show up. Smells have a direct line to the limbic system, which is called so because it controls your limbs; it literally makes you move, and it also controls your mood.
Incorporating scents into a VR environment suitable for spacefarers
Jan 2023, phys.org
Building scents into a VR nature environment: A user could walk near a river in the VR environment and not only hear the sound of rushing water but also smell wet grass. This is accomplished by using hitboxes, which are invisible shapes in the VR environment that activate when the avatar collides with them.
When conducting their study, Abbott and Diaz Artiles measured users' anxiety levels before and after experiencing a stress-inducing event. The results showed that adding olfactory stimuli not only decreased users' anxiety levels after experiencing heightened stress but also reduced their stress and anxiety levels from their baseline.
via Texas A&M University College of Engineering: Renee (Woodruff) Abbott et al, The impact of digital scents on behavioral health in a restorative virtual reality environment, Acta Astronautica (2022). DOI: 10.1016/j.actaastro.2022.05.025
Dogs can smell when we're stressed, study suggests
Oct 2022, phys.org
93.75% accuracy detecting changes in breath and sweat, before and after a fast-paced arithmetic task, along with self-reported stress levels, heart rate and blood pressure.
via Animal Behaviour Centre at Queen’s University Belfast, and Newcastle University: Dogs can discriminate between human baseline and psychological stress condition odours, PLoS ONE (2022). DOI: 10.1371/journal.pone.0274143
Chances are we can smell stress too, we're just not tuned-in to it. If you want proof, you can look at post-handshake-hand-sniffing behavior
and think about how we're subconsciously measuring the stress levels of the people we shake hands with as a way to assess how we should react to them.
And now for some thoughts about depression, anosmia and long covid:
Potential found to counter depression by restoring key brain rhythm
May 2023, phys.org
Effective communication between brain regions requires groups of neurons to synchronize their activity patterns in repetitive periods (oscillations) of joint silence followed by joint activity.
One such rhythm, called "gamma," repeats about 30 times or more in a second, and is an important timing pattern for the encoding of complex information, potentially including emotions.
Although its causes remain poorly understood, depression is reflected in gamma oscillation changes, according to past studies, as an electrophysiological marker of the disease in brain regions that manage the sense of smell, which have also been tied to emotions.
"Our experiments revealed a mechanistic link between deficient gamma activity and behavioral decline in mice and rat models of depression, with the signal changes in the olfactory and connected limbic systems similar to those seen in depressed patients,"
Feeding an amplified olfactory bulb signal back into the brains of depressed rats restored normal gamma function in the limbic system, and reduced the depressive behaviors by 40 percent (almost to normal).
via NYU Grossman School of Medicine and University of Szeged in Hungary: Antal Berényi, Reinstating olfactory bulb derived limbic gamma oscillations alleviates depression-like behavioral deficits in rodents, Neuron (2023). DOI: 10.1016/j.neuron.2023.04.013.
Partially unrelated post script:
In case you're ever wondering how do they actually measure depression in mice, they get dunked in a bucket of water to see how long it takes for them to stop swimming -- the sooner they give up, the more depressed they are.