Null Effect of Olfactory Training With Patients Suffering From Depressive Disorders—An Exploratory Randomized Controlled Clinical Trial

Abstract

Due to a close functional relation between brain areas processing emotion and those processing olfaction, major depression is often accompanied by reduced olfactory function. Such hyposmia can be improved by regular olfactory training (OT) over several months. As this training furthermore improves subjective well-being, we explored whether OT is a useful complementary strategy for depression treatment. A total of 102 depressive outpatients were randomly assigned to OT or a control training condition, which were performed twice a day for 16 weeks. Compliance was continuously monitored. Before and after training we measured depression severity and olfactory function. About half of the patients of both groups did not complete the training. Among the remaining patients, depression severity decreased significantly in both groups. The absence of an interaction effect indicated no selective impact of OT and the variance of depression improvement explained by OT was as little as 0.1%. The low compliance suggests that OT is not feasible for large parts of our sample of depressive outpatients, most likely due to a diseaseimmanent lack of motivation. In those patients who completed the training, lack of specific effects suggest that OT is not more useful then unspecific activation or attention training.

Symptoms of Depression Change With Olfactory Functions

“…However, according to the previously mentioned scale, a signi cant percentage of the present sample (one-third of the entire sample) was classi ed as depressed. That could probably explain why the depression severity before and after the medical treatment focused on olfaction remained the same, contrary to previous olfactory training work [29][30]. In this context, solid and moderate relationships obtained between change in TDI, I, and depression severity suggest that olfaction is related even to very subtle changes in mood.…”

“…Previous studies demonstrated that dysosmic patients can bene t from olfactory training to improve their olfactory abilities and reduce their depression severity [29][30]. Odor identi cation is an olfactory dimension with a solid cognitive association [48] that has been consistently reported to be impaired in depression [16][17][18][19][20] probably because of the cognitive impairment in recurrent depression [18].…”

“…Recent studies demonstrated that mood bene ts from improving olfaction via regular olfactory exposure, so-called "olfactory training, " leading to decreased depression severity [29][30]. The question remains open whether this effect is caused by the well-established positive impact of exposure to odors on mood [31][32][33][34] during olfactory training or whether improvement in olfaction, even without olfactory training, is directly related to the improvement in mood, presumably via neuroanatomical changes.…”

Olfactory training with Aromastics: olfactory and cognitive effects

“…In our sample, all subjects scored = < 9 points, suggesting none-to-minimal depression [ 34 ]. Subjects with low BDI scores are more likely to comply with the OT regimen, whereas those with high BDI scores may be discouraged to perform training and expect negative results [ 40 ]. Finally, the null results of OT on BDI symptoms and positive/negative affect may not be discernible, because both questionnaires (BDI and PANAS) relate to a shorter time frame than the period of OT used in this study.…”

Symptoms of depression change with olfactory function

“…Recent studies demonstrated that mood benefits from improving olfaction via regular olfactory exposure, so-called “olfactory training” (OT), leading to a decreased severity of depressive symptoms 30 , 31 . The question remains open as to whether this effect is caused by the positive impact of exposure to odors on mood 32 – 48 during OT or whether improvement in olfaction, even without OT, is directly related to the improvement in mood, possibly via neuroanatomical changes.…”